The Power Commander V Accessories AutoTune for Power Commander V. The Auto Tune kit monitors the fuel mixture (by installing the included Wide Band O2 sensor in the exhaust). It then sends this information to the Power Commander V and automatically corrects it while you ride. So, if you know that proper tire inflation increases fuel efficiency by reducing friction, that engines need air and fuel to go vroom, and that a buildup of crud (yup, that's a technical automotive term) on the engine can kill your car's performance, you just might be able to ace this quiz.
Understanding Fuel TrimSome of the most common pertain to fuel trim (rich mixture, lean mixture, etc.) Here is an explanation of fuel trim and what it does for us. The ECU controls Air/Fuel mixture in order to maintain power, efficiency, and emissions. A/F is expressed as either a ratio (14.7:1 for example) or as a Lambda value.
With iso-octane ('ideal' gasoline), Lambda of 1.0 is equal to 14.7:1 A/F. This is known as 'Stoichiometric', a condition where there is a perfect balance between oxygen molecules and the various hydrogen and carbon based molecules in petroleum. With the oxygenated gasoline that most of us use, actual A/F ratio of 15:1 is closer to stoichiometric.If Lambda is greater than 1.0, then there is a surplus of air and the engine is running lean. If Lambda is less than 1.0, then there is a surplus of fuel and the engine is running rich. It should be noted that the ratios are mass-based, not volume-based.So, why don't we always run at 1.0 all the time?
Well, we do MOST of the time. At cruise and idle, mixture is held tightly to 1.0 to keep the catalytic convertor at optimal efficiency, so the emissions are minimized.
However, when we need acceleration, the mixture gets richer. Maximum power is made between 0.85 to 0.95 Lambda (12.5 to 14.0 A/F with iso-octane). So, under acceleration, mixtures get richer. Sometimes you want to get even richer under acceleration to keep detonation (pre-ignition of the mixture from excess cylinder temperatures) away. The 1.8T has a relatively high compression ratio for a turbocharged engine, which especially under lots of boost, is very succeptible to detonation).So, now that we know that the ECU wants to be able to control the A/F ratio. It has a prescribed set of values (maps) for a given RPM, Load, etc. So, the ECU tells the injectors to pulse for exactly XX.X milliseconds and that SHOULD get us the proper A/F ratio that we want.
Well, if you tell an employee to go do something, you want to make sure they actually did it, right? The ECU has some snitches (the front O2 sensor and the MAF, for the most part) that will report back whether or not the desired mixture has been attained.
The rear O2 sensor is used mostly to monitor the condition of the catalytic convertor, although in some applications it also contributes to trim information.Based on feedback from the snitches, the ECU learns to apply a correction factor to its commands to the fuel injectors. If you know that your employees take longer than the standard allotted time to do a specified job, you will need to adjust for that in your planning (injectors are in a union, so it is tough to fire them ). The learned values go between the maps in the ECU's Flash ROM (the 'chip') and the signal to the fuel injectors. These learned compensations are known as 'trim'. So, when you see 'trim', it means 'compensation'.' Add' means additive trim, which is addressing an imbalance at idle. When the ECU is using additive trim, it is telling the injectors to stay open a fixed amount longer or shorter.
The malfunction (e.g. Vacuum leak) becomes less significant as RPM increase. For additive adaptation values, the injection timing is changed by a fixed amount. This value is not dependent on the basic injection timing.' Mult' mean multiplicative trim, which is addressing an imbalance at all engine speeds. The malfunction (e.g. Clogged injector) becomes more severe at increased RPM.
For multiplicative adaptation values, there is a percentage change in injection timing. This change is dependent on the basic injection timing.You can check your current state of trim by using VAG-COM or equivalent to look in Group 032 (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle) in your engine measuring blocks. The first two fields will have percentages.
The first field tells the fuel trim at idle (Additive). The second field tells the fuel trim at elevated engine speeds (Multiplicative). Negative values indicate that the engine is running too rich and oxygen sensor control is therefore making it more lean by reducing the amount of time that the injectors are open. Positive values indicate that the engine is running too lean and oxygen sensor control is therefore making it richer by increasing the amount of time that the injectors are open.It is totally normal for both the first and second fields to be something other than zero.
