1981 3CX Engine Reving problem...

[Tecky Pete]

Hi guys, so i have the 1981 3CX with the Leyland engine, however i have been using it most of the day and suddenly it wouldn't rev and would only tick over.... so i turned it off and checked the throttle lever and apart from the small return spring had come off, i couldnt see any issue. so thought it maybe out of fuel.. So chucked 30 Litres in and fired it up which seemed to have fixed it.... for 5 minutes!

now back to not wanting to rev and coming off the accelerator actually made it stall!, so pulled exhaust off, opened bonnet and still cant see any leaks etc... so tried the priming lever to see if there was an issue with the lift pump, but that moved and although wasnt loose it still did move...

in past experience with lift pumps on other vehicles, the lever would go firm when there was pressure. Is that the case with the Leyland lift pump?

So i started it back up and it would rev again, for a few minutes, then back to not wanting to again, so thinking there must be air in the fuel pump/lines, i cracked each injector open with the engine running and i could see fuel at each and hear the engine misfire each time i opened the fuel input.
So i dont think its air in the fuel now...

So im now at a loss... If i leave it for 5 minutes, it will rev and run for a few minutes and then RPM would go down..

What am i missing?

Many Thanks

[Billy26F5]

Sounds like various things but I suspect some blockage, possibly the lift pump screen. the lift pump diaphragm or valves might add to that too. the first pump or two should be tight but it should go loose after that. There's a leak-off from the filter which prevents high pressure but you can plug that to test the pump, it should hold for well over half an hour with no leaks, they'll show up by getting resistance in the pump lever. FRailing that there could be other blockages.
Sandy

[Tecky Pete]

Hi Billy, thanks for that..
so where should i start looking for blockages? i know there is a cartridge filter for the fuel, but i dont have another to replace it with.
Are there service kits for the lift pump? or would it need a new unit?

Cheers

[essexpete]

If you can, see if you can push some air pressure back from the just before the lift pump to shift any potential blockages. Perhaps then change the filters, check there is not a small primary sediment bowl that may have a gauze. The CAV rotary pumps also can have a tiny gauze on the inlet. Be careful in there as there are little poppets and a spring. If you get a good flow out of the injector pump bleed screws i would not touch the inlet gauze.

[Billy26F5]

There are kits for lift pumps but the parts can also be found separately. There's a CAV main filter (796 element) and a sedimenter to remove water and large particles, both have a drain screw that allows water to be drained. There's also a gauze in the fuel tank. Check the engine oil is not full of diesel. Also ensure the tank breather is not blocked and filters air.
Sandy

[gecko.cx]

Are there service kits for the lift pump? or would it need a new unit?

Check the price before committing - often a rebuild kit is similar price to a new pump.

Your description sounds like a fuel restriction to me too. Some 3CX's have a gauze screen in the banjo joints - worth checking.

[Billy26F5]

I wouldn't base it on price alone, the quality of new pumps is poor to say the least. You're much better to keep the original one and fit whatever new parts it needs if any.
Sandy