zexxe

I have a problem with Audi S6 2003 4.2 340Bhp.
The car is starting very badly when the engine is hot.
Cold engine starts perfectly, without any problem.
If the water temperature reaches 90 degrees, the engine starts but very difficult, and there is the smell of gasoline whoo make me think feel the engine is flooding.
After I start a cold engine, the car is working properly, and if we stop the engine will start again after hard cranck.
Please helpme to solve my problem.

Gerry

You need to pull the codes to see what is going on. There are a number of possibilities. I've had somewhat similar symptoms caused by an intermittent faulty engine speed sensor. If that is your problem the diagnostic code will specifically point to it. There are a lot of paths this could go down

zexxe

Thk for the answer !
I have no light on the dash , no error , nothing .
Tuesday I will go to a specialised mechanic to check on my audi.
Did error can occur without warning on the dashboard ?

Gerry

That sensor does not trigger a light, but there are many others that also will send a diagnostic code without a CEL light, so you'll never really know until someone hooks up to the car and scans for codes.

zexxe

Today i was with my S6 at a professional mechanic and my car doesn't have any error code, NOTHING !!!
I think is something wrong with vacuum or some valve that is not working properly.
I make the case that when the car is starting good , is accelerating well , but when has problem starting ( when the engine is hot , but not always ) the acceleration in dimminuated .
Is someone have some suggestion , please share it !!!

SloopJohnB@mac.com

At the back of the engine on the crossover coolant pipe. Somewhat difficult to get to. There's also a coolant temp sensor on the bottom radiator hose.

I tend to think it's not the CPS because it does start when hot, just badly. If you have a way to spray refrigerant or cooler of some kind on the CPS and that cures the hot start problem, that's about the only way to diagnose a partially failing CPS. They usually fail solid when hot and then may work again when they cool off.

There are ways to check the coolant temp sensor, i.e., what signal it should be giving above 90F…if it tells the ECU the engine is cold but in fact it is hot the ECU can flood/enrich too much. You'd have to pull the sensor and play around with a water bath, DVOM, and thermometer. If I had an original coolant temp sensor I would just replace it due to the hassle of getting the old one out. I might try to test the old one just on GP.

One other thing, I had an intermittent knock sensor problem on my 02S6 for a couple years…car would be really slow, shut it off and it would usually go away for a couple days. Finally got so bad I was able to keep the car in limp mode and get a VCDS on it that identified the knock sensor (I decided to replace both since the intake manifold had to come off and I had a shop do it, warranty, if the other one would have failed I would have had to pay double labor).

zexxe

I will try to scan the car after the engine become hot , and try to start the engine while scanning to see if the data from all the sensor in question.
Is a pain in the --ss this type of problem, is very difficult to fix the problem without an error code because you don't know where to start and where to finish.

zexxe

After 2h spend on my car with VCDS, we don't find nothing wrong , no code no error !
And strange enough , the car now start eaven with the engine hot .
I think the next step is to clan the engine as good as i can , and try to see all the vacuum hose .
If the CPS is not working proprelli when the engine is hot , will give an error code ?

clancy

pay attention to Sloop's suggestions. He is known to be knowledgeable. I had an intermittent CTS. No codes. Sometimes was fine, others, created issues. It is a cheap and easy replace. Search this forum for details. Also, if the CPS is intermittent it sometimes sets code, but not always. There is a diagnostic though. Using VCDS, not the dash tachometer, look at RPMs when cranking. If they are 0 then the CPS is faulty.

zexxe

I allready change all the vacuum hose and the purge valve .
If will matke the same problem , i will change the CPS and tha's it !!!