LS6 stroked and boosted new build. Huge coughing/studdering at 0 vac on acceleration

[Virtue]

Help please. I have gone to 3 tuners. So far, no one can fix this issue. I am running full SD. (I have a separate vacuum gauge in my pillar). My biggest issue is when I am gently accelerating, as soon as I am at 0 vacuum, the car starts to cough, sputter, and jerk. However to explain it.... But, as soon as I floor the gas pedal and pass that point, the car runs decent. Minus a few coughs in the top RPMs. The last tuner said my new 2.5 bar MAP is junk, get a new GM MAP. Unfortunately, I had already ordered another 3 bar MAP from EFI Source. They give the linear and offset numbers on their site for HPTuners. So, I just installed it in my car and it made no difference from my old 2.5bar MAP. Can someone help please. Is it ignition timing issues or what? Maybe there are other programming issues or improper tables filled too. Any help would be greatly appreciated.

And yes, it is now running pig rich because of the new MAP....

Stock 05 Cadillac P59 ECM. LS6 stroked, Pro Charger F1a. Maybe 15 pounds of boost. All forged. 230 AFR Mongoose heads. Stage 4 cam. 90mm throttle. 92 Fast intake. 9.5:1 pistons. 3 bar MAP. 800cc Siemans Deka injectors.

[SiriusC1024]

Tune.

[Virtue]

3 tuners and no go. The 3rd one has 20 years experience from Texas.... Any shop you might recommend? The sad part is that I live in Canada. I would have to send my log to them, to adjust.

[blindsquirrel]

Your tune file, the one that produced that log. Like it tells you in the 'sticky' thread at the top of this very forum.

[SiriusC1024]

3 tuners and no go. The 3rd one has 20 years experience from Texas.... Any shop you might recommend? The sad part is that I live in Canada. I would have to send my log to them, to adjust.

Your tune lol.

Right now it's pretty obvious that fueling is off, but there are many causes. Sometimes it's something stupid like wrong MAP sensor cal or injector data. It'd be helpful if you logged Injector PW.

If you don't want to worry about it and have a pro who will actually do a good job (no particular order):
https://forum.hptuners.com/member.php?4408-edcmat-l1
https://forum.hptuners.com/member.php?33521-GHuggins
https://forum.hptuners.com/member.php?5378-Alvin

[Alvin]

You really ought to delete the map sensor pid you are using and add "2/3 bar map" in the scanner. I'm assuming this has a 2/3 bar OS on it. If it doesn't it needs it.

A wideband would be helpful to.

[Alvin]

I would only use GM map sensors on this. There are plenty of options.

The aftermarket ones I've had serious issues with. There is a turbo company that sells one for around $40. I've had 3 come by the shop and all 3 have been bad.

[Virtue]

Tune.

Sorry, I didn't understand what you meant. I thought you are telling me to get a tune...
Here's my tune.

[Virtue]

Thanks Alvin.

Ok. So, question here. Knowing the limitations of my P59 ECM, would you go with a 3 bar from GM or a 2 bar GM. I do have a GM 2bar (that I know works), but, I have slightly more boost than it can read.

[Alvin]

That is a good question. You can use any map sensor with any OS.

You do loose quite a bit of resolution on these with a 3 bar OS. Considering you are only at 15 psi I might would stay with a 2 bar OS.

[Virtue]

That is a good question. You can use any map sensor with any OS.

You do loose quite a bit of resolution on these with a 3 bar OS. Considering you are only at 15 psi I might would stay with a 2 bar OS.

It was the resolution I was thinking about also. And the original tuner was thinking it would hit 19lbs, but, that was a guess. I have belt slip at the higher RPMs

[Virtue]

Come to think of it, my knock sensors should be engaging with this amount of coughing... Hmmm....

[edcmat-l1]

Most of the time, coughing, sputtering, etc. is caused by an ignition misfire. What spark plugs do you have in it? Do you know what the gap is? At the very least they should be a 6 heat range with the gap tightened up to .030 at the most. Higher boost, you need a cooler plug and tighter gap. If you're looking for 15 PSI plus, I'd recommend BR7EF plugs.

Also need to make sure your plug wires are clicked on the spark plugs and coils both. It is a very common problem, not getting them clicked properly, tightly, etc. However you want to describe it.

It's very possible this is totally NOT tune related.

[Alvin]

It was the resolution I was thinking about also. And the original tuner was thinking it would hit 19lbs, but, that was a guess. I have belt slip at the higher RPMs

If it will be at 19 psi I would for sure do a 3 bar OS.

[Virtue]

Most of the time, coughing, sputtering, etc. is caused by an ignition misfire. What spark plugs do you have in it? Do you know what the gap is? At the very least they should be a 6 heat range with the gap tightened up to .030 at the most. Higher boost, you need a cooler plug and tighter gap. If you're looking for 15 PSI plus, I'd recommend BR7EF plugs.

Also need to make sure your plug wires are clicked on the spark plugs and coils both. It is a very common problem, not getting them clicked properly, tightly, etc. However you want to describe it.

It's very possible this is totally NOT tune related.

I have iridium plugs installed. The second tuner insisted on them. He also insisted on doing a compression check. It took them 2.5 days to take my plugs out and do a compression test by hand. Yup, they turned the engine by hand and not by the starter. All measured good though. And they were not able to put the plugs back in. It was too difficult for them... so I had to do it. It has been a nightmare for me.

[Virtue]

Here's a thought for everyone. This coughing, sputtering is only at 0 vac. Thinking out loud here. Is this when my blow off valve closes? Maybe there is a rush of air going into the engine and causing a lean situation? I know my throttle would be open slightly because I am slowly accelerating.
Any thoughts?

[edcmat-l1]

I have iridium plugs installed. The second tuner insisted on them. He also insisted on doing a compression check. It took them 2.5 days to take my plugs out and do a compression test by hand. Yup, they turned the engine by hand and not by the starter. All measured good though. And they were not able to put the plugs back in. It was too difficult for them... so I had to do it. It has been a nightmare for me.

If it's difficult to put plugs in it, chances are you cracked one or there's an issue with the wires being fully snapped on the plugs.

Irridium plugs, the gap is too big for a boosted engine. If they weren't tightened up, that's a problem.

I do not use Irridiums in anything that makes any amount of boost.

Edit: You can't do a compression test cranking an engine over by hand. You can't spin the engine fast enough.

[Virtue]

If it's difficult to put plugs in it, chances are you cracked one or there's an issue with the wires being fully snapped on the plugs.

Irridium plugs, the gap is too big for a boosted engine. If they weren't tightened up, that's a problem.

I do not use Irridiums in anything that makes any amount of boost.

Oh man. I know my plugs are good and not cracked. The car takes off after that 0 vac transition point. They didn't realize you need to take the valve cover off to access the plugs easier. There's no room if you don't do that. And the headers make it worse. haha. And my wires are new.

I will check my plugs out again. 4 hr job.....

[bk2life]

NGK-BR7EF at high boost

i like this for plugs https://sites.google.com/site/sloppy...ls/spark-plugs

[edcmat-l1]

Oh man. I know my plugs are good and not cracked. The car takes off after that 0 vac transition point. They didn't realize you need to take the valve cover off to access the plugs easier. There's no room if you don't do that. And the headers make it worse. haha. And my wires are new.

I will check my plugs out again. 4 hr job.....

If I had a nickel for every time someone told me "My plugs and wires are fine" only to have been wrong, I woulda retired long ago.

Stutters, sputters, coughs, etc. are by a huge margin, caused by secondary ignition misfires i.e. cracked plugs, too wide of a plug gap, or wires not fully snapped on either the plug or coil.

New plug wires doesn't mean anything. It's typically installer error. And if they're MSD wires, that's double trouble. They're terrible. They lose their "snap" after going on and off a few times. And they pull apart inside way too easy.

AC Delco plug wires FTW.