[Boots]

Bit of a saga this one folks!

Car as decribed below 940, D24T, otherwise in rude health!

I hope someone can shed some light on my issues as this diesel newbie's about out of ideas...

The car's not driveable due to the problems now so I'd appreciate any advice - it's my transport to work!

Since I got the car about 10 months ago, it has run short of fuel when run at full throttle for long periods eg. overtaking. Power drops off for a second then comes back. It only did this if you used the last 5% of throttle though. Below that it was running fine.

About a week ago, it took longer than usual to fire in the morning, about 30 seconds cranking. Normally it kicks off 2nd or 3rd cylinder to see compression. I didn't think much more of it and later that day it started normally.

Over the course of the next couple of days, this delay in firing got steadily worse till it was taking a minute or so of cranking before it got any fuel.

This car has a piece of clear fuel line between the filter and the pump and on inspection, indeed you could see the fuel draining back the moment you stopped the motor.

Anybody tell me what's supposed to stop this happpening?

I looked at the bosch diagram for the pump and figured the pressure regulating valve may well double up as the non-return function. (My first mistake?) Popped it out and the lower o-ring looked pretty tired and deformed. I thought maybe this had been partially leaking for a while causing the pump to lose internal pressure at high revs and now, having lost the will to seal completely, may be allowing the fuel to drain back down at switch off.

Note: apart from the starting issue, the car was still driving ok at this point.

I had an o-ring kit at work and replaced the one on the bottom of the p-r valve with a new one. I didn't have the exact size, it was a tiny bit thinner in section than the original but at least it was round and springy not egg-shaped and stiff.

Well, it drove home fine, still with the fuel starvation at full throttle but otherwise ok. The next morning, loads of cranking to get going again and then the real issues started! Lost power gradually over a mile or so then stalled completely at a junction. Popped hood after cranking for several minutes - loads of air in fuel feed to pump. Waited a few minutes, cranked it some more and it fired up. Lumpy as hell but I was late for work and as long as I kept it above 2500rpm it would run! Got to work just.

After work, fired it up and watched the fuel line. Lots of bubbles, seemed more if you revved high. Running lumpy as hell but kept this up for 5 mins or so to see if the air would clear. Nope. Still loads of bubbles. Took filter off and inspected seals and housing - all fine. (Filter was new 4 mths ago.)

Borrowed works van to go home in! Next evening, popped flow and return off the fuel tank, stopped off return and slowly put up to 1 bar on flow line - no leaks anywhere. Lines, filter and pump good to 1 bar. wtf?

After much scratching of head, decided the smaller o-ring must be causing real trouble.

Anyone know what the pump would do if the pressure regulating valve had flow from one side to the other all the time due to too small an o-ring? I thought maybe this had caused the high pressure side to try and draw fuel in through the return line and when that ran out of fuel, draw in air?

Anyhow, I got an o-ring the right size today and fitted that. Now it starts after much cranking but runs really weird. Mainly all it will do is a sort of intermittent fire - brrmp, rest, brrmp, rest and so on. Whilst it is doing this there is no real response to any throttle position. If you crank it with the throttle full down and catch it unawares, it fires right up, all 6 and from 2500 upwards it behaves properly. No missing. Turbo kicks in etc. The moment you let it down towards idle it goes back to the intermittent fire crap and won't listen to the throttle until you turn it off and start again! No air in the fuel line now though until you turn it off and then about 5 inches of froth come back down the line from the pump.

Have I actually fixed it and I'm just being a diesel virgin i.e. need to bleed the pump properly or is it proper broken?

Sorry this was so long-winded but I thought the more info I put down the better chance of sorting the problem.

Hoping someone can advise, Boots.