Ok, so this is going to be a long post. So be forewarned. I have posted this on a few different websites now trying to find an answer Earlier this year, I upgraded the stock stereo system in my 94 Z28. Speaker change, new amp and a powered sub. Ran the power from the trunk to the red box under the hood (didn't have an adapter handy to put on the battery direct) and all the wires. For what its worth, and just to note exactly what I did, I bypassed the factory Bose amps completely and essentially just left them in to help hold the speakers. Get everything wired up, and turn it on. Aside for a very slight alternator wine, sounds awesome. The car had been setting for a few months, so I decided to take it for a quick drive to get a pack of cigarettes, and when I get onto the road I hit the gas. I start to speed up, and then it goes to shift (automatic), and it shifts HARD. Like, really hard. And then proceeds to run like its stuck in gear with some serious acceleration issues. The service engine light comes on as well. Its at this point I notice (could have been doing this prior and I not noticed,) but I see the speedometer isn't working either. Also, if it is running too long, it acts like it wants to stall out. I take it home and hook it up to a scanner and get the following codes.
​​​​​​Code 22Throttle position sensor low voltage, Code 42, 43electronic spark timing open or shorted; est low voltage; est circuit problem Code 44 (Had this and 45 for a while. Took the cats out)Lean exhaust code 45rich exhaust Code 51Pcm/ecm issue Code 53System voltage too high Code 54Fuel pump circuit fault. Code 55


Shortly after, started being nearly impossible to start, almost like it's out of gas. I can hear the fuel pump kick in, but it just spins without ever starting. Eventually, after some fighting, It will start, but want to immediately stall back out. Have to hit the gas and rev the engine up for a sec to get it going. Once its going, it will idle fine until it starts to heat up. ( Driving it will just give me a repeat of a hard shift followed by loss of power). At idle, once it starts heating up, the rpms start fluctuating. With a high of about 2.5k. and it will drop to the point it's about to quit running. It's worth noting the only mods aside from Cats and muffler is a COI. These are the things I have tried to fix it to no avail. 1.) Unhooking the stereo equipment. That was the last change, so worth a shot. 2) Did a visual check of fusable links. Nothing is burned on there. 3) looked around for loose wiring under dash since I was running the power for the amp through there. 4) changed VSS sensor 5) Changed throttle position sensor 6) Changed the alternator (to 140 amp)

7) changed the pcm.

I'm at my wits end. I'm guessing at this point. I have no earthly idea what to do. Does anyone have any insight? I even tried taking it to a shop, but everyone around here won't touch it because its too old. Say they don't have the equipment.

Did all those codes disappear after you cleared them?

DTC 51 is for an “EEPROM Programming Error”. Something upset the PCM. The low voltage code could indicate the PCM lacked the power to run the program, defaulting to limp mode. The EEPROM error and/or low voltage may have caused the other codes to set. When dealing with LT1 codes, use Shoebox's list specific to the LT1, rather than the generic descriptions indicated by the scanner.

http://shbox.com/1/Dtcs.htm

What scanner are you using? There are two or three brands out there (Innova, Equus) that have a faulty data base for the LT1 engine and give incorrect codes. There is no DTC 54 for your engine. Removing the cat will not set DTC 44 and 45. 44 and 45 contradict each other. DTC 43 is for the knock sensor. There are trans codes that will lock the trans in 3rd gear, but you didn't have any of those.

Is “COA” actually CAI for cold air intake?

Yes. Coa is for cold air intake. Coa is a code I have to use at work. I must have typed that out of habit.

The brand I have is Innova. Let me take a look at the shoe box codes. See if something makes sense finally.

Also, after clearing them they are gone until I start moving. Once it shifts, the codes all come back.

Check the PCM grounds. One is a stud on the passenger side of the block near the starter. Other is the stud on the front of the driver side head that the ICM/coil bracket bolts to. There should also be a braided ground strap attached to the head stud.