In fact, zeros IN BOTH FIELDS indicates that either you just cleared codes (which will reset fuel trim values) or something isn't working properly. If values get too far away from zero, it will cause a DTC (fault code) and can set off the MIL (commonly referred to as the Check Engine Light, or CEL). Specifications for normal operation are usually somewhere near +/- 10%.In general, an out-of-spec value in the first field (Additive) indicates a vacuum leak since it is mostly present at idle, when vacuum is highest. An out-of-spec value in the second field (Multiplicative) indicates a fault at higher RPM, and may point to a faulty MAF.Here's a good sanity check for the status of your MAF. Do a full-throttle run all the way to redline in a single gear (second works fine).
Group 002 usually shows air mass in g/s (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle). Your peak airflow should be roughly 0.80 times your horsepower if you are close to sea level. So, if you have a stock 150 hp 1.8T, expect around 120 g/s. If you see significantly less than that, you MAF may be on the way out.
Also note that airflow will be markedly different at higher altitudes due to reduced ambient air pressure, especially with naturally aspirated engines that do not have forced induction to overcome that deficiency. This still works if you are chipped, but 'race' programs may make more power through timing, rather than airflow. Therefore, take all readings with a grain of salt.11:30, 8 May 2006 (Eastern Standard Time)Video Link Fuel Trim.
After payment, the 20+ page printable PDF of these free online tips will be emailed to you.There are three basic items necessary to tuning your own LT1 (or other GM) PCM:. Software. Cable. Computeris your first step, the program I recommend to read your current PCM image, change its contents, and then reupload it to your PCM. It is a great program, also known as Computer Automotive Tuning Systems (C.A.T.S.), which allows the above things to be done, all for only $69.95. You'll also need an additional PCM file: $EE for the '94-'95 LT1/L99; $DA3 for the '93 LT1 F-Body; or $DA2 for the '92-'93 Y-Body (Corvette), which will cost you an additional $19.95 from TunerCat.
Your other (free) option is to use for flashing and data-logging, and plus the appropriate XDF (EE or DA2/3) for your PCM to do the tune editing.Second, you'll need the appropriate cable connector to go from your car to a computer. These can be bought from for a reasonable price ($60). For a '94, you'll need the 12-pin connector; for a '95, you'll need the 16-pin OBDII-style connector, but it's still OBDI protocol. If you have a '93, you'll also need to piggyback new chips onto your existing PCM ($35), ($85) and ($5), as their PCMs are not flashed based. It's important to be sure that your vehicle and engine are mechanically sound before you begin tuning. Run some engine cleaner through your fuel tank, throttle body and intake manifold (brake booster hose is a good entry for that).
I recommend using for this. After doing so, check your fuel injectors, that they are all flowing freely (not clogged/dirty) and are not pulsing intermittently. Consider replacing your fuel filter, and verify your fuel pump is in good working order. Make sure all parts of the electrical and sensor system are in good condition, including: spark plugs, plug and coil wires, coil, distributor (Opti-Spark for the LT1), ignition module, throttle position sensor (TPS) and IAC valve. If using a MAF sensor, gently clean its filaments with a cotton swab dipped in rubbing alcohol. Over time, dust and grit builds up on the filaments, which decreases sensor accuracy and leads to a rich combustion. You will also get the most consistency when tuning by leaving your MAF sensor stock, unported, with the screen intact.
Consider replacing your oxygen (O2) sensors. If your car has been running rich for awhile (low MPG, excessive black soot under rear bumper), chances are the O2 sensors will need either cleaned or replaced. To clean, try brake cleaner. For replacements, I suggest using only AC/Delco brand, as other brands have caused problems for some people. New/clean O2 sensors can make a huge difference in how well the PCM works (the PCM will read richer than it is when the O2 sensors are fouled).
