VE Correction Factor P01/P59

They go by many names, P01, P59, VPW, '0411 etc . Circa 1999 to 2006. All VPW OBD2 PCMs.
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VE Correction Factor P01/P59

Postby RADustin » Wed Jun 22, 2022 8:54 am


I have a tuning question, but to understand how or if to adjust I must first understand what the underlying code is doing.

I have a 496 big block running a P59 in speed density, uses an EFI COS based on OS ..618. Has large AFR heads and 244ish cam with a bunch of overlap. The VE table and everything else is tuned at operating temp as would be normal practice. What I realized though is starting cold and allowing the engine to warm up, the air mass model in the PCM is way off(high, so engine runs very rich) and tapers back to correct as the engine warms up. To fix this in a pinch, I'm taking out ~50% of the fuel at 40C and taper to 1EQ at operating temp. This works and keeps the engine from fouling out while warming up.

B3605, OLFA table, in lambda. This works, but I consider it a band aide to a larger problem.
B3605_OLFA_10_10.PNG (63.41 KiB) Viewed 826 times

This whole tuning process has been overshadowed by what I consider large amounts of desired base airflow and startup airflow. My theory is that if the airmass model is wrong at less than operating temp conditions, and reporting higher than necessary airflow and therefore providing more than necessary fuel, that any sort of RAFPN tuning would be skewed at lower temps and give me the higher numbers. I'll mention, the engine starts fine hot.

For whatever reason, it appears this engine combo is much less efficient at lower coolant temps, so I started looking for a table to adjust the VE based on coolant temp. I found the VE correction factors in the ...604 XDF as well as in HPT. So I ported those tables over to EFI for the ...618 OS and am ready to try modifying them, but I'm realizing I don't understand how the table functions.

VE Correction Factor.PNG
VE Correction Factor.PNG (60.42 KiB) Viewed 826 times

The description is that the VE Correction factors in the tables are used to initialize a value, which I figured is then updated. Without a MAF, running speed density I'm not sure how it can be updated? This is where I'm looking for some insight into the OS of the PCM to understand how the values from this table are used within the speed density dynamic air mass calc. Are the correction factors reloaded often from this table? or maybe only at startup? Are these corrections multiplied into the VE table, or divided?

Potentially I can log EQ error correction between commanded and actual and use that to 'tune' in this table for different coolant temperatures. At the least I figure I can set this whole table to 1.0, and set the min and max correction to 0.999 and 1.001 and at least make it one less modifier to get in the way.

If this table isn't what I need to modify then I guess I will stick to looking for a problem with the dynamic temperature calc. Potentially it is an issue with the IAT being mounted in the aluminum intake manifold and instantly heat soaking(single plane carb style intake)....but the IAT is believable as it's just a standard 14" airfilter that draws in underhood air.

Curious what you guys know about how these internal VE corrections are used, and how they are best adjusted for speed density tunes. From what I gather here I can make a plan for my next moves. Thanks!

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Re: VE Correction Factor P01/P59

Postby bubba2533 » Thu Jun 23, 2022 1:39 am

If you are using speed density (the MAF is failed) the VE Correction factor is not used at all in the fueling calculations.

You seem like you are changing the correct fueling table for open loop. I don't see that as a band-aid, but then again I'm no professional tuner.
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Re: VE Correction Factor P01/P59

Postby RADustin » Thu Jun 23, 2022 5:10 am

cool, this tells me what I need to know.

yeah the OLFA table works, just seems crazy its so far off when cold. but then again, all we're looking for is the right amount of IPW at the right if you get that then it's hard to complain.

I have a few different things I'm going to chase, we'll see if any of them make it better. one thing I am going to do is set all the VE correction stuff to 1.000 so it becomes a non factor.

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Re: VE Correction Factor P01/P59

Postby Phoenix » Fri Jun 24, 2022 12:54 am

Have you thought of trying to move the cylinder charge temperature bias more towards the ECT? I use this in supercharged applications where the IAT gets really high in idle situations while sitting in traffic, sounds like you are having a similar issue.
Charge Bias.JPG
Charge Bias.JPG (104.47 KiB) Viewed 723 times

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Re: VE Correction Factor P01/P59

Postby RADustin » Wed Jul 06, 2022 12:58 am

Phoenix wrote:Have you thought of trying to move the cylinder charge temperature bias more towards the ECT? I use this in supercharged applications where the IAT gets really high in idle situations while sitting in traffic, sounds like you are having a similar issue.

as I have a MAT instead of a IAT, I'm going to turn off the complex model and run it straight up on IAT. I haven't done this yet, but it's the general plan. When you're running down the street the charge gets cooler, and based on sensor location I believe the IAT only to be more accurate than blending with ECT. The air only travels ~6" past the 'MAT' sensor before it's in the cylinder.

this engine doesnt have an intake tube or anything, and will pull in hot underhood air all the time. So I think it'll be fine-we're going to see.

The VE corrections are neat to think about though while VE and MAF tuning at the same time using the EFILive method. The reported VE table lookup DMA pid is actually skewed by this correction, which EFILive method doesn't account for. For sure moving forward I will no longer use this method on MAF equipped engines, I'll tune VE in SD mode and then separately bring on the MAF and set the air model to MAF only to tune that.

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Re: VE Correction Factor P01/P59

Postby Cincinnatus » Sat Jul 09, 2022 8:54 am

Your engine is inefficient at low rpm with that cam and large runners. You're running rich because a stock engine makes it's torque down low in the rpm range (short duration cam, low to no overlap)and you're airmass is all wrong at low rpm with stock tune. I'm not a tuner with pcms, but have built and tuned carbureted engines. I'm getting ready to have to tune a small cammed 5.3 ls and will surely start a thread when I get it running. Wouldn't that EFI COS VE table need changed significantly for that cam? You have a wideband? I don't think your engine is inefficient at colder coolant temps, it's inefficient at all temps at low rpm. I think you might be rich at warm temps too. Would love to see what you have under hood RADustin

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