In the 25+ years I've been helping people with LT1’s I've never seen anything quite like this. If is only happened after you rigged the stereo equipment, might need to remove all connections to see if they are the cause. Are you sure you disconnected all the power connections? If something is pulling down the voltage to the PCM might be the cause. What is the voltage on the dash gauge while this is happening?

And as a detailed source of info on the codes, you can download a copy of the 1994 factory service manual here:

https://www.mediafire.com/?40mfgeoe4ctti

And just so you are aware, there are very few active members here, maybe a 1/2-dozen. Otherwise this site is dead.

Thanks for the link. Guage on the dash reads reads a fraction over the half mark. And I tried unhooking the stereo completely. Unfortunately, my problem wasn't too simple.

First: Innova makes no scanner that can read you car's computer. It seems to like it but is wildly off in reporting the data. If you want to know the real codes get a cloned GM Tech 2 from China. Or my app Scan9495 for free.

Second: It sounds like the computer is not getting full 12v power. Just a guess at this point.

Are you starting to see a pattern here?

Yeah, it does. Sounds like I've got to start wire hunting for maybe something shorted or grounded that shouldn't be. This is going to be tedious as heck lol

No need to be tedious. Buy a Tech2 clone (~$300 with a long lead time) or use my app to correctly read the voltage at the PCM. Again...no guarantee.

Did you drill/screw through the trunk floor to mount the amp? There is fuel pump stuff under there.

I have found what I believe to be my problem. I've been on a hunt checking the wires all over the place, and I think I know what the problem is. My transmission speed sensor wire. I pulled a little on the wiring and realized that one of the two (the grayish purple one) had a lot of slack. Lo and behold. The wire is broken.

Now, the wires go above the transmission, so I'm wondering: does anyone know where this thing goes so I can run a new one? My guess is the PCM, but I have no idea which one over there is the culprit and honestly, don't know how to tell. :/

See very top of this schematic:

http://shbox.com/1/1995_pcm2.jpg

For more detail, including routing, use the 94 factory service manual.

First off, I want to say thanks to everyone that has taken the time to help me out. It is greatly appreciated. I got the wire reconnected. Took it for a short drive and every symptom was gone. It shifted great, had all my power back. It was absolutely wonderful.

I only went about a mile and turned around because I was a little low on gas and it was late anyway. Got home, put my dash etc. back together. And decided to take it for a drive into town. Stopped and got gas about 3 miles from my house. After dropping 40 bucks in the tank (gas prices suck), I started the car up and noticed immediately it was a weaker start than normal, but the rpms were steady and the engine sounded good. I chocked it up to releasing the key a fraction too soon.

I pulled up a few feet out of the fuel island and into a drive through to grab a pack of cigarettes and sat there for about 10 minutes in the line, and noticed I started getting surges in the RPMs as if I were slightly revving the engine. And I swear for half a second it felt like the car lurched forward, but it only did it once.

I grabbed my cigarettes and went down the road about another mile and I started intermediately losing power. Almost enough to stall the engine out. I looked for a place to pull off and swung into a Wal Mart parking lot. Turned the car off, and ran inside the store to grab a few things. When I came out, the car wouldn't start. And its still there.

I've had intermittent starting issues before, but thought I fixed it when I replaced the MAF sensor. It seemed to be But I guess not. Historically speaking, I've had to let it set a few hours to cool completely down to get it going again. Hoping I can get it started to limp it home tomorrow. I'm about to drive it into a ditch somewhere and leave it. :'(

The new information seems to point to an electrical thermal failure since it requires you to wait for a cooling period. I suspect the ignition coil first. Have you replaced it?

I seriously doubt the electrical wire fault for transmission vehicle speed sensor was causing this problem.

Yeah, this was a problem prior to the shifting issue. I just thought I had fixed it already. To answer your question, no. Haven't changed it yet. If I can get the thing home, I'll take a Crack at the coil.