The specifics: '88 A4, 136,000 miles.
Motor is stock.

I'm having an intermittent problem. The other evening, taking off from a standing start I hit the gas pedal a little hard and then it started sputtering and died. Immediately after that it would start and idle (roughly) but as soon as you try to give it some gas it would sputter and die. It acts like it's not getting any fuel. I let the car sit overnight. The next morning I was able to start it up and drive it with no sputtering or bucking. It had done this to me a couple times before about 1 month in between occurrences. So it's not an everyday thing. My first thought was a clogged fuel filter so I replaced that and it ran fine the few times I drove it until the other evening when it showed the same symptoms again.

Could the fuel pump be going out?

Another thought that occurred to me is:
I've got true dual exhaust on the car, but still have the original pre-cats on. At 136K miles could these be bad and giving me the problem? My theory is that they're working well enough to let the car run during normal driving, but when the motor is at temperature and I tromp on the gas, the back pressure from the old cats causes the problem. Then, when the car is allowed to sit and cool and let the back pressure bleed off, the car will run fine again.

Does this sound possible?
Any other ideas?

Thanks for the help.

Anything is possible skidmarks but guessing at a solution is never the right direction for diagnosis, no matter how good the person taking a swag.
Your best bet is to get a Factory Service Manual, check to see if you have any stored codes and correct any that are present. Even if there are no codes the manual has several sections devoted to symptoms such as you describe and suggestions for troubleshooting. Checking the fuel pressure at the rail when it occurs would be a good starting point, best of luck, let us know what you find.

I just picked up an FP gauge today, so that will be at the top of my list.

Check the filter sock in the tank on the pickup. Also have the ICM checked to make sure its not failing when it gets hot.

Use the fuel pressure gauge to see if the fuel pressure drops when you nail the gas pedel or if the pressure bleeds or quickly after the engine is shut off. Might be a good idea to test the fuel injectors hot and cold to see if the injector coils are in good shape.

OK. Over the weekend I used the paper clip routine and jumped the pins on the data port to pull any codes that might be stored. All it flashed was a "12" which I believe means that the system is working and there are no codes stored.

I hooked a FP gauge to the fuel rail. As soon as I hit the key and the pump cycled. The pressure was immediately about 41 lbs. I started the car and at an idle it kept about 36 lbs and goes back up to over 40 when I blip the throttle.

I let the car warm up and took at for a drive with the FP gauge still attached and taped to the windshield. I tried to recreate the conditions of when the car gave me trouble but of course she drove just find. Pressure was a steady 36 lbs and rose back up to over 40 when accelerating.

Any ideas?


I check on the other things.

The pressure goes down when at idle and part throttle driving cause the regulator is controlled by vacuum, the more vacuum in the manifold, the easier the fuel will flow from the fuel rail (cause the vacuum will help draw it from the injectors), hence requiring less pressure to do so.

Pressure is down maybe 1 or 2 PSI, but that shouldnt be any sort of an issue, sounds to me as though that is all working exactly as it should.

Keep doing what you have started. You are using the exact correct method of testing. Unfortunately, you will have to wait for the problem to reoccur to know if it is a fuel pressure problem or not. It could be the sock as Case suggested or possibly something floating around inside of the tank, intermittently getting sucked to the sock, blocking the fuel getting to the pump. Your symptoms don't sound like any fuel pump failures I have experienced. The pumps I have seen go, either slowly weaken, where their output and pressure gradually reduces, or they just flat die instantly with no prior warning. I have never known a fuel pump alternate between working just fine, start to run weakly and then recover. My experience is that once they start to go bad, they continue getting worse until they totally fail.

If it isn't fuel, again, I agree with Case on the ignition module. But as much trouble as you are having with the fuel pressure testing, the module will be worse.

I wouldn't jump around trying a bunch of different things. Be patient and keep to a diagnostic plan. If you are getting restless waiting for another incident in order to check the fuel pressure, you could pull the pump and check the sock, the tank for debris, loose wires or any other anomalies.

RACE ON!!!

I think my next move will be to pull the pump to check on the sock and look for debris in the tank.

That will eliminate another one of the possibilities.