Bleeding the 300Tdi Defender

First of all good morning everyone. I have a technical question I was hoping someone out there could help me with, as two garages seem flummoxed by it.
Three years ago I was servicing my 96 300 Tdi vehicle and found it difficult to start. Going through the fuel system I found a second new fuel filter instead of the MAN one I'd fitted first cured the problem. On the latest service the problem re-surfaced and so far three different fuel filters, a new lift pump and tank sending unit, and daily bleeding hasn't cured it.
The new lift pump works fine, and the filter bowl fills as it should. Locking off the bleed screw gives first class performance all day so long as the engine is running - no problems. Switching it off, however, and the fuel in the bowl seems to fall away from the bottom of the pick-up pipe so that it has to be bled again before starting. We've checked all the lines for cracks, can't find any and as the problem only occurs when its switched off this makes sense. The last garage started talking about a new injector pump - said it could be the boost compensator diaphragm pressurising the system somehow to force diesel back up the injector feed out of the filter bowl! Technically I can't get my head around this theory, especially as a new pump will cost a lot, and need fitting. If there's anyone who can explain this to me, or even have an alternative theory, I'd be eternally grateful.
Sorry to be so long-winded on my first post, and nice to be here.
regards
HG

have you changed just the filter or the filter housing? porus filter housing?

doubt its injector pump ,its worth fitting a clear plastic pipe between filter and front banjo bolt on injection pump ,you can see whats happening then,leaky leak off pipes can cause issues ,as can 2 orings on filter head, lift pumps are often poor ,if oneway valves dont completely seal,check system front to back air can be sucked in were fuel doesnt leak out ,

Thanks for those suggestions. I've seen your idea for a clear pipe to show bubbles before on here, and will be doing that tomorrow. My first thought was a crack in the line somewhere, so it might pay to replace them all anyway. Anything's better than forking out for a new pump which I see you have doubts about too. Just couldn't see that somehow. It really annoys me how garages (even Landrover Agencies) go in for pot-luck mechanics these days, just keep fitting new things until they strike lucky. Thanks again.
regards
HG

Lyndon said:

have you changed just the filter or the filter housing? porus filter housing?

Click to expand...

Hi,
Yes I bled the first one so often I wrecked the ali threads in the filter housing. Bought a second-hand one off ebay and tried that, then sealed up the bleed screw in the first with 'putty-metal' and re-fitted it suspecting the ebay one may have porosity problems. Am now using the spare 19mm outlet to bleed daily. By the way, a new filter housing price I was quoted was £79.00! And they didn't have one in stock - good job, or I might have been tempted.

bleed it by slackening front banjo bolt on injection pump

jamesmartin said:

bleed it by slackening front banjo bolt on injection pump

Click to expand...

I've done that, but after I fit the clear pipe I'll certainly do it again. Thanks.
regards
HG

Hi There,

I had the same problem, but it eventually got worse and started to cut out at junctions etc.

I checked all the lift pumps banjos, return pipes and ithought i had checked the fuel line.

My fuel line was plastic and it had been rubbing on a brake pipe on coming up from the bulhead to the engine before the lift pump. As a result of the rubbing created a very very small pin hole allowing the fuel to run back to the tank once stopped, as the hole got bigger then the starvation at junctions started. But at first it took several seconds on the starter motor before my 90 would start.

I replaced all the fuel line with rubber pipes, after spending on a new filter, lift pump etc etc.

Hope this helps.

Cheers

Andy.

AABeds said:

Hi There,

I had the same problem, but it eventually got worse and started to cut out at junctions etc.

I checked all the lift pumps banjos, return pipes and ithought i had checked the fuel line.

My fuel line was plastic and it had been rubbing on a brake pipe on coming up from the bulhead to the engine before the lift pump. As a result of the rubbing created a very very small pin hole allowing the fuel to run back to the tank once stopped, as the hole got bigger then the starvation at junctions started. But at first it took several seconds on the starter motor before my 90 would start.


I replaced all the fuel line with rubber pipes, after spending on a new filter, lift pump etc etc.

Hope this helps.

Cheers

Andy.

Click to expand...

Brilliant, thanks! It's got to be worth changing the fuel lines up to the injector pump. All I need now is a roll of pipe. Thanks again.
regards
HG