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

problems recently--the car won't start after I drive it 20 minutes, the car won't start
after I turn it off after driving a short distance unless I wait several minutes, the car
made me wait 20 minutes at the grocery store then started and ran fine...ones like
this, that all sound to me similar to the problem that afflicted me a while back, which
was cured by a new fuel pump relay. My problem was sporadic, and the symptoms
varied, but boiled down to a well-running car simply, now and then, refusing to start.
Given that it now seems clear that the FPR is fairly often culprit in these cases, and
given its low cost, I'm wondering if maybe trying to replace the fuel pump relay, after
checking for loose wires and that the fuses are content, shouldn't be the first line of
attack. What I mean is that intermittent failure in the FPR is not uncommon once you
get into years and miles, it's something most of us would not have a hard time
replacing, and it seems, from many of the postings, to be not only the usual suspect,
but actually the real culprit. Sure, there are lots of other things it *could* be, but it
seems that this is what it comes down to more than 2/3 of the time. Starting with the
FPR should, on average, save most people a lot of time I think.
Car Stalls During Turn; Bad Fuel Pre-Pump Likely Cause. See Fuel Pre-Pump
Problems for more information about pre-pump problems causing odd stalling
situations.
Poor Performance; Rich Mixture Smell: Diagnostics [Inquiry: Jarrod Stenberg] My
non-turbo, auto transmission car has been running real crappy for a while now; I think
it was gradual. Sometimes when I start it it takes forever. This can include some
backfiring. When it finally does start it sometimes spits out a cloud of smoke. It often
smells like gas as well. Seems to be running rich. The oil smelled like gas. I replaced
it since this scares me for good reason. Of course this improved nothing but my peace
of mind. When idling it will race a bit and cycle back down to near stall (to and fro to
and fro but not REAL bad). Things I have checked and symptoms: Weak spark?
Replaced the plugs and I have new wires. Checked the distributor cap and rotor. All
are good. I have done the easy checks for vacuum leaks: sprayed wd40 around and
listened for the engine to choke on it. I am pretty certain this is not it.
[Diagnostic Notes: Don Foster]
Failing FPR. First, it certainly could be a failing fuel pressure regulator. Pull the small
vacuum line and sniff for gas -- possibly the diaphragm has a pinhole and is bypassing
fuel directly into the intake manifold. But even if no gas smell, the
regulator could have increased the fuel pressure creating an
always-rich condition -- this is not uncommon.
Fuel Pressure
Regulator
Failing ECT. Second, my favorite is the connections at the
temperature sensor -- the two-connector sensor under intake
runner #3. (The single connector sensor under runner #2 is for the dashboard temp