A4 Fuel System Problem

[engineer68]

Looking for some help diagnosing a fuel system problem. I have a 2001 Audi A4 Quattro 1.8T (AWM engine) and it does not start after sitting overnight.

When checking the fuel pressure coming out of the pump with just the ignition on and after the relay depowers, it was 20 psi. The pressure increased to 30 psi after removing and re-inserting the key and then placing the ignition switch to "On" for a 2nd time. Doing this again for the 3rd time increased the fuel pressure to 43 psi, a 4th time to 54 psi.

After the 4th time, I was able to get the car started but I could not accelerate the engine for the first couple of minutes without it sputtering and nearly shutting off. Pressurizing the system works consistently to get it started.

Once I am past this, the engine idles smoothly and is able to accelerate without any problems. Shutting off the car and restarting is not a problem within a few hours of shutting it off.

I did a pressure decay test and it took 55 minutes to drop down to 29 psi.

I have replaced the fuel relay, filter, and pressure regulator with no change. I also checked for spark during cranking and all four plugs spark.

I struggle to believe that the pump is the issue given how the car performs after I get it started and stabilized. I don't want to go through the trouble of replacing it unless it will definitely solve the problem.

Please help!!!!

[Golten951]

The fuel pump could be good, but the check valve is failing that is apart of the fuel pump system. I was having a similar issue in our B5 Passat. ended up changing the fuel pump. they are like $40 or so on Amazon. Have not has a issue with it since. over 22k miles on it.

[Dmitry at Pelican Parts]

Originally Posted by engineer68

Looking for some help diagnosing a fuel system problem. I have a 2001 Audi A4 Quattro 1.8T (AWM engine) and it does not start after sitting overnight.

When checking the fuel pressure coming out of the pump with just the ignition on and after the relay depowers, it was 20 psi. The pressure increased to 30 psi after removing and re-inserting the key and then placing the ignition switch to "On" for a 2nd time. Doing this again for the 3rd time increased the fuel pressure to 43 psi, a 4th time to 54 psi.

After the 4th time, I was able to get the car started but I could not accelerate the engine for the first couple of minutes without it sputtering and nearly shutting off. Pressurizing the system works consistently to get it started.

Once I am past this, the engine idles smoothly and is able to accelerate without any problems. Shutting off the car and restarting is not a problem within a few hours of shutting it off.

I did a pressure decay test and it took 55 minutes to drop down to 29 psi.

I have replaced the fuel relay, filter, and pressure regulator with no change. I also checked for spark during cranking and all four plugs spark.

I struggle to believe that the pump is the issue given how the car performs after I get it started and stabilized. I don't want to go through the trouble of replacing it unless it will definitely solve the problem.

Please help!!!!

Hello and welcome to the forum! Are you able to pull any codes? Is the CEL on?

Might be a good idea to see if anything comes up to help you carry down where the issue is coming from.

[engineer68]

That was the one thing I forgot to add in my original post. There are no stored codes and the CEL is not on even after repeated cranking attempts.

[engineer68]

Well, it turns out that I had a coolant sensor which had coolant in the contact pin area and was causing the problem. I replaced the sensor and the problem went away. I can't explain why the coolant sensor pays a role in the engine starting cycle but it does.

This is the coolant sensor at the rear of the engine, mounted on the coolant flange.

[Golten951]

That is interesting. but if that coolant sensor is reading the engine too hot like over 220degrees, it will cut fueling. the 944 coolant sensors do the same thing.