Fuel pump relay again - I give up!

[Clifford Pope]

I have been trying to sort out a long-standing but intermittent trouble, both here and at Brickboard, but no one it seems can suggest anything further to try.
About one in ten cold starts the engine is reluctant to fire. I have checked all the usual culprits, and recently replaced the relay with a new Volvo one. Nothing has made any difference, except that if I link fuses 4 to 6 so that the pump runs continuously, it fires immediately. Once started, the link can be removed and the car runs and restarts perfectly for about 2 weeks.
So my idea is to abandon all the fuel pump wiring and start again. New fused relay connected directly to the battery, feeding both fuel pumps. This to be triggered by a fused outlet operative when the ignition is on.
I know there is a safety feature in the present set-up which turns off the pumps if the engine stops, but I have known other, older cars with electric fuel pumps that did not even have a relay, such as my Series III Land-Rover, so it is clearly not a vital feature.
Also my main concern is to have a car that works reliably, and a safe non-working one in the garage is no use at all.
Has anybody any observations on this problem, or has anybody found another way of overcoming the inherent failings of the Volvo fuel pump circuitry?
Many thanks,
Cliff Pope

http://pic7.picturetrail.com/VOL188/...8/23744414.jpg

Cliff,
If you connected your proposed new relay and triggered it from the "start" position of the ignition switch but left the original relay in circuit it should fire up straight away and still have the cut off feature of the standard set-up once you release the key.

It rather sounds as if your fuel pump relay is having trouble getting a reliable ignition signal at cranking speeds, possibly due to a high resistance somwhere in the connection between the coil primary circuit and the relay.
Try running a jumper wire between the two points if you haven`t already.
Good luck,
Colin

[John Davies]

Just for a novice - I haven't had a fuel injected 240 before, so am only used to mechanical fuel pumps - where is this relay on a 1986 240 with 'mechanical' fuel injection? The haynes manual is silent on the matter. I have looked under the dash as suggested a few days ago but can't find it - although I have found a mysterious green relay under the leading edge of the passenger carpet.....! Is this it? I would like to smear some vaseline on the terminals as a precaution.

Thanks.

J Davies

[Clifford Pope]

Thanks Colin, I'll try the bypass wire. Can you point me to the connections I am looking for - which terminal on the relay, where should it go to - coil itself, the control module ?

I fear the trouble may not be fuel after all. This morning it wouldn't start for a while even running the pumps continuously during cranking. Then suddenly it fired. Ran perfectly after that.
Every theory I try works for a few weeks, then the problem recurs and it seems the 'solution' was just a coincidence.
Is this the sort of problem one of these mobile diognostic services would sort out, or am I forced to take it to a Volvo service agent and pay the earth?

http://pic7.picturetrail.com/VOL188/...8/23744414.jpg

Cliff,
Can`t help with specific connectors etc. on the 240 as I don`t have a wiring diagram.
My post was based on the assumption that you were dealing with only a fuel system fault, but now it seems as if you may have an
intermittent ignition failure.
This of course, will stop the fuel pumps running as the system thinks the engine is not turning over.
It might be an idea to have a look at the Brickboard 700/900 series FAQs section on ignition problems.

http://www.volvoclub.org.uk/faq/FAQSummary1.html

The EZK ignition system used on 740s is the same as yours.
Any diagnostic system won`t find a fault if it`s not happening at the time it is tested.
This is what makes finding intermittent faults so difficult.
By comparison a permanent refusal to start is relatively easy to trouble shoot and fix !

[Grizlyadams]

Sounds like the ECU has lost control of the fuel pump. Now unless you have a parts car, new ECU's are a lot, get it tested, there is a company that will repair this type of fault, carnt find the URL and cannot remember the company, I will have a look.

Griz

[Grizlyadams]

>Sounds like the ECU has lost control of the fuel pump. Now
>unless you have a parts car, new ECU's are a lot, get it
>tested, there is a company that will repair this type of
>fault, carnt find the URL and cannot remember the company, I
>will have a look.
>
>Griz

Found it, http://www.atpelectronics.demon.co.uk/ they will do an exchange or a rebuild on ECU's and there in the UK, not USA or Japan like everyother company I can find.

Griz

[cbyard]

A bit of a long shot here, but I once had to find a starting problem on a 340GLT which had similar symptoms to those described- turned out to be the carbon brush feeding the rotor arm in the distributor cap.

Fixed it for nowt by disembowelling an old "C" size battery and extracting the carbon anode.....

Chris

[Clifford Pope]

Thanks everyone.
Fingers crossed, I may have found the fault, or at least a fault.
The otherday the engine suddenly started pinking and the engine light came on. Diagnostics said 1-4-3 = knock sensor.
I had read that build up of dirt and corrosion round the bolt holding the knock sensor can cause problems, so I removed, cleaned and replaced and retorqued correctly, and reset the OBD. That solved that problem, and also surprisingly the engine seems to have recovered its old willingness to spring into life when starting up.
I cannot see the connection, unless perhaps it sometimes failed to reset the ignition timing to a fully retarded position appropriate for start-up.