Be sure there are no exhaust leaks anywhere before the oxygen sensors; also check for vacuum leaks, around the throttle body, MAF sensor, and the intake manifold (they commonly leak on these engines).If any of these things are in poor repair, they can cause the PCM to think the engine is running one way when it is not. CellsThe PCM uses a table of cells to modify both spark timing and fueling. The cells are usually referenced by a combination of load/vacuum (kPa) and engine speed (RPM), with three grids or 'blocks' for each.Where the different blocks begin and end can also be modified, with the stock tune having the vacuum blocks set at 30 (32 for A4s), 50 and 80kPa, and the RPM blocks set at 900 (700 for A4s), 1200 and 2000.Combining these, one can see how there will be 16 total blocks: below 30kpa, at 0-900RPM, 900-1200, 1200-2000, and 2000-7000RPM; then the same for 30 to 50, from 50 to 80, and from 80 to 100kPa. There is another modifier for both the engine load and speed boundaries called hysteresis. This affects how adjacent blocks of cells are combined when on the edge of a boundary (say right at 30kPa at 1200RPM).These grids are how the fueling is trimmed, depending on O2 sensor feedback (seen in detail below under 'BLMs'), so how they are set can be important to getting a car running efficiently, whether you are running a MAF sensor or in speed density off the VE tables.When modifying the engine, especially with cams with more valve overlap, increased displacement, or ported heads, these will need to be adjusted accordingly.
The modded engine will tend to spend more time in different ranges than the stock engine. BLMsBLM stands for 'block learn multiplier.' As mentioned above, the PCM uses the grid of cells referenced by engine load and speed to correct for discrepancies due to air and fuel quality.
The PCM will be expecting the engine to run a certain way depending on the MAF sensor calibration or the VE tables.But because the car is not running in an ideal world, there will be correction needed for differences in air temperature, density, humidity, as well as fuel octane, quality. On top of those two big variables, there are also the changes that happen due to normal wear and tear on the engine and its sensors.The BLM is how the PCM adjusts to correct the fueling. By default, in closed loop, it attempts to get an air:fuel ratio (AFR) of 14.7:1 (or whatever else is specified as the target in the PCM).
When at this ideal, the BLM will read 128, or no correction.If the PCM senses the combustion is too lean (not enough fuel), it will add fuel and the number will increase ( 128). If it senses the combustion is too rich (too much fuel), it will remove fuel and the number will decrease (. When tuning an LT1 PCM, one of the first things to do is remove things that you dislike or physically removed. Then you may change constant values.
Idle & Closed-ThrottleTuning your idle and coast-down can make a big difference in MPG and overall throttle response. This is especially important with modified engines, but can affect stock engines too.The first thing to change at idle is the spark timing.
Increasing the advance will usually increase MPG, and can actually decrease engine temperature too., which found that a big bump over stock can make a noticeable difference, especially with an aftermarket cam (notably one with a lot more valve overlap).Increasing spark advance at idle increased fuel efficiency/MPG (by requiring less pulsewidth from the injectors, and less airflow through the MAF sensor), and also lowered engine temperature. He found 34° as the ideal spot for idle, for his LT1 with the Hotcam and a full point increase in compression ratio (11.4) over stock (10.4).
I, too, have noticed a great effect when substantially increasing timing here (on my 236-242/114 cam).The table to use is 'Closed TPS Spark Advance vs. It affects not only idle, when the car is not moving, but also the timing commanded during coast down when the car is moving: for example, when you have just done a WOT run, and let off the throttle; or, when you down-shift and allow engine braking to slow down the car.Advancing timing in non-idle closed-throttle areas, like coast-down, will also affect MPG, and help to keep the engine from stumbling or stalling in setups that have more valve overlap than stock. It will tend to make throttle response 'crisper.' To fine-tune this, simply increase the values and log the car. Look for any spark retard, and back off the timing a degree at a time wherever you are getting knock. You can also look at your MAP and airflow (when using a MAF sensor) values, which will let you know how efficient the combustion is; the more efficient it is the more vacuum will be pulled (= lower kPa values) and the less airflow will be required (lower gm/s reading from MAF).You will find changes here will also affect emission output; usually more advance leads to higher NOx and lower HC, with a usual sweet-spot found in the middle somewhere.
