1987 CWA 45

We have been working on this old tipper for a couple of months, on and off.
When we got her she went like a rocket, but was getting hot- which we eventually tracked down to a hole in a liner, which has now been replaced.
After a fair bit of body and tyre work we were to take her for rego inspection today, however she will not pull in the high box - almost as if governed at about half revs. Pulls OK up to that and then won't rev any more. In any gear. Revs right out in the low box. Anyone have any suggestions? Starts easily no excess smoke, no apparent engine issues - except won't rev out in high range.
(This has been relayed to me from a son, I have not been able to check it due to being 1000 km away and covid)

First check is it getting full throttle?
Any smoke when it runs out of go?
Cheers Steve

I am told it is getting full throttle, was the first question I asked and is revving right out in all gears in low, but in no gears in high, I will ask about the smoke.

If it has sat for awhile, may pay to change the fuel filters and see if anything has taken up residence in the air take system. Also check the fuel tank vent/s are clear.

Symptoms are of fuel starvation. So you need to rule out filters and fuel lines by fitting new filters and blowing the fuel lines in BOTH directions - it is not unknown for something in the lines to act as a one way valve. The other tricky one is the intake in the tank. Infamous intermittent blockages reported here are rags in the tank and on one occasion newspapers! Don't rule anything out.

pretty familiar with fuel starvation, does not seem to be the case here, revs freely in the low box, does not rev in any gear in the high box. No tailing off of power as with fuel starvation, just can't get up to revs in any gear in the high box.

When in the higher box the governor needs to open to allow more fuel through. As in theory you are now travelling faster it needs more fuel and could possibly be starving even though it gets enough in the lower gears.
I too would be looking at the simple things first like air vent in the fuel cap, fuel lines and filters then after that the pump itself.

Bit more complicated with turbo engines ,as it has a boost modulated fuel delivery .....may be some problem there .....

Do these motors have something like a Mack style puff limiter to limit governor travel in certain gears

If so I would think its plausible that this could be a problem

I know zero about these motors, just throwing ideas out there

Paul

I am not familiar with these, but is the exhaust brake coming on when high range is selected? Either by means of electrical or air?

I know it sounds stupid, but i once saw a truck that every time the key was turned to start, the trailer tailgate flew open!

And another truck that every time the headlights were turned on, the engine stopped, which over time eventually changed to being every time the lights were turned on, the starter motor spun. The latter turned out to be a faulty relay that i think the manufacturer started with, and built the whole cab around.