BigMac76

iTrader: (5)

Ok guys, been dealing with something here last few days that's really driving me crazy. I've got a 99 Z28 m6 and here recently the car has been doing something that's just weird so to say. It will act fine for a bit while driving and then all of a sudden it'll act like it's bogging down. The oil pressure, and everything are fine and the car will still be acting like it's running but there is no audible sounds from the fuel pump. I can downshift and it'll stay running until I get down to about 1000rpm or less and then she'll die out. Now while this is happening, if I press on the throttle, it does nothing at all. Sounds like it's sucking in air, but kind of hard to tell with the exhaust system on the car.
Now if I turn off the ignition key for a little bit, anywhere between 10-30 seconds, and turn the ignition key back on, you can hear the fuel pump kick on and it'll start. But sometimes it'll go back and do the whole thing all over again in less than 100 feet after, sometimes 5-10 mins or longer. It's not something that you can set your clock to, at times it's pretty random and intermittent.

So here's a few of my ideas as to what could be causing it:

1- Fuel pump: Maybe there is something going on with it that causes it to shutdown, almost like an overtemp/thermal cutout switch because of it running too hot?

2- Fuel pump relay(s): Maybe one of the fuel pump relays are going and causing it to cutout and act like this? Either one thats under the hood or possibly the one that's in the drivers side kick panel.

This is my first 4th gen so I'm not that experienced with these cars. I am more used to the old iron block 2nd gens than anything. Not sure if anything with the maf or tps could possibly be causing this issue?

Has anybody seen this before? Any help would be greatly appreciated because this is driving me crazy and making me want to dump the car and get something else.

97camaroguy

iTrader: (5)

Start by replacing all the relays and fuses associated with the fuel pump. If that doesn't work then replace your fuel filter. And obviously the last resort would be to change out the fuel pump altogether. If you don't want to drop the diff to do this you can always do the cutout mod seen here : https://ls1tech.com/forums/lt1-lt4-m...-mod-pics.html. The wires inside the tank and even the connector are known to melt which could have something to do with the problem. These are just helpful tips and I'm sure others will chime in soon enough! Good luck man

BigMac76

iTrader: (5)

Ok, so the underhood relay isn't the problem. Also decided to look for the relay inside of the kick panel. Only one I seen was an OMRON 4 pin relay tied in to the harness on the drivers side. Decided to try and start the car and it started without priming the pump, or so I thought. I left the relay disconnected and decided to pull the underhood relay to make the car run itself out of fuel. Turned off the key and replaced the relay. Turned the ignition key back on and the pump primed, wtf? Thought that was the relay that controlled the pump prime? Anybody else has a suggestion or location with images or description of the relay or location?

maxharvard

I've had this with bad gas, did you fill up recently at a shady place?

BigMac76

iTrader: (5)

94 octane @ Sunoco. Fuel pump cuts out, wondering if the ignition relay could possibly cause it.

Thanks for the input guys.

maxharvard

I'll just throw this out too since it's a similar idea.

Fuel pressure regulator?

BigMac76

iTrader: (5)

Just an update to help anybody else in a similar situation. Come to find out it was the wiring terminals to the fuel pump relay in the fuse panel under the hood. Had Slowhawk take a look at it since I was at a loss of what it could have been. He had it figured out and had a new relay wired into it and it has been working great! Thanks for all the suggestions guys, and thanks for the help Slowhawk!