I am having a problem with my otherwise reliable 1988 Volvo 740. For
several years now when I turned the car in very cold weather the idle
would falter a little. If I touched the gas pedal it would be just
fine. Then I started noting several months ago that when I was driving
in the highway (~70mph) occasionally when passing or going up hills,
the RPM would completely drop and the car was coasting. If I let go of
the accelerator completely and step on it again, the car would
continue right away just fine.

Well, at long last one day I was driving in the highway and after
about 1 hour. The car lost power and coasted to a stop. I couldn’t
restart the car. And after being towed home, I noticed fuse #1 was
blown. So I replaced it, but the fuse blew again when I tried to move
the car. Spoiling my victory dance, I might add

I am in a new town, and my new mechanic didn’t want to look at the
fuel pump (small town). I took it to another guy who noticed that fuse
#1 will only be blown if the distributor was connected (he loosen the
wire harness from underneath the distributor and showed me). So he
replaced the distributor with a new one ($400 ouch!).

Unfortunately after driving the car home, the next day when going up a
hill near my house, fuse #1 blew again, and again, and again. So a
neighbor helped me move my car home, where it is parked now.

Following some advice on the internet about checking the fuel relay I
short-circuited to terminals, but fuse #1 simply blew right away. So
today I got under the car and unplugged the fuel pump, thinking that
the fuel pump was draining too much current. BUT when I cranked up the
engine with the fuel pump wires disconnected (from under the car). The
fuse just blew up again, and again.

I remembered reading on the internet that fuse#1 was also the fuse for
the air sensor (I am not sure of this). So I went and unplugged the
wire harness for the air sensor (because it is so easy right next to
the air filter). And no difference, fuse #1 blew up when cranking the
car.

What else might be fuse #1 protecting? Right at this moment I am
thinking that the wires from the fuel pump to the fuse box have a
short circuit somewhere, but I can’t tell. I cut my hand trying to
remove the plastic of the 2 wires that connect the fuel pump, but they
look ok (I didn’t remove the whole plastic). I am removing the front
seat to see if I can track the wires from the fuel pump to the fuse
box.
Any other ideas or suggestions? Anybody knows what else could fuse #1
protecting, or what could be making the short circuit? Thank you very
much for your help, I’d appreciate any insight or suggestions. Thank
you.

Darien

Darien wrote:


With the distributor disconnected the ignition system won't report
engine rotation to the ECU and the fuel pump won't be turned on. I
cannot imagine what the mechanic was thinking by replacing the
distributor, there is absolutely no way that a bad distributor can blow
the fuel pump fuse, there is just no connection, so first things first,
find a mechanic who actually has a clue, this guy is incompetent. Look
for someone who specializes in European cars.

Diagnosing this problem is really simple. Reach under the car and unplug
one of the wires from the fuel pump. Put in a new fuse and crank the
engine, if the fuse doesn't blow, the pump is probably bad. If it does
blow, unplug the fuel pump relay and try again. If that stops the fuse
from blowing, then there's probably a short in the wiring from the relay
to the pump, it comes up through a rubber bung above the pump and runs
along the edge under the carpet up to the relay in the dash.

James thank you very much for your help. I live in a 15k little town
in central Missouri, I couldn't find any mechanic that knows about
European cars, unfortunately.

I did unplug both wires in the pump from under the car and the fuse
keeps blowing with BOTH wires disconnected. Do you know if there is
anything else I should be looking for? Is fuse #1 protecting anything
else besides the fuel pump?

As you suggest, I will try replacing the wires going from the fuse/
relay to the pump, but it is a such a cramped space. I don't know how
to work there effectively. I wonder if there is some particular trick
I could use. Else I'll do what I can. Thank you very much for your
help.

Darien

Ah, yeah the West coast over here is swarming with Volvos, it's rare to
find a single residential street without at least a couple of them in
driveways, so specialists are a lot easier to find here. These cars are
very easy to work on in general, however they are different, and someone
who is not familiar with the difference can have a lot of trouble.

