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Uneven slow running. 2.5 D


Paddy
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1991 2.5 D na. 90000 km, runs and pulls well  (for a 2.5 nad)

At minimum speed, on a very light throttle, on the point between overrun and slight acceleration the engine surges slightly then drops back then surges etc.  As though it can’t make its mind up which it should do !!     Started about 6 months ago and a service of tank, sedimentor, fuel filter, Wynns injector cleaner, slight alteration to tick over has made no difference.  Any suggestions before I think about expensive replacement parts?

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Eric, maybe but I thought it would have more of an effect at higher speed or under load, which doesn’t happen.  If someone had the same problem and cured it with a new pump I’d give it a go.

Ralph,  the throttle, cable, linkage all free and smooth.  The problem  “hesitation and surge” happens more often on a static throttle, at low speed just above tickover.  The best description is the engine can’t make its mind up if it should be just on overrun or just on acceleration on a static throttle, so it alternates between the two until I accelerate slightly, then it picks up smoothly.  It’s subtle and is more of an annoyance than a problem.

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Sounds like you have checked the easy (cheap) stuff, could it be a well worn/slack cambelt? if that is ok then It's maybe pump rebuild time.

A lot of the old tractors and lorries used to do that slight surging at tickover and it was said the engine was "hunting" it was always put down to worn injection pump.

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I was thinking pump/injectors too when I read your post, is it smokey? Although I remember my old car years ago (mondeo with the Ford 1.8TD engine) behaved like you have described at tick over and got worse and worse quickly - it turned out to be the cylinder head gasket. If you have access to getting a compression test done and the coolant checked for exhaust gasses then that might be an easy and cheap way to rule a head gasket out before you get the pump/injectors inspected.

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Thanks for the input guys.

Kev, cheap stuff first is right !!  Tick over when stationary is steady but it is like ‘hunting’ when at that point of over run bordering on slight acceleration. Cambelt is 2 years old and low mileage,  I might have to up the ante..

Monkie.  Not smokey at all and the problems been like it for 6 months without getting worse.  I’ve no reason to suspect head gasket but I will get a compression test.  But I’m starting to think injector/pump too.

Pat.  I haven’t noticed the hiccup but will try to induce it tomorrow.  I adjusted the throttle after having the problem for a few months.  In ignorance I did adjust the stop/anti stall so I’ll reverse this and use the idle adjuster (once I find it !)

I think the next step will be injector service and maybe pump service if that fails.  The problem is subtle and of hardly any consequence its hard to justify big expense but it can only get worse.

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Mine started surging momentarily on idle when i took the throttle offto change gear. turned out to be a frctured injector pipe causing air to get in. Of course when the fracture got worse later on it just sounded like it wasnealry going to stall, smooth enough with a bit of throttle though

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  • 3 weeks later...

Problem cured.. (but not solved !)

Injectors out, serviced, back in and all is well.  Service guys reckoned nothing wrong when testing them so just cleaned them up.  Maybe it was a speck of carbon, not 100% sealed (new washers fitted) or just one of those things.

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