View Full Version : Bad fuel pump?
dgcole01
10-10-2020, 12:09 PM
I've got a Mark 2 roadster. Finished in 2005. I'm the third owner. Got the car a year ago with 4900 miles and it has 9000 now. It has a combination of new and Fox body donor parts. It has a Fox fuel tank and I assume a stock in-tank efi pump. Unknown age. Donor car was 89 Mustang GT. Might be original pump. 340 hp crate efi. This week I noticed the car didn't fire on the first hit of the key as normal. Had to turn it over a couple of seconds. Drives fine and no noticeable loss in power.
The pump sounds normal when you turn the key on.
Put a pressure gauge on it today. When I put the gauge on there was no pressure in the lines. Car had sat ~36 hours and all pressure had bled off.
Did 3 tests:
1. Turn key on engine not running. Pumps sounds normal. Pressure jumps to 35 psi for about 1.5 sec then instantly drops off to about 7 psi.
2. Engine running at , pressure regulator vac line disconnected, pressure goes to stays and stays at 40 psi. Rev the engine and dip to 35 and then recovers to 40.
3. Engine running pressure regulator vac connected, stays at 35 psi, rev the engine and there is a slight dip to 31 ish then recovers.
I'm thinking the check valve in the pump is bad along with possibly a weak pump.
Thoughts?
I think you should look at the pressure regulator. I don't think there is a check valve at the fuel pump, pressure regulator controls that. Note the pressure regulator is at the end of the fuel run, on the engine, before it returns to the fuel pump/tank. So, in reality, your pressure regulator is your check valve. Mine, which is an Aeromotive adjustable one, will leak down to 20psi overnight and stay there. When I turn the key on, no start, it goes to 40psi then drops to about 37psi.
Pull your vacuum hose to the regulator and see it there is gas in it.
George
dgcole01
10-10-2020, 01:20 PM
I think you should look at the pressure regulator......
Pull your vacuum hose to the regulator and see it there is gas in it.
George
Just checked it. No gas in the vacuum hose, but I connected a Mityvac hand vac pump to the regulator. It will not hold vacuum. Pumped it to 20" vacuum and it dropped to 0 in about 10 seconds.
But....I still think it may be the pump. Researched it and there is a check ball inside the pump itself to keep the fuel from running backwards out of the pump. I disconnected and plugged the return line. Pressure jumped up on prime, but then dropped to nothing. With the return line plugged the only way it'd lose pressure is back through the pump. Injectors leaking could cause it, but that would take several minutes and no sign of gas dumping into the engine.
But....I still think it may be the pump. Researched it and there is a check ball inside the pump itself to keep the fuel from running backwards out of the pump. I disconnected and plugged the return line. Pressure jumped up on prime, but then dropped to nothing. With the return line plugged the only way it'd lose pressure is back through the pump. Injectors leaking could cause it, but that would take several minutes and no sign of gas dumping into the engine.
Thinking this out.
Yes, there is a check valve in the pump. The fuel pressure regulator stops it at one end and the fuel pump check valve stops it at the other end.
Just did a search and yes there is a check valve and from my reading a failed check valve has symptoms similar to yours.
At least, with the roadster, the fuel pump is fairly easy to access. In the Mustangs sounds like it's a bear to get to.
George
michael everson
10-11-2020, 06:26 AM
I really don't think you have a problem. Who cares what the pressure is when its not running. Bet you will find that most systems bleed off the pressure pretty quick.
Mike
rich grsc
10-11-2020, 07:43 AM
I really don't think you have a problem. Who cares what the pressure is when its not running. Bet you will find that most systems bleed off the pressure pretty quick.
Mike
I'd make that 'all'.
I'd make that 'all'.
To Mike and Rich's comments.
I'm thinking they have a check valve in the pump for a reason. That reason being to have the enough pressure upon turning the key once after the car has sat for a while and starting. If that pressure bleeds off too quickly and the car sits for a few days, it would require several cycles of turning the key on and off to get the system up to the correct pressure for an easy start. In my instructions with the Ford Racing wiring harness, it states to cycle the key on and off before the first start to get the system up to pressure so the injectors can deliver the proper amount of fuel for that first start.
