I just rebuilt the engine in my 02 vette and changed a bunch of parts. It has NOT ran yet. The problem is that when I turn the car to the RUN, (not start) position I hear the spark plugs firing all at once. I pulled a wire off, inserted an old plug, and grounded it to confirm this and the plug constantly (continually) fires WITHOUT the engine turning over. I checked one from the other bank and same thing. Only thing I can think is bad (new) Crank position sensor. Also, I tried to hook two different scanners up to the port and they both said "unable to establish link" and the dash says "reduced power mode".

Thanks in advance.

 

Your PCM is what tells the coils to fire and also lines up with you not being able to connect to it. Probably need to check it out make sure the connectors are seated and then check out powers and grounds to start. Hopefully it's something obvious and not your PCM is smoked.

 

Maybe completely unrelated, but....

I saw this happen of all things with a gas stove. Every once in a while the igniters would just repeat fire - click-click-click - for minutes at a time until it finally stopped for a while. It was the board that controlled the ignitors. If you think of the igniters as spark plugs, which they are, then I would say it points to a bad pcm.

 

Or a weak board on the smart coils if equipped..

 

Yeah, I am leaning towards ECM as the car has been without power (battery disconnected) for about two months while I was working on it. The way I figure it is the crank and cam position sensor tell the computer where the engine is to adjust the spark, and the ecm tells the coils when to spark. I am pretty sure I got all the grounds back on but I will do a quick look again to make sure. I did what I dont like doing in making a lot of changes at once. I changed fuel pump, fuel filter, transmission, shift kitted it, stall converter, rear differential with better gears, rebuilt the engine with a bigger cam. So the ecm might be confused as hell right now lol.

 

None of the mods you did should cause the issue you are having.

 

I agree. I saw a video that went in depth of the issue and it turned out to be the computer. I am checking the other things now before I buy another computer.

 

^^ You're on the right track. Scanner Danner and the South Main Auto youtube channels are excellent for diagnostic processes and both have a wealth of experience and knowledge on this. If it was me I'd be trying to make 100% sure it was a PCM before I wanted to walk into the giant pain in the *** of replacing one.

Out of curiosity have you tried unplugging a bank of coils and seeing if the other keeps firing?

 

I took my PCM to my tuner and he tested it and it tested good. his suggestion is the Crank position sensor or possibly coil packs on wrong side. I cleaned grounds, and swapped coil packs from side to side and same issue. I will pull my header, starter, and crank sensor tomorrow. possibly a pinched wire.

 

Start with, what did you change that could impact PCM? You could pull cam and crank sensor connectors. You could back probe the cam and crank signals at the PCM to see why they may be triggering the ignition coils. I would look into the communication issue with the PCM. Verify power and grounds. Without comm, hard to see what's going on. Do you have engine controls wiring diagram?

 

no pinched wire. A spot of dirt on the end of Crank position sensor but nothing else. same issue 1 coil bank only connected. Same issue crank position sensor hanging loose. same issue crank position sensor disconnected completely. I guess I can disconnect things one by one and see if it goes away. running out of options.

 

I am thinking somewhere there is something connected incorrectly. Tuner told me that crank position controls spark, cam position controls injectors. So as I have crank position loose I will trace wires back to pcm. then do the same with cam sensor just for grins and giggles.

 

new engine, transmission, fuel pump, and differential, all at once. lol

 

How did your tuner verify the PCM? As far as I know right now you'd have to scope those sensors to see what is being commanded from the PCM to the coil and what the signal from the crank and cam sensors look like.

We know your coils are good since they all fire and the odds of all 8 failing are pretty slim, really only leaves the cam, crank and PCM as variables in this problem. It's very odd your PCM won't allow communications unless you got that fixed if not I'd look into troubleshooting comm issues to PCM as that may lead you to the root problem as well.

I would probe the PCM connector where the cam and crank sensor inputs come in and the PCM output at each coil and see if one of them is just constantly sending voltage down it like it shouldn't. The coils 4 wires should be from left to right 12v at keyon, control signal, a reference low (from the PCM), and a chassis ground. I'm really leaning to PCM after seeing the wire diagram, I believe that PCM will only attempt to fire the spark 1 time per event from the crank (believe this is what the reference low wire is for as all coils on a bank share it back to the PCM so it can see coil fire events) not continuous like you have and removing the crank and cam connectors I believe should stop this behavior if they are doing something crazy there.

Pinched wire doesn't really make sense as you would have had to mess up a whole bunch of signaling wires and not just a ground or something as then they wouldn't fire at all.

 

Also another quick though is have you pulled the connectors and verified the pins are all good, straight, and seated well so they don't push back into the connector? I've seen bent pins bridge things and cause crazy **** like this before too.

 

 

Well, I checked all the wires to make sure they were on the right thing. They were. I disconnected everything I connected, Crank sensor, cam sensor, Oil sender, Knock sensors, oil temp, Intake, starter, Alternator, oil level, and one coil bank. I didnt disconnect transmission or differential. With EVERYTHING front end disconnected, it still constantly sparks without the engine even turning. Run position only. Only thing left is PCM I think. Sooooooo, I will change that when it arrives and hopefully that solves the issue.

 

All pins looked good. PCM was plugged into his laptop and he acted like he wanted to put a tune on it. It was accepting of the tune. So, my guess is that didnt actually check the communication FROM the PCM, but simply allowed communication to go TO the PCM.

 

Bizarre. I believe that HPTuners requires bi-directional communication so it can verify VIN and whatnot for licensing. At that point unless you want to buy a scope or take it somewhere I'd probably be trying a junkyard PCM at that point too. Keep us posted.

 

A junkyard PCM was 40 a "rebuilt" pcm with my vin installed was 60. so I got that one and bought a HPtuner to put on a running tune if this solves it. I am leaving everything disconnected just in case it does the same thing then I will have to get more in-depth with the wires and testing components separately.