LSX454 w GMPP E67 ECM - Idle Surge

[LastCall]

Working on a GMPP 454 LSX with matching GMPP E67 ECM and it has a bad idle surge. Surging a few hundred RPM, mostly shortly after start up when it transitions from cranking to running. Looks like timing is the main culprit, but it affects everything else. I've played with min idle air, base idle timing, high octane timing, prop gain for idle, idle under/over timing, closed/open loop, etc. Better, but still there. Do the maf readings look too choppy? I assume cam reversion? There are points when the TPS does not move, but the idle is swinging a 150-200 RPMs, from timing. It's weird, as if I'm fighting another issue, outside of the tune.

Any ideas?

[joecar]

MAF signal looks odd... what does MAF duct look like...? Can you reclock the MAF...?


( Jason, I meant to call you, but I'm having trouble with my phone "invalid battery" )

[LastCall]

MAF signal looks odd... what does MAF duct look like...? Can you reclock the MAF...?


( Jason, I meant to call you, but I'm having trouble with my phone "invalid battery" )

I thought so too. It

[camaro10]

Working on a GMPP 454 LSX with matching GMPP E67 ECM and it has a bad idle surge. Surging a few hundred RPM, mostly shortly after start up when it transitions from cranking to running. Looks like timing is the main culprit, but it affects everything else. I've played with min idle air, base idle timing, high octane timing, prop gain for idle, idle under/over timing, closed/open loop, etc. Better, but still there. Do the maf readings look too choppy? I assume cam reversion? There are points when the TPS does not move, but the idle is swinging a 150-200 RPMs, from timing. It's weird, as if I'm fighting another issue, outside of the tune.

Any ideas?
What are the LTFTs at? Looks like they are enabled, also 02s are not switching, at that rpm Id expect it to switch somewhat. Seems like an awful lot of min idle air although I have not tuned any big cube engines yet. You may have to do corrections on the maf transfer table based on your ltft just to get it close if they are way negative. Is this the original calibration? Can you post it if its not? B0138 also has a lean spot in it for cranking, I would make it match the rest at 0.95 lambda.

[LastCall]

What are the LTFTs at? Looks like they are enabled, also 02s are not switching, at that rpm Id expect it to switch somewhat. Seems like an awful lot of min idle air although I have not tuned any big cube engines yet. You may have to do corrections on the maf transfer table based on your ltft just to get it close if they are way negative. Is this the original calibration? Can you post it if its not? B0138 also has a lean spot in it for cranking, I would make it match the rest at 0.95 lambda.

Thanks for the reply.

The LTFT are enabled, but I was logging the STFT during these logs as I wanted to see the error at the time of the surge.

The factory O2's are lazy at idle with the big headers and dual 3" exhaust. They are very slow to switch, and hang lean and rich for extended periods of time. It's actually just 1 gram of air over what GM provides in the GMPP ECM for this engine. But yes, its a ton of idle air, more than anything that I'm used to. I did not change the cranking fuel, that is also what GM provides. I did use the trims to adjust the MAF table. See attached original GMPP tune.

One note, and something that is an issue, the MAF is not in an ideal location as it required almost a 20% bump in airflow values across the entire MAF curve, more down low in the idle area. For example, idle at 2500 htz, is 10 grams of air in factory cal. Trims were super lean, so I increased those values to bring them inline with the trims, which was about 36% more, at 15 grams of air.

[camaro10]

The STFTS will go towards zero as the LTFTS are learned. I guess Im confused why your looking at the STFTS with the LTFTS enabled? Not sure where you have the maf placed but Id start by copying roughly where it is placed on a 5th gen Camaro aftermarket intake if it is a card style. Do you have a wideband to confirm Its running around stoich? I would go into your dvts on the scan tool and set it in open loop and reset your fuel trims so they are at zero while in open loop than see where it is running roughly. That cam is bigger but not crazy big. Do you have any vacuum leaks?

[camaro10]

21672

Give this a try and post a log if it helps

[LastCall]

I was trying to post on my phone, but it was acting up.

Thanks for the feedback.

To answer a few of your questions, I was looking at STFT to see if they were making a significant fueling adjustment at the time of the surge.

The MAF is in a straight pipe, but upside down. Going to re-clock per the GMPP instructions (between 9:00 and 3:00).

I did not have a awideband installed on Saturday, but did previously and it was idling in the low 14's.

I did to trim reset and open loop in DVT, same thing. Unfortunately.

I don't think so, but will check for vacuum leak.

