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1999 GMC Suburban 7.4L Engine P1351 Code: Long Crank Time, Stalls, and Injector Leak Diagnosis

Model: 99 GMC Suburban Fault Code: P1351 Posted: 2007-09-16 19:56

I'm completely frustrated with this issue on my 1999 GMC Suburban with the 7.4L V8 engine. After replacing the Ignition Control Module (ICM) twice and following all steps from AlldataDIY, I still intermittently receive a P1351 code. Here's what I've done: 1. Cleared the DTC (Diagnostic Trouble Code) 2. Disconnected the injector harness and cranked for 15 seconds — the code reappeared 3. Reconnected injectors and then disconnected the ICM connector 4. Measured voltage from terminal B to ground during cranking: 2.2V 5. Tested terminals C (with test lamp) to B+ — lights illuminated 6. Tested terminal A to ground — lights illuminated 7. Checked for loose or corroded connections on the ICM — no issues found The symptoms are consistent: it takes 15–30 seconds of cranking to start, then stalls. On subsequent attempts, it starts immediately. I've seen many similar posts about this issue with GM trucks, but no clear resolution. The long crank time and rich fuel smell suggest a possible leaking injector or fuel pressure regulator problem. My question: How can I accurately identify which of the 8 injectors is leaking? And what steps should I take to confirm if it's a false P1351 due to extended cranking? Any advice or troubleshooting tips would be greatly appreciated!

Related fault codes
P1351
Comments (10)
Anonymous 2007-09-17 16:24

Extended crank times can trigger a false P1351 code. Does your vehicle require long cranks to start? If yes, the code might not actually point to an injector issue — it could be caused by fuel pressure loss during cranking. Install a fuel pressure gauge and check if pressure holds when the key is off. If it doesn't hold, you likely have a leaking injector or a faulty fuel pressure regulator (which may only leak when running). A rich condition from excess fuel can cause long crank times to clear the system before starting — this sets the P1351 intermittently. Start with fuel pressure testing and update me on your results.

Anonymous 2007-09-18 07:57

Thanks for the insight! This makes perfect sense. My truck does require a long crank time to start, and when it starts, there's a strong rich smell — consistent with excess fuel in the system. If it's a leaking injector, what’s the best way to isolate which of the 8 injectors is causing the issue?

Anonymous 2007-09-18 08:21

That’s definitely challenging. Are there individual fuel lines leading from each injector that you could cap off for testing?

Anonymous 2007-09-18 08:46

Yes, it's possible to isolate each injector individually — though it requires some mechanical setup and patience.

Anonymous 2007-09-18 10:04

To identify the faulty injector, you’ll need to test for fuel pressure drop when each injector is activated one by one. If pressure drops significantly during activation, that’s likely your culprit.

Anonymous 2007-09-18 11:22

I’m not sure what you mean by 'spider injection' (CPI), but yes — the CPI injectors are located under the intake plenum. Some users report better performance after replacing them with aftermarket port fuel injection systems that relocate each injector to individual intake ports, effectively turning it into a port-injected system instead of a CPI setup.

Anonymous 2007-09-18 18:36

I'm not familiar with the exact testing method — how do you test for individual injector pressure drop?

Anonymous 2007-09-18 18:37

You can search online for 'how to test injector drop' or look into GM truck owner forums. Some recommend using a fuel pressure gauge and a scan tool that can individually activate each injector. Linder is one brand known for aftermarket CPI replacements — Darkrooms might have used those in the past. I don’t have a direct link, but searching 'Linder CPI replacement' or 'aftermarket port injection for 1999 GMC Suburban' should yield good results.

Anonymous 2007-09-19 07:15

I believe the original CPI unit was from Borg Warner. I don’t have the part number, but you can find it at most auto parts stores by describing the setup — retrofitting to port fuel injection is common and often improves performance significantly. If your CPI is old, replacing it (even if not faulty) may improve reliability and eliminate the P1351 issue.

Anonymous 2007-09-19 08:13

I agree — using a scan tool to activate each injector individually while monitoring fuel pressure drop is the most reliable way to isolate a leaking injector. This method will show which one causes a significant pressure loss. If you replace the CPI unit with a modern port-injection system, it may resolve both the P1351 code and the long crank time issues.