924Board.org

[Disco Stew]

My '81 924 seems to run quite rich and fouls the spark plugs every thousand miles or so. Am I right in thinking that the only adjustment you can make is to the idle speed? Is it possible to lean out the fuel mixture at all?

Any advice appreciated.

[augidog]

There is a way to lean out the mixture.
Your opening a big can of adjustments.
If its running well,
Check all the basics first.
Maybe go to a hotter plug.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

[Paul]

How's your gas mileage?

[dpw928]

There is an air/fuel adjustment on your 81 but it shouldn't be touched until all the other components of the CIS have been checked. If your car starts OK when both hot and cold, there probably isn't any injectors leaking, so a check of the electrical/running components will probably find the problem. I would start with the thermotime switch that controls power to the cold start valve. If it is bad(shorted) it could cause the cold start injector to spray full time while the engine is running. A properly working thermotime switch will cut the power to the cold start injector in 2 to 12 seconds depending on engine temp.

The next item I would check is the control pressure regulator/warm up regulator(WUR). Check the inlet connections to make sure there isn't a blockage. Further checking will require a CIS fuel pressure test set to measure control and system pressure reading.

Another possible culprit is the frequency valve if you car is equipped with an O2 sensor.

The tech section of this site contains a detailed explanation of the CIS system and should be read before attampting any adjustments.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[Smoothie]

Of course the previous owner/s didn't necessarily have access to all this good advise and may have had their hands all over the mixture setting. In addition to the plugs, you can check the exhaust for black smoke. When I first got my car it was way rich with black smoke exiting the tailpipe at idle.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[John Brown]

Set the mixture by ear just like any other car. No big deal. It's easy so I'd start there too.

The start up stuff only gets power, from circuit 50, when the ign sw is in 'start'. However, leaking cold start injectors can cause rich mixture.

The warmup regulator, aka fuel control pressure regulator, can cause either rich or lean. But the only way to know is with a pressure test guage.

CIS should be quite accurate. If the plugs are truly fouled from a rich mixture the changing to hotter plugs is not the answer.

Buy the Haynes manual.
_________________
John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

[Disco Stew]

Thanks for the advice. When I got the car, the cold start valve was disconnected so I suspect there might be a problem with this.