Re: Volvo 740
"kiromarc" <firstname.lastname@example.org> wrote in message
> My old 740 keeps cutting out, one moment it is fine, next nothing, the
> engine just stops in an instant, kinda dangerous when the PAS and PAB
> stop! Ive replaced the coil and HT leads, no change !!! Any ideas anyone
> out there?
If it truly stops in an instant, and the tach plummets like a stone, it is
almost certainly the ignition rather than the fuel.
Besides the Hall effect sensor in the distributor, I understand there is a
radio suppression relay in the ignition circuit that can become
intermittent. I've looked for mine a few times since Mike F mentioned they
can be trouble, and for the identical relay beside it that can be swapped
for troubleshooting, but I haven't actually seen them... or looked very
The "power stage" mounted to the fender above the battery is also a frequent
complaint, but most people report a more gradual loss of power rather than a
switch-off. If you get bored or ambitious or desperate you can unmount it,
clean under it and remount it with silicone grease (I like the dense white
"heat sink compound" electronic and computer stores carry). I don't know if
they ever actually fail completely, or just overheat and get tired of
Finally, it's worthwhile to clean up the battery terminals. If that separate
ring terminal on the positive post doesn't make good contact the engine will
cut out just as you describe. I scrape it every time I clean the posts.
You'll probably do the easy things and leave the more expensive Hall effect
sensor for last. The sensor is hard to pin down as the cause because they
typically fail on their own schedule. A replacement from a wrecking yard may
be an affordable alternative.