No Fuel Pressure after Rebuild

[vristang]

I just finished getting the motor back in and tried to start the motor.

I hear the fuel pump fire up when I hit the key

The motor cranks just fine, but does not fire. It doesn't even stumble.

The fuel pressure gauge on the fuel line shows the pressure come up, but the pressure is not maintained.

In the time it takes for me to get out of the car and look at the pressure gauge it has already dropped to less than ten psi. I can then watch the pressure drop to zero.

Checked under the car for fuel leaks after kicking the pump on and off for several minutes. No leaks and I cannot smell fuel anywhere around the car.

The supply line to the fuel rail does get fuel. I disconnected it and got fuel all over my hands.

The only things I changed with the rebuild were internal; rings, bearings, and balancing.

Anyone know what I forgot?

 

[sweet88gt]

What brand fuel pump do you have?? I have a Walbro and the stupid thing has a check valve in the pump. Its about 2 yrs old and you can watch the fuel pressure go down when the car is off. Maybe the same kind of problem only yours wont hold any pressure. Just a thought.

 

[vristang]

What brand fuel pump do you have?? I have a Walbro and the stupid thing has a check valve in the pump. Its about 2 yrs old and you can watch the fuel pressure go down when the car is off. Maybe the same kind of problem only yours wont hold any pressure. Just a thought.

I think the pump was a Holley unit.

I just pulled the codes and got a system pass. Not much of a surprise I guess.

It has been sitting in the garage for about 8mo.

Maybe water plugged up the filter? I think I'm grasping at threads now.

 

[sweet88gt]

Is it possible that the fuel may have gone stale? 8 months with no fresh fuel I would look at the filter as a first easy change.

 

[vristang]

Thanks for jumping in sweet88.

I will pick up a fuel filter tomorrow. It's about due anyway.

The problem may actually be spark though.

I gotta get to the parts store before they close but will explain better later, I hope?

 

[HISSIN50]

There are two biggies for pressure loss. the aformentioned check-valve and the FPR.

One can use a return-line crimping tool (carefully!) to crimp the return line. If pressure goes up or holds, that suggests the FPR is like me after a spicy burrito (passing too much gas).

If pressure does not hold with the line crimped, that suggests the pump's check valve is dropping the 'ball'.

if you cycle the key a few times (assistant watching), does it build enough pressure to be able to start (30+ PSI)?

You can jump the self-test connector to make the pump stay on, if this helps with diagnostics or troubleshooting.

Good luck.

 

[vristang]

Thanks for the advice guys!!!

I did get the motor started, good lord it sounds mean!

Turns out the fuel filter was bad and causing some problems with the fuel pressure.

I had also put the dist in way out of whack. Completely missed top dead on #1. Kinda embarassing. I guess too much cold medicine can affect you.

Still needs some tuning, but 408 cubic inch motors rock

Thanks again.

 

[HISSIN50]

Glad to hear you got it whipped. You are a smart guy, so it was just a matter of checking a few things.

 

[slo65]

better no fuel pressure than no oil pressure

 

[vristang]

Glad to hear you got it whipped. You are a smart guy, so it was just a matter of checking a few things.

Gotta call

A smart guy would have thought of this stuff before cranking the motor!

I keep telling myself that this is part of the fun, but it isn't working.

 

[1988WHTGT]

I'm having a similar prob right now....I have stock pump and fpr and I get 40 psi at idle, but when I rev it up it drops to around 8-10 psi....could this be the pump or reg? I hope so cuz I just ordered both

 

[HISSIN50]

I'm having a similar prob right now....I have stock pump and fpr and I get 40 psi at idle, but when I rev it up it drops to around 8-10 psi....could this be the pump or reg? I hope so cuz I just ordered both

Stock pressure is ~39 PSI with the vac line off and capped. WIth the line attached (as if driving), it should be at or above 30 PSI.

VRI, It is still running good? Like I said, nice work.

 

[1988WHTGT]

So I should be alright cuz I just ordered both or it doesn't sound like the pump or fpr is the prob? Sorry, I've been up for 20 hours and things are starting to not make sense, ha

 

[HISSIN50]

So I should be alright cuz I just ordered both or it doesn't sound like the pump or fpr is the prob? Sorry, I've been up for 20 hours and things are starting to not make sense, ha

I misread your post before - I thought you had an 8-10 PSI drop, not that your pressure went down to 8-10 PSI. That AINT right. LOL. Are you sure it drops that much (i.e. bad gauge), because I dont see an EFI stang continuing to run with so little fuel pressure.

One can carefully crimp the return line (they make special pliers for this) to see if pressure still drops. If it does not, that suggests the FRP is passing too much fuel (it is at fault). If you crimp the line and pressure still drops, that suggests the pump is on the outs.

And what happens if you remove and cap the vac line to the FPR and then do your test like you did before? Does it act the same? (This is not real important, so dont worry about it if you did not do it before).

If the pump and FPR are original, then tossing in a new pump and reg is not a bad idea anyhow. That should take care of the issue - those are the two biggest items which can cause low pressure.

Sorry for my misread before - good luck with it.

 

[vristang]

I'm having a similar prob right now....I have stock pump and fpr and I get 40 psi at idle, but when I rev it up it drops to around 8-10 psi....could this be the pump or reg? I hope so cuz I just ordered both

Sorry to say this but my problem was a little different. I would hear the fuel pump come on, pressure would come up to 40psi, but when the pump shut off there was no maintenance of fuel pressure. The engine never started. Pressure would drop to 0 within 3-5 seconds. After replacing the fuel filter, pressure is able to hold just fine. Pressure leakdown takes a long time now.

The only direct link I can see between fuel pressure and rpm is the regulator (more rpm means more vac.). It seems unlikely that a regulator failure would behave this way though.

How does the car run with the vac line disconnected?

Or, maybe the pump can no longer flow well enough to maintain pressure at elevated rpm?

I would try the reg. first since you already bought it, and it is the easiest to do. I can't give a good guess as to what it is, but I would like to hear how you resolve the issue.

Best of luck