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98 chevy suburban 5.7l with "spider injection" (sfi,cfi). Came in with a intermittent hard start issue. Found fuel pressure to be 45psi, spec is 60-66. Installed new pump, reset timing and did a much needed tune up. Still had low pressure at 55psi but truck was starting and running great so I sent it out the door. Fast forward about a month customer comes back with the same complaint. I decided to check the injectors for bleed down by pressurizing the fuel system and then blocking off both fuel lines one at a time upon there still being a 20+plus psi drop within an hr as well down to 0 over night i blocked off both line and still had sizeable bleed down and no visible leaks. So I installed a new injector assembly with pressure regulator built in. Same thing, with actually a quicker bleed down. Up until this point I had been using parts that the customer supplied to please his desire for a particular brand, against my advice. I did the same tests as before and determined the only cause could be the injectors once more. So I installed a set an injector assembly from a brand I trust. Before installing them under the plenum I placed them on cardboard, connected the fuel lines and pressurized the system to 55psi and let them sit for 3 days it dropped to 49psi in this time so I installed them properly. SAME ISSUE!!! Fuel pressure bleeding off in a matter of hours. This time I decided to hard block the return fuel line since I had only been pinching off the lines using line block pliers. This time fuel pressure went up to 75 but still bled down to 50s within minutes and down to 0 within hours. After discussing it with some other mechanics I decided to throw a better pump in it since the only spot it could be going is back thru the pump. Installed an AC Delco pump, now I'm still only getting low to mid 50s psi koeo and bleed down. Other things to not vehicle primes better when the key is turned off rather than turned on, also had a code for high coil circuit cyl 1 and 4 on cranking which went away with the install of new injector assembly. Any advice from more experienced techs? I'm all ears! Thanks
Last edit: 5 years 1 month ago by Noah. Reason: Remove confidential status
I would be more focused on the low fuel pressure than the bleed down.
I feel like the bleed down you experienced is acceptable. Someone can correct me if I'm wrong.
Those Suburban trucks were famous for a poor fuel pump ground on the frame.
You drop the tank to change the pump, disturb the ground and everything is great for a short time, until the ground acts up again.
I know a tech who went through 4 pumps in his personal Suburban before I helped him find the circuit issue. By that time he got tired of dropping the tank and cut the floor.
I think a voltage drop test is order on the fuel pump connector.
I agree with Noah and checking the grounds but I'd go farther than the connection at the frame I had a 99 suburban a few years ago that was a no start didn't matter how long you cranked it but if you hooked jumpers up to the frame or body it would fire right up and run till you shut it off where it would again not start turns out the body ground was corroded and the engine to frame ground strap was wrotted out . Have had several other vehicles be no starts from bad engine to frame grounds as well , this theory of corroded ground makes more sense since your pump primes better off then on(other loads taking the amperage)
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