What year is this car again? There was a redesign of the 740 at some
point, '90 I think, I'm less familiar with those but on the earlier
700's the fuel pump relay is in the fuse box which resides behind the
ash tray under the radio. In those, if you pop off the little cover
around the cigar lighter there's a screw, take that out, and you can
pull out that whole pocket assembly under the radio. Once you've done
that, there's a pair of clips you press and the whole fuse/relay panel
lifts up and pulls out on an umbilical cord of sorts which gives you a
lot more room to work with.

Either way, when you find the relay, unplug it and see what happens. If
the fuse still blows, then something else is wrong, but I suspect the
culprit is something simple. I would carefully inspect the wires that
come from the pump where they go up through the rubber bung in the floor
pan and pull up the edge of the carpet to make sure they have not been
damaged there. Also, don't forget the pre-pump which is located in the
fuel tank and runs on the same circuit. You might have a short in the
wiring back in that area too, on the sedans you can get to the top of
the tank easily though a cover panel under the carpet in the trunk, I
don't recall where it is in a wagon though.

One other helpful trick that will save you some fuses. If you have an
old headlight bulb laying around, use some clip leads and wire the high
beam filament in place of the fuse then place the bulb somewhere where
it will not melt the carpet. If the bulb glows brightly there's still a
short, if it glows dimmer or not at all, the short has been cleared.

The 740 has a little primer pump in the tank which delivers fuel to the
main pump.If the in tank pump has gone the main pump works overtime and the
fuse melts in the holder or blows or both in my wifes 740 1988.The tank pump
needs to be replaced .This is most common when the tank is low on gas (very
common with women drivers to run the tank till its almost empty) .Mind you
if you keep the fuel at a sensible level you avoid getting condensation and
other issues in your fuel.


"James Sweet" <jamesrsweet (AT) gmail (DOT) com> wrote

Jon Robertson wrote:

I just had to deal with that this week on my brother's 760. The fuse
didn't blow, but the car did die. I found that the pre-pump had failed
and the bellows connecting it was split. Lots of fun laying in the trunk
removing the hoses and then maneuvering the pickup assembly out of the
bung hole and through the little access panel.

Jon Robertson <jon5707 (AT) optusnet (DOT) com.au> wrote
I usually run my (petrol) V40 until the tank is almost empty, and I am
not a woman.
Last night for instance, I travelled for miles after the fuel warning
light came on, then put 58 litres in (60l tank).
sensible level as far as I'm concerned.
I fill it to the brim, run it to almost empty then fill it to the brim
again, and think that doing it this way keeps the whole fuel system as
flushed as possible.
--
Roger Hunt

Roger Hunt wrote:

That's what I do as well, the pumps are fine as long as you keep fuel
flowing through them. They don't need to be submerged in fuel to stay
cool, the rotor which is where the heat is produced is submerged in fuel
whenever fuel is flowing through the pump.

They normally last in the ballpark of 200k, and by the time they're worn
out, the rubber bellows has usually split too.

Thanks everybody for the suggestions, I have had no time to look into
the wires more. But I'll try this weekend. My 740 Volvo is a 1988
Sedan. I will look at those wires. When I did remove the pump relay
the fuse did not blow. But it did blow at once when I replaced the
relay with a wire (to shortcircuit the relay). I'll try checking
continuity of the wires between the fuse box and the pump. I just need
to try to get good access to the cable which seemed hard last time I
tried. I will report back as soon as I get a chance. Again, thanks for
your suggestions.

Darien

Darien wrote:

As I recall, you have to remove the side trim strip under the door and
then you can pull up the carpet enough to get to where the wire goes
through the floor, or maybe I'm thinking of a 240, I don't recall, but
the 700 series pump is much further forward.

You can also unplug the pre-pump in the trunk. There's a three pin
connector behind the plastic cover over the fuel filler pipe under the
side of the trunk carpet, it goes to the pre-pump and the fuel level
sender. I'm guessing one of the wires has chafed somewhere and shorted
to the body of the car.