hungryhobo

I've recently acquired this vehicle. It was a 1200$ craigslist special that I snagged after an uninsured motorist took out my prized '85 firebird. Low on funds and desperate for wheels. I bought this thing, knowing it would need some tlc, and happy to give it.

I enjoy tinkering, and wrenching, however this current issue has me banging my head against the wall.

The car was badly neglected by the PO. When I got it..coolant was leaking from the fitting under the throttle body for who knows how long..it had a high idle issue, the thermostat was stuck open..it seems to be leaking oil from the rear main..the thing is a mess..however i needed a new hobby toy/daily driver, and it had fresh rubber on it and drove in a straight line (and i wanted my t-tops back!) ..even with 207k on the clock.

I fixed the coolant leak. I fixed the vacuum leak (high idle) by removing the plenum and replacing the gasket as well as new injector o-rings. All was well for a few weeks after.

Then, this current issue hit me..which I think was there all along, just not in such severity. When i first test drove the car and stomped the throttle it fell on its face when it hit around 4500 rpm..I didnt think much of it because i dont do much WOT driving..Ive nothing to prove with a tiny 3.4 and just need a daily driver.

However it started getting worse. It started falling down around 3k rpm. Then it progressed to the point where i couldnt even limp around under 2k without the hitting this ceiling where the tach needle flutters about and the car can barely catch itself to stay running...To the point where i couldnt even get it to start.

I didnt have an aldl cable at the time. I checked every sensor I could. I replaced the 3x crank sensor and the wires. I managed to find some bad wires inside the 5 pin harness to the icm. they had seemingly melted together (presumably from a bad ground). I could wiggle the wires in that harness and cause the car to die before i butt spliced them (not the best fix..i know)

Then I get to the point where im up and running, but if I push down on the lower coil (directly under the icm guts) that it would die. So i figure I had it then and bought a new coil. Still dies by pushing down on it. So I logically take the next step and replace the ICM (even though it tested good at a parts store). Same problem. I took the icm back, because 100$ is a big hit to me..but I kept the coil. I could get it to start and run but anything over 3 grand and the tach flutters, exhaust popping, care catches itself sometimes..sometimes it dies.

I keep thinking ground issue. So I run a direct ground from battery to one of the coils. (tried the icm base as well) I thought i had it whipped. It ran good for a whole weekend. Im constantly stressing it meanwhile..running up the rpms to see if it will falter..Eventually it does, when i finally think its fixed.

Ill go above 3k and it will hit a wall and stumble..sometimes die. I broke down and bought a breakout board for 20$ shipped that allows me to just hook two wires to it directly into the aldl connector in the car, and with the aid of the awesome scan9495 software I can now read anything and everything the pcm is doing (thanks GaryDoug).

I think a lot of this is anecdotal..meaning, something else is the problem, and while im playing while ground wires..whatever is really the issue im inadvertantly "fixing"..

Well Ive been logging data for a few days now and nothing really pops out at me like I hoped it would. Granted one has to really know how to interpret the data thats in front of them..Which is why Ive come here for help. I saw the misfire thread above and I was hoping Injuneer or GaryDoug could maybe chime in and give a hand.

Today I messed with the main engine ground. Took it off and Cleaned it. It wouldnt start afterwards. I gave up and went back some 5 hours later and it fired right up. However I couldnt get above 2k again without it dying. Ive played around so much that now ive managed to strip the ground threads in my battery, which i now have to re-tap unfortunately..and it being lead..Im not sure how well thats going to go..It just seems like every time I mess with the main ground I can get it to at least start..Like maybe its inside the connectore that bolts to the battery. I ended the night when I couldnt get it to start..again.. Im really at a loss here and Im hoping someone can see something in these logs that I cant..Im wondering if maybe the injectors are at fault, as was the case in the misfire thread stickied above since I did have them out when I redid the upper intake gasket..

