Fuel Pressure Drops Rapidly after Sitting 7 months

[Schmieder]

When the pump primes at key on it builds weak pressure then drops it's pressure in seconds. The engine will want to run but stumbles and stalls as fast as the pressure drops. This is what I ruled out so far.

The car did sit outside for 6-8 months. Did a manual swap during that time. It took some time but everything went well enough. No accidents or damages along the way. My fuel fill cap has a lock on it so I rule out general vandals. The EVAP lines are disconnected though, but the engine operated fine like that in the past.

CHECKS
- No smell of fuel when the closed fuel system is primed
- No sign of fuel leaking any where along the fuel lines
- Checked Injectors and no leaking at the rail or the nozzle
- Checked with a known good FPR, no change
- Fuel Filter is clean and free flowing
- Fuel is flowing well from the FPR port when pump is primed (when I had FPR removed)
- Fuel pump makes a normal healthy sound (opinion, could be wrong)
- Tank has 4 gallons, fuel gauge registers above empty and car is level
- The Fuel Pump is only 1-2 years old w/ no more then 2,000 miles on it

There is a hissing noise at the fuel rail. But no air or fuel is seen leaking. Not even out the FPR. It is really strange, and I will say there is NO fuel leaking any where outside the fuel tank. So why do I hear hissing at the fuel rail?

I want to say it is the Fuel Pump or the Check Valve (still replacing the pump if so) but wow, not many miles it lasted. Can stale gas ruin a pump?

Can anyone else tell me other possibilities (if there are any)?

Cause at this point it looks like a fuel pump replacement but dang-it, I did that grueling task not too long ago....... /sigh

Please Help

[Schmieder]

I'll simplify my question, lol....

Can a fuel pump die from simply sitting 6-8 months?
(outside weather)(inside Fuel Tank w/ ventilation)(very low fuel level in tank)(Fuel wasn't gel, still very fluid)

Or can an electrical problem arise that weakens the fuel pump dramatically? Such as a partially burned up fuseable link? Or 1 of more relays going bad?



I doubt the relay but.....

[Joseph Upson]

Low fuel pressure with no external leaks suggests the fuel pump is bad with a possibility of it being the regulator which you can quickly rule out by crimping the return hose if you have one. If the pressure increases to normal and holds, it's the regulator but I doubt it. Sometimes the hose connecting the pump to the in tank line fails but you probably wouldn't get enough pressure to start the engine in that case.

Yes a pump can go bad from sitting for long periods of time if enough of the right contaminates are present in the fuel and especially if it's a non OE part which doesn't require long periods without use to fail in my experience. I had a new pump fail before I could put the wheels back on the ground after installing it. Never go cheap on parts that can deadline the car if they fail when possible.

[Schmieder]

Low fuel pressure with no external leaks suggests the fuel pump is bad with a possibility of it being the regulator which you can quickly rule out by crimping the return hose if you have one. If the pressure increases to normal and holds, it's the regulator but I doubt it. Sometimes the hose connecting the pump to the in tank line fails but you probably wouldn't get enough pressure to start the engine in that case.

Yes a pump can go bad from sitting for long periods of time if enough of the right contaminates are present in the fuel and especially if it's a non OE part which doesn't require long periods without use to fail in my experience. I had a new pump fail before I could put the wheels back on the ground after installing it. Never go cheap on parts that can deadline the car if they fail when possible.

It was a walbro high flow. I swapped the FPR with a known good one and it didn't change a thing. The fuel pressure drops off so fast the car doesn't get a chance to start. It sputters and stalls out if I try to start it during the fuel pump prime. If I let the fuel pump prime and wait a few seconds then it won't even sputter at all.

I suppose it is possible the fuel line in the tank aged and split open? I never heard of that before but hey, I'm sure it can happen. It's hard to believe a Walbro would fail like that, unless I got a cheap imitation Walbro. I don't remember where I bought it but it was online.

