Fuel pump mystery

[bimotablue]

Hi,

My sons 1996 940 estate has been with our local garage for 6 months as they try to work out a fueling issue, running lean.
They skimmed the heads approx 8 months ago after checking why it was losing coolant. Ran fine then lumpy then stopped...
As it stands they have tried many options, cleaned injectors etc etc and have discovered when the fuel line is clamped, increasing the pressure, the car runs fine. However they are sure the pump is operating at the correct pressure, which they say is 5bar. Is this correct? They estimate by clamping it increases to 7bar. My main questions are:
1) is 5bar the correct pressure for a 940 fuel pump? (if not a new pump is worth a try?)
2) any "start with" suggestions, as I am bring it back home to have a go...

Many thanks in advance

Alan

[TonyS9]

It should be running 3bar roughly, but it should run ok with 5, maybe a little rough on idle (I have an adjustable FPR).

If your mechanic has not solved in 6 months I think its time to try someone else.

What is the actual symptom, and how do you know it is running lean, or is this something the mechanic has said?

I'd also say skimming the head is not a normal response to lean running, really I cannot imagine any problem where the engine runs but leaks air on the intake stroke. Either they are taking the p1ss or they are absolutely useless.

[bimotablue]

Head skim was for the loss of coolant I believe
Yea, it has dragged on a bit... They seem to be a good outfit but are stumped with this one.

[Jebus]

If they have had it 6 month and go no were you need to send it somewhere else, should be 3 bar at the rail, so 5 and 7 is far to much.

You are going to have to start from 0 and go from there, 6 months on a modern can-bus car...maybe there are lots of things to go wrong but on a 940 it just isn't that complicated.

[TonyS9]

You didn't say there was a loss of coolant, what has this got to do with 'lean running'?

Anyway lets start with the problem you are/were experiencing. 'Lean running' is not something the user experiences, its a partial diagnosis.

What does the car not do that it should do?

'Lumpy idle' is about all I can find, and that could be from an air leak. Presumably they couldn't find said air leak and have decided its fuel related. If they have increased the fuel pressure, increasing the fueling and balancing out the leak, it is more evidence that there is an air leak. Sounds like they just didn't look hard enough.

In my mind, I'd be suspecting anything past the idle valve, throttle body gasket, inlet gasket.

[Laird Scooby]

I'm with Tony on this one, it sounds very much like an air leak. Something very common is the large bore air hose between the throttle body and MAF develops pinholes or splits, or going on everything else you've said about this garage, they just haven't tightened the Jubilee clips properly on each end!

It does make a difference!

PS - Tony, second line of first post "They skimmed the heads approx 8 months ago after checking why it was losing coolant."

[TonyS9]

I see it now, it just seemed like the mechanics thought this was relevant. Its like saying the tyres where changed because they were worn. Difficult to see the wood for the trees.