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Discussion Starter · #1 ·
My new-to-me project car is throwing code 51 after running for a couple of minutes. The Service Engine Light takes something like 1 - 3 minutes to display and the only code stored is 51. I'll be replacing the alternator a little later today (seems to have a bad voltage regulator; the lights flicker) and I'm praying that does the trick. Anyone have any pointers to offer?

Possible clues:
  • Replaced the PCM; no change in symptoms
  • Fans kick on when SEL turns on
  • Scanner can only pull the code when I set the model year to 92' in scanner (this scanner)
 

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Welcome to the forum.

I'd start by downloading the 94 factory service manual at the following link. Go to page 6E-A-103. It explains code 51.
www.mediafire.com/?40mfgeoe4ctti

Hoping your bad alt has something to do with the problem with the PCM programing. But is alt doesn't fix the problem, you need to have pcm programred to the specs of your car. Or replace with fully programed pcm.
 

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Discussion Starter · #3 · (Edited)
Thanks Coco.

Thanks for pointing me to that section in the manual. Somehow I hadn't read that yet. I replaced the PCM with this unit a couple of days ago. After running for a bit the SEL came back on and I got the same code 51. The seller seemed to know what they were doing since they asked for the VIN and told me they programmed the unit before shipping, so I'm kind of trusting that this means the problem isn't in the PCM.

Replaced the alternator last night and it solved the flickering lights problem, but same SEL and code after a short while.

I'm thinking the next most likely problem is a bad ground or electrical connection in general. Does that seem sensible to you? I'm just now starting to navigate the service manual's wiring diagrams to see where I should check. Looks like starting around 6E3-A-3 and 6E3-C1-1 is the way to go
 

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Best to check out all alternitives to getting a new pcm. If you had a spare pcm, that's known to be good, swapping them out would tell you if pcm or something else is the problem. In addition to info in chapter 6, there are complete wiring diagrams in chapter 8.

There's always the possibility that pcm you bought wasn't programmed correctly. Since the company you bought pcm from doesn't have a 94 lt1 equipped camaro or firebird, they can't do a road test to confirm the operation.

Did the old pcm also give a code 51? If yes, keep looking for a wiring problem.
 

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Discussion Starter · #5 ·
Yeah, either PCM installed leads to a 51 code. I've since swapped back to the original PCM and plan to ship the new one back if possible.

I'm dreading troubleshooting the wiring. Haven't really done that before.
 

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Troubleshooting wiring problems needs an organized approach. In chapter 8 of manual, they have every power wire and every ground wire. At the back of each section will be a component location list. It will tell you where each ground is, where each component is, etc.

At the very back of the wiring diagram starting on page 8A-201-0 will be a component view section. This will show components, grounds, power wires, etc. Starting om page 8A-2-0 will be basic diagnostic info.

Then starting on page 8A-5-0 will be the electrical repair section. Starting on page 8A-9-0 will have zone #'s shown. The zones start with 100 zone and end at back of car . Starting on 8A-10-0 is the power distribution diagrams.

Starting on 8A-11-0 is fuse box info. There are 2 fuse boxes in your car. 1 at dash board, & 1 under hood. Starting on 8A-14-0 are the ground wiring diagrams. Starting on 8A-15-0 will be all component wiring diagrams.
 

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As you planned, start with grounds. Also troubleshoot connectors. Look for loose, burnt, & corroded terminals. After grounds do the power supply wiring. And connectors also. A single loose or burnt, or corroded terminal, can cause all sorts of problems.

Next start with interior fuse box. Pull 1 fuse at a time and see if problem goes away when engine runs. If no help with i\1st fuse, put it back in and pull another fuse and run engine again. Be sure to study the fuse diagrams in manual. You don't want to pull a fuse for components vital to engine running. After doing interior fuse box, moce to underhood fuse box. Do the same proceedure to those fuses. You can also remove reklays, one at a time, to see if that helps. Don't remove relays that are vital to engine running.

All of these things should keep you busy foe awhile.
 

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Discussion Starter · #8 ·
I greatly appreciate the comprehensive pointers. Will use this as my playbook for tackling this project.

I'm going to look into one last possible easy step before going ham on the wiring/electrical stuff, which is to verify the diagnostic info I'm seeing is accurate in the first place. I'm suspicious of the scanner I'm using for a couple of reasons. I also want to check out some of the free scan software options I'm just now finding out about regardless of this DTC. So, I ordered a USB to OBD1 adapter and will check things out that-a-way before really diving in. There are plenty of other easier projects to tackle on this car to keep me busy while I for delivery of the cable.
 
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