with these guys
Fuel Pressure
Thread Starter
Racer
Joined: Oct 2004
Posts: 288
Likes: 18
From: Somerset PA
Fuel Pressure
Can anyone tell me what fuel pressure I should have on a bone stock 89 L98?
I just hooked up a gauge and checked it, and here's what it showed.
Key on, car not running - 24
Car at idle - 42
Shut car off, and it within 10 seconds, it's back down to 20's and then slowly leaks down to nothing.
So, I guess this is just leaky injectors. I know they are problems because I ohm'd them out and got readings all over the place. I bought some used ones from ebay and plan to replace them soon anyway.
Should the fuel pressure be the same with the key on and not running as it is at idle? What pressure should I be seeing?
Thanks!
I just hooked up a gauge and checked it, and here's what it showed.
Key on, car not running - 24
Car at idle - 42
Shut car off, and it within 10 seconds, it's back down to 20's and then slowly leaks down to nothing.
So, I guess this is just leaky injectors. I know they are problems because I ohm'd them out and got readings all over the place. I bought some used ones from ebay and plan to replace them soon anyway.
Should the fuel pressure be the same with the key on and not running as it is at idle? What pressure should I be seeing?
Thanks!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Your fuel pressure should be holding much longer than it does. If your injectors were leaking that bad, it might be hard to start or smoke some as you burn up the excess fuel and then smooth out. Chances are a check valve in the pump or that area that is getting weak.
However, there was a guy that had a long post where his resistance readings were all over the place also. That didn't mean that they were leaking, but did cause poor running. It was also noted that vintage of vett has a problem with the injectors those years. So since you are planning to change the injectors anyway, do that first and then take it from there. No need to go into the tank unnecessary. Good luck
However, there was a guy that had a long post where his resistance readings were all over the place also. That didn't mean that they were leaking, but did cause poor running. It was also noted that vintage of vett has a problem with the injectors those years. So since you are planning to change the injectors anyway, do that first and then take it from there. No need to go into the tank unnecessary. Good luck
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
24 is to low, you should be around 40-45 with key on, idle seems ok, but dropping that fast means you have either leaky injecrtor(s) bad pressure regulator or check valve in the fuel pump-one guy reported a fuel pump pulsator was his problem, but that seemed very unigue.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
24 is to low, you should be around 40-45 with key on, idle seems ok, but dropping that fast means you have either leaky injecrtor(s) bad pressure regulator or check valve in the fuel pump-one guy reported a fuel pump pulsator was his problem, but that seemed very unigue.Obviously if they ohmed all over the place you have bad injector(s) they should ohm within .5 of each other, and should be ohmed both hot and cold.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Woe Jo, don't go through the dismantling of the upper intake and not know what is exactly wrong. The injectors could be fine, you will need to ohm them and all 8 should be around 16+/-. You might have a leaky diaphram in the fuel pressure regulator on the fuel rail. Also the check valve is know to loose pressure. Check in the vacuum at the FPR and see if you see gas. Crank the car and turn it off while someone pinches off the fuel return line at the tank. If pressure still leaks down the injector(s) are suspect. IMO I would do the troubleshooting before pulling your hair out trying to fix a good part.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
24 would be low but because the fuel pump only runs for about 2 seconds, try ignition on/off about 3 times and see if the press. reading isn't a bit closer. You ca pull the vac. line from the regulator and if fuel is leaking from it bad fuel press. reg. Look in your HELMS for the complete method of testing your fuel system.
Last edited by mseven; May 2, 2006 at 08:24 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Racer
Joined: Oct 2004
Posts: 288
Likes: 18
From: Somerset PA
Thank you all for your reply...
I think I have the mystery of the 24 PSI reading figured out... The battery was pretty low when I first turned the key on and checked the pressure. I'm betting there wasn't enough voltage to run the fuel pump at full pressure. I had to hook the battery charger up to start the car, I should have checked the pressure at that point, but didn't think of it. So, I think that's why the low initial pressure was there.
As for changing out the injectors when not needed; The injectors are definitely bad! When I ohm'd them only 3 were around 14, one was at 10, and the rest were real low! One shows no resistance at all! I'm going to replace them this week if I get enough time. I'm hoping that this fixes the rough running problems. It certainly should help!
I think I have the mystery of the 24 PSI reading figured out... The battery was pretty low when I first turned the key on and checked the pressure. I'm betting there wasn't enough voltage to run the fuel pump at full pressure. I had to hook the battery charger up to start the car, I should have checked the pressure at that point, but didn't think of it. So, I think that's why the low initial pressure was there.
As for changing out the injectors when not needed; The injectors are definitely bad! When I ohm'd them only 3 were around 14, one was at 10, and the rest were real low! One shows no resistance at all! I'm going to replace them this week if I get enough time. I'm hoping that this fixes the rough running problems. It certainly should help!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
My assessment of the info
Even if your battery was low initially that would not account for loosing the fuel pressure that you had. The fuel pump only requires a few amps to run unlike the starter requires lots more amperage to turn over engine obviously. Under normal conditions a low battery should have plenty of power to run the pump or lights in the car. Unless the battery was so low that your inside lights and such barley came on, then I could understand the pump not pumping enough pressure. It doesn't really take 2 seconds for it to reach pressure, it really comes up almost instantaneously and the excess goes back to the tank thru the fuel regulator.
Don't let this change your course of action, but just consider this as additional information.....or not.
Don't let this change your course of action, but just consider this as additional information.....or not.