Ok, so this is going to be a long post. So be forewarned.

Earlier this year, I upgraded the stock stereo system in my 94 Z28 (auto trans). 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 whine, 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 22
Throttle position sensor low voltage,

Code 42, 43
electronic 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 45
rich exhaust

Code 51
Pcm/ecm issue

Code 53
System voltage too high

Code 54
Fuel pump circuit fault.

Code 55

It's worth noting the only mods aside from Cats and muffler is a COI. Tried resetting the codes, and they stay gone until I start moving. They all come back when the car shifts from 1st and I lose a crap ton of power.



These are the things I have tried to fix it to no avail.

1.) Unhooking the stereo equipment.

2) Did a visual check of fusable links. Nothing is burned on there.

3) looked around for loose wiring under dash (particularly where I was running the power cable)

4) changed VSS sensor

5) Changed throttle position sensor

6) Changed the alternator (to 140 amp) and PCM at the same time

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.


(edited in a few details I forgot to mention)

 

Does it start right up? Sounds like battery issues,is the alt. new or rebuilt I've seen many bad rebuilds before with alternators and starters
Bat. cables in good shape and clean?.

 

Yeah, starts no issues. The alternator is, as far as I know, new. Bought it from Summit Racing. Wasn't listed as rebuilt.

The cables have new connectors, and actual terminals on the battery are good and clean. I can't see any issues with the wires. No corrosion or anything on there.

 

Well, went out to try and fiddle with it some more, and have a new symptom which, ironically, is starting. Had to put my foot on the gas to get it to start.

Edit: to be more clear, it turned like it was trying to start, but took about 5 minutes for it finally land. When it did, it was barely was running. Had to stomp the gas to "kickstart it" and rev the engine up. Then it idles fine for a bit. Once it starts warming up, the idle becomes erratic and it wants to stall. Exhaust smells INSANELY rich when it starts doing this.

 

That could be a few things,I wonder if your Opti is going bad. When they go south they can cause a lot of symptoms that will drive you crazy.

 

Have you cleared codes yet? I would just to see what resets right away. A single issue can cause a lot of codes over time because that issue causes things to happen the PCM cannot adjust for. A simple Example: a plugged exhaust can cause a MAP sensor error and an O2 sensor error.

Once you clear the codes you want to recheck them right away to see what codes set first. Some codes could set as soon as you turn the key even before you start it, and some may start as soon as the engine starts. These are called hard codes. You need to address them first.

I hate to guess at issues but the fact that you have a code 51 and your alternator was damaged right after a radio install could be indicators of a voltage spike. All the surge protection for your cars computer system has is inside the alternator. If you had a defective capacitor or even a bad connection on a large cable it could damage the PCM. I don't normally even talk about "it could be" without any tests but in this case if code 51 is a hard code you may need to replace the PCM. You really do not want to hook the stereo back up just to fry another PCM.

 

I did clear the codes. And no hard codes. When I reset them, they are gone until I start moving. Then as soon as it tries shifting from first (it is an auto), all the codes come back.

But in case I wasn't clear, the alternator wasn't showing damaged, its just one of the things I replaced trying to fix the issues. It actually seemed to be keeping the battery charged.

I also tried changing the PCM (programmed to vin). I installed that at the same time I did the alternator. Forgot to list that one. Sorry about that.

 

So all 4 of the 50 series codes come back the first time it shifts? And you already change the PCM. That is not good. For me I am going back a lot of years, back when I did warranty work for GM with a focus on drivability (AKA engine running) The 50 series are just the worst. The reason is they tend to be internal issues to the PCM that can be caused by wiring. So if you have more than one of the 50's you cannot even be sure what wiring issue is tracking it. I have seen many mechanic fry several PCMs because they thought they had the wiring issue sorted out but as soon as they plugged in the new PCM, zapp it was gone.

I am not saying that it cannot be an external issue like something drawing too much power or something like a bad ground. I was lucky in the fact I had the GM CAM systems. I could connect the ECM harness to the CAM system then just run a connector from the CAM system to the ECM and run the car. It would monitor and record all the line voltages. GM tech support could also modem into the CAM system and see what I saw. Tech support would have you verify and clean all the grounds related to the PCM and may even have me run a temp ground wire from the battery to the ground cable of the ECM before you even hooked up the CAM system.

I got to the point the only time I used the CAM system was for the 50 series codes. While you could use the CAM system on any computer issue in most cases once I knew the code I knew what to check for and had spare known good parts at my box for test purposes.

Might be time to call in a heavy hitter tech with one of those high end snap-on scanners. Back in the day I would have said take it to a dealer but the last time I was at my dealer I don't think there was a tech there that born before 1997.

 

Well dang. I may have to look at the possibilty of sending it a good piece out. None of the shops around here will touch it. I already tried. Say they don't have the equipment to hook up to something that old.

Anyway, I greatly appreciate all the help.

 

For what it's worth and to possibly help anyone with a similar problem down the line, figured I would keep this updated. While I was fiddling on it the other day, I noticed the plug in on the MAF sensor was a bit corroded (not the part connected by the wire, but the part connected to the sensor itself) So I went ahead and ordered one. It came in today while I was at work and I threw it on really quick during lunch. The starting issues are now gone, and it seems to idles the right way now. Haven't been able to take it on a test drive yet, but fingers crossed that was solution to the other issues as well.