I see your tune below, thanks for sending. I'll give it a shot. Doing a quick compare, it looks like you added some P and I airflow, reduced how much the blade can open (hard limit ETC limit), min idle airflow, and idle spark corrections. I get all those changes. But what does reducing the throttle percent closed do?

Thinking more about this - I need to determine if the GM cruise and connect trans module is telling the car it's in P?N or drive. As you can see in the log, putting it in drive puts a big load on the car. 64-65 KPA in park to 70-71 KPA in drive. It also looks like the engine is super sensitive to timing or the TPS movement at .4% is causing too much of a swing in RPM.

[camaro10]

I was trying to post on my phone, but it was acting up.

Thanks for the feedback.

To answer a few of your questions, I was looking at STFT to see if they were making a significant fueling adjustment at the time of the surge.

The MAF is in a straight pipe, but upside down. Going to re-clock per the GMPP instructions (between 9:00 and 3:00).

I did not have a awideband installed on Saturday, but did previously and it was idling in the low 14's.

I did to trim reset and open loop in DVT, same thing. Unfortunately.

I don't think so, but will check for vacuum leak.

I see your tune below, thanks for sending. I'll give it a shot. Doing a quick compare, it looks like you added some P and I airflow, reduced how much the blade can open (hard limit ETC limit), min idle airflow, and idle spark corrections. I get all those changes. But what does reducing the throttle percent closed do?

Thinking more about this - I need to determine if the GM cruise and connect trans module is telling the car it's in P?N or drive. As you can see in the log, putting it in drive puts a big load on the car. 64-65 KPA in park to 70-71 KPA in drive. It also looks like the engine is super sensitive to timing or the TPS movement at .4% is causing too much of a swing in RPM.


All of the changes listed is correct. I did alot of tweaking on the proportional idle side of things on 2 ls3s I did this spring. If they were tamed too far the surge got worse. That is why I want to see how it behaves with the stock ls3 settings as far as proportional and integral. Idle area was reduced because if the e67 is anything like the e38, it has hard limits. 2.5+ is probably past that point. The percent closed is mainly for tip in, like a parking lot setting, the stock values cause it to do seem weird things with timing at extremely light pedal. Almost like it thinks you are off the pedal completely and it tries to correct timing. May also be torque management too for some strange reason. For whatever reason, lowering these values a large amount fixes that and allows it to go to the high/low octane base table upon the slightest tip in . It did on these 2 e38s atleast. I do not have your tune open in front of me now, but you may need more over under spark for in gear. .4% is the least amount of blade movement you can get as far as corrections go. That is why I upped spark corrections some to see if it helps. They both have to work hand in hand, right now the airflow side of corrections is over powering the spark side if that makes sense

[LastCall]

All of the changes listed is correct. I did alot of tweaking on the proportional idle side of things on 2 ls3s I did this spring. If they were tamed too far the surge got worse. That is why I want to see how it behaves with the stock ls3 settings as far as proportional and integral. Idle area was reduced because if the e67 is anything like the e38, it has hard limits. 2.5+ is probably past that point. The percent closed is mainly for tip in, like a parking lot setting, the stock values cause it to do seem weird things with timing at extremely light pedal. Almost like it thinks you are off the pedal completely and it tries to correct timing. May also be torque management too for some strange reason. For whatever reason, lowering these values a large amount fixes that and allows it to go to the high/low octane base table upon the slightest tip in . It did on these 2 e38s atleast. I do not have your tune open in front of me now, but you may need more over under spark for in gear. .4% is the least amount of blade movement you can get as far as corrections go. That is why I upped spark corrections some to see if it helps. They both have to work hand in hand, right now the airflow side of corrections is over powering the spark side if that makes sense

The throttle closed values makes sense. Limiting the blade by using max area might also help with the over/upper corrections as the blade will not go past that hard limit.

I️ agree, the airflow is overpowering the fluctuations. The thing is that spark and airflow are both working together to increase RPM, and then cutting it back as well. I

[camaro10]

The throttle closed values makes sense. Limiting the blade by using max area might also help with the over/upper corrections as the blade will not go past that hard limit.

I️ agree, the airflow is overpowering the fluctuations. The thing is that spark and airflow are both working together to increase RPM, and then cutting it back as well. I

Try that tune out and see after you reclock that maf. A factory ls3 uses alot more spark correction for large errors. I think around 26 degrees. I would try it than start sneaking in more timing if it helps.

[SPi]

Any word if this has helped your issues. I am currently tuning a GMPP ECM and harness with an LS3 crate motor and I'm having exactly the same issues. Only mods are longtubes and a cam 233/250 .619"/.595" 113+5. I have worked with this cam and many GMPP harnesses before without issue, not sure why I'm having problems with this one.