JT-RRC

Hey Hey! I've got an '88 2-Door 2.4 VM diesel here in New York, car was originally from Spain. Well aware of the love/hate (mostly hate) for the VM's - but it's what I got and I honestly don't mind it too much. I have had the head gaskets done before, but when it runs, it runs great hah. It's really hard to find much info on working on these engines, so I'm often flying a bit blind - my first time posting here and would love to meet some other VM owners that can help share advice. Right now - I have quite the squealing Belt/pump...something? Not too long ago I replaced the fan belt. This belt connects with the alternator as well. Here's how it's current squeal seems to work; The squeal seems to kick in most at 1800 rpm and above. When it does squeal, the tacho also stops read, usually drops to zero. Which tells me the alternator is not giving a reading? I've tried watching/looking at the engine and the belt while I give it some revs. Everything is turning, the belt from what I can see is still spinning, fan is going etc etc. But that dqueal starts shouting when the revs pick up. I've tensioned the belt and from what I can tell it should have adequate tension and I can't visibly see it slipping while revvving? Is this a water pump sound? And if so. how would that be affecting the tacho reading? I'm trying to avoid replacing parts it might not actually be yet. I'm going to try tensioning the belt again, but I get the sense it could be something else, I just can't figure out how the squeal sound and the tacho reading are connected?!