Audi 7a revving issue

[willmears]

Hi,

I am currently having problems with my early 1990 Audi cq 20v 7a (all hitachi and 2 plug ecu).
It pulls fairly well up until about 3-3.5k revs then it feels like its running into a brick wall, the car then struggles to reach redline. This is even evident when just revving up in neutral.
Quite stuck with where to look next for issues.

Current parts replaced:
New bosch thru bolt style knock sensors.
Used maf
Used throttle position switch
New spark plugs and leads
New fuel lines and filter (fuel pressure checked all good)
Cambelt and waterpump

I did buy this car from a hedge that it had been lovingly dumped in 15 years ago.

Any help would be greatly appreciated.

[Lago Blue]

Hi Sir,

May I suggest a few ideas of things to check to start this conversation off as follows:

- Stock air-filter box? no chipmunk nest inside?
- See 20v.org re how to pull fault codes, you may have a serviceable blink light in the dash display already? If not check bulb is serviceable.
- Pull codes, record and erase. Do they return during next engine run?
- Engine vacuum, how many inches of water do you pull at warm idle?
- Fuel pump relay, does it have a fuse holder on top? Is the fuse holder empty?

[willmears]

Hello thanks for your reply,
The only code I have now is 1231, which checks out as my Speedo stopped working.
original airbox with standard filter.
Engine pulls 5bar vacuum at idle.
Relay has the empty slot for the fuse.

I originally had these codes:
2232
2142
2242
2212
2121
4431
Hence replacing all of those sensors.

I have just discovered a tooth missing on the flywheel, which might be causing some issues due to the engine not reading speed properly.

[John.]

This is even evident when just revving up in neutral.

Try splitting the exhaust after the manifold to confirm the exhaust is/isn't blocked.

I had similar issue with an NG, the cat was blocked.

[willmears]

My cat seems to have accidentally fallen out (due to previous owner of course).So likely not the issue but i will give it a go anyway.
There was a large dent in the down pipe just before the junction to the cat, due to i presume the previous owner hit a rock or something.
I have detached the pipe and heated it up, and massaged out the dent to it is back to almost full volume now.
Going to reassemble the head tomorrow as I have just put new tappets and cam chain in, then will give it a go again.
Whilst I was in there i checked the gear on the end of the distributor as that is supposedly a weak point but mine already has a metal version in good condition.

[willmears]

Just an update.
issue is now fixed.
i changed these things between the last time i checked if it was working (not 100% sure what the fix was):
fixed the dent in the downpipe that was causing restriction.
New tappets and cam chain
Retimed the cam belt
new flywheel ring gear