2.5TD high reving.

Hi Guys,

after replacing a head after a over heat blow my head gasket, I have had running issues.

The 90 starts well although splutters when just started. When he has warmed up he runs fine, however when warming up (and not every time) the engine will run at high rpm for a few seconds, this is combined with a loud "pinking" sound from the engine. It seems more prone to doing this when it has sat idling for a while.

I have also noticed that the fuel cap is almost blown out of my hand when removing due to a pressure build up in the tank.

After the cylinderhead replacement the 90 was sat for 1yr, started occationally but not driven.

Any ideas guys??

Hi Guy's any ideas this is very bizarre!

Sounds like a pressurisation problem to me. Have you checked the vent pipes on the fueltank??

Hi Redhand,

no not checked the vent, do you know where this is on a 90? Would the pressurisation cause the sudden high reving with knocking?

I remember seeing a thread on something like this and it caused high reving.... try a search. Also check your filler cap.... Busterbus helpful tips shows how to clean it. I believe the cap has to breathe

thanks mr jc, what is busterbus? any idea what the thread was called?

Is the filler cap the only vent for the fuel tank?

In addition, would we expect the tank to draw vacuum (as fuel is used)? i'm not sure how so much pressure could build up.

Hi,

Fuel pressurisation in a 2.5TD can be caused by the little rubber diaphragm in the fuel pump rupturing. It is found where the pipe runs from the turbo round to the fuel pump.

This pipe carrys turbo boost pressure to the fuel pump and increases fuel flow when the turbo boost increases but when the diaphragm ruptures this pressure is passed along the fuel return pipe to the fuel tank.

Other symptoms include engine cutting out, spluttering when warm and you put your foot down to go uphill for instance, feeling of lack of power when accelerating.

If it runs at high revs momentarily then this could be the problem, engine thinks the boost pressure has risen and feeds more fuel so higher revs because diaphragm is knackered.

About £15 (?) for the kit to fix it. Experts can do the job with the fuel pump in place lesser mortals tend to remove it first.

Regards borntobemild

Chunky Engineer said:

thanks mr jc, what is busterbus? any idea what the thread was called?

Is the filler cap the only vent for the fuel tank?

In addition, would we expect the tank to draw vacuum (as fuel is used)? i'm not sure how so much pressure could build up.

Click to expand...

Bustersbus is one of the guys on here. He does lots of repairs etc, talks us through it and takes pics to help us out. Click on 'forum' on the top left and scroll down and you will see his pages.
I am sure you will get the answer on here... the 'search' window at the top is a good one as more than likely most problems has been discussed.

Thanks borntobemild. By fuel pump do you mean injector pump (not lift pump)?

Yep, I mean the injection pump not the lift pump. Follow the thin pipe that comes from the top of the turbo round across the front of the engine and down to the left hand side (from the front) and it goes into the fuel injection pump on the engine side. Under that little cover is the rubber diaphragm.