2003 Chevy S10 4.3L Engine Misfire & P0172 Code: Injector Not Working Despite Power

The PCM is typically not the first suspect for P0172, especially since this code points to a rich mixture in bank 1. If cylinder #1 isn't receiving fuel, it's more likely that the system is misdiagnosing—bank 1 should be lean if only one injector fails, not rich. I suspect you'll need to reinspect the intake manifold for leaks or consider rebuilding the spider assembly.

The #1 cylinder injector was initially non-functional and wasn't delivering fuel at all. After replacing all injectors, that same cylinder still fails to deliver fuel despite receiving power. My mechanic has ruled out common issues and believes the problem may lie with the ECM. I have a scan tool and can check STFT and LTFT values if needed.

I've checked everything—compression, spark, wiring, vacuum leaks—and now the P0172 code is gone. The truck only shows a P0300 random misfire, and it shakes at idle and when accelerating from a stop. I'm not sure what's causing this sudden change.

I've verified the following: good compression, strong spark, clean wiring with no shorts or voltage issues, all injectors replaced (including #1), no vacuum leaks, and the PCV valve tested. I even added a small amount of fuel into the intake—cylinder #1 picked it up, confirming it's not a fuel delivery issue. The only code now is P0300.

Are there any other diagnostic codes? I'm thinking about p0201 or p026x—these often appear when the injector-to-PCM circuit is compromised. Also, why was the spider assembly replaced? That might offer insight into the root cause. For reference: in a 4.3L S10 system, all injectors receive 12V via the pink wire; the #1 injector control wire (black) goes directly to the PCM. You should verify: 1) 12V at the injector connector, 2) integrity of the black signal wire from injector to PCM (no open/grounded/shorted), 3) condition of the PCM connector, and 4) whether the PCM driver has failed—this is rare but possible. Check for history or stored fault codes in the ECM.

I replaced the spider assembly because I was told cylinder #1 injector wasn't working. After removing it, I found that the original injector was cleaner than the others and would work when connected to another cylinder—this confirmed a faulty injector in the new assembly. I’ve verified power at the connector and cleaned all connections to the PCM. The issue persists, and now only P0300 is present.

Thanks for the insight—I'm going to try replacing the ECM next. If that doesn’t resolve it, what other options do I have?

No injector-specific codes or pulse detected on cylinder #1. The new spider assembly was installed with proper wiring—12V confirmed at both terminals of the injector, signal wire (black) is intact and not grounded or shorted to voltage, PCM connector appears good. The only plausible explanation left is a failed PCM driver circuit—the switch that grounds the injector circuit. While uncommon, this failure can occur. You may consider sending in a remanufactured PCM—some providers offer same-day turnaround with reprogramming from an original unit. This could be a viable fix if other diagnostics fail.

I replaced the ECM, but there was no improvement. A Chevrolet dealership ran all tests again and confirmed everything is functioning correctly—yet cylinder #1 still doesn’t fire properly. I then replaced the injector with a known good one, but it still fails to work. The dealership is now baffled.

Check the connector at the PCM—it's a common point of failure and often overlooked.

I’ve already had them check that. I told them everything you suggested—injector is getting full power but still not working. I have no idea what’s going on now; I’m completely stuck.

Let's simplify this: a basic circuit. Imagine replacing the injector with a light bulb. - Does the injector get 12V? Yes or no? - Is the control wire (black) grounded but showing 12V? Yes or no? - When the PCM grounds that wire, does the injector spray fuel? I believe the noid light is not pulsing. If the PCM grounds the circuit, it should trigger a pulse—this indicates a failure in the signal path. A bad waveform from the crankshaft or cam position sensors could also prevent one cylinder from firing. I'll post more details later.

Okay—I did a test: key on, engine off (KOEO), cleared codes. Then turned the key off while someone watched the noid light. During startup, the light flashed briefly but stopped—no sustained pulse. This suggests no proper injector command from the PCM.

I'm now going to order a new brand-name injector as a next step. The dealership has been replacing parts at my expense, and I've already spent $1700. If this fixes it, I'll update the thread for others facing similar issues. Thanks so much for all your help and suggestions.

I thought the spider assembly was brand new—was that correct? Can you confirm whether the noid light flashes or stays on during engine start?

Yes, the spider assembly was brand new. The injector in cylinder #1 failed to work, which is why I purchased a full spider assembly instead of just replacing that single injector. It turned out the new spider had a defective injector already—right out of the box—and it happened to be installed in cylinder #1. That explains everything. What are the odds of such a defect? Thanks for all your help—I now understand what went wrong.

I don’t know about cylinder #1, but on this spider assembly, injectors can be mixed up during installation—each has a number and must be installed in the correct position. A misalignment could cause a single-cylinder misfire or poor fuel delivery.