300TDi flatspot at 3100rpm

[Tank]

My son's 94 Disco 300TDi Auto loses power at 3100 rpm, revs out OK through the gears till 3rd (top) and 4th (o/d) when this loss of power occurs at 3100rpm, like a flat spot.
At 3100 rpm, where the power drops off, if you lift totally off the throttle and straight away reapply the throttle the flat spot disappears.
Any help solving this problem or a diagnosis would be much appreciated, Regards Frank.

[rovercare]

First step would be basics, fuel filter etc, blockages air/fuel, purge the lines, then hope to god, that fixes it:D

[JohnM]

Intercooler hoses???? Sounds like the 90 degree bend near the turbo is possibly delaminating blocking the inlet, then once you back off its okay until it gets sucked back up again. Worth a check at least.

[camel_landy]

Yeah... I'd also suggest going back to basics.

Check the air hoses, etc... clean the EGR (if fitted) and generally start by looking for anything obvious.

M

[BigJon]

Fuel lift pump?

[Tank]

Thank You All for your helpful advise, I will post the results when we fix it, Regards Frank.

[Tank]

Reporting back on fix for flatspot at 3100 rpm, wasn't the lift pump or crap in the filter, even though there was some crap in the sediment bowl near the tank, anyway cleaned that and fitted new fuel filter, tested lift pump, no problems, vacuum tested fuel lines, no leaks.
Turned out to be a tear in the Turbo Compensator diaphragm on the injector pump. Patched the hole with some rubber cement and silicon, let set overnight, refitted and flat spot gone, goes like a rocket now, now waiting for new diaphragm to arrive, Thanks again for all your advice, Regards Frank.

[rick130]

Thanks Tank, who'd have guessed that one !

[camel_landy]

Reporting back on fix for flatspot at 3100 rpm, wasn't the lift pump or crap in the filter, even though there was some crap in the sediment bowl near the tank, anyway cleaned that and fitted new fuel filter, tested lift pump, no problems, vacuum tested fuel lines, no leaks.
Turned out to be a tear in the Turbo Compensator diaphragm on the injector pump. Patched the hole with some rubber cement and silicon, let set overnight, refitted and flat spot gone, goes like a rocket now, now waiting for new diaphragm to arrive, Thanks again for all your advice, Regards Frank.

Splendid...

Not sure how that caused a flat 'spot' as I would have just expected it to top out at whatever engine speed (which is what happened to a 300TDi I saw here which had a perforated diaphragm).

Thanks for getting back with the solution. ;)

M

[Tank]

Splendid...

Not sure how that caused a flat 'spot' as I would have just expected it to top out at whatever engine speed (which is what happened to a 300TDi I saw here which had a perforated diaphragm).

Thanks for getting back with the solution. ;)

M
I would say that because the fuel rod that is controlled by the diaphragm would only be allowing a set amount of fuel through, when it reached 3100rpm there was not enough fuel to rev higher, as a working diaphragm is pushed down by boost from the turbo the fuel rod moves backward, increasing fuel supply, if it doesn't move the rod will be in it's furthest ahead position and supplying that amount of fuel which was not enough to rev past 3100rpm, hope this helps, Regards Frank.

[camel_landy]

I would say that because the fuel rod that is controlled by the diaphragm would only be allowing a set amount of fuel through, when it reached 3100rpm there was not enough fuel to rev higher, as a working diaphragm is pushed down by boost from the turbo the fuel rod moves backward, increasing fuel supply, if it doesn't move the rod will be in it's furthest ahead position and supplying that amount of fuel which was not enough to rev past 3100rpm, hope this helps, Regards Frank.

Hi Frank,

Yeah, I'm very familiar with the workings of the Bosch pump which is why I was curious...

You originally said that the flat spot disappeared if you lifted the throttle & then reapplied. With the tear in the diaphragm, when you re-applied the throttle, I would expect to see it flat spot at exactly the same place again.

Anyway, I think it's one to tuck away in the back of the mind in case I see it again. (I suspect that as these vehicles get older, we're going to see more & more fueling issues like this.)

M

[Tank]

Hi Frank,

Yeah, I'm very familiar with the workings of the Bosch pump which is why I was curious...

You originally said that the flat spot disappeared if you lifted the throttle & then reapplied. With the tear in the diaphragm, when you re-applied the throttle, I would expect to see it flat spot at exactly the same place again.

Anyway, I think it's one to tuck away in the back of the mind in case I see it again. (I suspect that as these vehicles get older, we're going to see more & more fueling issues like this.)

M
M, I was quoting my son's description at the time, I never drove it, so maybe it wasn't just a flat spot, Regards Frank.

[camel_landy]

Ahhh... OK.

BTW - When you re-assemble, you might want to give everything a smear of grease as it has now been exposed to the 'moist' air. Over here, it's common for the pin to seize completely as we add a nice mix of salt during winter too!! :(

M