artracer.com

What are the symptoms of a clogged fuel filter? Besides no start.

NJRoadFan

It depends on the pump though, some are louder then others.

Katman

Clogged Filter can allow car to start, but run like crap once any power is required, as miture goes *way* lean as no fuel can flow.

If you do a 'flow test' (Disconnect return fuel line, and run pump for "x" seconds, and see how much fuel comes out), you should get a good idea if pump/filters are OK or not.

Bently has the important details, like how much fuel in how much time.

artracer.com

So could a partly clogged fuel filter be causing my lean condition?

Katman

If the filters were clogged enough to make problems at idle (as idle uses almost no fuel compared to driving around), then you would have *real* problems driving the car at all, and a good chance that teh fuel pump wold also be complaining. FLow test will tell you if they are a problem.

It can't hurt to have fresh filters, (and couid be a problem) but don't count on it.

ECU and O2 sensor have to be working right too. (And if the ARE working, they will correct any slight changes to the mixture that you try to do. THat's what the o2 sensor & ECU are supposed to do..!)

artracer.com

So maybe it's getting enough fuel for idle but not at those speeds. The brand new fuel pump just started whining and the car stalls right after start up now, then it starts back up fine. The car seems to drive fine, but I haven't driven it at highway speeds yet.

NJRoadFan

My car seems to cough and almost stall out on cold starts. I solved most of it by fixing vacuum leaks and cleaning the ISV.

Emissions wise the car barely passed (quattro got a 2500RPM idle text, no AWD dynos here) with very high HC (the car basically sat for 9 months prior and I didn't change the oil), but the NOx was no where near the limit. This was before I fixed the vacuum leaks.

If you haven't done it already, replace all the cloth vacuum lines you can find, and clean out all the rubber breather hoses with throttle body cleaner (not carb cleaner!), cleaning the throttle body helps too, but is annoying to remove. With the motor running, spray the TB cleaner at each of the fuel injectors to find leaking injector seals. After everything is back together, check and adjust idle and static mixture (this one is likely fine if never messed with).