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

If You Have a Turbo: Boost Overpressure Switch Failure (if so equipped). See the
FAQ file.
Intermittent No Start: Fuse Contact Failure. [Tip from Roman Shestakov] I had a
situation when my 1990 740 GLE just would not start. Engine turns, lights come on the
dash, but does not start at all. No pre-charge noise from the fuel pump could be heard
before turning the engine. After pulling out the relay tray to inspect the fuel injection
relay, I found instead that fuse #1 that supplies power to ECU and fuel pump was
making bad contact with connector in fuse box. Plastic around that fuse was melted
and looked brown. You immediately could tell that there was an excessive heat
around that fuse. Repairing it was easy. After pulling the fuse/relay assembly box out
of console, remove all fuses. Take a flat screw driver and pop the fuse box upper
cover out by prying on its sides (there are already slots available for that kind of tool),
exposing fuse contacts. Examine the fuse contacts. Mine were all oxidized and looked
very brown (heat caused copper to oxidize and made contact surface even less
conductive over time) causing current to heat up the contacts. Take a small piece of
sand paper (spread contacts apart with screw driver if necessary) and clean contacts
inside surface from deposits until it turns copper-red like other contacts next to it. In
my case, I had to scrape them with a knife as well. Then straighten contacts carefully
so that they are parallel to each other and "lean" against each other as tight as
possible, similar to undamaged fuses. Your fuel injection fuse is rated at 25A and must
go in tight, or you will be facing the same problem again. Then pop the top cover back
on and reinstall all fuses. Re-install everything back into console except the fuse cover
box. Test drive the car for 5-10 minutes, and while you are driving, put a finger on fuse
#1 and the plastic upper plate around it. It must be cool to touch.
Intermittent No Start: Water Leaking Onto Distributor.
Leaking Washer Fluid Line. [Tip] My 940 suffered from intermittent no starts until I
discovered that the windshield washer fluid anti-check valve on the firewall was
leaking and squirting water onto the distributor cap. A new valve, cap and rotor solved
the problem.
Rain Leaking Past Failing Firewall-Hood Gasket. [Tip: Georege Pigg] My 93 940 went
through a period of time where it would randomly fail to start. On one occasion the
engine even quit as I was making a right turn. Looking back over all of the "no starts" I
discovered that all of the events occurred during rainy weather. Further investigation
revealed that the weather stripping seal between the rear of the hood (engine lid) and