Im sure there is some info Im leaving out but that the gist of it anyway..I doubt with me being a new member that Ill even be able to upload these logs but Ill try anyway..I appreciate any suggestions I can get here and Ill definitely answer any questions on the topic as soon as possible/

hungryhobo

most recent log. shows me idling, then revving, and it dies..a few times

Injuneer

I'll take a look at it tomorrow. I've only looked at one other V6 log so far, and it was a lot different than what I'm used to looking at with the LT1.

hungryhobo

Hey! I'm so glad the master has replied! Thank you so much for joining in.

It fired up easy as ever today. Can't get past 3 grand still though.

I hate to throw more money at the problem but I'm thinking I may have to buckle down and buy an injector or two. Idk if I can afford a whole new set, even though I know they're supposed to be replaced as such

Injuneer

I need to understand what you posted above:

What part is "under the ICM guts"? There is a rectangular bracket under the coil/ICM assembly. The matching rectangular size ICM sits on the bottom bracket, and 3 dual-tower coils sit on top of the ICM. All this bolts to the ICM and power steering pump bracket. Are you describing some sort of a sensor on the engine below this area?

With regard to the data log, I don't see where you actually got it up to 3,000 RPM while actually being driven. Was this because it wouldn't go above ~2,500 RPM, which is the max that I see?

The thing that stands out to me is the discrepancy between the RPM indicated by the 3X crank position sensor and the RPM indicated by the 24X crank position sensor. When the 24X sensor seems to be "stuck" on ~2,000 RPM, the 3X RPM gets strange and starts jumping up erratically, at one point reaching 5,800 RPM, which is probably enough to hit the rev limiter, IF the PCM uses 3X signal preferentially over the 24X signal.

I need to review the 3.4L ignition control system a bit more, to see how it uses the 3X and 24X data. There may be an explanation of the differences in reading in there.

hungryhobo

I used that description to badly explain which coil I was pushing down on. Which would be the lowest one. The one that sits directly on top of the rectangular ICM box..or the brain..or guts.. So it would be the coil firing number 1 and 4.

I noticed the discrepancy between sensors as well. The 3x is brand new. Installed it a few weeks back.

The way I understood it after reading on the ignition system myself is that
The 3x is used primarily by the ecm. With the 24x being pretty much for the tach only.

The 24x being higher resolution.. Can't accurately read at higher rpm. (It can, but it uses up too much valuable pcm bandwidth) It's used at lower rpm to some extent. But at higher rpm the 3x is what counts. The 3x feeds directly into the ICM. The ICM then relays that signal to the PCM.

So the way I understand. I shouldn't think too far into the huge difference between them at high rpm. They tend to match at lower rpm.

I think in that log I may have mad eit to around 4k at one point. I do have a couple other logs of me just driving around town. I just figured the meat was inside the one I posted.

Sorry for the rushed response I typed this up at work..

Injuneer

Appears it stalled at some point, and when you tried to restart it, DTC 82 set, which is a problem with the 3X crank position sensor. That code only sets when trying to start the engine. The ICM sends the 3X signal to the PCM. The ICM also sends the RPM signal to the tach. The 24X sensor is only there to provide a higher resolution crank position signal at idle and during low RPM, which explains why it doesn't go much above ~2,350 RPM.

Definitely pointing to some sort of problem with the 3X crank sensor. That connects directly to the ICM. It has a pair of wires that have to be "twisted" a minimum of 9 times per foot. I suspect that is to resist high voltage interference. Is this possibly the "coil" under the ICM you replaced?

Injuneer

Skip the question about the coil you replaced being the 3X sensor. I was still typing when you posted.

hungryhobo

I had assumed the 3x code got set while it was stumbling around trying to stay running after revving.

