Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

out all the excess fuel that the computer is blindly dumping in. May die
repeatedly during this time. Small amount of black smoke flows from tailpipe.
● During 5 minute crap idle time, car will not tolerate any accelerator input.
Depressing accelerator kills the car immediately.
● After the 5 minute extreme fuel enrichment exercise, the car lets out its last
puffs of black smoke and you can drive off.
● Idle once engine has 'stabilized' is a fairly steady extremely high idle. It will be
quite noticeably higher than normal (over 2,000 revs). I thought my computer
had fried the IAC motor circuit with it stuck full open. Turning the idle bypass
screw all the way closed can only bring the idle down to 1250rpm.
● Smell of unburned fuel floats around car at all times. Gas mileage is atrocious
under all conditions. I achieved 16-17mpg on my last tank.
● Power is fairly crappy, though not much worse than usual.
760T Floods and Stalls: ECT?. [Inquiry:] I have a 1986 volvo 760 turbo with 207,000
miles on it. I recently purchased and at the time it was running on three cylinders and
had sat for about six months. I replaced the flux amplifier and it ran on all cylinders.
The man who sold it to me also told me that he had an intermittent problem... It would
stall out occasionally. He was true to his word...If it is cold (running about 15 min. )
and you give it too much gas it starts to flood out. If you floor it while it is flooding out it
starts to catch on the other cylinders and eventually will go. If you stop the car while it
is flooding out it will either stall or run on 1 or 2 cylinders. One time I disconnected the
map sensor while it was flooding out and it started to idle normally. While driving
behind the Volvo it spits black smoke when it is flooding and sometimes even when it
isn't acting up a little bit of black smoke will come out of the exhaust. The problem
clears up if you drive about 30 miles on the highway at constant speed. After that you
can stop it idles pretty good.... misfires a tiny bit.... and you can take off like a bat out
of hell...also about a week ago I tried to start the car and it would only run on 1
cylinder, then not at all. I pulled the plugs and they were all fouled I put in new plugs
and it fired right up. I tested to make sure every cylinder was firing and they were...is it
my computer??
[Response: Don Foster] I'd consider looking at the temperature sensor or connections
to it. There are two sensors -- one for the temp gauge, one for the FI ecu. The gauge
sensor is a one-wire device, the FI temp sensor is a two-wire device. The FI temp
sensor is mounted in the head, under the intake manifold, approximately under runner
#3. It's not impossible to get to -- just almost. (The gauge sensor is under runner #2 --
ignore it.)
The sensor is an NTC thermistor -- that's "negative temperature coefficient", or as the
temperature drops, the resistance rises. If the sensor fails or if you have a bad,
broken, or corroded connection at the sensor (or anywhere in the harness going to it)
the FI ecu measures high or infinite resistance. The ecu thinks it's about -100 degrees,