CARSNPLANES

Can somebody tell me what the jobs are of these two components?; The fuel pump check valve and the fuel accumulator. I read the FP check valve retains the overnight pressure. If so what does the accumulator do? Sometimes I smell a faint fuel smell near the back of the car after shutdown but there is no leak anywhere underneath. ('87 5000CSTQ avant). This morning it took several attempts to finally catch. I could tell it was fuel related because each time I stopped cranking you can hear the pump just finishing it's cycle from the start and then stops. Every start attempt, the fuel pressure gives a little more fuel and starts filling the lines and fuel dizzy with proper pressure. The next attempt gets better, tries to catch until finally getting the proper amount and finally starts. Tnis doesn't happen all the time and in fact I hadn't used it for a couple of days last week and when I went to start it then, it fired right up. This is the car I'm about to trade for a BMW635csi. Is she mad at me or something?

boxerfan

The check valve keeps the pressure in the fuel lines. It should hold over night. The accumulator is a reservior that reduces pulsations from the pump allowing the pressure to maintain a more stabe value.

Here's what I'd try. Bridge the FP relay. When you are going to start your car turn to the 'ON' position and listen for the fuel pump. Allow it to run for a few seconds and then try starting. I just read up on the specs for the CIS dizzy and in doing so learned that system pressure should be optimum after running the pump for about 10 seconds. Give that a shot and see if it helps with starting.

As for the small of fuel... fuel line leak was my latest experience with that. I'd have a look at the accumulator since it sits under the rear of the car and is very exposed. You might find a weeping situation there.

CARSNPLANES

I thought about that and figured if there was a weeping situation, that that might be enough to lose my pressure. However you're saying that any fuel accumulator issues shouldn't cause me to LOSE my pressure overnight if that is the job of the checkvalve. I would love to make a "switch" from the FP bridge and mount it on the panel for times like this, but I know if everything works , one shouldn't need one. As mentioned, I'm swapping this car for a BMW and i hate to give this car up especially with a new problem that I'm having. If I were to keep her, this little problem wouldn't concern me too much but I don't like giving a car to someone with a problem that could get worse. T44 owners are a special breed and not everyone out there is as patient or knowledgable about the some of their problems and what to do about them. I have had two other Audis before this one, '84 5000s, '86 Coupe GT and this one for five years, and I'm still learning.

875kcstq

From the Bentley manual: "The accumulator halps maintain RESIDUAL pressure and damps the pressure pulsations from the pump" It has been my experience that if the accumulator (diaphragm) leaks, it will drip out through a designed orifice; the symptom is a very hard to start engine when HOT condition. Hope this helps.

Randolph

I smelled gas by the rear pass side of my car and then I started getting extended crank. By the time it started to crank longer I also noticed the same day a few drops of gas under the fuel accumulator. Long story short, my accumulator was so rusy that the gas was starting to leak through it causing a slight loss of Fuel pressure during startup. Once the car was running it was fine. Installed a new accumulator and all is well. HTH

Randolph
87 5KCSTQ
93 928GTS

CARSNPLANES

Come to think of it, when I park overnight engine lower than tank, I have no problem starting. With engine higher ,that's when it gets intermittent. related?

audiqv8

Check the cold start valve and also the MFTS (Multi function temperature switch). Since the car appears to have problems starting cold.

CARSNPLANES

The MFTS is only a couple of years old. I havn't checked the CSV at any time since I've had the car but judging by the way it has started ok, i can't see that as the culprit unless the signal to it is intermittent.

RussB

. . . to maintain residual pressure.

When you turn off the car, the fuel pump stops and the check valve closes. Then the accumulator provides residual fuel pressure.

The classic symptom of a failed accumulator in all CIS equipped cars is when the engine's thoroughly warmed up, you park the car, switch off the engine, spend 20 to 30 minutes in the supermarket, and when you return to the car the engine cranks forever before it starts. Nevertheless, the car starts fine when cold the following morning.