85 fuel pressure problems HELP!
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 895
Likes: 3
From: toledo ohio
85 fuel pressure problems HELP!
i have an 85 vette and i have some severe fuel pressure problems. when i put a gauge on it and turn the key to prime the pump it will shoot up to about 40 psi and about a second later will drop right back down to zero. if i do this enough times it wont even go up anymore it will just stay at zero. so far ive gotten a new fuel pump (this is not put on by my but aaa car care, so i dont know how much i trust it) used ford fuel injectors (guy said they were ok) and a used afpr and no matter what i set the afpr to it will always shoot up and then go right back down. im not in a super hurry to get this fixed as its a show car not a daily driver but i would like to catch the end of the driving season. any help greatly appreciated thanks!
oh and a ps i took one spark plug out and a little bit of fuel came out, but it was a very inconsequential amount and no more came out when i primed the fuel pump again.
oh and a ps i took one spark plug out and a little bit of fuel came out, but it was a very inconsequential amount and no more came out when i primed the fuel pump again.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
If you got any fuel out of the cylinder when you removed a spark plug, you have a bad injector. I's not supposed to release any fuel unless the computer tells it to, and it is a measured amount,
I would guess that if you got new injectors, your main problem will go away.
The other problem as I see it, is that your fuel pressure regulator is cranked up way too high. You need to block the fuel line before it goes into the fuel rail, and take the pressure right at the fuel line to get a base reference pressure.
If the fuel pressure will still not hold, you eiter have a bad check valve in the pump, or the fuel pulsator is leaking so bad that it will not keep the fuel line pressurized.
You have to remove the fuel rail to change injectors anyway, so that would be a good time to check the line pressure.
If your fuel pressure regulator is bad, no matter what you do, it will fight all of your troubleshooting efforts.
I would guess that if you got new injectors, your main problem will go away.
The other problem as I see it, is that your fuel pressure regulator is cranked up way too high. You need to block the fuel line before it goes into the fuel rail, and take the pressure right at the fuel line to get a base reference pressure.
If the fuel pressure will still not hold, you eiter have a bad check valve in the pump, or the fuel pulsator is leaking so bad that it will not keep the fuel line pressurized.
You have to remove the fuel rail to change injectors anyway, so that would be a good time to check the line pressure.
If your fuel pressure regulator is bad, no matter what you do, it will fight all of your troubleshooting efforts.
Race Director
Joined: Jun 2009
Posts: 10,428
Likes: 9
From: Southside of Western Norte Americano State of Confusion, ColoFornia
St. Jude '13
That sounds like a stuck cold start valve.. If its bleeding off all that pressure without the engine running.,. It would have to open all the injectors at once or the cold start injector .. just a guess.. unplug the cold start and see if you still get the pressure drop
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 895
Likes: 3
From: toledo ohio
thanks for the help. i tried it again with the cold start valve disconnected and still nothing... so im going to rip everything apart (for the 3rd time lol) and send the injectors out to jon at fic and see what he thinks. im also thinking of putting the stock fuel pressure regulator back on at first because i know it works, and then putting the adjustable one back on later. and if none of that works then i know its the fuel pump and hopefully thats still under warranty. i figure this is a good time to do a port and polish job on everything since i have slp runners and a 52mm throttle and havent done that yet so.... winter project here i come! thanks guys
Team Owner
Joined: Jan 2003
Posts: 20,292
Likes: 239
From: Summerland B.C. Canada
Before you pull anything, you should isolate where the pressure loss is.
http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
