I have a 1990 80 quattro with the 2.3L motor that I'm having a little problem with. It wont start when it's warm.
When the engine is cold the cold start valve pops it off and it runs good. The car will run all day long. When I shut the car off and go to immediately restart, it just cranks and cranks without firing up. I wired a manual switch to the cold start valve. When it doesn't start, I just hit the cold start once to give it a shot of fuel. Then I crank and it fires right up and runs great again.
So I don't think the issue is spark or fuel pressure. I think it's a matter of fuel delivery.
I saw on another post mention that the RPM sensor but my tach jumps while cranking so from what I can tell the sensor is good.
My question is, what is telling the system to inject fuel while cranking?

 

There is a temp sensor on top of the housing of radiator hose connection on the head. This sensor tells the ECU how warm the coolant (and the head) is. If it cannot tell that it's warm, it may be dumping too much fuel (cold start mode). It's a $15 sensor and takes 2 minutes to swap out. Make sure the car is cold when you swap it out. You might lose a little coolant doing to the swap but be ready with the new sensor. But it won't gush out being near the top of the water level anyway.

HTH,
Dave
03 A8L
87 5000S Q
87 944 N/A
84 928S

 

I have already tried replacing that temperature sensor. No change. I just changed out the O2 sensor this past weekend. That wasn't it either.

 

The O2 sensor only helps the ECU regulate the fuel mix with the car after it's running. It still sounds like a temp sensor issue. Let me do some digging when I get home this evening.

 

When I installed the new temperature sender and it would run I started unhooking a few things.
When I unhook the temperature sender, it starts warm. When I also unhook the CSV, it will no longer start warm. From that I concluded that the temperature sensor was working. Unhooking it makes the ECU think the engine is cold and fires the CSV. So I was thinking that it's a matter of no fuel being injected while cranking warm. As to why this would happen, I have no clue.

 

Pull the connector off the temp sensor and check to see if you have voltage on both terminals. 4.5-5.5V with the key on. There are actually 2 sensors in the single unit. One side for the Fuel Delivery and the other for the Ignition System.

Have you pulled any codes from the ECU? If the 80 uses the same CIS system, you can get them using a fuse and reading the number of blinks of the check engine light.

 

I haven't attempted to pull any codes as of yet.....mainly out of laziness.
Are you saying that the 2-wire temp sensor should have voltage on both wires? Or are you referring to the four wire temp sensor on the lower part of the hose fitting flange?

 

Yep. The two wire sensor on top. The engine serves as the ground for the two circuits in the sensor. Voltage on both with the key on. The 4 wire sensor underneath is the instrument panel gauge sensor.

Pull those codes. They may reveal something that we're not looking at.

 

Both the wires have 5 volts.
I'll look at pulling codes and update. I'm sure there is already pretty good instructions on this site somewhere.

 

I'm sure there are posts already out there that cover this but I'm having some trouble finding them. Can someone point me to the directions that will tell me how to pull my codes?