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Re: Wierd start problems.

   For a couple of years, I have had the problem where my car won't start
   after sitting between 1-4 hours after being run. It seems like if the
   car is hot or cold it works fine, but if it is just warm, it gives me
   So, another data point. Any ideas???

I'd originally sent this out as email, but since there is apparently
more-than-one-victim's interest...


Sounds to me like the proverbial "Hot Start Pulse Relay". Do you hear a
distintive "clicking" sound about every three seconds as you vainly wear
out your starter? (Assuming of course that your car is the proper vintage
to be, um, blessed with such a beastie...check your owners manual to see
if the relay diagrams show any such thing)

early/mid-80's vintage: the cold start injector is powered directly off
of the "START" circuit, and through the "thermo switch". If block is cold,
the CS injector is powered, enrichening the mixture so you start. "Hot",
the thermoswitch is open and nothing happens (except killing your battery
and engendering lots of language of which my mother wouldn't approve). The
"Hot Start Pulse Relay" is supposed to trigger the CS injector every few
seconds hot or not (by the way, I think "hot" in this context is some
fairly tepid temp like 70 to 90F, so it takes a LONG time to get cold 
enough to start again!) so that you can start the engine.

A less likely problem (although one that was **** hard to identify) is
that the ECUs are notoriously voltage-sensitive (at least the MAC-02
series). when I bought my UrQ, it had the usual butcher-job antitheft
alarm "professionally-jury-rigged" in place. Turns out there were enough
shitty crimps/etc that the voltage to the ECU was borderline. The car
would crank happily, and run happily once I got it started, but would
"occasionally" just not start at all. I finally noticed that when I
jumped it from my boringly-reliable Mitsubishi, it would always reliably
start if the Mitsu was running (i.e., supplying 14 volts), but would al-
most never start if I just jumped from a non-running battery (i.e., a
mere 12 volts . . .)! But this was cold or hot...so probably not your


Further reflections, etc...

The basic problem is that a cold engine needs lots of extra gas (aka
enrichment) to start, and a hot engine doesn't...(it just floods and
becomes even HARDER to start)...and someplace inbetween is lots of room
to guess wrong!

The Audis of the early/mid-eighties vintage (only one I'm familiar
with is my '83 UrQ, upon which all my observations and experiences
are based) had a coupla different problems with "hot" starting. One of
them is that, since Audi in their infinite wisdom, crammed everything
under the sun over on one (the left) side of the engine, the hot HOT
exhaust (and the turbo for cars so equipped) bake the daylights out of
the fuel injection system, which is why Audi added that damnfool in-
jector cooling fan kludge to attempt to keep the injectors for hot-
boiling away all their gasoline...anyways, Audis of certain 5-cylinder
configurations tend to suffer greatly from "vapor lock" problems (i.e.,
won't start "hot"). The "Hot Start Pulse Relay" is one way around this
problem -- while "hot" and cranking, squirt some raw gas into the intake
manifold to see what happens. In cars so equipped, you should be able
to hear the relay clacking away on about a three-second cycle interval.
This also helps the car that has sat long enough that everything has
cooled down, but not long enough that normal "cold" enrichment will turn
on the CS injector. (i.e., you've still got the aftereffects of the
vapor-lock -- no gas in the injectors -- starting is a real hassle
without any gasoline to run the engine).

One early "fix" is "The Little Red Button". This is long enough ago
that I don't remember the details, but I think the "thermo-switch" on
the block is after the CS injector, and just completes the ground to
allow the CS injector to actuate. The little red button parallels
the thermo switch (much as the Hot Start Pulse Relay does), and allows
me to manually actuate the CS injector. As I say, I think this is just
a wire from the relay through the switch to ground. (The switch is a
momentary push-ON switch; the CS injector is only powered when the key
is in the START position, so you can't flood out a running engine; you
can definitely (and easily) flood a warm engine, however!) This gives
three ways to actuate the CS injector: the thermo-switch completing
the circuit to ground, the Hot Start Pulse Relay doing the same, and
The Little Red Button.

The Little Red Button predates my complete understanding of the Hot
Start Pulse Relay, but solved 98% of my starting problems (no effect
on the starter just simply deciding to take a coffee break -- try
again in 15-20 minutes).

Eventually, one hot summer day when the car started flashing its over-
temp light, I tracked down the "Truth"...  Gee, it's not all *that*
hot, and the radiator fan is running, but gee, it seems to me that it's
not running all that fast (didn't it run faster with the ignition on
than off; doesn't seem to now) ... anyways I started tearing into the
wiring to see what the **** was going on this time ... finally tracked
down a faulty ground connection -- wow, this whole *bank* of relays
is missing their ground. Guess what other relay didn't have its ground?
Yup, the infamous Hot Start Pulse Relay. After running a nice new line
to ground (never did figure out where the "stock ground" wire was sup-
posed to reappear from the wiring nest...easier just to run a new known
wire to ground!), lo and behold, I had a new 3-second-interval clicking
to add to the Audi Relay Cacophony, and the car has hot-started much
much better ever since. (I think I've resorted to The Little Red Button
twice now in three years or so, as opposed to approximately twice a
week, like *EVERY TIME I WENT TO THE GROCERY STORE!!!* OK, 'twasn't 
really that bad, it was more like every second or third time I went
shopping; I learned to either get all shopping down in less than 15 mi-
nutes, or take an hour or so... Yea verily I provided much amusement
to the Audi Gods, I'm sure!)

Ho hum . . .