Heys guys this is my first post so let me know if I ramble.. I have a 95 gt with 5.0 in it, with koeo I get no fuel pressure but once I start the engine, it slowly goes to 32 psi and stays. turns over a few times before it will start. Any ideas why I have no constant pressure with koeo?....thanks
SN95 5.0 no fuel pressure with koeo
- Thread starter 95yellgt
- Start date
If you don't crank the engine and just turn the ignition on do you hear the fuel pump cycle? Since there is power to the fuel pump in both KOEO and KOER what you are describing doesn't seem possible. Will pressure build if you leave it in KOEO for a minute or so? It doesn't sound like a FPR issue but try pulling the vacuum line from the FPR and see if you smell gas. You shouldn't. A slow building of pressure if the filter is fresh points to a fuel pump problem. Perhaps the fuel pump relay (integral to the CCRM) or the pump itself.
if i leave koeo no pressure builds. that is why im confused. I can here the pump cycle when I turn on the key then after that there is still no pressure. I have tried 3 different gauges to rule out a faulty gauge. The thing is that when I turn it over a few times it fires up and idles fine at 32 psi. As soon as I shut it off I loose all pressure again. I just thought the pressure stayed for a little bit even after I turn it off like every other car I have checked. I dont know that this will cause any problems but it bothers me knowing somethings not right. Any ideas?
Have you tried cycling they key a few times before ever cranking it? One prime-out period might not be long enough for you to see pressure.
If you happen to have an aftermarket FPR, dropping pressure quickly after shut-off is not unusual.
Good luck.
If you happen to have an aftermarket FPR, dropping pressure quickly after shut-off is not unusual.
Good luck.
Zero Signal
Active Member
Pinch the fuel return line and try to prime it again. If it builds and holds, the FPR is bad. Otherwise, it's almost certainly the pump or cracked supply hose on the pump. Far less likely; but it could be a leaky injector.
The fuel system should hold pressure for a good 20 minutes+ with factory pump and FPR.
The fuel system should hold pressure for a good 20 minutes+ with factory pump and FPR.
Long-dead thread, but I am having the exact same problem. Did you ever find a solution?
When I KOEO, I hear the pump come on. But I am getting no pressure until I crank the engine. Then I get pressure. This makes me think it's a vacuum issue with the fuel pressure regulator? I think I will disconnect it and try again and see if it stays flat when cranking.
OK, went and tested. If I do multiple KOEO, the pressure will eventually build to about 25 psi and then quickly bleed down to 9 or so PSI.
I disconnected the vacuum line from the fuel pressure regulator, and it still fired right up and then went to 41 psi.
My guess is as long as the pump is running there is plenty of pressure. But when it is off it is bleeding down. Is there some kind of valve on the return line that could be going bad?
When I KOEO, I hear the pump come on. But I am getting no pressure until I crank the engine. Then I get pressure. This makes me think it's a vacuum issue with the fuel pressure regulator? I think I will disconnect it and try again and see if it stays flat when cranking.
OK, went and tested. If I do multiple KOEO, the pressure will eventually build to about 25 psi and then quickly bleed down to 9 or so PSI.
I disconnected the vacuum line from the fuel pressure regulator, and it still fired right up and then went to 41 psi.
My guess is as long as the pump is running there is plenty of pressure. But when it is off it is bleeding down. Is there some kind of valve on the return line that could be going bad?
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Well, I replaced the fuel pressure regulator, and no change, so it wasn't that.
I listened to 7 of the 8 fuel injectors with a stethoscope, and they are all ticking along merrily, so I don't think it's a stuck injector. I could not reach the back one on the driver's side due to the intake manifold.
I'm suspecting a check valve in the fuel pump assembly. There must be one there or the fuel pressure would bleed back into the tank after the pump shuts off.
I listened to 7 of the 8 fuel injectors with a stethoscope, and they are all ticking along merrily, so I don't think it's a stuck injector. I could not reach the back one on the driver's side due to the intake manifold.
I'm suspecting a check valve in the fuel pump assembly. There must be one there or the fuel pressure would bleed back into the tank after the pump shuts off.
Yeah, ancient thread. Well not ancient maybe but old just the same.
Do you have a thread for this issue?
What's the KOER fuel pressure with vacuum line on and then off regulator?
So if you remove the vacuum from the regulator it goes wide open so lack of vacuum will increase pressure.
Have you replaced the filter? I do not think this is the issue but wanted to ask.
I really think it’s one of three things. Least likely is the sock filter has collapsed. Pumps can start falling off on pressure as they age which means it’s failing. Another possibility is is the rubber hose between the pump and hanger. These were not meant for ethanol based fuels and even with non-ethanol based fuels they will age and crack so the gas will recirculate in the tank thus the fuel pressure will drop.
All this is based on your comment of it building to 25 psi and then falling off. I realize when you removed the vacuum it went to 41 psi but replacing the regulator did not fix it.
Have you replaced the filter? I do not think this is the issue but wanted to ask.
I really think it’s one of three things. Least likely is the sock filter has collapsed. Pumps can start falling off on pressure as they age which means it’s failing. Another possibility is is the rubber hose between the pump and hanger. These were not meant for ethanol based fuels and even with non-ethanol based fuels they will age and crack so the gas will recirculate in the tank thus the fuel pressure will drop.
All this is based on your comment of it building to 25 psi and then falling off. I realize when you removed the vacuum it went to 41 psi but replacing the regulator did not fix it.
No, I have not started a new thread.
KOER pressure with line on is about 34 PSI. Off it is about 41 PSI.
Yes, I replaced the filter last week. I was replacing the rear axle bearings and seals and while I was fiddling with the differential the fuel filter was right in my face so I replaced it while I was there. I was having this problem before that and of course still am. So, fuel filter was not the culprit.
If the car has been sitting an hour or more, on KOEO prime I get zero pressure (I have wired in a digital gauge for fuel and oil pressure so I can see it at all times). If I repeat the KOEO prime several times pressure will climb slowly to around 25 psi or so, going a bit higher with each KOEO. Then it will slowly leak down to around 9-11 psi. I imagine if I sat there long enough it would bleed back down to zero.
Presumably the pump assembly must have some kind of check valve to prevent the pressure from bleeding back through the pump after it turns off when it finishes priming. Or, it could be a shot hose as you state. I do run the standard ethanol gas that everyone has these days.
Sounds like it's time for a new pump.
The pumps do have a check valve. The Walbro 255 lph pump in my Coupe pressures up fast and looses pressure fast when the key is off. Zero affect on how the car starts or performs. Previous pump did it as well which is why I replaced it.
If you drop the tank you may think about getting a new filler neck grommet/gasket as they do harden up over time.
If you drop the tank you may think about getting a new filler neck grommet/gasket as they do harden up over time.
With the (presumably) stock pump and zero PSI on the rail my car is taking a couple of seconds of cranking to actually fire off.
I will be replacing the filler neck grommet/gasket when I do this job.
It was the fuel pump. Replaced it this yesterday and today and now everything is fine.
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