Fuel pressure falls imediately
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
Fuel pressure falls imediately
Happy New Year everyone 
.Just replaced fuel injectors. Ford Bosch 22 lbs. Got it all back together and went to prime up the fuel rails. First turn of the key and it went to 40 lbs. and held slightly and then bled down. I thought " first turn no problem". Then I purged all the air from the fuel rail. Now the fuel pressure reads 40 lbs. and then falls quickly to 0. It started rough but ran good as I purged the fuel rail. Idles good, runs good at 2000 rpm with a slight stumble. Holds at 32 lbs when idleing. Thoughts on why it drops to 0, when gauged with the motor off ?
.Just replaced fuel injectors. Ford Bosch 22 lbs. Got it all back together and went to prime up the fuel rails. First turn of the key and it went to 40 lbs. and held slightly and then bled down. I thought " first turn no problem". Then I purged all the air from the fuel rail. Now the fuel pressure reads 40 lbs. and then falls quickly to 0. It started rough but ran good as I purged the fuel rail. Idles good, runs good at 2000 rpm with a slight stumble. Holds at 32 lbs when idleing. Thoughts on why it drops to 0, when gauged with the motor off ?
Advanced
Joined: Sep 2005
Posts: 64
Likes: 1
From: Columbus Ohio
Given what you describe it sounds a check valve problem in the fuel pump or that the fuel pressure regulator is bad and letting fuel leak back to the tank on the return line.
Did you have similar problems before you replaced the injectors ?
Did you have similar problems before you replaced the injectors ?
Burning Brakes
Joined: May 2006
Posts: 857
Likes: 1
From: Morrisonville Illinios
Might be bad injector if it won't hold when pump is off. You can pull the plugs and see if any are wet then leave them out and you might hear them leak. Had the same problem when put some newe ones in bout because we just had the headers on could tell real quick which side was leaking. Ended up had 2 bad ones went with a completely different set and all worked well. Goo
d luck WRO87
d luck WRO87
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
If it didn't leak down fast before the new injectors (did you check??), I suspect a leak in that area.
Else I would pull the fuel door rubber boot and clamp the feed & return lines in turn. If it holds with feed line clamped it's the check valve it the pump; if it holds with return line clamped it's the FPR.
If neither clamping holds fuel pressure the leak is up front in the injectors or a connection.
Else I would pull the fuel door rubber boot and clamp the feed & return lines in turn. If it holds with feed line clamped it's the check valve it the pump; if it holds with return line clamped it's the FPR.
If neither clamping holds fuel pressure the leak is up front in the injectors or a connection.
Instructor
Joined: Dec 2006
Posts: 139
Likes: 0
From: Deep in The Heart of Dixie
Possible reasons.
1. Leak in supply line from pump.
2. Bad pulsator in tank.
3. Bad regulator.
If it was an injector, you would hear it hiss.
There is a good troubleshooting procedure in the FSM.
1. Leak in supply line from pump.
2. Bad pulsator in tank.
3. Bad regulator.
If it was an injector, you would hear it hiss.
There is a good troubleshooting procedure in the FSM.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
1. Did the pressure drop off before the injector swap?
2. Do you have the fuel pressure guage attached to the fuel rail good?
3. Did you use new o-rings on the fuel rail and/or fuel rail to line connections...any leaks there?
4. Have you pulled the vac off the FPR to look for signs of raw gas?
5. Have you pulled some spark plugs to see if they have raw gas on them?
6. Do you smell gas around the car?
7. Have you pinched off the feed line at the tank after pressure is made to rule out the check valve and pulsator?
8. Did you install a AFPR or use the stock FPR?
2. Do you have the fuel pressure guage attached to the fuel rail good?
3. Did you use new o-rings on the fuel rail and/or fuel rail to line connections...any leaks there?
4. Have you pulled the vac off the FPR to look for signs of raw gas?
5. Have you pulled some spark plugs to see if they have raw gas on them?
6. Do you smell gas around the car?
7. Have you pinched off the feed line at the tank after pressure is made to rule out the check valve and pulsator?
8. Did you install a AFPR or use the stock FPR?
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
Alright!!!
Well the car started perfectly this morning. This time the fuel pressure is holding !!! 40 lbs, turning the key, 30 lbs running, turn off it stays at 30 for a while, 30 minutes later 20 lbs, so on and so on. Running much smoother as well. Think the fuel swelled the orings ? any way its all good, thinks for the replies. Oh, I think the water pump is crapping out now. It set two weeks dry. Its making noise now.
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Team Owner
Joined: Jan 2003
Posts: 20,324
Likes: 250
From: Summerland B.C. Canada
O rings shouldn't swell. 
The check valve at pump may have been hung up. If you want to diagnose where the pressure loss is, read this http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
My pressure loss was at the dampner above pump.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
fuel pressure
sometimes the injectors are sprayed with a preservative that keeps the seats from tarnishing/corroding because of the unknown shelf time before installation.
the gasoline softens this preservative, and it takes a little bit to soften it before the valve in the injector seals tight.
It happened to the lucas injectors I installed on my 86.
it ran crappy for about 3-5 minutes, then bing, like a light switch, it ran perfectly.
the gasoline softens this preservative, and it takes a little bit to soften it before the valve in the injector seals tight.
It happened to the lucas injectors I installed on my 86.
it ran crappy for about 3-5 minutes, then bing, like a light switch, it ran perfectly.
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
It ran like @#$ at first. I kept purging the air out of the lines and it smoothed out. Was just concerned when it wouldn't hold pressure after the first prime up. Thanks for the reply. Its running good now.