Part-ThrottleThis is the majority portion of where the engine will be running, from idle until about half throttle, from 800 RPM to about 2600 RPM. With engine changes like cam, heads, etc., this is an especially important area for tuning, with great results achieved in drivability and fuel MPG.In general, timing advance should decrease as load increases, and increase as RPM increases until the peak torque output is reached. Other things like the idle vacuum value can affect where the spark timing maps increase and decrease, which is why tuning is so important after substantial engine mods like an aftermarket camshaft.For stock engines, when running 92+ octane fuel, you can begin by adding about 2° of spark advance across the two Main Spark Timing tables, to get more power/better efficiency out of your combustion. Monitor this increase with a scanner/logger and make sure you aren't getting any consistent knock retard. If you are, note in which RPM range it is, and at what MAP value, and take 1° or 2° out of the appropriate Main Spark Timing cell.You can pretty much add advance until you feel the engine holding back or skipping, or get spark retard, and then back it off some.
This will generally produce the cleanest combustion and best throttle response. However, sometimes you can have too much timing without knock (power will fall off), so the best way to fine-tune timing is on the dyno. Using MAP & TPS%The other way to see whether your changes are having a good effect, beside 'feeling' the car while driving, is to check your MAP readings. Generally, a more efficient combustion will produce more vacuum (lower kPa).Therefore, if you are tuning your timing in the 'cruising' area-for example, in 4th gear in an M6-you will find both the approximate MAP value and TPS% needed to keep this cruising RPM.
Then, try increasing timing in that MAP/RPM cell; drive again with the new tune, at the same gear/RPM with the same TPS%, and see if your MAP has decreased. Or, see if less throttle is necessary to keep the car moving at the same speed as before the timing change.
If so, then your changes were good. If you get knock, then obviously you went too far. When you back off timing to prevent knock, you can use this to find out if you've gone farther than you need (if the MAP values increase a lot at the same TPS/RPM).
Wide-Open Throttle (WOT)Once your normal driving is fine-tuned, giving BLMs of near 128 (126-130) (or wide-band AFRs very close to what your Open Loop AFR table is targeting), with no knock retard, you can move on to tuning the power portion of your PCM tune. This is when you have 'the pedal to the metal,' or the throttle is fully open. The LT1 PCM calls this 'power enrichment (PE) mode.' In general, timing advance should decrease as load increases, and increase as RPM increases until the peak torque output is reached. On stock LT1 engines with aluminum heads, this is about 2800 RPM. As you can see with the factory tune, timing levels off around this RPM range. If you modify your setup, with aftermarket heads, cam, etc., you will want to determine where the new torque peak is reached, and tune accordingly.You will also want to tweak the spark advance values at the 95 and 100 MAP settings (the range of WOT).
Too much advance can not only cause spark retard (and damage to your motor), but can be needless for producing the most power. However, too little advance can severely reduce the potential output of your engine as well as lower MPG. Too Much, Too LittlePicturing how the engine works will reveal why too much advance can be detrimental to both power and engine longevity. As the piston travels back up the cylinder, the spark plug is fired and the air:fuel mixture is ignited.
If that spark happens too soon/advanced, the explosion of the combustion will begin expanding and pushing down on the piston while it is still traveling upwards.This will make the engine actually work against itself, with the crank pushing the piston upward while the combustion pushes it downward. Obviously this will severely hamper performance, but will also put undue strain on the crank and connecting rods.Conversely, too little advance will generally only hamper performance. If the plug is fired too late, the piston will reach TDC and begin moving downward again before the combustion can begin expanding and putting downward pressure on the piston. Power will fall off dramatically and can even stall the engine.Once your normal driving is fine-tuned, giving BLMs of near 128 (126-130), with no knock retard, you can move on to tuning the power portion of your PCM tune. This is when you have 'the pedal to the metal,' or the throttle is fully open. The LT1 PCM calls this 'power enrichment (PE) mode.'
![Fuel Fuel](/uploads/1/2/5/4/125411191/458080768.png)
Signs of Timing ErrorsIn my experience, there are a few signs of having the timing set significantly wrong for your particular setup.Too much timing advance tends to produce a bucking/skipping in throttle response, much like not having enough fuel. I'd suppose having the spark fire too early gives similar symptoms as the fuel hasn't fully sprayed and/or propagated throughout the cylinder before the spark fires in this situation. At WOT, too much timing will usually produce knock/pinging of some sort. At idle, too much can cause the engine to hunt, and will usually raise NOx and lower HC emissions, and affect exhaust smell.Too little timing advance tends to kill MPG and power, giving a lazy feeling to throttle response. With larger cams, too little advance at idle will make the engine 'chop' a lot more (less efficient combustion) and usually increase HC and decrease NOx emissions.
