Fuel pressure at 20 psi
11-26-2010, 08:36 PM
#1
Teching In
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Location: Alabama
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Fuel pressure at 20 psi I have a 94 z28,auto trans.
I have a couple problems with it.
1. Engine turns over 8 or 9 times before cranking.
2. Every now and then...id say 4 out of 10 crank ups the engine will run rough under load for about 30 to 45 seconds then it smooths out( idels fine).
Had a tune up and new opti 20,000 miles ago,problem just started.
I changed the fuel filter today it was old...oem? I dont know but it was an ac delco filter and was full of crap. I checked fuel psi today after fliter change it was at 20 psi. Fuel pump bad? Would low fuel pressure make it run bad like every now and then?
Thanls Matt
I have a couple problems with it.
1. Engine turns over 8 or 9 times before cranking.
2. Every now and then...id say 4 out of 10 crank ups the engine will run rough under load for about 30 to 45 seconds then it smooths out( idels fine).
Had a tune up and new opti 20,000 miles ago,problem just started.
I changed the fuel filter today it was old...oem? I dont know but it was an ac delco filter and was full of crap. I checked fuel psi today after fliter change it was at 20 psi. Fuel pump bad? Would low fuel pressure make it run bad like every now and then?
Thanls Matt
11-26-2010, 09:34 PM
#3
You need to check fuel pressure under a few conditions.
-Key on engine off should be around 43.5psi (41-47psi is acceptable).
-While cranking (41-47psi).
-With the engine idling (drop 3-10psi from your KOEO pressure).
-Under throttle (should slowly increase with throttle position).
Poor fuel pressure can be caused by a few things:
-Weak/dead pump
-Bad fuel pump check valve
-Kinked, pinched, or broken lines
-Leaky fuel pressure regulator
-Leaky fuel injectors.
Any way you cut it, 20psi at ANY condition is not good.
-Key on engine off should be around 43.5psi (41-47psi is acceptable).
-While cranking (41-47psi).
-With the engine idling (drop 3-10psi from your KOEO pressure).
-Under throttle (should slowly increase with throttle position).
Poor fuel pressure can be caused by a few things:
-Weak/dead pump
-Bad fuel pump check valve
-Kinked, pinched, or broken lines
-Leaky fuel pressure regulator
-Leaky fuel injectors.
Any way you cut it, 20psi at ANY condition is not good.
03-06-2011, 04:19 PM
#4
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Sorry to revive, but I've got almost the same symptoms.
95 Z28 Manual, stock injectors, stock fpr, stock fuel pump.
Started the car up and it was rev'in high around 1.4k and wouldn't come down. Also smelled like gasoline.
First thing, I got a fuel pressure gauge and a fuel filter. Obviously wasn't the filter, but it was well overdue for a change.
At KOEO, fuel pressure is 22 psi. If I relieve the pressure in the system and KOEO, I can hear the pump working, and it climbs to 22 psi fast, but it sounds like the pump is getting capped at 22 psi, like there's too much resistance to continue.
Is there a definite test that can determine weither it's the fpr or pump? All signs point to fpr afaik. I'm hoping the OP comes back on.
95 Z28 Manual, stock injectors, stock fpr, stock fuel pump.
Started the car up and it was rev'in high around 1.4k and wouldn't come down. Also smelled like gasoline.
First thing, I got a fuel pressure gauge and a fuel filter. Obviously wasn't the filter, but it was well overdue for a change.
At KOEO, fuel pressure is 22 psi. If I relieve the pressure in the system and KOEO, I can hear the pump working, and it climbs to 22 psi fast, but it sounds like the pump is getting capped at 22 psi, like there's too much resistance to continue.
Is there a definite test that can determine weither it's the fpr or pump? All signs point to fpr afaik. I'm hoping the OP comes back on.
03-06-2011, 04:22 PM
#5
Applying vacuum to the FPR should change the fuel pressure. If a difference in vacuum does not change the pressure then the regulator is faulty. You could also check to see if there is fuel in the vacuum line, indicating a torn regulator diaphragm.
