Fuel Delivery Issue/ No Start
Thread Starter
Heel & Toe
Joined: May 2021
Posts: 15
Likes: 0
From: Sarasota, FL
Fuel Delivery Issue/ No Start
I have a 1985 C4 that will crank, but not turn over. I replaced the fuel pump and filter. After replacing both, there was a stutter/rattle in the fuel line around the filter, but no start. I hear the pump engaging, and upon doing a fuel pressure test, I am getting 15 psi. I have been reading through a number of threads, but I could really use some guidance. Thank you for your insight!
Le Mans Master
Joined: Feb 2005
Posts: 6,479
Likes: 565
From: Clearwater Florida
..... When was the last time that this car ran ? Did you test the fuel pump by "hot wiring" it ? If your test was performed simply by turning the key , you need to know that this will only activate the pump for a few seconds and may not build full fuel pressure . The lack of pressure may be due to a faulty fuel pressure regulator . Its also possible that there is some blockage in the fuel line itself . When you changed the fuel pump did you eliminate the pulse dampener ? .....
Thread Starter
Heel & Toe
Joined: May 2021
Posts: 15
Likes: 0
From: Sarasota, FL
The car last ran a week ago. It died while idling in my driveway for 2 minutes.
The pump is a brand new AC Delco part. Because the pump replacement did not do the trick I'm wondering if the old one is actually bad.
The dampener was not on the pump; someone took it off previously, and I did not replace it.
Thank you for your reply!
The pump is a brand new AC Delco part. Because the pump replacement did not do the trick I'm wondering if the old one is actually bad.
The dampener was not on the pump; someone took it off previously, and I did not replace it.
Thank you for your reply!
Thread Starter
Heel & Toe
Joined: May 2021
Posts: 15
Likes: 0
From: Sarasota, FL
..... When was the last time that this car ran ? Did you test the fuel pump by "hot wiring" it ? If your test was performed simply by turning the key , you need to know that this will only activate the pump for a few seconds and may not build full fuel pressure . The lack of pressure may be due to a faulty fuel pressure regulator . Its also possible that there is some blockage in the fuel line itself . When you changed the fuel pump did you eliminate the pulse dampener ? .....
I replaced the pump with a new AC Delco part without doing a proper test. I'm wondering if the old one was actually bad! The dampener was taken off previously, and I did not replace it.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Clamp off the rubber part of the return line, re test. If pressure goes way up (60ish lbs or so) you have a bad regulator. If it doesn't try C409's suggestion:
When you changed the fuel pump did you eliminate the pulse dampener ? .....
Thread Starter
Heel & Toe
Joined: May 2021
Posts: 15
Likes: 0
From: Sarasota, FL
This is brilliant, thank you. I tested again, and got 15 psi. I clamped off the return line, the first time in accessory mode it read 25-30 PSI, then 40+ the second time. Is the FPR the sure next step?
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
I'd say so. It could have some crud in it, holding the return valve open....you can take it apart and look at it to see why it's not doing it's job. Simple device; a spring loaded restriction.
Thread Starter
Heel & Toe
Joined: May 2021
Posts: 15
Likes: 0
From: Sarasota, FL
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Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
That orange part is all of it other than the stamped steel housing. It's unlikely that your orange diaphragm is bad (torn) as that doesn't affect fuel pressure typically and it also causes too much fueling since the fuel passes through the tear in the diaphragm and goes into the intake. For the regulator to cause low pressure, either the spring has to be broken (never seen that happen), or there could be debris between the little round "button" in the center, and the orifice that it's trying to plug.
Le Mans Master
Joined: Feb 2005
Posts: 6,479
Likes: 565
From: Clearwater Florida
It ran up until last Sunday. It idled from a cold start for about a minute before dying.
I replaced the pump with a new AC Delco part without doing a proper test. I'm wondering if the old one was actually bad! The dampener was taken off previously, and I did not replace it.
I replaced the pump with a new AC Delco part without doing a proper test. I'm wondering if the old one was actually bad! The dampener was taken off previously, and I did not replace it.
Thread Starter
Heel & Toe
Joined: May 2021
Posts: 15
Likes: 0
From: Sarasota, FL
End of my rope
After switching the fuel pump, filter and fuel pressure regulator, I still have a no start. The fuel pressure initially spikes at 25. After a second turn to "on," I get 44 psi, but no start.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Not likely an ignition control module or anything ignition related if it fires on ether. Time to diagnose why the injectors aren't firing
Have. you checked the two "INJ" fuses in the fuse panel? Start there. Then, you can also probe for power at one of the injector plugs on each side w/the key on. Batt/ign sw/inj fuses supply power to the injectors, ECM fires them by grounding them. If all that is good...
If you have a few bucks, go buy a "noid light". It's a LED that you plug one injector plug into, crank the engine and it blinks when the injector should fire. If no money, pull the fuel rails (in tact) and keeping fire in mind, have someone briefly crank the engine and watch to see all 8 injectors fire a nice even cone/spray.
Report back.
Have. you checked the two "INJ" fuses in the fuse panel? Start there. Then, you can also probe for power at one of the injector plugs on each side w/the key on. Batt/ign sw/inj fuses supply power to the injectors, ECM fires them by grounding them. If all that is good...
If you have a few bucks, go buy a "noid light". It's a LED that you plug one injector plug into, crank the engine and it blinks when the injector should fire. If no money, pull the fuel rails (in tact) and keeping fire in mind, have someone briefly crank the engine and watch to see all 8 injectors fire a nice even cone/spray.
Report back.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Copy. I'd say that it's pretty unlikely that the injectors are bad, so I'd be looking at those fuses. It's possible that ONE injector shorted out, or the harness chaffed to ground and blew one of the fuses....I doubt that it would stay running on 4 cyl.
Thread Starter
Heel & Toe
Joined: May 2021
Posts: 15
Likes: 0
From: Sarasota, FL
A step backwards: I am a novice with checking fuel pressure. The psi spikes immediately in accessory mode. It goes to 45 psi when the pump primes, but then it shoots to zero immediately. Still getting a rattling sound from the fuel line periodically. Am I wrong thinking that the gauge should hold the pressure for more than 1 second?
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
No. You are not wrong. There is a check valve in the pump, and then your FPR "shouldn't" let fuel through so it "should" hold fuel. Most bleed down in short order, (30 seconds? A couple min?) but yours dropping that fast is not normal. NOW....it shouldn't prevent it from starting if you have your 45 PSI while cranking (while the pump is running)...it should still start.
But I'd be really curious as to why the pressure is falling so fast. If could be:
Pump check valve
FPR
Injector stuck open or leaking.
You can isolate by clamping the return line, the feel line immediately when you build pressure,
Obviously, if clamping one of those lines stops or slows the pressure drop, that is the side your leakage is on. If neither makes a difference, then the only other place would be through an injector(s)
But I'd be really curious as to why the pressure is falling so fast. If could be:
Pump check valve
FPR
Injector stuck open or leaking.
You can isolate by clamping the return line, the feel line immediately when you build pressure,
Obviously, if clamping one of those lines stops or slows the pressure drop, that is the side your leakage is on. If neither makes a difference, then the only other place would be through an injector(s)