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Not sure if this is the right place to post I'm just looking for some responses. I swapped the wiring harness for my ls2 swapped c5 back in the end of June, and i havent had it running since. At first its because the instructions were terrible. But now ive been through every inch of that harness. Ohmed most of it out, and checked my sensor readings. Basically the car cranks fine. It will fire momentarily and then go back to cranking and it wont fire again without cycling the key. If you time it and put the pedal to the floor right as it fires( not before so it doesnt activate flood clear mode) it will sometimes sot there and sputter at like 400 rpm for a few seconds before lazily revving up all the way to neutral rev limit. 5k ish. Presumably misfiring, but i just changed my plug wires and it seems a lot smoother but still doing the same thing, just with less backfiring. It has fuel pressure. Maps mafs tps cam and crank sensors and ect sensors all seeming to read correctly. O2 sensors are sorta unknown because of the shitty app and bluetooth scanner i was using. But ive read they wouldn't cause a motor to outright not even idle. So basically, im lost, please if anyone has any ideas what could cause this unusually specific set of symptoms i cant find anywhere else on the internet. Please help.
How are you reading your cam and crank sensor as you had mentioned ??…with a scope ??…if you didn’t that’s how you’re supposed to be checking it…sounds like a timing problem…now you using the PCM from whatever C5 you have ??…now isn’t the crank sensor on the LS2 a 58X reluctor ??…the LS1 uses a 24X crank and a 1X cam sensor…both use a 12 volt reference…does the LS2 use 12 volts or 5 volt reference ??…I don’t know for sure so those are the things you have to know !!
So i am reading the rpm signal. Not the crank or cam sensor signals directly. The motor is set up with 24x crank reluctor, and 2x cam. As far as i can tell by the color of the crank sensor. And right after swapping the harness is would idle fine with the tac module unplugged but had a dead throttle. Then one day the symptoms switched all up. Not idling. But throttle working perfectly. Still using the original 0411 pcm. Old harness was a chopped up ls1 harness. New one was made for ls2 24x with 0411 pcm. Made by PSI
Last edited by Plizhelp; Oct 11, 2021 at 08:41 PM.
The RPM signal isn’t really telling you if the relationship between crank and cam signal is correct…the OEM PCM is looking for a 1X cam signal and not a 2X which you say you have…the ignition and injector timing may be wrong…don’t know what else to tell you and like I said I don’t know if your cam and crank sensor use a 12 volt or 5 volt reference…OEM PCM is looking for a 12 volt reference as you can see in the cam/crank waveform on my 01…blue is crank and red is cam signal…your PCM is expecting to see this waveform !!
I see. All i know is it was running before i changed out the engine harness. I assume i am misinformed about which cam sensor goes with the 24x crank sensor. Also i believe it is a 5v reference. And unfortunately i do not have the tuning software or hardware to hook my computer up to the car and get that kind of information. Working on finding a friend of a friend to help me out. Sorry for the slow reply…college.
Last edited by Plizhelp; Oct 19, 2021 at 10:05 AM.
How about pulling the DTC codes. There may be a clue in the DTC’s as there are some codes related to the cam/crank sensor, particularly, for shorts and open circuits. When you say you swapped harnesses, that raises a big flag, as the LS2 came from a C6. The codes will tell you if you have wiring problems. There are many posts here to help you use the on-board diagnostic for codes. You only need the codes for the PCM for now.
How extensive was the harness swap. was this a wire-splice swap, or did you totally remove and only plug into the pcm, TCC, TB, fuse block, etc.
First thing I would do is put a pressure test gage on the fuel rail. Then a spark tester to make sure you have spark. You have to get the engine running to to a crank sensor re-learn, which is a key to proper timing. Of course if the engine has mechanical noise, your knock sensors could cause a problem.
I think you may be in a deep hole unless you can access a good scan tool and a good ‘scope (Pico)
I was seeing codes for cranks sensor variation not learned, random/multiple misfire, and map sensor circuit low or something like that i could double check. The whole engine harness was changed out, from pcm to sensors. Aftermarket fuse block wires in with the harness. I have not tested fuel pressure directly. But i put in a brand new higher flow fuel pump a month or so before the swap and it was running well, smoother than before. And not i have a hotwire switch running to the trigger post on a relay in the back that receives constant power from the alternator. I can hear it running when i flip the switch.
i also bought a inline spark tester, but i have not used it yet. Will get back to you with results when i do. If you think i should post elsewhere, please point me in the right direction. Thank you for your help.
Mass confusion
