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

Failing Distributor Shaft. [Andrew Smith] After noticing misfire and stumbling in my
110k 760, I discovered my distributor had mechanically failed: the shaft was worn and
allowed the rotor to wobble and miss contacts. A new distributor solved the problem.
Misfire Under Load: Ignition Power Stage. [Dick Riess] 1987
B230F has had a miss or hesitation under load for ages and I
have replaced or traded just about every possible item. This has
been one of the most tough to diagnose problems I have
encountered. Purchased a new power stage and plugged it in
(aftermarket) and this seems to have cured the problem. [Tip from
Matt] In my 740, this was accompanied by idle problems, misfiring, and a fluctuating
tachometer needle. Solved with a new power stage unit.
Stumble, Stall, Poor MPG: Bad Engine Ground Connection. [Tip from David
Hungerford] What appeared as fuel supply symptoms were not relieved by replacing
the filter, FPR, or both pumps (or by checking lines with vacuum pump/gauge). The
problem turned out to be a (very) loose FI ground connection. When reaching around
blindly to loosen the distributor mounting bolts (checking Hall's sensor connections),
my eyes happened to be looking at the intake when my arm brushed the ground strap
running from the intake to the firewall--the wires moved at the fuel rail mounting bolt,
which also serves as the main round connection for the injectors. It was loose enough
that the wires bounced around with engine vibrations. I just tightened it and all
stumbling/stalling/AND poor mpg went away. The main lesson here is to NOT skip
over the first instruction in all troubleshooting guides: First, check all connections for
tightness and evidence of corrosion. See also the section on maintaining engine and
chassis grounds.
Symptoms Related to Engine Sensors or ECU:
Engine Failure/No Start/Severe Stumbling: Bad ECU See the FAQ file for much
more information.
Common symptoms of a failing LH injection computer: