Tim Polzin

1999 A6Q with a 2.8. Normally, the car will start in cool weather with a bit of a stumble. The catch comes when I start it and then turn it off before the engine is warm. The very next time starting, it will be very slow starting, sometimes one cylinder catching at a time.

I read of a problem with the coolant temperature sender, but from what I've seen, it also impacts the gauge and on my car, the gauge seems to read correctly.

Chasing a cold weather fuel leak, I replaced all of the injector o-rings and cleaned the injectors. On the bench, they seemed to function ok and did not weep.

Any ideas?

Thanks, Tim

turbine guy

Ignition in good shape? Pulled the plugs and had a look at them lately? I gap mine down a bit from Audi's recommendations,specifically for colder weather. Seems to help.

If your valve cover gaskets weep at all, the 2.8 will fill the plug pockets with oil, and deteriorate the plug wires. Have a look and see if the wires are in good shape. (If they are the 1999 vintage originals, chances are they need replaced.)

Otherwise, there may be a minor glitch in the VCM, sensing the -40 outside air temp, when the engine is slightly warmed up, causing an overly rich A/F ratio when cranking. The older Mazdas were famous for this.

turbine guy

Tim Polzin

Good suggestions. Pulled several plugs and they looked OK. Wires are original and looked somewhat shabby. Didn't see any oil in the plug pockets. Plugs looked wet when having the problem starting.

Just to be clear, the problem is not occuring only in the extreme cold, but anytime the car is started cold (that is, not run for a day), turned off before it warms up then try to start again a while later.

I VAG-Com'ed the coolant temp sensor and it seemed to read ok. No DTCs. I have not checked residual fuel pressure.

Other than that, the engine runs fine.

I'll look into replacing the plugs and wires. Any other ideas?

Tim

Snow Rocket

I have been chasing the same problem on my wife '99 2.8 for over a year... It has never "not started", but sometimes it needs to be cranked for 5-10 seconds. What is this 'VCM' turbine guy mentioned?

turbine guy

VCM "vehicle control module" or engine computer. Used to be engine control only, but now they control the drivetrain as well, thus VCM.
My daughter's '99 A4 with 2.8 is occasionally tough to start, and you have to crank it longer than I think you should. Residual fuel pressure, I thought might be it, but this is easily checked by just turning the key to the "run" position for a couple seconds before cranking. If the fuel pressure has bled off, the delay before crank, will allow time for the fuel pump to bring the rails back up to full pressure. however this doesn't seem to help in my daughter's cars case. I'm going back to basics, buy making sure the ignition is up to snuff, and then good injector cleaner. (I use a pure naptha/toluene mix as cleaner, not the junk you buy at the corner store.) if your plugs are at all wet, the injectors are not spraying an atomized mix into the intake. Perhaps this all comes down to injector spray pattern. Try some good injector cleaner that contains toluene or naptha, and see if it helps your car(s).

turbine guy.

oops, sorry Tim, I re-read your post, it seems you had your injectors tested. They did a flow pattern check too? At crank, the injectors' duty cycle are really low, and sometimes pattern checking doesn't show any problems at the low duty cycles, as most testers are with the injector wide open. (100% cycle.)

Tim Polzin

Turbine Guy, you gave me an idea. I was thinking that the problem was due to an overly rich mixture, but now I'm wondering if it is caused by too lean a mixture on start. Is it possible that the coolant sensor could be intermittant, making the engine think it is a warm start, not a cold start? Although I've had the odd stumble on cold start, the problem is most severe only when:

1) I start the car (to move it out of the garage for example)
2) Stop the engine when it has only run for 30 seconds or so
3) try to restart a short while later

What else could affect the mixture control on start under these circumstances?

Tim