Hopefully someone can point me in the right direction here....
Got a 97 Disco 1 which runs great, recently had a new set of filters and oil, new lift pump. Yesterday for no reason it's developed a very weird fault - it starts and runs fine, but when trying to drive it and hold at a set speed on the flat or downhill, the engine revs will repeatedly completely drop off for 1-2 seconds before returning to normal revs again - you lose all power. if you try to maintain speed going up a hill and the engine is under more of a load, the fault doesn't occur, and if you floor it, the problem isn't there at all, neither is it there when just letting the engine tick over. No signs of oil or fuel leaks or anything unusual, happens with or without the MAF connected and air filter clear. Disco had been parked up for a couple of days without use before this happened. Its a pre EDC model, so no drive by wire causing the issues either....

Can anyone give any help at all?

bigi said:

Hopefully someone can point me in the right direction here....
Got a 97 Disco 1 which runs great, recently had a new set of filters and oil, new lift pump. Yesterday for no reason it's developed a very weird fault - it starts and runs fine, but when trying to drive it and hold at a set speed on the flat or downhill, the engine revs will repeatedly completely drop off for 1-2 seconds before returning to normal revs again - you lose all power. if you try to maintain speed going up a hill and the engine is under more of a load, the fault doesn't occur, and if you floor it, the problem isn't there at all, neither is it there when just letting the engine tick over. No signs of oil or fuel leaks or anything unusual, happens with or without the MAF connected and air filter clear. Disco had been parked up for a couple of days without use before this happened. Its a pre EDC model, so no drive by wire causing the issues either....

Can anyone give any help at all?

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You've certainly come to the right place for help, although the rules dictate that you introduce yourself before you start asking....you cant exactly walk into a bank and go asking for a loan just because you're broke without really telling anyone who you are.

You gotta understand that unlike a petrol engine which has an ignition system, complex fuel injection and control systems whose function or malfunction affect engine performance, almost all problems with the older all mechanical diesel engines have to do with the fuel system, and occassionaly with a blockage of some sort in the air intake system. Your best bet is to check if really there are no air leaks or restrictions in your fuel line or if any of your charge air hoses hasn't delaminated and restricting air supply to the engine.... All the best

ifloochies said:

You gotta understand that unlike a petrol engine which has an ignition system, complex fuel injection and control systems whose function or malfunction affect engine performance, almost all problems with the older all mechanical diesel engines have to do with the fuel system, and occasionally with a blockage of some sort in the air intake system. Your best bet is to check if really there are no air leaks or restrictions in your fuel line or if any of your charge air hoses hasn't delaminated and restricting air supply to the engine.... All the best

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Cheers for the replies - apologies for not following conventions - as you can see by the posting time it was getting a bit late after a long day....!

I've got experience of more "sensitive" diesel engines - my main car is a mondeo tdci(enuff said); the Landy is used as a weekend motor for 3 of us to mainly have some off road jaunts!

To fill in a few more details - the lr had just been in for some welding around the inner wings (battery tray/cruise control tray behind headlights), and the sills. It was ok before it went in there, but the garage is adamant that they haven't disturbed anything! they went through and found a completely destroyed air filter (at some point it had got soaked after one of us went to hill & ditch and through water deeper than meant to!) and in the hot, dry weather it had dried and the filter had come adrift from the foam surround - so that was pulled out and they cleaned the MAF, but claimed the problem was clearly that (although in my experience, if a MAF was at fault, disconnecting it would cause the problem to go away due to the ECU falling back to default stored values, surely?). Since digging around, it appears they also managed to catch the leak off pipe running to the fuel injection pump and there is a hole in that were some fuel has been leaking out - although i'm not convinced this would cause the symptoms being experienced? all the other hoses seem fine, the intercooler hoses seem to have been replaced not long ago..

seems my next steps would be to check the fuel tank pipes and the sedimentor perhaps....

I think I may have your answer and it's cheap to fix. I think you have a weak turbo hose which is collapsing in on itself when you have the engine up to speed then take your foot off the accelerator. This puts the hose under a vacuum and causes it to collapse, cutting off most of the air to the engine. Turning the engine off stops the vacuum and the hose pops back out to its normal size. The first hose on the turbo discharge is likely to be the culprit.