[urq] rough cold running, still

Brandon Rogers brogers at terrix.com
Tue Dec 16 11:37:51 EST 2003

Hi Nathan-
The inability of your system to hold fuel pressure after shutoff is a
problem I was all too well aware of...I replaced practically everything
(pump, filter, accumulator, check valve, injectors, FD plunger..) but still
had the problem.  My pressures all seemed to be to spec, however, as a great
friend and Lister says "These cars can't read".  Here was a clue: I could
actually hear a valve opening and closing within the fuel distributor after
shut off. Long story less long....previously I had found the problem but
didn't realize it.  The fuel pressure needed to be just 1 or 2 psi higher in
order for a "check valve" within the fuel distributor to hold pressure.

Maybe your plunger in the fuel ditributor needs to be replaced.  Maybe the
pressure needs to be adjusted slightly.  After shut down, listen carefully
to the FD for a faint ticking.  A stethoscope or long screwdriver will be
helpful, however I could hear mine without.


Good luck


----- Original Message -----
From: <n-engelbert at terrans.net>
To: <urq at audifans.com>
Sent: Monday, December 15, 2003 11:25 PM
Subject: [urq] rough cold running, still

Today I checked fuel pressures on Priscilla, ~85 psi supply, ~55 psi
control warm, up to that within 3 seconds.  Shut off car and/or pump,
pressure dies off immediately, to around 10 psi within 5 seconds and to 0
within a minute.  Obviously wrong, so the internal check valve in the fuel
pump must be bad, unless there's another way for fuel pressure to bleed
off like that (return line to tank)?  Pulled new fuel injectors, no
leaking, same with CSV.  I did, however, notice that my fuel injector
inserts weren't tight, so I tightened them into the head, still the same
rough cold problems.

Duty cycle readings seem to be about right when the car is cranking and
running warm.

Warm, idle switch closed, fluctuating around 35-40%, maybe a little low,
try to adjust with 3mm allen set screw on fuel distributor, value goes up
shortly and then settles back out to same value.  How far should I have to
turn the screw to get an appreciable increase?  I've only gone a max of
about 1/3 of a turn.
Warm, idle switch closed, full throttle switch closed, 50%.
Warm, idle switch open, full throttle switch closed, 80%.

With car cold this afternoon, cranking cold, 80%.

And here's the kicker, once the car starts running on its own, albeit
poorly, the duty cycle reading goes to 0%, stays there until about 10
minutes later, the duty cycle starts rising 1% 2%......30%....  It begins
to run correctly once it gets to somewhere between 30 and 40%.  The car
surges a couple of times and backs off again as it's nearly to correct
duty cycle when driving.  When I let the car idle in my driveway, the
radiator fan had run 2x before the car smoothed out.

When I first plugged the duty cycle meter in, I didn't realize that I
still had the positive probe plugged into the ammeter portion of the
meter.  Effectively, I closed the circuit at the duty cycle test point,
and the car began running beautifully (I forced the duty cycle to 100%?),
I shortly thereafter realized what I had done, switched connections, and
don't think that I've damaged anything.

The slamming of the airflow plate that I've experienced when cold is most
likely backfiring up into the intake manifold due to not enough fuel.
Spray some starter fluid into the air box, idle smoothes out and the car
will rev freely until the dose is depleted.

Ideas?  I'm swapping ECUs with another local UrQ owner tomorrow to see if
mine may have a bad warmup section?  Is there a schematic somewhere to the
ecu available for download?


Nathan Engelbert
83 UrQ 900453

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