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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: GM
Satisfied Customers: 1492
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I have a 03 chevy express 3500 6.0 after running hrs

Customer Question

i have a 03 chevy express 3500 6.0 after running for 3 hrs it starts to stumble and die! I checked fuel psi and I was low. I installed a fuel pump the pump I removed only had 1 plug on it and quick connect lines. the new pump has 2 plugs and threaded lines! I found second plug and made some fuel lines and installed the pump. truck ran good. after 3 hrs it acted up again and had a code for tps voltage low. I checked fuel psi and it pegged my gage over 160 and never came down and pump keeps running? than I found a wire at the pcm jumped in and goes to the fuse box to the fuel pump repay
JA: So many things can cause fuel pump issues. Some simple, some complicated. Fortunately, the mechanics we work with have tons of experience dealing with them. Are you hoping to fix this yourself?
Customer: ya I am a master auto tech and this one is blowing my mind!!
JA: Is there anything else the GM Mechanic should be aware of about your GM?
Customer: i tried replacing the tps and cleaning the plugs for the sensors and throttle body from the way it looks the wire was jumped in cause there was no signal power to the fuel pump relay
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the GM Mechanic about your situation and then connect you two.
Submitted: 5 months ago.
Category: GM
Expert:  Juan Crespo replied 5 months ago.
I'd like to help you, but I don't understand what the problem is. Are you saying fuel pressure goes to zero after the engine runs for 3 hours? Also, fuel pressure specs for that vehicle show to be 55-62 psi; are you also saying you installed a fuel pump that's different than the original and puts out 160 psi? If so, why would you do that? Have you scanned the onboard computer for codes? If so, what are the specific code numbers?
Customer: replied 5 months ago.
after running for 3 hrs it starts stumbling no power and dies. let it sit for 10 min and it restarts fine with a check engine light on. with the old pump it was going to 20 psi. the pump I replaced it with is the correct pump! the pump that was in the truck was incorrect i don't know y the psi is so high. and y is the truck still running bad after 3 hrs
Customer: replied 5 months ago.
the code is p0122B
Expert:  Juan Crespo replied 5 months ago.
OK. To start, you need to install a pump/regulator combination that puts out 55-62 psi. Once that's done, then you need to determine why the engine stalls after three hours of running - is it because fuel pressure drops down, or because injection pulse and/or spark ceases?Regarding DTC P0122, it sets when the onboard computer detects TPS voltage signal is less than 0.15 volts for more than 1 second. There could be multiple reasons for this to happen, from a bad sensor to bad connector/wiring to a bad computer dropping the 5 volt reference signal - the latter could be related to the engine stalling issue.To summarize; first, you need to get fuel pressure up to specs; then, find out what goes missing that causes the engine to stall - if there's no injection and or spark, check to see if the 5 volt reference signal at the TPS is missing. If so, replace and reprogram the onboard computer (PCM).Please let me know if further assistance is needed with this issue.Best Regards.
Customer: replied 5 months ago.
the only fuel pressure regulator is a vacuum type on the fuel rail! ive been working on this problem for a week on and off! and the way the wire is bypassed at the pcm leads me to a pcm issue
Expert:  Juan Crespo replied 5 months ago.
You asked us for expert advice, so I posted a comprehensive diagnostic path and associated procedures. It is up to you to follow it or not - one thing I can tell you for sure is that replacing the PCM is not going to bring fuel pressure to specs.Best Regards.

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