LS1 Swap Issues

UPDATED HPTUNER Logs page 2.

LS1 swapped (cams/headwork/professional dyno tune on stock PCM) Racecar ran amazing for 3 years. Then led a series of issues at the next 3 or 4 events; 

- Misfire feels like running on 7 cylinders so swapped wires after finding some header contacted wire and cured for a day

- Misfire returns next event feels like running on 7 cylinders again so swapped wires again problem continues

- New plugs/wires/sensors all over the motor, problem seemingly getting worse with now problems as soon as you go to tip the throttle in off idle

- Car bogs down with any throttle application

- Shop screws around with it for 6 months and replaces all the sensors I already replaced. 

- Now time for me to get back to actually diagnosing whats wrong. Have good fuel pressure so went to checking spark. 

- No codes being thrown or misfires being detected by the worthless GM PCM

Can anyone explain this? The plug wires induce the timing light/rpm detector on ALL drivers side plug wires but do this on the passenger side plug wires: 

https://www.dropbox.com/s/hxwxanzwn4noylx/2022-06-25%2015.38.05.mp4?dl=0

I swapped one of the "bad" coil packs to the other side and the problem remains. Do I start tearing apart the wiring harness all the way back to the fuse block for this side of the ignition bank or is there a better method for next steps? Do I run a compression test? Is there something I can monitor with my scanner while running that would help narrow this down? Guess I could check O2's for that bank and see if they are running really really rich or would it be fuel trims that would go really negative on that bank to compensate for lack of spark if that was the issue?

I recently found that my emergency shutoff seemed to be failing and intermittently screwing with my power feed to the fuse block so jumpered that for the time being while I sort this out (although that may have caused some of this issue to being with). 

Thanks in advance!

Bought a spark tester and spark is showing on those cylinders so hit a dead end there. damn.

Don't mean to be a downer, but I had an LS1-powered Camaro from new and had numerous engine issues. The worst was a very small water pump leak, which shouldn't have been an issue, but with this engine, it drips right down into the electronic distributor module.

While it's "probably" not your issue, you might want to look around that area.

If you have a pcm 12200411 -I would verify that there is battery positive voltage to pins c1-20 and c1 57 . If there is -I would send the pcm out for testing .Since it ran fine and abruptly  went flaky sounds like something is loose or fried .

o2 sensor voltages should be fluctuating  not flat lined .In fact this should probably  be the first check .

kb58 said:

Don't mean to be a downer, but I had an LS1-powered Camaro from new and had numerous engine issues. The worst was a very small water pump leak, which shouldn't have been an issue, but with this engine, it drips right down into the electronic distributor module.

While it's "probably" not your issue, you might want to look around that area.

You must have had an LT1, LS1s did not have distributors.

Pete. (l33t FS) said:

kb58 said:

Don't mean to be a downer, but I had an LS1-powered Camaro from new and had numerous engine issues. The worst was a very small water pump leak, which shouldn't have been an issue, but with this engine, it drips right down into the electronic distributor module.

While it's "probably" not your issue, you might want to look around that area.

You must have had an LT1, LS1s did not have distributors.

I, sir, shall go sit in the corner...

In reply to kb58 :

Is ok.  They decided to call one of the new direct injected engines based on the LS architecture the LT1, because Chevy gonna Chevy

dave215 said:

If you have a pcm 12200411 -I would verify that there is battery positive voltage to pins c1-20 and c1 57 . If there is -I would send the pcm out for testing .Since it ran fine and abruptly  went flaky sounds like something is loose or fried .

Any tips on where I can send the pcm to have it checked out? Would hate to lose this expensive dyno tune after it was running so well. 

My foxwell is showing it is sitting in open loop, won't go closed loop. For some reason it reads fuel trims at -1 for both banks ST/LT.

Guessing buying some fancy software is next. Maybe that would allow me on misfire detection so I can get some more info on what is going on. 

dave215 said:

o2 sensor voltages should be fluctuating  not flat lined .In fact this should probably  be the first check .

O2s are new and appear to be fluctuating. Both reading somewhere around 50mv I believe

In reply to Olemiss540 :

SIA electronics in Tilden ,Illinois did one for me several years ago .

In reply to Olemiss540 :

you should see  big swings  from 90 to 40 -if it's hovering around 50 -that's a default condition .

Have you checked all the ground wires with a meter ?

dave215 said:

Have you checked all the ground wires with a meter ?

