Power Drain Problem, Need Help Finding Switch

[Twizted_3KGT]

Hey all, i've got a '88 Formula 350 with a power drain...and I think the power drain is coming from the fuel pump, because it's running ALL THE TIME, even with the key off!!! It killed my last fuel pump and battery, so I replaced those (along with most of the 18 year old rear end). I've been unhooking the battery everytime I shut it off, but im going to sell it soon and would like to get it fixed if it's nothing big. Now I searched another forum and found someone said if the fuel pump/oil pressure switch sender is stuck closed the pump can run with the key off. I need to find the switch and my Haynes manual isn't helping. Anyone know where it is??? Thanks!

[83T/A98Blazer]

The oil pressure switch/sender is behind the intake manifold on top of the block, that's where mine is anyway and it's a 350. Does it have an oil pressure gauge? What is that reading? If it is reading normal the problem may be the fuel pump relay.You should check the relay itself and see if that is the problem also. If it has A/C you can switch the fuel pump and A/C relay, they are the same. Instead of unhooking the battery, there should be a fuse for the fuel pump, pull that instead.

[ponchonutty]

yeah, i'd be thinking the fuel pump relay too.

[Twizted_3KGT]

Yea I tried pulling the fuse, didn't shut it off. I'll try switching out the relay, but from looking at the wiring diagram the pump shouldn't be on even with the relay closed because the PCM still has to switch that oil pressure switch closed before any power goes to the pump.

The oil pressure gauge reads normally, but I don't think that has anything to do with the switch...I would think the switch is just a safety device to kill the fuel pump if the pressure goes too low because it's PCM controlled...I'm just making a guess though.

I'll check where you said, just wish it was in the freakin manual somewhere lol. hmm now that I think about it, thats gonna be a bitch to get to isn't it?

[83T/A98Blazer]

The oil pressure switch is definitely in hiding back there. I would check the relay first. The oil pressure switch does not send power directly to the pump, it should turn on the relay to send power to the pump.

[Twizted_3KGT]

I haven't gotten a minute to check anything yet, but I was driving last night and the oil pressure gauge kept dropping to 0 and then bouncing back up to 30, then back to 0 for a while and so on. It's a scary thing to see your oil pressure at 0, but I assumed it was just that switch, I hope??

[Twizted_3KGT]

Ok, turns out I have a massive oil leak and my pressure gauge was at 0 because well, there was no oil in the engine (maybe 1 quart was in there). The leak is coming from the rear lower intake manifold gasket, I changed it out about 2 years ago, but that rear never sealed correctly, it was leaking just a little, but now the leak is huge!! I'm adding a quart every 20 miles!! The entire underbody is coated with oil back to the muffler lol.

Anyways, if that switch is where you said it was on the back of the block, then all that oil is leaking right onto it...so I was thinking that is probably shorting it closed, and the reason for the fuel pump constantly being energized. Now I saw a plug and a sensor/switch looking thing right above the oil filter, is that the oil pressure switch by any chance?

Needless to say i'm going to have to replace that gasket tomarrow, I just don't know what I can do to make that rear seal. In the Haynes manual it says to use RTV to seal the front and rear...if I remember right I think I used the gasket that came in the kit...either that or I must not have used enough RTV...i don't remember what I did lol. Any suggestions on sealing that up?

[83T/A98Blazer]

On my 83, with a crate 350, the oil pressure switch is just on the driver's side of the distributor on top of the back of the motor. It is kind of large with a 3-wire plug. It is right above where the oil filter is on the bottom of the motor. If you have a switch right by the filter that may be the switch. I have one on that side of the motor in the middle, but I think that's a knock sensor. I usually use the rubber sides that come with the intake gasket and use a little rtv to seal the corners. Don't overtighten the bolts and tighten them in the right order, usually from the middle ones going outward in a circle pattern.

[Twizted_3KGT]

Hmm, I just took off my intake manifold tonight, and a couple of the manifold bolts were basically finger tight...now I don't remember what the torque was on those bolts, but that can't be right...and I clearly remember that I tightened them to the correct torque...i don't know if it was the proper order though. I'm gonna clean it all up in the morning and try to locate that switch, cuz I didn't see anything from the top of the engine.