Rough running discovery

[Black VXR]

My 1998 TDi 300 Disco runs great at speed but slower, under a bit of load, it misses (best described as dieseling). It has just clicked over 100k miles and other than this fault starts and runs well.

I have tried the 'add to' fuel cleaners (even the fill up a new fuel filter with the stuff trick, and let it run on it neat)

Any ideas really appreciated

[camel_landy]

I'd go around & check the 'usual suspects'...

• Timing
• Valve clearances
• Air & fuel filter
• EGR
• Hose delamination & condition of hoses.
• When did it last have the timing belt changed?
• Fuel pump boost compensation mechanism.

M

[Black VXR]

Whats the fuel pump boost compensation bit mean please? I did wonder if the lift pump was getting a bit tired, its been taking a while to catch when cranked from cold and I guess 1500 to 2000 revs is when the fuel pump is maxed out and before the fuel is pulled through. I was told to leave it for 10 mins after switching off and to see if the fuel filter is still full, it is...

[budrover]

dont the 200 / 300 tdi like a new head gasket around 100k miles ...may be blowing between cylinders

[camel_landy]

As the fuel injector pump is mechanical, it needs to have a mechanism which will increase the amount of fuel being delivered relative to the turbo boost. On these pumps, there is a pipe, coming from the turbo, which feeds into a cover at the top of the pump. Under the cover, there is a diaphragm, which when under pressure, pushes on a mechanism that increases the amount of fuel being delivered to teach injector.

This mechanism can sometimes seize up!

The simple test is to undo the 4x screw that hold the cover on, pop the cover off, push on the nut on the diaphragm and see if it pops up & down freely (there is a spring underneath). If it is moving freely, everything should be OK... If not, it is not too difficult freeing up but it does take a bit of typing!

Have a look and report back.

M

[Black VXR]

Thanks, I will check this out and report back

[Black VXR]

Just took this apart and its all is moving fine and in good clean order

Any other ideas please?

[Black VXR]

Fixed it, it was a faulty lift pump. Its running fine now

[camel_landy]

Nice one...

M