Hi,
I find many pumps that are getting pulled and rebuilt for no problem other than low case pressure. They can't maintain the proper advance w/o case pressure.
Simply pull out the case relief valve, next to the fuel inlet. It is the strange piece with 10mm flats. The insides begin to walk out over time. Just hammer the retainer back in so it's flush with the bottom of the valve. Be extremely careful not to get dirt into the pump, cuz this is right at the front lift pump. Spray with carb cleaner and use compressed air to blow away dirt before removing the valve. Use a clean hammer too so dirt doesn't enter the valve. This will allow air to enter, but most pumps will be fine and start up ok and reprime, no problem. Don't open or remove this valve with car running or you'll get a good shower.
If you're getting smoky starts, and poor performance, the timing piston isn't working. If it gets real bad, you'll get start of injection faults. If your car dies or runs very poorly w/o faults, it usually means it is running out of fuel.
The middle valve shows the problem. The right valve is fixed.
Also fyi, increasing case pressure doesn't improve performance in any way. The camplate timing solenoid controls the pressure to the timing piston wrt #3 lift sensor and rpms and load request. However, if the piston is scored and leaking badly, increasing case pressure and running bioD, with greater viscosity can make the pump work good enough to get it off the lot, if you're trying to unload a hunker w/a bad pump.
btw, the pic was from Jonathan B's pump I just rebuild that had gas run thru it. The insides were rusted, and the varnish from old gas clogged up all the passages.
Jeff
