Engine over-revving in neutral

JPS29

Hi.

Wonder if anyone can offer suggestions.

I have a citroen c25 tilt and slide recovery truck. Its a 1994 Lreg with a 2.5 turbo diesel engine.

It has been acting strange sometimes such as when stopped at lights etc. The engine will start overreving, prob about 2500 3000 revs? This isnt at each set of lights, or even every time it goes into neutral just now and then.

Any one think of possible problems?

Cheers

iceblue24

sounds like the idle speed contol valve needs adjusting. no idea where it is exactly on the citroen, but it is usually around the throttle body i.e where the air intake pipe goes into the engine

mikey72

1994 2.5 diesel?
All it has is a mechanical fuel pump, and a cold start thermostat.
Check the cables are slack when it's warm, (on the fuel pump), beyond that it's down to the pump over fuelling, or maybe the injectors.

JPS29

mikey72 wrote: »

1994 2.5 diesel?

Yes defnitely a 2.5 diesel. It may have been changed in its life as on the wing is a badge saying 1400. Either this was the model or an old petrol version (although would be underpowered for a van ?) could just be down to the wing being changed though also, didnt get any history over a year prior to me buying it.

I had thought about the idle valve but would have thought that if it was this it would high rev constantly.

optimus_primera

First things i would check are fuel filter (including any inline ones that may be fitted) then check airfilter for condition,and the air filter housing and associated hoses.
Its amazing what an air leak can cause.

mikey72

An old diesel doesn't have anything complicated.
It's purely a mechanical pump, the more you push the throttle down, the more diesel goes in. No air valves, no problems with air leaks, it just squirts fuel into the cylinder then burns it.
The way to speed up the engine is to put more fuel in, so it's either the pump, or maybe the injectors opening and letting fuel pass.
The only other way to speed it up is to burn engine oil instead, is the oil ok, or are you losing any?

JPS29

mikey72 wrote: »

The only other way to speed it up is to burn engine oil instead, is the oil ok, or are you losing any?

There is a drip of oil coming from a leak somewhere, I had put the oil usage down to this as its not that much tbh and there is always a patch underneath when i run it

optimus_primera

When have a 4 cylinder perkins not playing ball,you have checked the entire fuel system from the tank to the injector,found nothing wrong with any of it,pulled your hair out ... only to find a problem in the air system,then you learn not to rule anything out .....lol

And i'm talking basic perkins on a rd tow genset .......

mikey72

The only way to speed up a diesel is to burn more fuel. If you aren't losing oil, it's not a leak through the turbo, valves, or rings. These engines just suck in as much air as they want, my 1.9 has no air control at all, it's just the throttle cable to the pump, and a cold start thermostat that pulls the throttle a bit to increase the speed until it warms up.
Check all the cables running to the pump, and check they're slack enough, not catching anywhere, and keep an eye on the oil.
Beyond that, they're basic, and run forever.

JPS29

Thanks chaps, looks like I've got a good few pointers to investigate. Thanks again