bigchief

i finally got a fuel pressure gauge hooked up in my car to see whats been going on, and ill turn the key on the ACC position, and my pressure will shoot up to about 50 psi, but then slowly go back down to 0. I'm pretty positive its supposed to hold pressure for a long time.... does anyone know why this could be happening??? please let me know! thanks!!!

*this is on a 355 tpi

89gta5.7tpi

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.

jackballs529

What are the symptoms?

bigchief

thanks a lot gta, i tried turning the key on the acc position and clamping the return line, but it didnt hold pressure, so ill try that other stuff, thanks man... jack, the symptoms are high idle, bad gas milage, and if i rev it high, then completely let go of the gas, the idle doesnt come down smoothly, it kind of jumps down, its weird...

Irocz_newbie

Hey Im having the exact same problem. Mine i think is the fuel injectors because ive changed the pump and regulator. Did you ever figure out what was wrong with yours?? Thanks

IROCThe5.7L

After it bleeds down to 0, how does it start? If it were your injectors, it would be hard to start.

bigchief

yep, it ended up being my regulator actually, my pressure holds fine like it should now i just need to put the right chip back in b/c i originally thought it was the chip, and i've been running a chip set to 23# injectors to make the car run more rich, but im gonna go back to the 25# so it should get rid of the lean light, or faulty lean light...... im still not too sure how to fix THAT problem :-/

Irocz_newbie

If I leave mine to sit overnight, the next morning itll take more time than normal to start. Mine is wierd sometimes when i throw it into reverse it will die, but start up right away. I changed my pump and regulator already. Also i dont know if you guys would be able to help me here but it idles rough at about alittle above 500. Probably 525 in drive and in the morning when I first start it it takes like 5 minutes for it to drop down to just under 1000rpm. And it shifts really slowly and wont downshift when i floor it. Could it be the TPS?? Would a couple of bad injectors really cause the pressure to drop that fast?? Mine drops almost instantly, but will stay at about 44psi when running, But i get a bad idle. Any Ideas are appreciated. Thanks

bigchief

i would definetly say the bad idle has to do w/ the injectors, since you changed the fuel pump and the regulator... i dont think the TPS has anthing to do w/ that as long as your not getting any check engine lights. i changed my TPS recently but that was b/c i got a signal voltage low TPS code, and i had to change my plug too b/c it was broken. anyway, i think im gonna change my fuel pump soon, my cars running really lean now, im positive it has to be the pump....... I HOPE

jackballs529

Hey Irocz_newbie


Having the same exact problems... Everything is brand new in my car, and I am suspecting the injectors. I have new accells but a lot of people around here have said they are junk. Probaly will switch to Ford when I get some time...

vernw

iTrader: (2)

AS long as no one is using a Holley AFPR, then everything said is correct. Holley told someone on this board their AFPR is designed to slowly (20-30 minutes) bleed off the pressure for safety reasons....

bigchief

im using the stock FPR i just got a new one...

jackballs529

As far as I know they all bleed off after some time... Thats what everyone has been saying around here. I have an adjustable but it is not a holley. Can't remember which, its been years...

1992rs/ss

ok so I think I am in the same boat here. I turned the key to acc. the pressure goes up to 47psi and bounces a bit while the pump is running, as soon as the pump quits the pressure drops out to zero. I have braided fuel lines so I can't just pinch off the return line. so I pulled the return line off and plugged it with my thumb, pressure held. thing is if I test it while the car is running the pressure is rock solid at 44 psi with the vaccum line off, and it drops to 38psi when you put the line back on. from what I am told that is what it is supposed to do when running. I am using a BBK afpr.
the car just does not want to idle smooth. it is barely running at idle. I only have about 11-12 in of vaccum at idle and it jumps up to 17 when it is reved up. the engine is a stock lo3 with a tpi setup on it and I am going crazy trying to figure this out.

bigchief

my idle fuel pressure is like 37...... is that normal? i have the stock FPR and stock pump

jackballs529

Sounds a little low to me. My 87 350 TPI was supossed to be 43. Not sure what your 89 is. You definatly need to replace the stocker... tuning is a breaze with AFPR's.

jackballs529

By the way, you should check the reading with the vacuum line off for accuracy.

Jacques101

did you ever figure out what was making the fuel pressure drop as soon as the pump quits?

cwb90

I just replaced injectors and fuel regulator diaphragm. Car want to stall and stumble when first started. I checked for vacuum leaks and all is good. Fuel pressure is good but will not hold, drops right away to zero. I pinched the return line and it holds. What does this tell me? Still trying to learn, lol.

Komet

Sounds like fuel pressure regulator is not doing its job.