Too little at WOT will definitely reduce power. Transmission tuning is almost a separate undertaking, because of the many variables and wide range of driving the tables affect. But, once you understand and apply the logic, you'll have your car running even better, especially once you do engine mods or drag racing at the track.
Shift PointsThe stock tune has these set pretty tame. They don't rev very high at part-throttle (1400-2000), and tend to shift too late at WOT (5300) for the stock engine.
Many performance-minded people like the feeling of the engine revving higher, even for everyday driving. And, once you modify the engine, it usually lowers VE at lower RPM areas, which means the shifts should be later to take advantage of the moved-up power-band.If you change gears or tire size, which would affect your speedo, that will also affect your shift points; if it's a substantial gear change, the shift points can be broken to the point of not shifting at WOT. So, tuning shift points is an important area for performance tuning.The quick way to start, when changing gears, is to use TunerCat's Speedo Correct Tool, which will automatically update all MPH-related shift tables based on the gear/tire change. If you aren't using TunerCat, you can just divide the gear size in your current tune (say, 3.23) by your new gear size (say, 3.73). Then multiply that value (0.866) by your shift points. For example, the stock 1-2 shift with little to no throttle is at 11mph; the new value for 3.73 gears would be 10.
This will need tweaking, but it's a quick way to start.To fine-tune, you will need a calculator that takes into account your tire size, final gearing, and individual gearing (1,2,3,OD). One good website that does this for you is:.Choose your year and vehicle, entire your tire size or diameter, and it will calculate the speed at which your car will be moving at a specific RPM in each gear. You can use those values, along with your known power-band, to modify your shift points. Obviously, the best way to tune this way is trial-and-error in your car. Only you can decide how much throttle you want to give to get a specific shift. Anything over 20-30% TPS/throttle will be outside normal 'cruising' driving-style.The primary tables are 'Normal Mode Up/Down Shift Points.' For those who have installed a performance transmission switch, you can also setup a separate profile for 'performance mode' (most likely, shifting later).
Kickdown ModeThe important thing to remember is that for tables which have both MPH and RPM settings, such as 'Kickdown Mode' (WOT), both values must be met in order for the shift to take place.On a stock LT1 A4 car with 3.23:1 gearing, this means that if you have the Kickdown MPH table set to the stock value of 36 (equating to 4600RPM), and leave the Kickdown RPM table at the stock value of 5350RPM, then the transmission will not shift until 5350RPM.If, for example, you set the RPM value to 4000RPM, then the shift will happen at 4600RPM, the speed to which the MPH value corresponds. So, keep this in mind when tuning shift points. My preference is to set the MPH values for WOT lower than you intend, and use the RPM table to set shift points for WOT ('Kickdown Mode').
Allow for a DelayDepending on your transmission build, your stall converter, your engine power, and your shift firmness, it may take anywhere from less than 100 RPM to more than 300-400 RPM for a shift to complete at WOT. This can obviously seriously affect where you should set your shift points.You may specify '6000' in the Kickdown RPM tables, but that only means the shift will start then. It may not complete until 6200RPM, and if your rev limit is not high enough above your shift points, you may bounce into it.Most often, this effect can be lessed by increasing line pressure in the areas of WOT (93+ TPS%), and by decreasing the same areas in the 'Shift Time' tables.
Shift Pressure/FirmnessThe other side of transmission tuning is shift firmness. This is directly related to line pressure to the transmission; the higher the psi, the firmer the shift. The stock transmission will only firm up to a point, because of the mechanics involved. But, you can definitely firm up part-throttle shifts. Part-ThrottleThe main tables, not a surprise, are 'Main Line Pressure,' split between 0-64MPH and 64-128mph. They are divided by TPS%, which again brings you back to tuning via in-car feedback; only you will know what feels best to you. I suggest starting with increments of 5, whether to soften or firm the shifts.You can also add extra pressure: when at WOT at specific RPM points (increments of 512RPM); based on TPS% in each gear; and even based on tranny temperature.
