1991_305RS

The fuel pump in my car continues to make the priming noise after the car has been shutoff. It does this for about 5 seconds then turns off. It's kinda got me worried because it never used to do this and also I am about to go in a 1400km road trip with the car. Anybody have any idea what this means?

camaronewbie

Sounds like the Oil Pressure Sending Unit is stillsensing oil pressure after the car is shut off. The OPSU will run the fuel pump, even when the key is off - it has a direct connection to the battery.

If you are sure it's the fuel pump, and not the electric fans still running (they will run after key off), then try replacing the OPSU - it's about $30 and it's directly above the oil filter - has a 3 wire connector on it.

It can go bad in such a way that it'll make the fuel pump run 24/7 until the battery dies.

1991_305RS

I just replaced the OPSU a coupe months ago because the guage was pegged out, now it seems to read correctly, so im not sure thats the problem. I am also sure that it is the fuel pump making the noise. Any other ideas?

I also put a new ac delco lock cylinder in recently, just incase somebody thinks that the switch is stuck on run or something

1991 Camaro RS 305TBI T5

camaronewbie

There are only 2 sources of power to the fuel pump, the fuel pump relay and the OPSU. The fuel pump relay is activated by the ECM, so it's not getting any power with the key off, that only leaves the OPSU. Just because it's new and is making the guage work, doesn't mean it's working properly.

Try disconnecting the connector to the OPSU, then take a short spin around the block, and shut it off and see if the problem stops. Unplugging the OPSU won't cause any other problems (unless the fuel pump relay circuit is bad, then you're car will take a few extra seconds to start).

OHHH - BETTER YET - EASIER - behind the battery, tucked in the fenderwell, there is a weatherpack with a fuse in it - that's the fuse for the OPSU fuel pump circuit - take that fuse out, and then drive and see.

1991_305RS

Lol that would be awesome if i could just hop in the car and take it for a drive right now! But i will start the engine and let it idle and see.

1991_305RS

Ok, I unhooked the OPSU, started it up, shut it off, no noise. Hooked the OPSU back up started it up, shut it off, fuel pump noise.

So i guess the new OPSU I got is faulty?

camaronewbie

Sounds like it's 'sensing' oil pressure after it shouldn't. As long as the pump is not running continuously 24/7, I wouldn't lose any sleep about it - just make sure it does cut off BEFORE you leave the car for the night. And if it doesn't, then you know why, and can take that connector off, or pull that fuse out to save your battery until you get back and get time to replace.

But, if it's not been that long since you bought it, and you still have the receipt, might want to talk to the store you bought it from. Sometimes these parts aren't returnable, but I'd make a case for a return and try. It will be aggravating wondering all the time if it's gonna stop. It takes the fuel pump about 2-3 days of 24/7 running to completely drain the battery, so even if it did run overnight, you'd still have enough battery juice to crank it the next day.

camaronewbie

Guess how I know all this

1991_305RS

Ha yeah it sounds like youve been around the block with this problem. The pump actually only runs for about 5 sec. then a click noise (relay?) and its off, ALWAYS. What a load of crap, I remember buying that thing, $42!! For a piece of poo. I definatly have the receipt but not the little box or anything. Ill see what they say.

91350rs

iTrader: (2)

I've had the same problem for the past year now except mine isn't consist and only does it about half the time

1991_305RS

Yeah it gets annoying, anyway thanks for the help camaronewbie, now i know what I have to do to fix this.

iban

(so much for Delco parts) I got stuck had the fuel pump go. was towed the last owner told me a line of crap and said it was a high flow installed. I had the shop it was towed do repair to it ouch and the put in a deco replacement. I told the shop owner it very loud I don't believe that any one would have put up with that in a new car and had changed the switch after with the tow it was over 500$ I read somewhere that Delco new about some problems and never did anything was thinking fuel pressure reg other that that the car runs great

86LG4Bird

iTrader: (1)

As camaronewbie said, I wouldn't worry too much at this point. That new OPSU probably just has a lower pressure threshold where it cuts the power to the circuit, eg. the oil pressure may need to decay to 2 psi rather than 5 psi after shutdown.
Also, since it's winter, cold temp will exacerbate this behavior. Do you notice the issue is worse after just a start-up and shutdown rather than after a full warm up? Recent oil change to a different type of oil?
Bottom line: don't lose sleep over it.

iban

I have the car up for the winter I have 1991 with 130k that got it with 116k and had problems right from the start I drove the car and it seemed ok he told me it needed a tune-up I and told me that he had rebuild the tpi intake
well I got half way home and I hear raw fuel back firing in the exhaust and I said to my self o uck what have I done. well I was able to unscrew a couple of plugs by hand and I couldn't understand why the car look like it had been care for. that took care of that cap wires oil still getting smoke on start up but not all the time. over the next 3000k I watched the oil level and could not understand the smoke will after reading a lot and talking to other owners I got mixed answers had gone over every sensor on the car and was on second oil change consumption was low and I had suspected the smog egr system from the start would like to get rid of the smog pump after I have the compression test done.I don't no what the true mileage is the speedo was from a 89 when I had that out. nobody wants the car and I have put 1000 into it have two bad shoulders witch make everything harder to do. iban I no this was a different subject but if you have seen threads related to my story just send me a email thanks