Engine No fuel pressure
- Thread starter AJdiebo1
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Could be a few things. Failed regulator, broken fuel line, or a ruptured fuel pump nipple in the tank.
arnie93lx
Active Member
Do you have a gauge mounted on the factory schrader valve? I suppose you checked for fuel leaks and all.
Please clarify that last post. What never moved from zero if you had no gauge?
What was your test procedure?
What was your test procedure?
I connected a fuel pressure tester from autozone to the Schrader valve.
Update: after dropping fuel tank to make sure the seal around the filler neck was sealing i pulled the pump out of the tank. And replaced it with a new one. Which means. I have an intank fuel pump and an external pump bolted to underside of rear bumper. The car has 40psi at schrader valve now and the car start right up.
Once i turn the car off the pressure does not hold. It drop right too zero.
I bought the car as a roller and the previous engine was a turbo engine. Not sure about turbos. Do i need both pumps? It no longer has turbo 302 B cam explorer heads and intake
Blown88GT
Founding Member
All the newer pumps have no anti-drainback. The best solution is a fuel pressure regulator with the anti-drainback feature. Kirban is the only one I am aware of which has this feature.
Blown88GT
Founding Member
The secondary pump is a boost pump. They were common when the in-tank pumps did not provide the increased fuel flow that turbos & superchargers require. The OEM pumps were 88 lph, replacement pumps can have much higher capacity. Don't know what your replacement is but you can probably eliminate the boost pump.
Blown88GT
Founding Member
Bypassed the secondary pump and it run alot better. But still a little rough hesitation with acceleration. Will be installing a pressure gauge with adjustable regulator this weekend. I think my harbor freight fuel pressure tester is crap. On another note is there a such thing as roller rockers being over tightened?
- Mar 2, 2015
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Yes, they can be over tightened or shimmed incorrectly depending on the type of roller rockers used. There are two main types...stud mount and pedestal mount. Pedestal mounted get shims and the stud mount get adjusted with an adjustment nut. Shaft mount rockers won't be found on the average mustang engine.
Mine did the same thing when I had the original pump. As soon as you turn the key to off, the pressure would drop. However, I never had an issue starting the car. I cycle the key, let it prime for a second and then start and it would fire up. Drove this way for 10 years?
I changed the pump to a Walbro 190lph a couple years back, not the car does hold pressure when I turn the key off. It will slowly bleed off, but it will take 5 mins or so to do this. Eventually it does drop to 0. I did buy that pump back in 2005/2006 though, so no idea how that compares to the new Walbros.
- Mar 2, 2015
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Unfortunately, I have nothing to compare to. My pump was replaced in 2015 when I installed this set up. I believe it's a 255lph...or 340lph walbro. ( would have to check my thread ). I thought I had an issue at first and did several checks on the fuel system. Even contacted the place I bought it from and Kirban. The pump was holding pressure, the diaphragm was OK inside the Kirban, no leaking injectors. I did some quick research and found several people with Kirban and the same issue. I deemed it normal. They were going to send me a replacement but I canceled it. If I plugged the return line the fuel pressure held for a while. The pressure was bleeding off through the regulator out the return line.
There is also a check valve in the pump. This is usually the main cause of the failure of the fuel system to hold pressure. The FPR just acts as a restriction in the line to build pressure ahead of the regulator (where the injectors are) but if the fuel pump check valve has failed, there is nothing to prevent backflow through the pump relieving all pressure in the line.
I haven't handled a walbro pump in a while, so I don't know if the new ones still have it or not. I think I still have my original pump somewhere to take a look at.
I haven't handled a walbro pump in a while, so I don't know if the new ones still have it or not. I think I still have my original pump somewhere to take a look at.
Blown88GT
Founding Member
That's how my kirban looked inside. Definitely a check valve.
In order to hold pressure in that line, since the fuel pressure guage is between the FPR and the pump, you need a check valve on both ends (when the pump is not running) otherwise pressure will relieve itself through the pump.
Unfortunately it appears I discarded my original fuel pump (thought I kept it) so I can't dissect it to take a look at that check valve.
But my experience summed up:
Kirban AFPR plus stock pump with failed check valve: pressure drops to 0 as soon as pump is off
Same kirban with new 190LPH Walbro: Pressure holds for 5-10min or so but eventually drops to 0
Car ran perfectly fine for years in the first condition
In order to hold pressure in that line, since the fuel pressure guage is between the FPR and the pump, you need a check valve on both ends (when the pump is not running) otherwise pressure will relieve itself through the pump.
Unfortunately it appears I discarded my original fuel pump (thought I kept it) so I can't dissect it to take a look at that check valve.
But my experience summed up:
Kirban AFPR plus stock pump with failed check valve: pressure drops to 0 as soon as pump is off
Same kirban with new 190LPH Walbro: Pressure holds for 5-10min or so but eventually drops to 0
Car ran perfectly fine for years in the first condition
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