Uneven revs

[Dollywobbler]

When I got my TXD, I thought it was behaving a bit oddly, with the throttle sometimes reluctant to close fully. Goodbye engine braking!

It's getting worse though and when re-starting after at least 10 minutes being parked up, the revs will suddenly raise to 2000rpm before slowing settling down to just over 1000rpm. When warm, the revs seem too high all the time. I'd expect just below 1000rpm, not just above.

Not sure what to do. The throttle lever is physically shutting correctly. I did disconnect what I thought was the throttle damper at one stage but this made absolutely no difference at all.

[Defender110]

What pump?

[Dollywobbler]

Good question! Bear with me. Mr Fenwick thought Lucas but I've not yet double-checked that.

[Dollywobbler]

Here it is.


Can't find anything that says one way or the other. Certainly not that much like the Bosch one on the Green Tiger, but then this is a turbo with a very different fuel supply system (filter in the 'stat housing).

[citronut]

thats a Lucas pump Ian,

regards malcolm

[Dollywobbler]

Thanks. Any thoughts on why it's playing up?

[mat_fenwick]

There's no throttle in a diesel, so it must be extra fuel getting in somehow. But how I don't know! Not very familiar with the Lucas pump, but is there a cable leading to the thermostat housing?. I can't remember if there is a cold start enrichment (waxstat) or not. Even if there is I can't see this being solely responsible for raising the revs that much.

[Dollywobbler]

There is, but there's plenty of slack in it when it's doing this. Not sure the waxstat is working. I'll have to check the cable tension when cold. Could be that someone has just upped the tickover to compensate for cold starts hence why it seems a bit high all of the time. Doesn't explain teh high revving though. I really don't like that!

It really is very time sensitive. 10 minutes is about right. Shorter or longer than that before restarting and it's fine.

[barry badger]

It might be drawing air in from the throttle spindle. Pump the primer bulb several times and see if any fuel weeps out of the spindle.

[Dollywobbler]

Nope. No weeping. It must be getting extra fuel for the revs to rise to 2000rpm. Like I say though, it only does it when left for approx. 10 minutes.

[Defender110]

Not sure this will be the problem but your throttle cable looks very tight, there is usually a little free tension and I can't quite make out from the picture if the throttle arm is actually hitting the throttle stop screw or relying on cable tension?

[Dollywobbler]

It is hitting the stop. No time now as it's packing-for-the-show time, but I shall explore further next week.

[thorter]

Check for a small air leak somewhere along the fuel feed all the way from the tank. As the pipe operates in "suck" mode, there may be no leakage visible. Disconnect at the pump, and then check for any sign of a leak, and perhaps pressurise by blowing.

With the Lucas pump, there is quite a volume after the fuel metering. If air is getting in, it expands when the high pressure piston sucks in the next shot, causing over fuelling. Not a good design feature!

Fred

[Dollywobbler]

An air leak is a possibility. The primer bulb doesn't go as hard as I'd expect.

[Brian]

Replace the rubber feed tube from the filter to the pump with clear tube.
Pump the bleed bulb to remove air in the clear tube before connecting the end to the pump.
Run the engine and look for any air bubbles in the clear tube.

I had a Lucas pump on my Visa RD that produced those symptoms, Lifted the top cover of the pump, full on metal swarf...

Change it for a Bosch pump pipes and injectors, that fixed it..

Hope it's an air leak, good luck.