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Fried ECM on 1992 Chevrolet C1500 TBI After Jumper Wire Mistake - Code P12 Detected

Model: 92 C1500 Fault Code: C1500 Posted: 2016-07-03 03:04

I recently had a serious issue with my 1992 Chevrolet C1500 4.3L engine, which has over 220,000 miles. The motor was rebuilt at 179,000 miles and I installed a new TBI (Throttle Body Injection) system in December. A few days ago, the truck began running poorly and eventually the catalytic converter caught fire. After removing the cat and installing a test pipe, it still ran extremely rough and was clearly running rich. I don't have an OBD-II scanner, so I used a jumper wire to retrieve fault codes — all I got was code 12. In my frustration, I forgot to remove the jumper wire before attempting to start the engine, which led me to try starting it with the jumper still connected. As a result, I now have no spark at all and suspect I may have damaged the ECM (Engine Control Module). The truck previously ran perfectly, so this sudden failure is very concerning. I’ve checked fuses and confirmed they are fine. There’s only 10.89V at the ignition coil, and no voltage on the injectors (red and white wires). When I disconnected the injectors, there was still no power — indicating a possible wiring issue under or near the air filter assembly. I’ve searched online and found many similar cases where users report 'dumping' fuel symptoms without any codes. However, none have successfully resolved it. My truck is now completely non-responsive with no spark, and I’m not sure if this was caused by a wiring fault or an ECM failure due to the jumper wire incident. I'm looking for advice on how to diagnose this properly — especially whether the lack of spark means the ECM is fried or if there's another electrical issue that can be fixed without replacing the entire module.

Related fault codes

C1500

Comments (10)

Anonymous 2016-07-03 05:19

Hi, I have a Ford Fiesta diesel and am having trouble starting it. It seems to want to start but won't — similar symptoms to what you're describing. Any advice on diagnosing fuel dumping or no-start issues with older TBI systems?

Anonymous 2016-07-03 09:15

kevinbeam 74 Using a jumper between the ALDL terminals will not damage the PCM in older systems, but these units are outdated and memory may degrade over time. If the catalytic converter caught fire, it likely means excessive fuel delivery — however, the lack of start is more critical. I recommend checking fuses first: ensure there's 12V at the ignition coil and injectors with the key off (KOEO). Also inspect the wiring where it passes through or under the air cleaner assembly — this area is prone to grounding or short circuits.

Anonymous 2016-07-03 11:58

I'll check all voltages now. I've lost everything after trying to start with the jumper still connected. The most bizarre thing is that before the jumper, it was spraying fuel like crazy — but only had 11 psi. That doesn't make sense. I’ll restart and update if I can figure this out.

Anonymous 2016-07-03 12:01

I've searched Google all morning and found many people with the same problem — no codes, engine runs rich, won’t start. No one seems to have a solution. This feels like my $1000 truck is going to give me fits, but I’ve had it for 4 years — can't complain.

Anonymous 2016-07-03 12:31

Don’t jump to conclusions — let’s test systematically. There are several diagnostic steps we can take before trying to get the engine running. These 1992 TBI systems are relatively straightforward to troubleshoot. PS: Using a jumper during engine operation is known as 'field service mode' — it's not an unknown issue, but it can cause unintended electrical stress on components.

Anonymous 2016-07-03 12:49

This is a TBI system. 11 psi is normal. Is there 12 volts at the ignition coil (pink wire)? Are there 12V readings at the injectors (red and white wires)?

Anonymous 2016-07-03 19:36

Sorry, it was a crappy weekend for my truck. Voltage on the coil is only 10.89V — and no voltage on injectors. All fuses are good. The truck ran perfectly before this — now I’ve completely messed up the fourth system! I’ll be back tomorrow after the rain ends. I’ll keep my phone handy to respond faster. Thanks for helping.

Anonymous 2016-07-04 09:29

Okay, with injectors unplugged, there's still no voltage on any wire — red and white wires show only 12V supply. Check the injector wiring several inches back from the injector, especially where it goes under the air filter assembly. This area is a common failure point. If not fixed, you won’t get power to injectors. This circuit is labeled 'inj A&B' — fuse #10 (10A). Don't just check fuses — verify they're actually supplying voltage. The 10.89V reading isn't ideal — what's your battery voltage? PS: Do you have a remote starter that might have caused this issue?

Anonymous 2016-07-04 18:52

Sorry, I ended up coming down for the 4th. I’ll check all wiring and voltages now. My battery was low from trying to start — I’ve charged it. No remote starter. Thanks again.

Anonymous 2016-07-05 18:25

After a long morning of troubleshooting, I finally found a bad spot in the injector wire. Now I have 12V on both injectors and at the coil — but still no spark. This suggests either a faulty distributor cap or a failing ignition coil.