Significant leak down and hard starting
03-10-2024, 04:33 PM
#1
Significant leak down and hard starting
I have a 1988 350 TPI Camaro with ALL original parts. Even the distributor when I bought it a couple years ago. 119k on it but all those parts are well past their prime. It ran rough when I bought it and it was because the distributor couldn't hold up under any sort of revolutions above 2k. I replaced and properly times it per the service manual. However, it only starts well when it is cold and has sat for a few days without running. Most of the time it will cough and then crank for 3-5 second or just crank and slowly start firing on one or two cylinders and then slowly the rest will start popping off. I know the fuel pressure regulator and injectors are all original and ordered new ones from rock auto and south bay respectively. I did a leakdown test with my pressure tester and as soon as I shut off the car I could watch the fuel pressure gauge drop, slowly but visible. Within 5 minutes it has dropped from 42 to 25 PSI and within 10 it went from 42 to 22 PSI. Is this likely the source of my issues with starting? Also what other parts should I replace assuming they are original. Did plugs and wires last year, all AC Delco.
03-10-2024, 05:21 PM
#2
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Location: Mint Hill, NC
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Car: '90 Formula '88 GTA
Engine: 305 TPI 350 TPI
Transmission: T5 700R4
Axle/Gears: 3.42 10 Bolt 3.27 9 bolt
Re: Significant leak down and hard starting
you said the FPR and injectors are all original, but you ordered new ones, which is it? do you mean you replaced them with OEM parts?
Copying a post from and old thread about fuel pressure dropping when keyed off:
Copying a post from and old thread about fuel pressure dropping when keyed off:
I've had this problem three different times and each one had a different solution.
1. faulty fuel pressure regulator seat
2. faulty injectors
3. faulty check valve in fuel pump
You can check to see if it is a regulator problem by pinching the return line off to see if it holds pressure. If it does then you know that is it. If it doesn't then that leaves the fuel pump and the injectors. To check the pump you'll have to hook up a gauge to the pressure line and cap it off so that it doesn't pass through the injectors/regulator/return line and see if it holds pressure. This should get you to the injectors, which would have to be tested with specialty equipment. Just make sure to have some way to relieve the pressure from the pump and also to not run the pump very long when testing because the pressure will rise above 50psi in seconds.
1. faulty fuel pressure regulator seat
2. faulty injectors
3. faulty check valve in fuel pump
You can check to see if it is a regulator problem by pinching the return line off to see if it holds pressure. If it does then you know that is it. If it doesn't then that leaves the fuel pump and the injectors. To check the pump you'll have to hook up a gauge to the pressure line and cap it off so that it doesn't pass through the injectors/regulator/return line and see if it holds pressure. This should get you to the injectors, which would have to be tested with specialty equipment. Just make sure to have some way to relieve the pressure from the pump and also to not run the pump very long when testing because the pressure will rise above 50psi in seconds.
03-10-2024, 06:02 PM
#4
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Join Date: Jan 2008
Location: Mint Hill, NC
Posts: 249
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Car: '90 Formula '88 GTA
Engine: 305 TPI 350 TPI
Transmission: T5 700R4
Axle/Gears: 3.42 10 Bolt 3.27 9 bolt
Re: Significant leak down and hard starting
ahhh ok gotcha... well sounds like you are planning on replacing those anyway, its one of those three things, so if injectors and FPR don't fix it, then you know its the fuel pump. you can preform some of those pinch off tests in the meantime if you really want to diagnose it first
03-10-2024, 09:47 PM
#5
Re: Significant leak down and hard starting
ahhh ok gotcha... well sounds like you are planning on replacing those anyway, its one of those three things, so if injectors and FPR don't fix it, then you know its the fuel pump. you can preform some of those pinch off tests in the meantime if you really want to diagnose it first
03-10-2024, 09:49 PM
#6
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Join Date: Jan 2008
Location: Mint Hill, NC
Posts: 249
Received 56 Likes
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46 Posts
Car: '90 Formula '88 GTA
Engine: 305 TPI 350 TPI
Transmission: T5 700R4
Axle/Gears: 3.42 10 Bolt 3.27 9 bolt
Re: Significant leak down and hard starting
yes definitely not a bad idea to replace the pump anyway while checking out the tank if you suspect its original. Personally I would rather drop tank/fuel pump than do injectors any day, those intake manifold bolts live in my nightmares.
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