Quite the B5 Puzzler

[dcllanos]

Hey All,
Ok anyone up for a good puzzler? My B5 S4 is having hot start issues. Vag only showing O2 sensor issues. I changed the coolant temp sensor, Fuel filter (What a Pain) and then fuel pump. New battery, plugs, Checked fuel pressure (between 3.5and 4), Still having issues. Car starts fine when cold, runs fine once started, never hesitates or anything. We started looking at ECU and whenever you pull the ECU and reconnect, it starts fine, even when hot, so...... Is it ECU or possibly crank sensor? I am hoping crank sensor(G28). Any thoughts would be appreciated.

D

[S4_NE]

Are you running stock everything or do you have a fuel kit ect, I know good shop in southern CT that could help you out if you can't figure it out on your owen, LMK
just PM me

[dcllanos]

Totally stock. In Ct. but thanks.

D

[CONTROL ONE]

If you VAG is showing o2 sensor issues.....................maybe it's the o2 sensors?

Just taking a wild stab in the dark here though.

[S4-Casa]

what happens when you dont disconnect the ecu? I know it doesnt start but what happens? crank? spark? fuel? -- air?
does it at least want to turn over? or nothing? check the spark plugs after? how about the cam sensors? crank sensor?
could be a number of things
Are you always clearing the codes? i wouldnt worry about the o2 but I would start to look at the spark and then diagnose from there.
I would run the car - get to a shop turn it off and then try to start - doesnt start then look into the spark plug are they working? if not then sensor related - but since your o2 is the only code I am assuming its mechanical.

[dcllanos]

So we re-vagged the car after changing the crank sensor, and pull up code P0605 Internal Control Module ROM error... kiss of death for my ECU as I understand. Arrggh.. Any one else have this fault and it wasn't the ECU? I would love to investigate other causes before replacing the ECU. Thanks.

D

[BlueturboS4]

If you VAG is showing o2 sensor issues.....................maybe it's the o2 sensors?

Just taking a wild stab in the dark here though.

nicely said!!!

[Turtle]

Sucks, Dude. what year is your car?? Just asking cause I have a spare Ecu. pm me if you want.

[seadoo4563]

So we re-vagged the car after changing the crank sensor, and pull up code P0605 Internal Control Module ROM error... kiss of death for my ECU as I understand. Arrggh.. Any one else have this fault and it wasn't the ECU? I would love to investigate other causes before replacing the ECU. Thanks.

D

search the forums for that code....

02 sensors should not make difference when trying to turn over the engine.

[haus4]

Im not computer whiz, but a ROM error doesnt sound good.

[dcllanos]

The puzzle has been solved, new(used ) ECU and the car starts and runs like a charm. So if you have hot start issues, check everything; climate sensor, plugs, fuel filter, fuel pump, crank senor, but be aware of the infamous P0605 Fault in the the ECU. Lesson learned. Hopefully this will help others.

[MacDaddy]

I've never heard of O2 sensors causing a no-start condition.
some guy had a similar issue with his old ass Audi 90, aparently it was thew camshaft position sensor would get too hot and cause the engine to shut off.

sometimes a bad ECU will show itself if you give it a thump with the end of a screwdriver or something (don't hit it hard enough to damage anything of course) if it hickups or stalls, the ECU is suspect.

[megafreakindeth]

havent seen too many newer vag ecms having bad solder joints. they do fail due to bad coding causing an occasional windows style glitch in the system. i used to have a program that could read the code and find the bad line but i lost it.

another hot no start causer can be the gas cap. if you have a hard time starting and ur absolutly sure that your car is in good order just losen the gas cap and crank it, alot of hard/long cranking cars or no starts have this problem