'91 100q 5 injectors replaced - now car wont start

[Mike Arman]

1) Get the car away from the mechanic. He doesn't want to work on it. It also sounds like he doesn't 
know Audi I-5 engines very well.


2) You're in NJ - there MUST be someone on this list who lives within a hundred miles of you and 
knows something about this engine. It would be well worth you paying that person for transportation, 
some time and dinner at a decent restaurant in order to get your car running again, or at the very 
least get a competent diagnosis.


3) The lifters aren't pumped up, moving the car with the starter didn't puke the engine, the head 
gasket didn't blow from sitting, the injector gaskets don't affect the compression because the 
injectors don't go directly into the combustion chamber (like a diesel) but into the inlet tract 
BEFORE the inlet valve. You'd have compression with the injectors OUT and lying on the bench. Aliens 
didn't steal the compression from all five cylinders and fly off to probe them either.

I do, however, get the impression the the mechanic is probing your wallet . . . and that's why he 
doesn't want to continue.

4) I'm leaning very much toward the sheared crank key theory. That's about the only thing that would 
affect all five cylinders. This is easy to diagnose - pull the plugs, put the engine on TDC as 
indicated by the pulley timing mark and stick the end of a long coat hangar into #1 cylinder to see 
if it really IS at TDC. Rotate the crank 360 degrees and check again. Remove the cam cover and 
verify that the cam turns with the crank and both valves are fully closed at one or the other TDC 
positions.

Since this is not an interference engine, even if the Woodruff key did shear, there *should* be no 
damage to the valves.

5) Since all five cylinders are equally and similarly affected, it has to be something that is 
common to all five cylinders - which pretty much points to the cam belt/pulleys/keyways, etc., since 
the only other thing that was done to all five cylinders (the injector seal replacements) wouldn't 
produce these symptoms.


6) In my 55+ years of experience of working on cars, motorcycles, airplanes, electronics equipment 
of ALL kinds, wristwatches (electronic, hybrid and mechanical), right down to and including the 
faucet on the kitchen sink, 99.999999% of the time it is the SIMPLE things that go wrong, not the 
exotic, expensive, unlikely stuff.

7) Conclusion - think simple think simple think simple - some assumption is being made that all the 
underlying components are blameless, and that doesn't seem to be the case. Something very basic is 
wrong, and looking for "exotic" causes is a waste of time and energy.

Where did the compression go? Why are all five cylinders low? What affects all five cylinders 
equally? The timing marks on the cam and crank need to be verified as accurately reporting the true 
position of the cam and of the crank, and I don't think that's been done yet. These are really 
simple engines, look to the basics.


Best Regards,

Mike Arman
90V8Q, and a *long* history of other stuff.