meternerd

It was several years ago, but I remember that the gauge worked fine, but the ECM was getting bogus info. and I had no codes. Maybe I just thought there were two separate sensors. If they are both in one "module" then I stand corrected. I do remember that the engine ran fine once it cooled enough to start, but that it took at least half an hour for that to happen. I was halfway through a cross country trip, just outside Yellowstone and fought it for three more days 'till I got home. This forum pointed me to the problem. Love this place.

jcman

I'm mulling over this very subject with Jared427 this momment about the cts and checking it.

Airbag

As a general rule warm start problems are generally fuel pressure related . On a cold engine you have enrichment to help start the car ( in the Audi indicated by the CTS ) . if the CTS is in fact working properly it will turn off any enrichment if it feels the engine is warm or hot. Then you are just depending on fuel pressure to get you started. If you lose Fuel pressure while standing for a while you will have a difficult time restarting until the engine cools off enough to have the enrichment circuit activate again.
These are just geneal principles that may assist people in general that are troubleshooting warm start issues.

Just one more point. Dont assume that the sensors always fail ( we know that in some cases they often do ( CTS ) but try to think of things more haulisticaly . The sensor is trying to tell you something . in a lot of cases during troubleshooting people often " shoot the messenger" by just changing sensors not realizing what the sensor is trying to tell you.

Good Luck.

devinsixtyseven

I think jcman is correct with his assessment of the camshaft errors, and while I agree that a "holistic" approach makes sense on a car with multiple sensors reading similar values, I prefer to think of it as a logical problem, or picture it as a system of equations...too many threads here with multiple VCDS errors, often solved by replacing a single fouled sensor. In this case and others, whether the CEL lit or not, the only rational solution is start with the codes from VCDS, and the codes did not indicate a problem with the coolant temperature sensor.

In related news, replacing the CPS on a 2.7T is a real bitch. It's like a pre-cat O2 sensor (same location), but more so (deeper), and it's likely from the cable routing (behind a small heat shield aft of the combination valve, toward centerline, then between the block and the coolant pipe, then shrouded with a heat reflective wrap and down to the transmission) that the sensor was installed while the engine was out of the vehicle and prior to final assembly. It's not physically possible, as far as I can tell, to pull the sensor or the connector through the finger-sized gap between the block and the coolant pipe.

I'm taking pictures as I go. It's certainly possible at home in the garage, just tedious, and I already look like I stuck my hands elbows-deep in a sack of angry cats. Breaking for a barley pop then back to it...

Cheers,
Sean

*edited* camshaft errors not crankshaft

Airbag

yes looking at the system as a whole does not mean to disregard logic
I had exact same issue with post cat o2 sensor BTW and the stringing of the cables . SOOOO frustrating . i just cut the wires to remove and reinstalled new sensor without passing under that coolant pipe.

You just know they are laughing as they hook up those sensors then put the engine and transmisson in the car .

hwks1

Following this to see how it turns out I really don't see the G28 causing the hot re-start issue - but it most likely is the cause for the stall. The G28 wouldn't have any priority on start.

Most likely I expect, you will solve for the stalling but not really the hot re-start problem. I still think the engine is flooded on the hot restart, giving you cranking - no start problem.

Airbag

Actually I am of the opposite opinion he doesnt have enough fuel to start .. thats the thing about opinions .

I would think if it was the CPS it would run , or it wouldnt. not run but not idle ...

SO to ask the totally obvious one just so we can dismiss it and move on .... fuel filter ?

jcman

Sean's problem is in the G28 code that does exist (16706, Engine speed sensor (G28) P0322 No signal, intermittent), it is a known fact that if the ECM does not see a CPS signal that engine will not start, if the code is P0321 G28 - (Ignition Engine Speed Input Circuit Range/Performance) or Implausible Signal it will run like crap and throw other codes too.

Lets not jump to conclusions that don't exist Gentlemen, go on the codes that are present and the most obvious.

devinsixtyseven

Thanks everyone for the discussion and feedback. The CPS was the issue, the car is running very well at this point. I've some photos of the process that may help others--this repair on a 2.7T is largely done by feel.

jcman

I'll raise a few pale ale's this evening in honor of your victory.