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cant fix hard hot start for the life of me

3646 Views 27 Replies 6 Participants Last post by  dkozloski
I have tried everything. new FPR, new fuel injectors, cleaned throttle body. anyone know what causes a hard hot start? i will go through and check all that apply.
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Hard hot stars are usually the FPR or leaky injectors. How about the fuel pump relay?
well i replaced the FPR not too long ago with a brand new one hoping to fix the problem. but it didnt. then i started getting into the injectors. i purchased a new set off ebay. hoping that it would fix the problem. but has same problem as before. i havent checked the fuel pump relay, how do you do that?
also the car when driving also has a jolt when you give it some gas. its like a hesitation then a little powerful jolt for a second. as you keep your foot depressed on the gas pedal it smooths out. but whenever you take off and put it back on it happens again.
Try tapping on the relay with the handle of a screwdriver. If that does not help, swap it with a known good one to see if it does the trick. If not, then that is not your problem.
well i went out and tapped the relay with the head of screw driver. it seems to have helped with the gas jolt. it didnt go away completely but it seems to have lessen the occurance of it.

what exactly does tapping the fuel relay do? should I just replace the fuel pump relay? my father has a 96 deville that runs perfect, i will take his out and see if it fixes the problem. its gonna be a shame that i spent all this money on fuel injectors and it turned out just to be a fuel pump relay. but hey atleast i learned to perfection how to replace injectors. i can probably set a record for changing them the fastest.

there seems to be a piece of black electrical tape wrapped around both the fuel pump relay and AC relay. could someone in the past have tried to fix the problem with this piece of electrical tape?
i will try replacing this fuel pump relay. then im assuming tps is (throttle position sensor?). where is that located and how do you check it?
Tape on the relays is likely from the factory. Tapping it may jar the contacts loose if they are stuck open. The relay comes into play during cranking only, so it has nothing to do with your "jolt".
Tape on the relays is likely from the factory. Tapping it may jar the contacts loose if they are stuck open. The relay comes into play during cranking only, so it has nothing to do with your "jolt".
right ok i see. i have noticed today that it hasnt hard started since tapping on it. but yeah it still has the jolt. any ideas how to fix this problem?
Ok, sounds like you had a relay stuck open so the fuel pump would not energize till you built enough oil pressure to take over and do what the relay was supposed to be doing. If it happens again, R & R the relay.

Not sure what to say about the "jolt'.
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well I replaced the fuel pump relay with a known good one and I still get the hard hot starting. gah this is nuts. any other ideas?
Hows the fuel pressure?
I dont have a specific tool to check the fuel pressure. but from the FPR, I did replace it with a new one thinking that would fix it. It currently holds a vacuum. but I have seen faulty FPRs hold a vacuum. maybe I just purchased a lemon. today I am going replace the FPR from my fathers 96 Deville and see if that solves the problem.

I do have a small gas leak somewhere near the gas tank. Would that have anything to do with these problems.
Don't mess with your fathers FPR. If it holds a vacuum it is good. If you installed it wrong, it would be leaking. The leak should not have an effect. I'd get a fuel pressure gauge and check the duel pressure. Sounds like that is the only thing you have not checked yet.
well i just got the fuel pressure checked. he said it was good. it was at 45.
I'm running out of ideas. Maybe it is not fuel related.
today I replaced the control module and all four modules. to see if that would be the problem. its wasnt setting off a code. so i dunno maybe it will help. just took it for a spin to see how it works. i still have a little jolt when coasting above 40mph doesnt seem as bad. ill go out in about an hour and see if it hard starts.
well with the new control module and ignition modules in it still hard starts. i give up, im going to resort the always valid. "it must be gods doing." thanks Ranger for your patience and knowledge. If it ever gets fixed ill let you know what fixed it.
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