What homework have you done on the process for setting injection pump and camshaft timing on this engine? Do you have any service materials?
Are you aware that the timing is adjusted in increments much finer than a full belt tooth, using a dial test indicator?
The process is easy and the special tools are widely available and very cheap, but if you try to cut corners and do it with paint marks, you will get defeated. Even more so than an electronically managed TDI, the old mechanical engines are totally intolerant of "workaround" attempts. You would think they would be simpler, and they are, but that actually makes them more demanding since they have no way to compensate for any fudge work. The timing has to be set correctly, to the right spec, using the right process and right tools. That's the ONLY way. If it's not, it'll run like dog crap.
Check out
@Vince Waldon 's great website for lots of info on the old IDI era engines. Ask him questions if something doesn't make sense.
This HOW-TO describes using the factory-proscribed "dial indicator" method of setting the timing on a VW IDI diesel engine.
vincewaldon.com
Why was the injection pump replaced to begin with? Was the timing belt changed as well? If not, do you know how old the belt is?
