JCB 3c III - Fast running engine problem problem - help

[stevejcb]

Hi,

I have a JCB 3c iii (1980) excavator which I have recently purchased. Everything was going fine when suddenly the engine began to run fast at high revs. I have checked all cables to foot pedal etc and can find no fault ie:- they are all returning normally. Does any one have any idea what the fault could be?

Steve

[philwheelton]

sounds like the metering valve in the injection pump needs looking at or the sump is filling up with oil or fuel and it's running away on it

[agrimax]

If there is a thermostart(heater plug) in the inlet manifold,check if it's leaking fuel into said manifold.

[stevejcb]

Thanks guys. I'm no mechanic so I might need a little more help on the investigation side - one thing occurs to me though, would it not burn the fuel if there was excess and then return to normal quite quickly - should i disconnect the fuel supply? As soon as you start the engine it runs at max so i'm loathe to leave it for a few seconds for fear I will damage the engine permantly - is there a risk?.

[agrimax]

When it revs flat out,I assume you can stop the engine by pulling the stop knob? If so,the engine is not running away and the fault likely lies within the injector pump. Check the throttle lever on top of the injector pump. This lever has an almost square(or could be semi circular) hole that fits onto the spindle and has a nut to hold it tightly in place.If the nut loosens,the hole becomes worn.Could be that the spindle has turned inside the hole and stuck in full throttle position. Just a thought.

[stevejcb]

Hi,

Thanks for your suggestions - this is what I have found.

Agrimax - I have checked poss fuel leak to manifold everything is fine, dry and clean.

philonwheelton - no apparant fuel in sump.

Agrimax - Yes the stopknob does work (thankfully). I removed the throttle lever and whilst there was some wear to the lever slot it still functioned. When it was off, I rotated the spindle in various angles between full and closed and found that it made no differences to fast running speed. I could hear what was attached to the spindle in the upper injection pump body rotate inside(appearing to shut and open also)

Agrimax/philwheelton - Not sure what a metering valve is, where or what it does? Is it in the top half of the fuel injector body? if so can I unbolt the two nuts and look inside to see/replace, without causing further issues? (Its a Cal type injector pump on a 4/98NT leyland).

I've not been able to locate a spares/service diagram for the Injector pump on the downloads - do you know if there is one?

Any suggestion would be more than welcome - regards Steve

[Jeremy Rowland]

Steve fuel injection pumps are for specialist repair so you will not find a manual for one very easily; you may find a sectional drawing of one but that is about all, I have not messed with rotary injection pumps myself so unfortunately I cannot offer you any advice on the pump. However other CMN members have possibly taken parts off them before so perhaps they will offer you some sound advice.

Jeremy

[agrimax]

Steve,the attached file will (if it works!) give you an indication of what is inside the dpa pump but it really isn't recommended to open it.
If you do remove the two nuts to lift off the cover,the governor spring has to be detached before it will lift clear. It must be reattached to the correct hole on the throttle spindle and the idling spring also put back where it came off. It's easy to forget where they locate. You would also definately require a new gasket between the lid and pump body. The stop spindle must also be relocated into the hook of the shut off bar as the lid is set back on. Better off removing the pump and having it checked by a specialist.

cav_dpa_pump_rebuild_manual_sec_wat.pdf

[stevejcb]

Hi,

Agrimax - From what you've said and what I suspected it sounds like a definite no. thanks for the file.
I have a question though - is it possible to remove the Fuel injector pump (CAV DPA) and fit another (if you still think thats where the problem lies) without having to go through all the rigmarol of retiming ie: visually match the correct spline of the old pump against the new and insert?

Steve

[agrimax]

Steve,I have never removed a DPA pump from a BMC engine and looking at various pictures,I assumed there would be a master spline so you couldn't go wrong.However,having looked at the workshop manual,it suggests timing tools are required.You can download that manual in the JCB downloads section on here.Perhaps Phil will know more?