WOTFor increasing pressure at WOT, especially when upgrading your transmission, you must first increase the Max. Line Pressure Constant.
It is set to 90, which is the max set in the tables too. Many set the Max. Constant to 120, and then work up the WOT areas from 90. For WOT, you will want the 100% TPS table values, and also perhaps the 93.8% ones.Many people have warned against increasing line pressure via the PCM when you have also installed a 'shift kit.' Some think this creates too much pressure; others use both. Talk to your transmission builder if you have any questions about that. TCC LockupThis is the last 'phase' of transmission tuning, the control of the torque converter clutch (TCC).
Similar to a manual transmission's clutch, locking it (clutch pedal out) decreases slippage while increasing horsepower to the wheels; unlocking it increases slippage but increases torque to the wheels (via a multiplier).Depending on the RPM and engine type, locking the TCC too early can 'bog' the engine, much like letting the clutch out all the way on a manual tranny while in a high gear and low RPM (which can stall the engine). But in the appropriate RPM/load ranges, it can improve power and track times.There are varying opinions on the mechanical effects of locking the TCC at WOT; some think it lengthens its life due to less slippage (slippage creates more heat), and others think it shortens its life because of the increased strain from being locked under high load/RPMs. Only you can decide which is best for you, with the help of your transmission builder.The easiest way to lock the TCC at WOT is to use the tables labeled for this; use the calculator listed above to find the MPH at which your engine is near its torque peak and set the TCC to engage then; also be sure to update the 'release' table to a value lower than the engage, or you will keep the TCC locked permanently.The other side of TCC lockup is when at part-throttle, especially cruising like on the highway. Having the TCC locked will increase MPG.
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Aftermarket Stall ConvertersThere is a fairly well-known issue with OBDI LT1 PCMs ('94-'95) that can prevent shifting at WOT when using a high (2800+) RPM stall converter. It will cause the engine to hit the rev limiter, and once you let off the throttle, it will upshift.The easiest and surest way to solve this problem is to increase Line Pressure in the high TPS% areas of those tables, and to decrease the Force Motor Current (+ and -) values in the high pressure areas (90+).To prevent limp mode which also sometimes results from big stalls or short gears, set the 'VSS Diagnostic Enable Min RPM' constant to a RPM higher than the engine will ever see. After installing a different cam in your LT1, timing and to a degree also fueling will play an even bigger role in both drivability and power.Most often, new camshafts have more valve overlap than stock, which often results in a power increase. However, the down side is that this means part of the incoming air & fuel is never ignited and passes right through the head along with the combusted gases. IdleOften, the throttle body and/or its blades will need adjusted with significant engine changes like ported heads, new cam, etc.Generally, you will want a cold start to have IAC counts less than 160 (the max), so that your cold idle is able to hit its targeted value.At the same time, you don't want the IAC counts ever to hit 0, which can happen with a hot engine when the blades are open too far.
This will cause the idle to remain higher than is being commanded.With many aftermarket throttle bodies, the bleed hole will need drilled through, to match the design of the stock throttle body, to get the best possible idle quality and throttle response. See these links for more information:It involves making sure your TB has a bleed hole straight through front to back, like the stock TB, which connects to the hole on the front of the intake manifold. That hole distributes idle air evenly to each individual cylinder intake port and will give you the best quality idle and throttle response.Most aftermarket TBs do not have the hole drilled all the way through, only to the IAC passageway, so you'll need to drill it straight through to line up with the hole in the intake, and make sure the rear of the TB is sealed around that hole so that the hole is separated from the main IAC opening on the bottom.The factory hole size is about 9/64'; for aftermarket cams/heads, you will probably need to start with at least 11/64'. Enlarge the hole until your cold-start idle quality is acceptable (and the IAC counts are below 160) when the TB blades are closed all the way without sticking, and the fully hot idle IAC counts are no lower than 10-20 or so. TimingUsually, when valves open sooner, the spark should fire sooner.
