devinsixtyseven

04 A6, 6spd 01E manual, BEL 2.7T block, 140k miles.

I'm putting it on the VAG-whisperer later today, but in case the problem might not show in the system, and just for grins, here are the symptoms if anyone has any guesses.

When the key is inserted and turned to "on", all proper lights come on, the fuel pump relay cycles and the pump primes. When cranking, plenty of power, engine turns over fine. If the car is cold (coolant temp gauge at the bottom), the engine starts. If the car is warm (temp gauge any higher than the line), the engine fails to start.

While driving, everything is normal when cold, initially. As the car warms up, something feels...off, about the engine...hard to describe, just doesn't respond right, like it has *too much* power for the throttle position...too eager, hard to explain. Definitely not normal.

When the engine is hot (normal operating temperature, for most of my driving, is one bar left of center...IIRC that's 225 degrees F), when the clutch goes in, the engine dies if I pause too long between gears. I can restart the engine and accelerate (again, more power than seems normal), if the car has enough momentum to ease the clutch out. It does not die, and the fuel system is feeding the engine, when the clutch is engaged. At one point, I felt the engine die under moderate throttle while climbing a gentle hill, clutch was out, transmission in 5th...I could feel the powertrain jump and feed back to the engine, keeping it turning. After a few seconds, I was able to add throttle again, shifted to 4th, and kept the RPMs around 3K for the remainder of the drive home...thank goodness no lights and almost all downhill.

The engine died when I shifted to reverse to back in to a parking spot...bad move, the RPMs dropped too quickly to re-engage the clutch, and the engine died.

Two hours later (engine cool again), the car started normally, and I was able to finish parking :P.

I replaced the primary coolant temperature sensor at 98k miles, also cleaned the throttle body and replaced the spark plugs. Timing belt/water pump/thermostat/cam cover gaskets/fan switch coolant sensor all done by the shop, at 120k. Coils were replaced via recall before I owned it.

Searching here & elsewhere, possibilities include ignition module, camshaft position sensor, and crankshaft position sensor. Each one of these (plus the CTS) will prevent the car from starting if it fails, and all are known (based on my web searches) to result in a failure to start when warm.

So, before I plug it in, any of those items sound more likely than the others, given the symptoms?

TIA,
Sean

*Edit* The CPS looks easy to replace. Where's the ignition control module (I assume there's only one)?

hwks1

I'm suspecting fuel injectors - or something causing flooding the engine when hot.

GTA_Driver

Camshaft position sensor, crank position sensor will throw codes. You need to replace your coolant temp sensor (CTS), what you took paragraphs to describe is a classic bad CTS symptom.

You can verify via VAG-COM by going to measuring blocks and seeing what coolant temp the sensor is reporting.

devinsixtyseven

Bwahahaha...nope . My own diagnosis was based on a bunch of old posts here and at Audizine, but here's the breakdown and the VCDS report.

I replaced the coolant temperature sensor at 98K...different symptoms for a bad CTS. It'll idle rough, and the idle will vary up/down a couple hundred RPM, plus not starting when warm, plus a bad CTS lights the CEL on the instrument cluster.

If it were fueling...ok, it could have been the fuel pump, but I can hear the relay trigger and the pump prime, and if the pump were dying, it wouldn't be possible to get a rolling restart or accelerate at the same time the engine is unable to idle on its own. That last one is a major part of this...can't idle by itself, but throttle keeps it going.

From VCDS:
16706, Engine speed sensor (G28) P0322 35-10 No signal, intermittent. This is the CPS, aka RPM or impulse sensor.

16405, 16395, Camshaft A (intake) banks 1 & 2, retard setpoint not reached (over-advanced), intermittent, etc...

My guess for now is 16405 and 16395 are triggering from the busted CPS. None of these codes lit the CEL.

70$ part, back of the head. Any advice on the repair?

Thanks,
Sean

GTA_Driver

Interesting. I would start with the crank speed sensor (G28).

By the way, I'm hoping this will fix your problems, but here's the description of the cam sensor codes:

16395/P0011/000017 - Bank 1: Camshaft A (Intake): Retard Setpoint not Reached (Over-Advanced)
Possible Symptoms

Power Loss

Possible Causes

Camshaft Adjustment Valve 1 (N205) faulty
Fuel Pump Relay (J17) faulty
Mechanical Timing not correct, including Chain and/or Belt timing.

Possible Solutions

Check Camshaft Adjustment Valve 1 (N205)
Check Fuel Pump Relay (J17)
Check Mechanical Timing

Special Notes

When found in Engine: 4.0l W8
Check TPL 2010059(RoW)
Check/Replace Oil Sieve in Timing Case (Camshaft Adjuster)

4Driver4

While it does appear that the CPS is the issue, I'd still like to point out that your statements about the CTS are false (for future STFA'ers)

Parts replaced 50k miles ago should never to given a pass as known good, especially a CTS.

Maybe. Depends on how it fails.

Maybe. Depends on how it fails.

devinsixtyseven

For the record, the symptoms I described (rough idle, no hot start, etc) existed when the factory CTS failed, and disappeared with the new (green) CTS.

Information at Ross-Tech mentions the camshaft codes are likely to trigger with a bad G28, and my car's symptoms match others with a G28 failure.

I'll update post-fix.

jcman

Well Sean it's been mentioned before that one error will trigger others in a specific order, the G28 CPS will only show two codes like a maybe something is there or notta there and the notta won't start at all.

I'd bet that the cam related ones were the aftermath of an engine running with no crank signal "at times" throwing the cam position sensors into unkown territory and with report "codes".

meternerd

Yup! My money is still on the CTS. Remember that there are two on the 2.7. One for the gauge and one for the CPU. CPU is on the passenger side aft (sorry, old submarine sailor)of the head. Won't throw a code, but will NOT start when warm. Dumps black smoke out the exhaust trying. At least that's my experience. Hope yours is as simple.

jcman

G62/gauge and G2/ECM are in the same CTS for the BEL 2.7, are you sure your not referring to the exhaust temp sensors?