1999 Audi A4 Intermittent starting problem

1999 AUDI A4

120,000 MILES • 6 CYL • AWD • MANUAL

HSERREZE

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My car starts fine when it's cold. However, periodically (every couple of weeks) after I've driven anywhere from 2 to 10 miles, stop the car, come back 5 to 15 minutes later and restart it, it won't start. The battery is strong, the engine cranks over fine, but simply doesn't fire. Finally, typically after 5 to 10 minutes and a dozen attempts, it will finally start. When it does start, it does so instantly, there's no sputtering, smoke, or anything unusual. The car acts like nothing was wrong at all. In general the engine runs well, has good power, etc. Also, when all this happens, there are no "check engine" messages.

When I've brought the car to my local shop, of course it starts fine so they don't have any idea what to do. I went to my nearest Audi dealer and they gave me a Technical Bulletin that suggests things including decarbonizing the engine, changing plugs (which I had done recently), replacing the fuel injectors, the thermostat, and the coolant temperature sensor. Some of these don't make sense and some I've done.

Do you have any idea how I can fix this?

Thanks.

Mar 15, 2009 at 8:58 AM

DAVE H

CAR REPAIR CONTRIBUTOR
13,384 POSTS

Hello .. thanks for the donation .. much appreciated Try removing and cleaning the CMP and CKP .. both of these should show fault codes but it is worth a try !! hope this helps ..let us know Camshaft Position (CMP) Sensor CMP sensor is located at the end of left cylinder head camshaft. Signals from the crankshaft position sensor and the CMP sensor are used to identify ignition TDC of No. 3 cylinder. When starting engine, the first ignition and injection points are triggered by the PCM after receiving both signals. Crankshaft Position (CKP) Sensor CKP sensor identifies TDC of No. 3 cylinder. A notch (located at 62 degrees BTDC in counterweight of crankshaft for No. 3 cylinder) is used as the reference point. The notch, along with reference sensor, generates one signal per crankshaft revolution. The signal from reference sensor, along with a signal from the CMP sensor, is used during starting to identify TDC of No. 3 cylinder ignition point.

Mar 15, 2009 at 9:50 AM

HSERREZE

MEMBER
3 POSTS

Hi Dave:

Thanks for your suggestion. I will look into it.

However, the fact that the problem seems to be engine temperature related bothers me. First, this problem has NEVER occurred when the engine is cold (in the morning when I go to work or at the end of the work day when I leave to go home). All instances seem to be when the car either is warming up or had warmed up and was cooling down). How could this be connected with either the CMP or CMK sensors? Do you think the coolant temperature sensor could be involved as per the Audi Tech Note? If so, how difficult is this to access and replace?

Thanks.

Harvey

Mar 16, 2009 at 6:19 PM

DAVE H

CAR REPAIR CONTRIBUTOR
13,384 POSTS

Hello Harvey. The CKP especially has a tendancy when dirty or worn to send bad or no signals to PCM when at higher temps .. then when cool seems OK .. I was an RAC tech for 10 years and have seen it hundreds of times and not just on audi's The temp sensor TSB relates to crank no start at any temperature .. and then also goes on to say if no fault is found on ECT sensor then check thermostat/injectors/fuel pressure/compression .. you could check the ECT sensor !also the TSB state that the dates for Bad sensors after week 19 of 1998 !! check your sensor for this # or after (ie.) 20/1998

Hope this helps ..let me know

Mar 16, 2009 at 6:53 PM

HSERREZE

MEMBER
3 POSTS

Hi Dave:

Shortly after your last reply, I went to my local independent garage and between the two of us, we decided to replace the coolant temperature sensor and the fuel pump relay. Unfortunately, this did not fix the problem.

Finally out of desperation, I went back to the Audi dealer and spoke with a different representative. He was able to replicate the problem, got two error codes from the computer and had the engine speed sensor and air pump relay replaced. This was back on May 29. The car has started fine since then. The only problem is that this last fix cost over $600 -- Audi repair isn't cheap!

Jul 18, 2009 at 7:56 AM

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