Volvo FM12 Water truck- no revs

[Oldboy]

I have a Volvo FM12 (water truck) built 1999 6 x 4 configuration.
380 or 420HP engine
A good old truck it runs well.
But it has some electrical problems.
No tacho, no speedo.
No revs.
It gets to about 1/2 max revs and won't go any harder.
We have checked fuses
Replaced fuel filters
No relevant fault codes showing
Other electrics working okay.
Do I need to find a Volvo truck mechanic with appropriate tools to look it over?
Any ideas most welcome, thanks in advance. Michael.

 

[funwithfuel]

What engine, is it Volvo or Volvo/Penta? There is a difference. If you can't identify the engine, maybe post a pic. Lots of resources here.

 

[funwithfuel]

If what I found is correct, you have a D10B. It's a pump line and nozzle engine. I would start by checking fuel pressure after lift pump and check restriction at primary filter. Pressure should be no less than 3 bar/45 psi and restriction should not be greater than 4" of vacuum.
If these steps don't make sense, yes, you should call a truck mechanic.

 

[Oldboy]

If what I found is correct, you have a D10B. It's a pump line and nozzle engine. I would start by checking fuel pressure after lift pump and check restriction at primary filter. Pressure should be no less than 3 bar/45 psi and restriction should not be greater than 4" of vacuum.
If these steps don't make sense, yes, you should call a truck mechanic.

Thanks for your help funwithfuel I have posted a photo of the engine serial number if that helps. If you cant read it, it is: D12143195A
We will investigate along the lines of your suggestion when we get a chance.
cheers Michael.