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

of the regulator vacuum line, there is a hole in the diaphragm and that is the source of
the fuel. Replace the regulator and change the oil and filter. This is a fairly common
problem.
The second source of fuel in the crankcase is an over-rich engine. First, if this is your
problem, your mileage will be terrible - on the order of 12 to 16 mpg. If so, it can be
EITHER leaking injector OR a clogged injector, or possibly a bad oxygen sensor.
Leaking injector can be checked by removing the injectors, leaving them connected to
the injector rail. Cycle the fuel pump several times with the starter, then wipe the
injector tips and observe for droplets forming. Also, have someone crank the engine
while you observe the injector spray patterns (CAUTION: RAW FUEL WILL BE
SPRAYED. BE SURE TO DISCONNECT THE SPARK AND OBSERVE SAFETY
PRECAUTIONS.) Look for spurts, squirts, etc - basically anything other than a nice
even cone-shaped spray. Poorly atomized fuel may not burn completely and result in
some fuel getting to the crankcase. Also look for a CLOGGED injector. A clogged
injector will make one cylinder run very lean, but the computer which looks at the
average will try to compensate by richening up ALL injectors and net result is engine
running very rich on 3 cylinders and lean on 1 cylinder. Don't forget to check the cold
start injector if installed - some engines have them, others do not depending on year
and type of injection system.
Other Running Problems:
Car Stalls Repeatedly on Startup: Fuel Pump Check Valve. [Inquiry:] I have a
1985 740 GLE and every morning when I start my car it will stall approx. 3 times
before leaving the driveway. After this it works fine, and if I park the car and then come
back a while later it starts right up and is fine. It just seems to have a problem when
it’s been sitting a while, i.e. overnight and getting to/leaving for work. It has new Bosch
platinum plugs as well as new ignition wires. And this problem occurs regardless of
the temperature both summer and winter in upstate NY. [Response: Steve Seekins]
This sounds like a classic fuel pump check valve problem. The check valve is there to
prevent the fuel from draining back to the tank when shut off. In the AM, try ticking the
starter just enough to make the fuel pump run for a second or so - but not enough to
start the car. Do this 3 times, then start the car. If it starts and runs normally without
stalling, replace the check valve located back at the fuel pump. Other things to check -
make sure that throttle body is clean, check injector seals, wiring harness, etc. Clean,
replace, repair as needed. Consider running a can of BG44K through the fuel system
to clean it -particularly if this car has not had regular maintenance of the fuel system.