Hey guys,

Ok here's the deal. I've got a 96 Z28 M6. Had it for over a year and a half now. Pretty soon after I got it, it started having trouble starting. It cranks and cranks for a while before it will finally start up. Sometimes it takes a lot longer than other times.

It does start up every time however. Sometimes when it starts up the idle is real choppy and it takes a few seconds or up to a minute for it to idle normal.
There have even been a few times when it runs choppy too. For example when I'm accelerating it will rev up to like 3K and then bog out for a second like 4k bog out for a second and so on.

It has no catalytic converter, Hypertech power re-programmer, MSD Ignition Coil, MSD Wires, Cold Air Intake, Custom Intake Plenum, 3.73 Positrack, K&N filter.

Any input or ideas would be much appreciated.
Thanks for the help! It's much needed.

 

Any ideas?

 

I'm thinking possibly a weak fuel pump. It may test fine with a pressure gauge, but if it's not pushing enough volume, you can easily get those symptoms.

At cold start after the car has sat overnight, there's a check valve that's part of the fuel pump. It's not supposed to hold fuel pressure overnight, rather it's supposed to hold the fuel in the lines going up to the fuel rail. If the valve leaks, the fuel will drain back to the tank. On cold start, the fuel has to fill the lines and the fuel rail, purging the air.

In some cases the engine will start before all the air is purged and that can make it stumble because the injectors are not spraying 100% fuel. If it clears up after a reasonably short time, that's probably what's happening.

Also, if the pump has low volume, it won't be able to purge that lines and rail when it primes(runs the fuel pump first key on). The bogging could easily be related as well.

Try cycling your key to run, but not start first thing on a cold start. That should run the fuel pump. Leave the key on for 3 or 4 sec. Then turn off for 5 sec. repeat three more times. This should run the fuel pump and get all the air out of the lines prior to cranking the engine. If it starts right up and runs smooth, you have to go get yourself a fuel pump.

 

Alright i'll try and do that.
Thanks for the help!

 

No problem, just let us know what happens.

 

So...I've tried the cycling of the key twice now, and the car has started right up and ran perfectly each time! Guess that I need a new fuel pump, is there a particular brand or size that I should get? And is the the fuel pump right there basically under the driver's seat? Sorry for sounding so ignorant.
Also thanks on the great advice Granite!

 

Yep, sounds like you need a fuel pump. They are located inside the tank. You have to drop the tank and it is a little project. Search the board for how to's on replacing fuel pumps. I'm sure you'll find the instructions.