Even though I know for sure the fuel pressure is far too low, I decided to buy a pressure gauge for the Shrader Valve later today when I pick up the replacement. This would be the third time I could have used the fuel pressure gauge.

This project was supposed to be 2-3 months max. It was dragged out to 7 months so far.....ugh



Thanks for the advise, I kinda knew it was the pump but I was hoping for an unknown circumstance.

[AleroB888]

The Walbro has no check valve. Extremely low level in the tank could cause a pump to fail, and I would even guess that the lack of a check valve makes the pump more prone to it. I use an external check valve on mine, yet still maintain at least a 1/4 tank level.
Does your pump use a rubber tube or plastic flex tube on the outlet?

[Schmieder]

Does your pump use a rubber tube or plastic flex tube on the outlet?

Not sure, I will know when I drop it later today or tomorrow. Amazing about the check valve, I wish I knew that. Then is it the pump itself that holds the fuel from back-flow? I guess it really doesn't matter as long as it does the job.

I have a new pump. I can't boost up a lot on it but thats okay for now. Because I need to break in the clutch and perfect basic tuning before I put on full 8-12 psi boost. Plus I want to investigate how to switch to an external pump. I'm sick of this internal tank pump crap....lol.

I always try to keep above 1/4 tank as well. But more importantly, I should be adding small amounts of Seafoam or Techron to my fuel. It is a pita to add just enough per gallon for continual use, but it's worth it. I feel ethanol is too dry for the pump and the upper cylinders.

[trotterlg]

I would first try powering the fuel pump directly from the battery, eleminate the start and run circuits. Could be the relay or whatever keeps power to the pump while the car is running is bad and the only fuel you are getting is in the prime mode. Larry

[Schmieder]

I would first try powering the fuel pump directly from the battery, eleminate the start and run circuits. Could be the relay or whatever keeps power to the pump while the car is running is bad and the only fuel you are getting is in the prime mode. Larry

I tried known good relays, checked fuses, tested voltages and all checks out good. I have a good question, the relay is for prime and then when the oil pressure sensor registers pressure for the PCM to keep the pump on (run mode) what relay? Or is it shared?

I have attempted a start at the end of (but during) the prime cycle and it sputters badly with backfire through both intake and exhaust (the joys of waste spark I guess). yes everyone, the spark cables are correctly hooked up

The pump is getting power.......if it is possible the pump can get partial voltage or low amps? Maybe a damn squirrel chewed on my fuel pump power lines and it's connected by a thread.

Honestly though, the pump sounded louder then I remember and now it is quieter again. Realizing that, I am pretty confident the pump took a dump on me while sitting above the fuel level for 8 months.

Do I know you Larry?



Does anyone know off hand the volume of fuel I should get during the 2 sec prime cycle? While I'm draining the tank that may indicate what I already suspect.

[Joseph Upson]

My Walbro pump apparently has a check valve as the electric fuel pressure gauge always reads ~50 psi continuously with the engine off after the pump primes and before start up.

Your relay is fine, the pump wouldn't prime if it was bad and you'd end up with long cranking times to start via the oil pressure switch which is backup to the relay.

There was a discussion about knock off Walbro pumps from China like so many turbos only these were actually being passed off as genuine Walbro pumps. I'm not sure but I believe they had plastic impellers instead of metal like the Walbro which makes it so noisy.

Sometimes I do hear some kind of phizzing noise when the pump is primed for the first time of the day as if there was a leak in the flex hose but the pressure always reads about the same.

I've only known low fuel levels to damage pumps as a result of fuel starvation in cornering. One thing for sure is my suspicion it was not an OE pump proved correct as OE parts tend to endure unusual circumstances such as this.

[pocket-rocket]

I have a good question, the relay is for prime and then when the oil pressure sensor registers pressure for the PCM to keep the pump on (run mode) what relay? Or is it shared?

The OPSU switch and fuel pump relay from the PCM are wired in parallel. This way if for some odd reason the output on the PCM or the relay itself fails, the OPSU continues to send current to the fuel pump so you can make it home.

