Weird fuel pump operation

[sy#2921]

Truck has a walbro. Its running on completely stock wiring.
Went to start the truck last night, pump primed and the truck started. Turned the key off and took it out and the pump was still running. I hit the master cutoff switch and turned the truck back on about 20 sec later and the pump stayed off.
The truck will now do this every time. prime, start, shutoff and pump still runs. Now if i just turn the key on then back off after it primes it shut off like normal

Anyone have any idea? bad relay?

 

[SBNova]

Re: Weird fuel pump operation

The fuel pump relay could be sticking. Its one of the two right there by the brake booster. Try swapping it out with the IC pump relay and see if that fixes it.

 

[JSM]

Re: Weird fuel pump operation

My pump which is triggered by stock wiring, runs for a few seconds after i shut the truck off. How long have you given it to shutoff?

 

[sy#2921]

Re: Weird fuel pump operation

the longest I have given it was about 15-20 secs. I was kinda thinking the relay was sticking closed but figured someone on here has had this issue before

 

[sly dvl]

Re: Weird fuel pump operation

The oil pressure switch also powers the fuel pump in case of relay failure. If you start the truck and only run it for a few seconds the oil pressure will remain high, powering your fuel pump.
15-20 seconds seems like a long time. I'll bet if you time it it only runs on for no more the 8-10 seconds. Let it run and see what happens. If it is indeed running for 30 + seconds then you might have a relay issue, as mentioned earlier.
Just tap the relay and see if the pump stops, but let it run for a while to be sure it's not the oil pressure switch powering it.

 

[JSM]

Re: Weird fuel pump operation

20 seconds is a bit long. Has anybody messed with the fuel pump wiring?

Try different relay, 1 min or less to change.

 

[sy#2921]

Re: Weird fuel pump operation

The fuel pump wiring is stock right now and worked fine last fall. I didn't change anything in the fuel system besides the filter. The oil pressure sensor is new

I was thinking the relay but figured I would ask first to see if it might be something else

 

[sy#2921]

Re: Weird fuel pump operation

Last night I swapped relays then fired the truck up. Once I shut it off the pump ran for about 15-20 but did actually shut off on its own. If I were to just crank the truck but not let it start the pump shuts off right away.

 

[sly dvl]

Re: Weird fuel pump operation

If you really want to verify the reasoning behind this unplug your oil press. sw., then start the truck. I'll bet your pump won't run at all after shutdown.
I suspect the oil oil press. sw. you replaced is holding pressure after shutdown which is not a bi deal.
What grade oil do you run?

 

[sy#2921]

Re: Weird fuel pump operation

Well I can honestly say the oil has not really got up to a good temp yet. With it being 15-40 I think that might have something to do with it. Motor still has about 40-60psi of oil pressure when I shut it off.

I will try to get the motor and oil up to temp tonight or tomorrow and see if it changes.

 

[sly dvl]

Re: Weird fuel pump operation

15-40? That's pretty thick oil. No wonder the pressure stays up there.

 

[sy#2921]

Re: Weird fuel pump operation

Dave you are one smart person. I am currently running rotella t 15-40 diesel oil and will switch to the syn version after about 1k miles. I am doing it exactly for the reason you stated about the ZDDP content and other stuff it has that newer gas oils are missing. It was the oil I was told by the engine builder to use so I have to honor that if I want him to honor the work. I use to own an late model diesel jetta and had much fun with deciding the correct oil for it. Had better luck at the time with the rotella line over the delvac. Since learning of the fact it is a better oil since its an "older" formula I have switched everything I own over to diesel type oils both dino and syn versions.

 

[sy#2921]

Re: Weird fuel pump operation

I plan to stick to the diesel type oils just a synthetic version more for comfort and also familiarity with them. I can get rotella t syn for about 10cents more a quart than just the standard rotella t. When I had my diesels I tried both types and many brands of oil and sent a few samples out to blackstone for inspections even. Not that I trust them 100% but they always showed better results with synthetic being used even when I never told them what the oil was just the mileage.

Also, You can say its habit. I have always run up till about 2 years ago mobil1 syn in all the forced induction vehicles and castrol gtx in the regular DD's. Now I have since changed to diesel specs in everything but still synthetic in the FI trucks.

Right now the Sy is getting the rotella T 15-40 during break in. The procharged s10 has syn rotella T. The 97 sierra with a magnacharger gets syn rotella T. The other 3 daily drivers get rotella T. Seems complicated I guess switching back and forth but its easy knowing the toys get syn and the DD's get regular. I guess I just listen to the turbo manufactuer that wants synthetic run with their turbo and plan to run it .

I was explained that ZDDP isnt as important the newer roller motors as it was with the flat tappets but still its better than the crap they call car oil now. Even the DD's see just as much stress with the stop and go traffic and heavy idle times and temps than the toys will see at the track, might as well use a better oil to protect from excessive wear.

That would be great if you could find some of those articles. I am always down for a good read.