My car has sat for two days without cycling the starter key and it sits at 18 psi as it did several hours after cycling the key to get pressure without starting. I had adjusted and cycled the pump to get 60 psi to check for leaks and have let it sit for those two days.
That remaining pressure makes it easy for the fuel pump to get to 40 psi for the next start.
George
Just puttering
10-11-2020, 12:38 PM
Try turning on the key then count to one then start. See if that fixes your problem.
Some after market regulator info states the pressure will drop to zero. And is normal.
Mine goes to zero quickly, when i turn the key on it jumps to 40 psi. Have someone turn on the key and see how fast you are getting 40 psi.
Gwl,
I would think the first start key cycling is to clear air out of the system, not a first start of the day idea?
Gwl, I would think the first start key cycling is to clear air out of the system, not a first start of the day idea?
Makes sense, thanks for the note.
George
dgcole01
10-11-2020, 10:37 PM
To Mike and Rich's comments.
I'm thinking they have a check valve in the pump for a reason. That reason being to have the enough pressure upon turning the key once after the car has sat for a while and starting. If that pressure bleeds off too quickly and the car sits for a few days, it would require several cycles of turning the key on and off to get the system up to the correct pressure for an easy start. In my instructions with the Ford Racing wiring harness, it states to cycle the key on and off before the first start to get the system up to pressure so the injectors can deliver the proper amount of fuel for that first start.
My car has sat for two days without cycling the starter key and it sits at 18 psi as it did several hours after cycling the key to get pressure without starting. I had adjusted and cycled the pump to get 60 psi to check for leaks and have let it sit for those two days.
That remaining pressure makes it easy for the fuel pump to get to 40 psi for the next start.
George
I think mine has been holding pressure up until this problem started last week. For the past year I'd turn the key or, hear the pump run 2-3 sec to prime and then turn the key. Instant start. Last week I had the car down at Cruising the Coast. Turn the car on, hear the pump prime and now it's taking turning it over 2-3 seconds before it would fire. Started the problem all of sudden. I've got a Walbro replacement pump on the way. Stepped it up one notch over stock with the new pump 155 lph.
michael everson
10-12-2020, 05:09 AM
Just because there is no pressure, doesn't mean the lines are empty. They wont bleed back.
Mike
Do note, in the original post he says the engine takes a few moments 'longer' before firing up.
Additionally, the gauge jumps to 35 psi, then it immediately drops to 7 psi after turning the key to 'on', no start. Now, yes, if the key continues to 'start' the fuel pump should continue running to keep that pressure at 35 psi. But what is slowing the initial start up as noted by original post and does it matter?
George
michael everson
10-12-2020, 02:41 PM
In an EFI car the fuel pump only cycles for a couple seconds. So a pressure loss isn't necessarily wrong or bad.
Mike
dgcole01
10-14-2020, 08:40 PM
Update. put a new fuel pump in today. Upgraded 1 step up to a 155 lph Walbro. The stock pump was a Walbro as well. As far as I can tell it was stock from the donor circa 1989. It's much better at holding pressure now. Key on and it primes. Pressure goes to 40 and the drops off to 20 psi after about 5 minutes. Stays at the 20 psi and is still holding there after 2.5 hrs.
Was worth the couple of hours. Most aggravating thing was just siphoning 3/4+ tank of gas out and then putting it back in. Pump was 90 % plug n play. The nipple on the new pump was taller so I had to shorted the corresponding tube on the hanger by the same amount to be able to get the short runner gas line hose on.
Noticed:
1. The new pump is not nearly as loud as the old one. Prob half.
2. Car starts instantly just like before this issue started. No turning the starter for 2-3-4 seconds.
3. New pump makes about 5 psi more than the one. With vacuum to regulator unplugged its at 45 psi, old one was 40. Set the regulator to 39 psi with vac.
Great!
My new pump is holding at 18 psi and has been there for about 4 days.
George