One misconception people have is that once the engine is running the OPSU switch feeds the fuel pump to keep the engine running. I've run 60v6s without the OPSU in place because I needed to run a pressure gauge on a vehicle that had a dummy light and the vehicle ran just fine after the initial prime on the fuel pump. The OPSU either wasn't on the car at all, or I plugged it in for some reason, but left it hang (which would still register 0 pressure to it anyways). Once the PCM registers RPM and that the engine is running, it turns the fuel pump back on by way of the fuel pump relay.

[trotterlg]

Guess you could measure the prime pressure, but if it tries to run on prime then it sounds like it is getting some fuel, so I would either direct wire the pump or measure the pressure you are getting on prime. Seems like an easy test to avoid pulling the pump. Larry

[Schmieder]

I don't have a pressure gauge handy atm, but i can tell for sure there is not enough pressure. I tapped the Schrader Valve many time in the past to check for pressure hours later and immediately after prime. There is just not enough pressure and what little pressure there is drops off to zero in seconds. As it 'wants' to run immediately after prime but refuses any combustion after sitting a few seconds after prime.

I know it is a ghetto way to diagnose fuel pressure, I should get a gauge. But it is too obvious. Oh wait a minute, I have an electric pressure reader with a schrader valve adapter It is a dash gauge from Glowshift but it should work just fine.

I'm going to hook that up so I can get some real numbers. Just for curiosity to see if I even come close to 44psi before it drops off like a rock.

When I push the schrader valve, I get a weak spit of fuel and a trickle. But I get good flow from the fuel lines.....


Thanks for the help guys, at this point I really think the pump is dying/dead. But I will try the wiring fuel pump to batt idea, after I digest the pinout.

[Schmieder]

update, I got a wiring diagram. After digesting it I found several ways to test the pump.

One, I'm going to 'jump' the relay terminals. ORG to GRY, This will be conclusive regarding the relay.

During that jump I can insert a pin into the pump wires in the trunk to verify the voltage is good.

Then test the ground.

Should all that be ok, then it really is the pump. I have already ruled out the filter, FPR, leaky injectors, leaking lines, etc.

[pocket-rocket]

When I push the schrader valve, I get a weak spit of fuel and a trickle. But I get good flow from the fuel lines.....

This concerns me.

[Schmieder]

This concerns me.

I hot wired the fuel pump relay terminals 3 & 5 and also measured 12v.

Well, not the best flow but it is apparent it has a push behind it. Though, from the fuel filter quick disconnect, pumping fuel at a very slow rate. Roughly 5 minutes plus just to get 3/4 a gallon. It is getting worse though, the flow was greater during the fuel rail test yesterday. It is a trickle flow now and I still have 1/4 tank.

The Fuel Rail is clean and obstruction free, that I remember checking while swapping injectors. I'm going to blow out the fuel lines when the tank is removed with mild air pressure.

It very well could be bad wiring issue but I strongly feel the pump is dead/dying. And at this point I should just get the pump swap over with before I continue onward. It would make it easier to start diagnosing an electrical issue ruling that out. I may even route my own (heavier gauge) wiring replacing the original wires to the fuel pump. As for the pumps ground wire, can I ground it to the frame using far less wire or is the ground routed to the PCM as a switch. I heard they are ground controlled.

I come to realize how simple the circuit is for the fuel pump and checked all angles. I pierced the GRY wire in the trunk leading to the pump and the voltage was good there too, 12v. The grounds, both, were strong. One was for the fuel level sender so I tested both to be sure I got the right one.

I have a good question for you guys. This is a techy thing I want to try if it is okay...........I want to place the fuel pump relay in the trunk and wire the fuel pump w/ heavier gauge and MUCH shorter use of wire. The battery is in the trunk as well so the circuit to the fuel pump would be roughly 2-3 feet versus 9+ feet. I would get a spare fuse box and rig it up like a factory would and bolt it down somewhere safe and out of the way.

What do you guys think? If I had an electrical supply issue, that could solve it.

I will update the thread after I swap the pump.