New issue, well kinda...
 

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/voltage/fuel gauge, and everything are reading normally 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 around 1000rpm or less and then she'll die out completely and all the lights on the dash will come on as if you just turned the key on. 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 or more, 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 than that. 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 someething 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 if it needs to be cleaned or something with the tps that 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 because it's my daily driver.

I'd say pump but you shouldn't hear the stock pump unless your on top of it they are usually quiet so probably time for a new one either way

All you need is someone like myself to scan the car. Pretty sure I've said this before.

Thought that myself too, but wasn't sure if there was a thermal cutout in the pump.

Don, would love to bring the car to you, but unfortunately its my only car right now as my girl needs the other car to get our daughter back and forth from school. Unless you had an opening sometime soon to do it, or I am going to have to start tossing some coin at it piece by piece.

Thinking of going with a racetronix unit, any suggestions? Don't need the top of the line since the vehicle only has light bolt on mods right now. Was also thinking of going with the Hotwire kit as well.

Just put a fp gauge on it see what it is doing. Probably overworked the pump with the dry kit

ive hardly seen a fuel pump be intermittent. they either work or they don't. so do what john sed FIRST before just throwing parts at it. Then check the wiring to verify you have 12 volts for 2 seconds(fuel pump prime) when you turn the key to ON not start. there is a connector above the rear end in the floor of the car. if you have 4 channel then you should have 2 connectors. the one with the orange connector lock should be the one.

I agree with Don and pizza on this. Scanning it would be the best thing to do. But like pizza said the pump usually just dies. One of the main reasons I put a fuel pressure gauge in my car with nitrous.

Well, you can keep throwing things at it till you get the right part/fix. Fuel pumps just don't randomly drop pressure under normal driving.


This could easilly be avoided with coming here and having me scan it for 10 minutes and tell you exactly where to look.

You really should just do that, don't you work in his area anyways or down 495 near 24?

At least put a fuel pressure gauge on it and drive it while monitoring the gauge. If it starts acting up look and see what's going on with the gauge. Easy and free.

Calling you in the morning to set something up, Don. Will be working all week and best day looks like some time this weekend. Will talk more tomorrow morning.

My scan tool unfortunately isn't anything more than a scanner. And the fp gauge I wanted isn't in stock anymore, so gotta find another one and get it tee'd into the nos cutoff switch.

For fuel pressure you just take off the nitrous and hook up the gauge/line for testing.

hes got a dry kit so no line?

Correct gotta pull the shrader valve and put line at end of fuel rail and since your bigmac put some special sauce on it!

Lol, yeah dry kit and schrader valve was removed to put the nos cutoff switch on it already. Car was fine in colder weather, but now it warmed up a bit its acting up. Gonna call don when I get a chance. It's been a madhouse here at work and dealing with a buyout of my company.

It has a safety pressure switch as he said. Part of the dry kit.

Ok, so anybody know where/what the prime relay for the fuel pump is located on these sleds? Only one I could find was on the drivers side behind the kick panel, but I pulled that relay and turned on the ignition and didn't hear anything. Car started normally, so obviously that wasn't it. Pulled the underhood relay and the car died out. Turned the key off and replaced the underhood relay. Left the relay from the kick panel unplugged and turned on the key, and the pump primed. So that definitely wasn't the one. Anybody know what it looks like and the actual location of it?

This pic is from the drivers side kick panel. See the green wire? Follow that up and you will see the connector block. The second is the relay, the wiring is wrapped as the original wiring harness is in the car.

Relay

pretty sure thats just the vats cut off relay. fuel pump is fired from a seperate relay. that one just cuts if activated. i believe the fuel pump relay is on the pass side kinda near the center console. under that big stupid black plastic cover with foam on it! gunna say though 90% of the time it aint it. but if you want it just to check for voltage?

Fuel pump relays usually just die and stop working. More than likely you have a lazy sensor somewhere. Makes the car run shitty but not bad enough to set a code. If fuel pressure was bad the car would throw lean codes.

It's not throwing any codes other than the p0161 (post cat o2 sensor heater pass side). Only seems to do it when it gets warmer out, leading me to believe its a thermal breakdown some sort. That's what has been leading me to believe that it's either a relay, the fuel pump, or a sensor. When the temps were below 40 Fahrenheit it wouldn't really act up at all. Thursday last week it cut out on me 4 times within 3 miles, let the car sit about 3 hours before going home and almost made it without any issues. died out on me about 2 miles from home. had to let it sit for like 2-3 mins before it would restart, and made it the rest of the way home fine. Then the next day, Friday, it died out on me at least 4 times within a 15 min period. Had to limp it back home using a series of different things. I would pull the fuel pump relay, cut the key to the off position and let it sit for anywhere between 10-45 seconds, sometimes upwards of 2 mins before it would restart again.

Since it is so intermittent, it would lead me to believe that it could very well be a relay that has been triggering for the last 13+ years to beginning to fail. Any contact after that long will begin to show signs of fatigue. This is why I am tracking down the fuel pump relays and the relay that triggers the pump prime. No codes have shown up aside from the one mentioned above. I have the sensor just been lacking the time to put it in the car. If it was a MAF sensor, I would think it would throw a code, unless its not a complete failure?

Don, what are the shop hours? This way I know how early/late it would be acceptable to contact you.

Thanks for all the input guys.

Never seen a fuel pump relay cut out while driving. Have seen them stick and not let the cars start.

Replace the ignition and fuel pump relay under the hood.

Right now we are just pissing in the wind.

hours 9-5 M-F

I've had the ignition relay stick before and like Don said it wouldn't start.

I'll bet it's the wiring to the fuel pump relay. LOL

Nah, couldn't be that simple...

Lol, thanks Don!