My C4 AAR 2.3E 1991 Audi 100 refuses to start after being totally OK
the day (and many years) before.
It cranks OK. Battery is fully loaded.
I've checked the ignition (coil cable sparks 15 mm against motor bloc,
plugs spark). Seems thus OK but I do not know if the timing is OK
I suspect the fuel pump relay (I hear the pump running for 2-3 secs
every time I turn the ignition key, then it stops).
I want to bridge this relay to prove the point.
Where is it in this model ? It is not in the big fuse box in the
bonnet (almost empty if you except the "retarded fan relay").
And, by the way, where is the pump ? Not under the back seat, in
Thanks for any help !
Fuel Pump relay would have been my first guess but you say that you hear it
running for a few seconds when the key is first turned. That is what it should
do. It runs until it reaches the correct pressure then stops. I am quite sure
that it would not run at all if the relay were bad. Still worth a check.
You can use a jumper to connect the large holes if the relay socket to eliminate
the relay as the problem.
Relay is in the main fuse box by the drivers side hood hinge. Some of the years
do not have the fuse position in the top of the relay.
Check your fuses too as there should be one for the fuel pump in addition to the
relay. Still if it cycles when you turn the key they should be fine.
Other than the relay there can be a number of things to cause a no-start:
- Bad ignition switch
- sticking air plate in the fuel distributor
- vacuum problems
- non-functioning cold start injector or its temperature sensor
- compression problems
Check to see if you can see fuel one spark plugs after trying to start.
'91 100q 5spd
'98.5 A4 1.8TQ 5spd
Thanks for the hints !
Your suggestion #2 was the right one (sticky air inlet platter) !
By the way and for future documentation: when you say that the fuel
pump relay is in the main fuse box, do you mean behind the fuses
cluster at the driver's side (continental Europe)of the dashboard or
somewhere between the pedals and the door hinge ?
All the best !
I have owned four T44s (84 - 91). The 87 and 91 have both a relay and fuse for
the fuel pump in the main relay box that is located under the hood by the hood
hinge and just in front of the windshield.
IIRC the 84s seemed to only have the relay.
Hope you got it running.
If you remove your air filter you can reach up into the fuel distributor and you
will feel the plate. It should lift quite easily and return when you drop it.
If it doesn't move easily it could be binding ad affect mixture, idle and
possible no-start condition.
Don't force it.
If you are having a similar problem this could be something to look at but other
things can also be involved.
Christoph Bollig wrote:
I haven't got a no-start problem, but idle is sometimes iregular (not
always) and I recently checked the current into the idle stabilisor
valve. In addition, it seems to be slightly down on power, but I am
not too sure. Will see how the fuel consumption is when I fill it up
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