Low compression on 1.6l diesel

First thing you do is find a new mechanic! One that understands how this VW of yours really works.

I will give him credit for measuring the compression of the cylinders and telling you they are low. I believe the minimum PSI is 400 but that one at 350 being your best shows you have a ring and a bore of the engine in your future. Those 3 at 290 are just so far from doing the job I can see why you need the a can of coercion to keep it running.

The air flow into the cylinders has nothing to do with fuel delivery. That comes from the injectors, it is sprayed in when the cylinder hits TDC. The injection pump has a low and high pressure side. The big part of the body contains a wheel that has four little squares of metal equally spaced around the edges. That is the vane pump, it is what pulls fuel into the IP. It pushes it to a second part of the pump where a 9 mm or larger plunger then compresses the fuel and pushes it into the correct delivery tube to the injector. All a very nicely coordinated dance for the diesel.

If you have decent fuel delivery and it sounds like you do as it did run in a manner of speaking, I would be rebuilding the pistons, cylinders, head and once you have the proper level of compression, 480 PSI/ cyl. Then start measuring the amount of diesel being pumped out at idle. That is about 1 liter per 90 seconds if I remember it right.

How many miles on it? Timing belt and tensioner pulley in good shape? Any records of past maintenance?

IIRC the minimum pressure is @ 400. Max being @ 495. There should only be 75 psi difference between cylinders. He measured 2 cylinders? To measure the pressures yourself be sure that you buy a diesel gauge that goes to 500-600psi.

In the days prior to the interweb when I owned my Diesel Bunny, I had a fueling issue, So I bought a used pump, that didn't work any better and decided to tear my original one down. I didn't buy a rebuild kit. I tore it all apart and cleaned everything, I even polished the vanes on the injector pump...which is where the issue was I had 2 vanes that didn't slide. When I reassembled it I had to bleed it at the Iron Manifold as there was air trapped at the Injector Stand-offs.

Think no interweb no digital cameras, I just drew pictures of things...to get them back correct.
I had that car running in about 4 days, and it kept running for another 8 years before I sold it.

Timing belts are tricky, there is no error allowed in timing. One tooth off and you can have massive ca-ca to occur.
The Diesels are interference engines, where the Gassers are not.


http://vwdiesel.net/forum/index.php/topic,4353.0.html