This means more timing advance; especially at low-RPM, part-throttle areas of driving. You will also find less vacuum being pulled with such cams, making idle as well as cruising kPa higher. The timing curves need to be adjusted for this.More efficient engines will generally require less advance, as the combustion happens quicker and more efficiently, so the spark does not need to be fired as much in advance of the piston reaching TDC. Less advance is also necessary when running lower octane fuel.More advance is necessary with less efficient engines or range of engine operation, such as the low load and RPM sections of an engine that has a cam with a lot of valve overlap (more further below). Using MAP & TPS%As mentioned in the main 'Part-Throttle' timing section, you can use TPS% and MAP values in your logs to determine if your timing increases have actually had a good effect. Read that section for more.Besides the two main timing tables, it is also a good idea to increase advance in the closed-throttle table; this is when the engine is idling, either at a complete stop or while cruising.You will need to reorient the closed TPS table to the main timing tables, to be sure the timing is increasing as you go from no-throttle to part-throttle.
Where this happens will depend on the amount of vacuum that your cam pulls, so check your data-logs and be sure your spark advance is increasing from idle to off-idle, or else you will get bogging and back-fires off-idle. Fueling & BLMsThe BLM (block learn modifier) is the PCM's way of adjusting fueling in order to achieve the ideal AFR (in most cases, 14.7:1). Having them much different than 128 will cause your engine to not achieve the most power or MPG it could, and can even cause dangerous lean conditions in extreme cases. BLM MAP BoundariesWhen installing a new cam, the vacuum the engine pulls will usually be less at idle and part-throttle. The PCM has a table for adjusting where each cell of the fueling map begins and ends.
For stock tunes, it is set to 30-50-80kPa, with the engine idling around 30kPa. Cams with more overlap should cause the lower limit to be set higher, starting with 35 and going as high as even 50 or so.The way to find the ideal spot is to log your driving and see what the lowest kPa reached during cruising is, and set it a couple points below that.
You can do the same for the other two settings, but I suggest not changing the high value much, because of the PCM not using BLMs for fine-tuning when at WOT.If you want a good idea of whether your boundaries are spaced out evenly, run a 'normal-driving' log of your car through VEMaster. It will give you the total amount of records per block, showing where you need to adjust both the MAP and RPM boundaries (if you have a lot more in one section than another).Changing this table can increase your MPG as well as improve overall drivability. DFCOAs mentioned in the 'Idle' section above, DFCO has an effect on engine braking and thus also MPG.Because of the decrease in vacuum pulled with 'bigger' cams, the stock settings for DFCO will never be reached and will need to be increased. Looking at the stock settings, it has the disable kPA (25) set about 5 less than idle kPa (30). But because larger cams still reach more vacuum when at part-throttle than when at idle, you cannot simply set the disable 5 below your idle kPa.I suggest going no higher than 35kpa or so for disabling DFCO, or you may run into severe RPM dropping or even engine stalling when coming to a stop. These days, getting better MPG (miles per gallon) out of your vehicle is even more important, with prices at the pump increasing so quickly.Thankfully, there are several ways to substantially increase your LT1's MPG (as well as with other vehicles with similar PCMs).There are at least two main ways to affect MPG: fueling and timing. The first is probably obvious, but many people don't realize that reduced timing can reduce combustion effeciency, which in return uses more fuel to get less torque (which moves the car).
FuelingWe'll look at fueling first, since it's the easiest way to get better MPG. There are several areas and tables to be addressed, as there are several types of driving that affect MPG. Fuel PressureThis has to do with general tuning too, but can severely impact MPG.If your fuel pressure is set higher than stock (43.5psi on the LT1), and you have not accommodated for that in the PCM tune (by adjusting the fuel injector constant), then your car will run rich. The O2 sensors will sense this and try to correct, but the stock tune can only correct so far.
