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Does anyone have digital copies, or pictures, of the Engine Controls Service Manual Section: "Fuel Pump Electrical Circuit Diagnosis" for a late 2003, LS1 Corvette that they could share with me? I have the 2001 manuals, but I want to make sure that the procedures and details are correct for the upgraded 2003 pump.
Does anyone have digital copies, or pictures, of the Engine Controls Service Manual Section: "Fuel Pump Electrical Circuit Diagnosis" for a late 2003, LS1 Corvette that they could share with me? I have the 2001 manuals, but I want to make sure that the procedures and details are correct for the upgraded 2003 pump.
What do you mean "upgraded"? Do you have an aftermarket pump, or do you have FFS?
By "upgraded" I've read where Chevrolet redesigned the fuel pump system, for late 2003 and C6 corvettes with a totally new system with pumps that were relocated to the top of the tanks. You probably know a lot more than I do about this. I'm Googling. The FFS system is shown in my 2001 manuals, which seems strange if it was not used until late 2003.
Last edited by GrantandGrace; Jul 5, 2025 at 09:29 AM.
Reason: incomplete statement
I may have a problem with my "ignition reference pulses". The car will start but only runs a few seconds and stalls. No fuel pressure on the rails then. Where do the "pulses" come from?
They come from the crankshaft position sensor…when you start the car and that signal is being received by the PCM the Fuel Pump Relay Control circuit will apply 12 volts to the coil feed circuit of the fuel pump relay…one can simulate the crank sensor signal with a test light and you will hear the fuel pump come on…you will normally see the fuel pressure drop from 55-62 while trying to start the car.
Thanks, C5 Diag. I greatly appreciate your input! The no-run condition appeared after we replaced the old shorty headers with long tubes. The shorty's were a PITA to get out. We had to raise the engine and squeeze them out the bottom. This was done with the help of a very experienced corvette guy. Electrical gremlins can be so time-consuming. I'm trying to troubleshoot the source of the problem waiting for some space in his air-conditioned shop.
We did but have checked and reconnected all the engine grounds associated with the Fuel system. I'm leaning heavily toward a problem with the Crankcase Position Sensor. Since it will start every time I turn the key, it's getting enough fuel to start. If the PCM shuts off power after a couple of seconds, that would cause it to stall out. That's gonna be my first area to check when I get it back on the lift. If that's it, I'll post some comments on what I found. Thanks again for your help.
Yes, the PCM automatically performs the 2 second prime upon power up, and then after it receives a continuous pulse train from the crank shaft sensor which tells the PCM that the engine is running it turns the fuel pump relay back on.
I've read that your engine will not start (no ignition spark) if the Crank Sensor is bad or wiring damaged. If that is true, then my theory, that the sensor was my problem, can't be true because my engine will crank and run for a couple of seconds before "sounding like it's running out of fuel" and shutting off. Do you know if this is true? I'll check codes tonight and see if there's a hint.
Tonight I was able to get the Vette jacked up and get under there to find and reconnect the ringed-ground connection at G105. It was tucked back out of the way and was left off when everything else was reconnected. I just knew that my problem would be solved. Not quite. Now the engine just spins. No start at all. Before, it would crank every time for a couple of seconds and then it would cut off like it ran out of fuel. Now, not even that. Wait a minute.....
Right in the middle of writing this, I just went out and swapped the horn and pump relays....BINGO! I guess a good ground was more than it could handle after all the stress of needing one.
Thanks for all the help, guys. Especially C5 Diag and Lucky131969. I learned a lot working through this. I'll be purchasing a relay or 2 tomorrow and then get it back on the rack soon to continue with the transmission fluid change and new exhaust system leak check.
Fuel Pump Electrical Circuit Diagnosis
