and win a PS3!!!*

Recently I got a free volvo 740 (2.0 injection), it's got a fuel/ignition problem that I'm trying to figure out. After being left for a few hours it tends to start after a few cranks, when it runs it always does so for about 30 seconds pretty much bang on (not timed it though) then it dies and won't restart until left for a few hours/overnight.

I've had the fuel line off between the pump and the inlet manifold and sometimes there's fuel and sometimes there isn't (when there is it starts) So when there's fuel, there is for about 30 seconds, what could be causing this?

Is the pump controlled by something and this has become faulty? Does the ignition module have anything to do with this? Pump on the way out? (weird that it always works for the same amount of time though)








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I am not up on my volvos but would think the fuel pump is driven by the ecu via a relay. The ecu will be an earth.

Find the relay and work out the earth with a multimeter.

Run a switch to the dash and job done

or it could be a duff relay, or a duff fuel pump but by manualy switching the relay you will find this.

[Edited on 22/8/10 by big_wasa]

sounds just like a problem i had. Had ecu changed and only 1 key mapped to it. Key not mapped would start engine and it would run for 5 seconds.

Another idea would be blocked fuel filter, when left 30 seconds fuel drips through, start and its used.

Similar problem on an MGF once

When turning the ignition key the fuel pump would prime for different lengths of time ie sometimes for as long as it should and sometimes just a quick squirt

After a fair bit of diagnosis it turned out to be the ECU which had an intermittant fault

Probably is the ECU, but I would take a look at the pressure regulator on the fuel rail before spending any dosh. They are vacuum controlled and perished/damaged rubber will give similar results.

Last time I came upon a similar problem on a Volvo (740 2.0 IIRC) it turned out to be the ignition leads and a relay on the inner wing. Between them they put 30 (YES 30) fault codes on the ECU. The HT leads checked out fine with all the HT lead checks. It took a fully qualified auto electrician the best part of a week to find the causes.

Maybe to see if it is a relay you could run the fuel pump directly from a battery? If it keeps running then a relay at fault, if it stops then the pump?

I seem to remember a very similar problem from my days fixing stuff, there was a relay that had a bad earth track on it that caused it.. the relay was in the centre of the dash behind the radio area if memory serves me right...

Seen this on 1990s Rovers -- oil pressure switch holds on the fuel pump relay. On those cars the oil pressure switch operated in the opposite mode from most switches n.c instead of n.o ie it provide an earth path when the engine was running.

The other possibility is the imobiliser or main relay circuit board.

If non electrical I would suspect a block fuel pump inlet due to floating paint flake debris in the tank.

[Edited on 22/8/10 by britishtrident]

740's used to suffer from fuel pump relay faults quite badly. As already said te relay is behind the centre console/radio. Take the relay out and check all the soldered joints, one may be 'dry' meaning it's not making a good contact. They usually have a very small crack around the solder, just resolder and bobs your grandad.

Thanks for the ideas everyone, lots to be getting on with! ^_^

I'd go for fuel pump relay and fuse, in the centre console. This was the most common cause of breakdowns on 740's

if it is bang on 30 seconds each time, then sounds like microprocessor involved - i.e. ecu or alarm system.

try the fuel pump relay thing as that sounds like a cheaper option.
can you get the codes of the diagnistic unit?

I have 850 manual that tells ya how to do this - may not apply to yours but then there is google.

Right so far I've bypassed the fuel pump relay and even with pump definately working it's still not wanting to start. I started to drain the tank as the petrol is old and I filled up a 10 litre can, then started on another can and it started to splutter, there's more than enough fuel in the tank so maybe there's a blockage. The petrol is coming out like the colour of a very dehydrated person's pee :/

The old fuel can't be helping diagnose things (the car had starting problems before it was put into storage) so I'll drain the tank, fit a new filter and put new some fresh petrol in first.

not a blocked vent? try running it with the fuel cap off?

quote:

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Originally posted by dan__wright
not a blocked vent? try running it with the fuel cap off?

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yep, as your removing something from the tank (fuel) and you need to replace it with something (usual air coming in via a vent) if you don't you start to get a negative pressure in the tank and you cant suck any more out of it. given time the pressure could slowly suck some air in through the vent until its balanced but it cant suck it in fast enough to run.

try running it with the cap open and it might run fine.

[Edited on 23/8/10 by dan__wright]

Just tried without the fuel cap on and it's not starting, but by the looks of the petrol and the age of it (last tax disk is from 5 years ago) I'm guessing that this fuel isn't helping

The previous owners took the car off the road as it would die randomly, they called out the AA once and when they turned up 30 mins later it started and drove fine, hopefully that was due to the pressure equalising in the tank. I'm off for some fresh petrol!

[Edited on 23/8/10 by Benzine]

Just fitted a new fuel filter, put new contacts on the fuel pump and put some fresh fuel in. Started first time (yay i thought) but then died after about 10 seconds Still, that's some things ruled out...

Fuel pump works
Fuel filter is good
Injector pressure?
HT leads should be ok otherwise it wouldn't be firing
Same with spark plugs
Tank's vented ok?
Aside from this all I can think of is some sort of ecu problem.

Does it just cut out or sputter and stop?

It just cuts out like someone has turned the key, so looks like electrical. After a load of reading around the things I'm going to look at next: ignition module, crank sensor, coil.

Ignition module!

Coil's part of the spark system isn't it? Crank sensor shouldn't cause cutting out, at worst it should run like a bag of spanners because the ecu doesn't know where the crank is...

New ignition module sorted it New from Volvo £160


or £37 from Intermotor

Sweet, so in all you've got a Volvo for about £50

You might want to sell it to that guy on the other thread who wants a mule

Do I get the PS3?

Yes, but i'll buy you one in 10 years time when they're worth naff all It'll save me lots of cash and you'll get your PS3, it's win win!

[Edited on 25/8/10 by Benzine]