Until it corrects, you'll be running rich, which decreases MPG.Running rich, if it happens long enough, can also foul the O2 sensors, which will put you in a never-ending cycle, as the fouled sensors read less oxygen and think more fuel is needed for efficient combustion. Fuel Injector ConstantThis can be another obvious culprit, but can sometimes be partially overlooked depending on the brand of injector.Some aftermarket injectors are rated at a pressure other than GM's stock of 43.5psi. Even within the same brand , some injectors flow differntly than their rating at 43.5psi.For example, Accel's 24# injector flows 24.3# at 43.5psi (more than rated), but their 26# injector flows 25.6# at 43.5psi (less than rated). If you did not know this, and simply used their advertised flow rating in your tune with the stock fuel pressure of 43.5psi, your BLMs would be off. Obviously, the ones that flow more than advertised will make you run richer if set to the advertised number.Do your best to find out what the injector flows at 43.5psi, and use that number. If, for some reason, you are using a different fuel pressure than the stock 43.5psi, adjust appropriately.
Fuel Injector OffsetsMany people are familiar with this table from using Bosch/Ford SVO injectors, which have a longer offset than the stock AC/Delco injectors.In my experience, raising these values (to a point) will richen up the mixture. However, they should be set correctly for your injectors, as having them set incorrectly can cause driveability issues like bogging and backfiring.
Do your best to find the correct offsets for your injectors, and your MPG should increase. Open Loop AFRThis is a good table to use to increase MPG. Open loop is the area of driving when the car is first started, and its length will depend on coolant temperature and elapsed time after startup.By increasing the values in this table, less fuel will be used before closed loop (O2 sensor feedback) is entered. You can run up to 14.9-15.0 at idle and part-throttle MAP values when the car is fully warmed up (80.C+), without much if any impact on driveability (back-firing, etc.).You can also increase the length of time that the PCM stays in open loop, to give you a leaner AFR for more time, before closed loop is entered and an AFR of 14.7:1 is attempted. Initial Startup AFR EnrichmentThis was a fairly late table addition to TunerCat. Its use is not completely understood, but it must have to do with a richening of the AFR right after startup, depending on coolant temperature. It must be used at least during open loop, and perhaps also during closed loop if it is entered quickly.The obvious way to increase MPG is to lower these values, and even zero them at fully warmed up coolant temps (80.C+).
Less fuel will be added by the PCM during startup, which could be substantial if you use your vehicle for lots of short trips. O2 Rich/Lean Swing ThresholdHere is the great secret to increasing MPG!
A fairly late table addition to TunerCat, this one tells the PCM which voltage from the O2 sensors is the halfway point between rich and lean. Most sensors have their stoichiometric (14.7:1) point output at about 0.450V.
With that value entered in this table, the PCM will think that any voltage above.450 is rich, and any voltage below.450 is lean.The way to increase MPG is to lower this value. What you will be doing is telling the PCM that a lower voltage is the halfway point, which it will do its best to reach via the normal BLM setup. The result is that what used to be considered lean (say,.400V) will now be considered ideal, and the PCM will correct for that leaner output of the O2 sensors, thus giving an AFR of leaner than 14.7:1, which will use less fuel and increase MPG.Because stock-type O2 sensors are 'narrow-band' (they are only very accurate along a short range of voltage), you cannot go too far or you'll end up in the less accurate range of the sensor, and may get inconsistent results (a wildly swinging AFR, perhaps even dangerously lean). Exhaust temperature will also affect voltage, meaning at a different exhaust temp you may be at the same AFR but the sensor will read a different voltage.I can't recommend any particular value because of this limitation of the sensor; but anything lower than stock should increase your MPG. It is up to your accepted level of risk of running overly lean that will determine how far you should go.
Spark TimingTiming makes a large difference in combustion efficiency. A more efficient combustion means less fuel is needed for the same amount of torque output, which also results in better MPG.As mentioned above in the Idle tuning section, (probably due to less unignited fuel burning in the exhaust).Especially with aftermarket cams and displacement, more timing advance will generally equate to more MPG. The only reliable way to tune accordingly is trial-and-error, as mentioned above for spark timing tuning.
Most often, the top-end of timing that you can without any knock will give you the best combustion efficiency and, therefore, the highest possible MPG. MICROSOFT EMAIL USERS PLEASE READ!If you send me emails or signup and/or place orders from an @hotmail.com, @msn.com, @live.com, or @outlook.com address, but do not receive a reply from me or emails from my website, please do not think I am ignoring you! Lately, those email providers are randomly blocking emails from my servers. If you are on Facebook, like and contact me from there to ensure I've received your message and request a reply on there.
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