I will start this afternoon. Just setup multimeter between the negative on the battery and all my various chassis grounding points to make sure resistance is very low? 

Sorry for the questions, but electrical systems are not my strong suit whatsoever so patience is appreciated! 

dave215 said:

In reply to Olemiss540 :

you should see  big swings  from 90 to 40 -if it's hovering around 50 -that's a default condition .

I will check this out further. I really cant do much but idle since when I add throttle it bogs down. I can get it to rev up if I am very gentle with the throttle and once I am in the power band it seems to smooth out and blip. 

Revs/RPMs hang though on the way back down. Takes 10-15 seconds to settle back at idle (900ish rpm).

I am leaning towards a short in a O2 ground or power just due to the fact the car wont go into closed loop (per my handheld foxwell). 

The custom tune could complicate diagnosis -don't know what's  turned off ( if anything ) .All new sensors does not help -just introduces more variables . Good place to start is the grounds . Then wire continuity from sensor connector pins to ecm .

The scanner does provide valuable info -o2 sensors working -map values  -engine temp which is a critical sensor .

I have read that there were some sensor changes over the years might be good to compare original sensors to the ones installed .

The intermittent power to the  ecm is a concern -but the above steps may alleviate concern .

I have a LS1 swapped car as well.  My go-to at these times is to inspect and clean all of my harness grounds.  I also clean the terminals and clamps on the battery.

Will your scan tool force open loop operation to take the o2 sensors out of the question?

Have you tried shaking with wiring harness?  If that makes it better or worse will give you a clue about where to look.

I'm no expert, but this exact situation happened on my LS1 swapped 944 and it turned out to just be a massive vacuum leak...  Turned out the rear intake vac line had cracked on the hard plastic, so while the tube was attached, it was just open and floating around. 

I know you've proabably checked it, but figured I'd throw it out there just in case.  The most obvious solution is likely the simplest. 

Wait... check the dumb stuff first before you suspect the ECM.

My guess is that you have a valve sticking, or a pushrod too long.  Maybe just a leaking valve or a scored seat.

Are you sure the injector is squirting right?

Curtis73 (Forum Supporter) said:

Wait... check the dumb stuff first before you suspect the ECM.

My guess is that you have a valve sticking, or a pushrod too long.  Maybe just a leaking valve or a scored seat.

Are you sure the injector is squirting right?

Is there a good way to diag? Just run a compression test?

Don't know how to test the injector spray given I am not getting misfire detection due to tune. It's running RICCCCHHHHHH based on the smell of my garage.

golfduke said:

I'm no expert, but this exact situation happened on my LS1 swapped 944 and it turned out to just be a massive vacuum leak...  Turned out the rear intake vac line had cracked on the hard plastic, so while the tube was attached, it was just open and floating around. 

 

I know you've proabably checked it, but figured I'd throw it out there just in case.  The most obvious solution is likely the simplest. 

Pulled intake last night to check and found one vac leak but didn't fix my throttle tip in issue or car not wanting to go into closed loop. Will stay on the hunt maybe use a propane torch to see if I am missing a leak somewhere.

dave215 said:

The custom tune could complicate diagnosis -don't know what's  turned off ( if anything ) .All new sensors does not help -just introduces more variables . Good place to start is the grounds . Then wire continuity from sensor connector pins to ecm .

The scanner does provide valuable info -o2 sensors working -map values  -engine temp which is a critical sensor .

I have read that there were some sensor changes over the years might be good to compare original sensors to the ones installed .

The intermittent power to the  ecm is a concern -but the above steps may alleviate concern .

Intermittent power may not exist, could have been my AIM screen going kaput instead as it died last night during troubleshooting. 

I will get some video of the live feed scanner and put up a link in case anyone here spots something I dont.don't.

Will also focus on grounds for the next few days as it's a frequent issue with swap cars.

In addition to the grounds, I'd take a look at some basics:

-fuel pressure check under the following conditions:  not running, running at idle,  throttle tip in, gradual throttle application, and at higher rpm where you said it seems more responsive. 

- compression check warm and cold

- if you have cats installed, try unbolting the joint in front of the cart or removing the O2 sensor in front of the cat and running it to see if the tip in problem improves. Clogged/restricted cats can cause the bog at tip in, but the engine will accept gradual throttle application. It could also mess with O2 readings causing rich condition. 

- you can also use the propane torch to richen the mixture into the intake to check O2 sensor behavior and if the signal is real or default. 

You mentioned moving coils.  Have you tried moving injectors?