87ROCZ

iTrader: (3)

Hey,

I have a question that I am hoping someone can answer for me...

I am at the latter stages of doing my Vortec head swap on my car and last night I tried to start the engine. I turned the key ahead (no crank) and the fuel pump fired up, fuel pressure came up and held about 42 psi, everything else checked out fine.

I crank the engine and it she doesn't start. Just got a few backfires but I figured it out that I had the timing on the distributor 180 off (basically firing on the exhaust stroke and not the intake). Been there before when I tore this engine down 5 years ago on a rebuild (guess I have a short memory, haha!). I never had time to fix my mistake so I figured I would go at it later.

This is when I heard something a bit weird. When I turned the key off I could hear the fuel pump still running, I could also hear sort of a "gurgling/hissing" sound from the fuel rail, then after a few seconds you can hear the fuel pump relay click and everything goes quiet.

I know this is not "normal" behviour, at least not for my car. I can't recall this beahviour happening so this is leading me to believe that I got something done wrong somewhere!

I did the searches but I am coming up blank... can anyone help me out here?

Thanks!

vetteoz

iTrader: (13)

If you have the stock oil pressure switch wired up ( correctly ) then fuel pump will run after the Ign is turned off
until the oil pressure in engine bleeds down to 4psi

How have you wired the pump and OP switch?
Maybe you have the OP switch operating the relay ( wrong ) which would give the delayed relay cutoff you mention?
The relay and OP switch are independently wired to the pump so if the relay goes out the pump will still run
once you have OP up during cranking and the OP switch closes

87ROCZ

iTrader: (3)

Hey thanks for the reply.... I have the stock op switch and all stock harness wiring. I see what you are saying about the oil pressure bleeding off and thus keeping the Fuel pump going until it goes to 4 psi... but this goes on for I would say maybe 5 or 6 seconds and I wouldn't have thought that the oil pressure would have gotten very high just by cranking the engine???

vetteoz

iTrader: (13)

Only has to get 4psi to operate the switch , can much higher pressure than that cranking ( depending how good your engine is )
Easy check ,
pull the plug off the OP switch and see if you still get the same result.

87ROCZ

iTrader: (3)

Yeah my engine was completely rebuilt, all new mains and rod bearings, all new everything so I would imagine that the oil pressure is pretty good. A few years ago I had my engine rebuilt and it had really good OP (In case people are wondering, I rebuilt it this time due to a failure of the oil pump which sent shrapnel all through the bottom end scoring my journals and that nice stuff, all stemmed from a failed lifter cup clip which jammed the pump, talk about shitty luck).

Is the OP switch the one that screws into the top of the block at the back end of the lifter valley, or is it down by the oil filter? I thought that maybe there was two?

Apeiron

If you've got 2 in their original locations, then the one up top is the sending unit for the gauge and the one below is the fuel pump switch.

87ROCZ

iTrader: (3)

Cool, thanks guys for the feedback, really appreciated! Next time I go at the car I will unplug the bottom one and see if the fuel pump stops cycling when the key is turned off.

Final question... if it is the fact that the fuel pump switch is staying engaged until the oil pressure drops, would that explain the fuel pump relay being energized as well? Reason I say this is because I can hear it 'click" off once everything finally shuts down.

vetteoz

iTrader: (13)

No
Refer to the pump diagram I posted above, they are two separate systems in parallel to each other
OP switch does not operate the pump relay ( unless your wiring is wrong )

87ROCZ

iTrader: (3)

Well I know that the wiring isn't wrong, it's stock wiring and it worked fine before. So what could be causing the fuel pump relay staying engaged?

TTOP350

iTrader: (8)

Either the relay or the oil psi switch can get stuck in the on postion due to faulty contacts from sitting or power surges from over/under voltage.
Its weird but it does happen.
Replace the relay or the oil psi switch, if it still does it replace the other.
I'd replace the oil psi switch anyway if it was on your old motor. It could have a little metal in it.

eseibel67

This one's pretty easy to test without crawling underneath. When the pump is running at an unexpeted time, unplug the relay and see if it stops. That should narrow it down pretty quick.

vetteoz

iTrader: (13)

Are you sure it is the pump relay and not the MAF burnoff relay?
Maybe two independent things happening at same time.
OPSU running the pump till pressure bleeds down and the burnoff ( which happens after Ign is killed )

87ROCZ

iTrader: (3)

It could be the MAF relay, I never thought about that... the two are located next to each other and the click I heard could have been the MAF relay.

I think I will try unplugging the Fuel pump relay and see if it continues, if it does then the only other thing that it could be is the OP Fuel pump switch, I will try unplugging that and see if it continues.

I guess if it is the oil pressure keeping the pump engaged this isn't a bad thing right? Just accept that this is the way my car will be going forward?

vetteoz

iTrader: (13)

I would consider it perfectly normal , there is nothing you can do to prevent it and it is not causing a problem.
It is not as if your pump is continuing to run indefinitely when you kill the engine

87ROCZ

iTrader: (3)

Well...I went back at the car tonight...needed to straighten out the timing but after that was done she fired up. I decided not to bother messing around with the fuel pump run on considering it's a normal thing. So when I shut her down I noticed that this "odd to me" behavior wasn't doing it anymore, no more fuel pump running on after the key was turned off, no clicking relay, just shut down and quiet, just like it has always been since I have owned the car.....

Talk about weird or what!! I have had this car for a long time and it has taken a lot of my blood, sweat, and tears and I think it is either possessed or is turning into "Christine", lol....

Anyway, all normal again...