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Re: Weird hot start problem with 1990 Coupe Quattro
I have an intermittent problem with my Coupe Q, which is driving me
The car has difficulty starting _sometimes_ while hot. Cold start are
always fine. Some hot starts are ok; some require attempts to start
for about twenty minutes before the engine catches. The starter and
battery are fine. The longer the car is driven, the better the chance
of starting difficulties. This problem cannot be reproduced by idling
the car -- the repair shop did this for hours with no problems.
I believe that I can hear the fuel pump relay clicking on for a second
when the key is turned (correct, per the Bentley manual); sometimes I
can hear a faint whine from the rear of the car, which I assume to be
the fuel pump.
My guesses as to why I'm having problems starting this car:
1. the )$(#*&@ oxygenated gas -- it has been warmer in Seattle since
the problem first reared its ugly head. The oxy gas should have gone
away on March 1st; so I should be able to test this theory pretty
2. The fuel pump is intermittently dying. It obviously doesn't work
as hard while idling than when it's running at freeway speeds.
3. Some sort of vapor lock, cause unknown.
I'd love to hear any other theories. Answers would be even better. :-)
While I'm not sure how much of my '83 UrQ experiences will map to your
'90 CQ . . .
This is classic with the UrQ series. Mine had it in spades, right down to
the refusal to reproduce anytime it got near a dealer/mechanic!
The workaround that worked until I stumbled across the "real" problem was
to install "The Little Red Button". This button allowed me to manually
actuate the cold-start injector disirregardless (so to speak) of what the
rest of the car's assorted relays, electronics, switches, and other mis-
cellaneous gizmicry thought. Presto - instant (well, 2 seconds...) starting
Quickie check to see if this *might* help you -- next time it is in its
recalcitrant start mode, squirt some ether into the intake track. If the
engine starts and runs happily, this might be your underlying problem (ob-
viously ignition and "normal" fuel delivery working OK). ***CAUTION***
ether happily burns ("explodes") if you even look at it cross-eyed, so use
it sparingly (one-second "spritz" is "plenty")!
My "real" problem turned out to be a disconnected ground wire to a bank of
relays, which included the krock hot-start-pulse "relay" (which is the old
K-Jetronic's "mechanical" [non-computer-controlled] way of goosing the en-
gine mixture when starting) -- once I stumbled across that problem and fixed
it, I've only needed TLRB once (coupla years now). I have *NO* idea how the
newer models handle the starting mixture enrichment, but I have a sneaking
suspicion it's all computer-controlled... (Does it even *have* a separate
"cold start injector"?)
Of course exactly the opposite might be at fault -- bad temp sensor could
be telling computer engine is cold and needs LOTS (too much) gas (flooding
the engine)... - pull one of your plugs when won't start and see if wet or
The UrQs (5000's in general?) are also well known for baking the injectors
(with the intake tract conveniently placed on top of/nestled within the
exhaust manifold/tract, leading to SEVERE vapor-lock problems. Audi hacked
in this krock "injector cooling fan" and duct-work (not to mention the hot-
start-pulse relay...) to try to alleviate this problem. Does your car have
such a fan (and if so, is it working?).
One final thing - do you have any sort of after-market "anti-theft" sys-
tem installed in your car? (The one that was in my car when I bought it
was installed so poorly it was actually pissing off the computer by drop-
ping its +12 (bad/crimp splices in wiring) to the point that it would not
work sporadically -- symptom was car would not start, even if jumped un-
less it was jumped from a *running* (+14V) car, when it started instantly!
G((&*#@&^))@@*)^%^$(()#@( incompetent effing idiots!
Good luck, and be sure and let us know what finally works!