I think I mentioned before that the 5 oin harness next to the 3x..both plug lging into the ICM side by side..had a couple wires that seemed to degrade or melt together. I fixed those.. At that point I could wiggle the wires in the 5 pin and make the car die. I haven't followed the 3x wires all the way to the sensor mainly because it's buried inside plastic sheathing running under the car, although I have read reports of the wires melting the exhaust manifold.. I've tested the harness before with a dmm set to AC voltage and got a good reading while cranking. However maybe it's time that I take another look and follow the wires all the way back to the sensor :/

I do appreciate your guidance very much.. I'll tinker with it in a few hours when I get off work and report back

hungryhobo

Well..I did double check crank sensor wiring. All seems well in regards to that.

I still have this issue where I can kill the car by pushing down on the coil. I'm at a loss as to why that is happening since it did the same thing when I put a brand new ICM on there.
Still baffled. It's still sitting around waiting for me to solve it.

A few times after the engine died I could hear relays clicking as if the whole ignition system shorted out.

Also when I was checking out the fuel pump relay a while back I noticed when it falls on its face that the relay would start clicking around as off the computer was.killing the pump for whatever reason. Maybe that indicates something to amkore knowledgeable person?

Injuneer

Do any of your spark plug wires run very close to the twisted pair of wires from the 3X sensor to the ICM?

And you verified the 3X sensor wires were twisted per specification?

Are you sure you spliced the wires for the 5-pin connector in the correct order?

Is the 5-pin connector on the ICM anywhere near the coil that causes the engine to stall where you press down on it?

hungryhobo

The crank sensor wires are twisted. I made sure of that. I re routed the whole harness yesterday to get it as far away from the coils as possible

Today, I took the pins out of the 5 pin harness and re clamped the connectors to make sure it wasn't an intermittent connection. Reason being is this..

I was looking through the PCM pin out the other night. It hit me.. The DTC 82 was for a crank REFERENCE signal. Aka.. NOT the twisted pair. The reference signal is the red/black and blue wire in the 5 pin connector. The ICM received the signal from the sensor directly through the twisted pair. It then sends out a reference signal (5 volt?) To the PCM through the red/black and blue wires in the 5 pin. So I thought for sure I had it figured out..

That's what drove me to re route. Couldn't get it started yesterday after the re route. Took the ICM off and had it tested again. Still good. Today I took the pins out of the weather pack connector and went over them. It started today. Still the same issue.

I think it all still boils down to whatever is causing the car to die when I push down on the bottom coil (happened even with a new ICM) ..that's why I went down the road of adding ground wires here there and everywhere to the ICM bracket, the coil screws..etc..

It's really beyond reason to me :/ ( I haven't checked to make sure the plug wires aren't running over top of the harness though. I'll be sure to do that)

hungryhobo

When I'm scanning with scan9495 the "cam signal missing" flag intermittently flashes off and on. Everything I've read said that a cam signal isn't required but I wonder if the off and on is tripping up the PCM. I tried running with it unplugged but it still stumbled

Okay disregard the above paragraph. I've been reading through the other thread with the guy you helped with the v6. Apparently it's normal for the cam signal missing to blink on and off..

I do want to add though...since I ran into more injector info in that thread..I too, have seen the "injector fault this run" indicator.I've only seen it a couple times and it only happens after I rev enough for the car to kill itself. After the car dies I've seen that flag light up.. So maybe I need to invest in a noid light? Or at the very least go through the harness on the fuel rail?

hungryhobo

i have a log from this morning..actual road driving with it stumbling around. it died a few times and i limped to work. i havent had a chance to look myself but i did notice in ther few seconds i perused there are somne discrepancies between o2 banks

when i was pulled over after it dies, i started it back up and barely touched the coil and it died.
Which leads me to the reason I've tried running a ground to the coils themselves. There is no ground wire going to coils or ICM. Apparently it ground through the aluminum mounting tray

hungryhobo

Well there is no getting around it. The ICM and coil are the heart of this issue. I've spent 3 hours tonight trying to get it all torqued right.

If I tighten the coil screws or even push on it it kills the car.

I've not seen any more trouble codes at all. No misfires. No anything. None of it.makes any sense