874kkid

hi i have a 87 4000cs and lately i have been having a problem with it intermittently dumping fuel into the motor and bogging it down. i have no idea what is wrong. anyone have any ideas. thanks

audi-driver1126

im no proffesional, nor have i ever heard of that but heres somthing to try

while the car is running disconnect the temp sensor located under the radiator hose going to the engine. it sends signals to the ECU to give more fuel when the engine is cold meaning the sensor could be telling the computer that the engine is cold. without it it may run better.

if that doesnt fix anything then try disconnecting the idle stabilizer valve.

and if that doesnt do it either then try the distributor pressure regulator, located right on the fuel distributor itself. its a little grey bit with a plug going to it, unplug it while the car is idling

if none of that works ask rogviller he seems to know alot about these machines

cheers and good luck - Aidan

Rogviler

Does it send extra fuel to all cylinders or just one or a few?

I'm trying to come up with a way that this could happen...

If we had electronic fuel injection it would be easy, because each injector would be electronically controlled and I would say they're just getting a bad signal once in awhile.

But we have CIS (continuous injection system), which is controlled mechanically by the large air vane just above the air filter. So theoretically fuel shouldn't be going into the engine unless enough air is also going in to activate the injectors. That's why CIS is so great in my opinion, it's pretty robust.

I guess the other question is are you sure that's what's happening? Alternatively, something could be wrong with the spark supply, which would cause the car to bog down because there's nothing to light the fuel...

The other thing that comes to mind is a vacuum leak. This is super common, especially in the intake boot, which tends to crack.

Maybe one of those will get you on the right track, but certainly more info would help narrow it down.

-Rog

Rogviler

Here's a good diagram of the CIS system so it makes more sense:



-Rog

874kkid

there are a few hints to the excess fuel. when it starts to bog down there is a large amount of black smoke out of the tail pipe and i can see the gas gage dropping way more than it usually does. thanks fo the tips i am going to tey a few things and rply with my results.

Rogviler

Do you mean that figuratively, as in your gas mileage isn't very good or the gauge literally moves while it's doing it?

If the latter, then there is seriously something messed up. There are 18 gallons represented by a two-inch gauge, so it would take a lot to be able to see it.

To me the smoke and bogging down would say it's not burning all the fuel that's there. It could be a richness issue, but that doesn't usually cause it to bog down and it's weird that it's intermittent.

What about how often it does it? And the circumstances (hot start, cold start, et cetera)?

I would probably look more on the electrical side, such as making sure all the plugs are getting a good spark, making sure the cap and rotor and all the plug wires are good, stuff like that. A dead cylinder once in awhile or bad spark would certainly affect your gas mileage.

It's also still possible for there to be a vacuum leak causing it, though again it would have to be a strange one to be intermittent.

And as said above, there could be a bad switch or a bad cold-start injector. If you look on the drawing and follow the thermo-time switch to the injector you can see how that could cause it to go rich once in awhile.

-Rog

audi4000quattro

I too have a 1987 4K with the same issue. I was getting no fuel to the injectors and it seemed to be the control pressure regulator (gray bosch plastic piece with 2 wires). I placed a used regulator on the car and now the car starts but blows black smoke that smells of half burnt fuel. When I disconnect the regulator the car still runs but also still blows black smoke and runs rough. What steps can I go through to check to see if it is a vacum leak. Prior to this happening the car was running great. I stopped to fill with gas and the car never ran again until I brought it to a shop and they put the used regulator on. I am also told they adjusted the sensor plate, could that be an issue?