[v8volvo]

Should not keep your pump from getting prime, but it ought to be fixed. The solenoid needs to be powered at low altitude, and the compensation switch's job is to *remove* power from the solenoid above about 3300 ft (which it really should not do anyway). The system is best left disabled, IMO... but the trick is that to disable it, you need to provide constant 12V to that solenoid when the key is on -- not disconnect it. Running with it disconnected will cause the timing to always be excessively advanced, which has detrimental long-term effects.

This is just a pure guess, but I believe that the main fuel cutoff solenoid and the altitude compensation advance solenoid are actually exactly the same. Basing that conjecture on the fact that externally they look identical (at least the part that sticks out of the pump), and they have the exact same sort of job to do. So if you have a spare injection pump (off a Volvo or even an old VW Rabbit one) with a functioning shutoff solenoid, assuming my guess is right, you ought to be able to exchange them. Unfortunately I am a few thousand miles from my box of core pumps right now, otherwise I would be glad to check it out for you and satisfy my own curiosity.

If you do take one apart, make sure you also get the O-ring, plastic plunger, and spring that go with the solenoid. If one of those parts is missing when it is all reassembled, it will not do its job right.

Priming these can be a hassle. The only thing that works is extended cranking, some positive fuel pressure applied to the fuel supply line, or both. If the fuel system has been apart for a long time, installing a simple hand primer bulb in line before the fuel filter (or a low pressure (no more than ~5 psi) electric pump) to force feed some fuel to the injection pump will speed the process up dramatically. On one of mine I found it virtually impossible to get it primed without the hand pump method after replacing the injection pump.

Keeping those fuel line nuts open is a good idea too. Even after a few of them start running plenty of fuel out, I have found that it is best to keep all 6 open until the last ones finally start showing a steady spurt every time the pump comes around.

Another method I have been able to use a couple times on TDI's has been applying suction to the IP return port. However, this is a little tricky because you have to first have the fuel injection delivery pipe nuts closed at the injectors -- otherwise your suction pump will just be drawing air *in* through the injector unions rather than sucking fuel in from the tank. Overall the primer bulb method is usually a little faster since you can pump fuel and crank all at the same time... but if you don't have a bulb and you do have a MityVac or similar suction tool, the suction method can do the job OK and it is less messy. You just want to pull vacuum on the return with the injector unions closed until you see fuel coming out that way, then quickly remove the suction tool, re-connect the fuel return line, crack open the injector nuts, and crank away before the fuel has time to siphon back to the tank too much.

George