Aarononymous

I just started at a new dealer and we have a 93 S4 that the owner wants to part with. Needing an ECM, clutch worn but not slipping yet, although had a huge boost leak, rust on the pass front fender, from Canada. 122Km, not perfect but near mint black leather interior, one owner. Damn I can't wait, it's gonna be nice to get back in an old school german car. I'm a tech, but at my old dealer we never saw anything older than a 98, so I'll be in here soon on a regular basis.

UrS4boy

Why does it need an ECM/ECU?

Aarononymous

now cranks but won't start. Gives code for crank speed sensor, no signal, I tested resistance, ok, tested signal at sensor, ok. Tested wiring for open/short/cross short, ok. Checked signal at ecm, ok. Audi repair manual said if everything checks out to replace ecm.

Mr.FRU-T-Pants

I know that's not the code you logged, but ECU's very rarely go bad, unless the heater core has a coolant meltdown on top. Sure, it can happen, but I'd run through every trick in the book before trying to find an ECU. You're talking a *minimum* of $500 if someone is feeling really nice that day....*if* you can find one. New, you're looking at a cool grand.

They sure are fun rides once up and running though. Good luck.

UrS4boy

Agree. ECUs rarely die. They do die. But not often.

UrS4boy

The Crank Speed Sensor code is a red-herring. If you pull the codes when the engine isn't running, you will always get a crank speed sensor signal failed code (because its a hall effect sensor (magnet) that needs to be energized by the flywheel going around).

Running rich can mean a intake track air leak between the mass air flow sensor and the engine. The ECU thinks a certain amount of air is flowing by the MAF so it provides the appropriate level of fuel. However, if there is an intake hose leak or a split cross-over pipe, some of that air goes AWOL and doesn't show up at the engine. Therefore the engine gets too much fuel for the amount that showed up = running rich.

Stalling might be the cam position sensor Code 2113. Easy to replace. OEM CPS is expensive. Cheng Yeng hall sender CHMY301 is a replacement for the HKZ101 that is on our CPS "frame". They cost about $10. Dealer wants about $250.

If you get the car, you need to do a timing belt (water pump, etc. etc). Do the CPS at that time (it lives behind the exhaust cam sprocket).

ECU/ECM replacement is a "stealer" money making trick, not necessarily related to reality.

HTH

Bill the Cat

And when they do - they are usually executed. (Flood, improper chip replacement, etc.)

Don@STaSIS

and does not make a square wave like a hall does.

Cheers,

Aarononymous

However the official audi reference says if the code is present that to do all the appropriate checks and if the sensor is ok to replace the ECM. I even called audi techline, they said the same...I know they probably have little experience with the older models like myself. The crank is just a 2 wire inductive sensor unlike the cam sensor which is a hall type sensor. I found the leak causing it to run rich with no power, the "michelin man" hose was shot from a leaking PS pump hose. When I initially saw the car the codes were for crank speed sensor, o2 sensor lower limit exceeded (false air), and smething related to a possible MAF problem or air leak, I don;t have the codes with me. I am wondering about the MAF causing the no start, I found the car would stall with the MAF unplugged.


Thanks guys

UrS4boy

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