Altitude compensator solenoid stuck on ground.

[Grubby]

I hope one of you guys can help me figure this out: I'm trying to start an engine that was rebuilt in the 90's. My altitude compensator solenoid (the one at the bottom drivers side of the pump right under the pump label/stamp) has continuity between spade terminal and ground, the plastic is melted a little from a previous encounter with electricity. It was blowing fuses when I turned the key to position 15, and when I checked it I found that it is stuck on ground. Would this keep my pump from priming properly, or would it not make a difference and should I just leave it out of the circuit? The fuel solenoid is clicking. I am getting a little bit of fuel to the injectors (all lines are cracked at the injectors. More fuel from the one closest to the pump, and a little less as you travel to the front of the engine. there is none at the injector furthest from the pump. Not a whole lot of fuel, all together. Any ideas? Can the solenoid be removed from its housing and replaced? Any sources on the part? I live in Georgia and I'm not sure of the elevation here, but surely its not high.
Thanks a lot.
Abe

[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

[Grubby]

George,
Thank you very much for your reply. This helps. I have heard they are a bear to prime. I actually hooked up a primer bulb to it today after excessive cranking didn't work, but I got pulled away from the procedure before I had a chance to try it (I have two small children who need lots of attention). I will try that technique. I knew it needed some help. I like your idea about the two solenoids being the same. Maybe I could salvage one from the local volvo dissasembler.
Thanks again.
Abe

[Grubby]

George: you said:

"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."

But I thought it already had constant power to it when the key is on. My interpretation of the D24T glow plug wiring schematic shows that it shares a circuit with the pump shut off solenoid, which is hot with key on, of course. Is there an external switch in the circuit? Forgive me if I sound stupid, but I'm confused. Thanks.

[Wren]

Originally Posted by Grubby

George: you said:

"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."

But I thought it already had constant power to it when the key is on. My interpretation of the D24T glow plug wiring schematic shows that it shares a circuit with the pump shut off solenoid, which is hot with key on, of course. Is there an external switch in the circuit? Forgive me if I sound stupid, but I'm confused. Thanks.

Abe, the solenoid does get constant power, but only when below 3000-4000 ft. elevation. The switch is normally closed until elevation increases and then the circuit is open, cutting power to the solenoid.

Here's the picture from your greenbook.

Wren

[ian2000t]

Can't comment on the high altitude - don't think my UK pump has this.

Re: Fuel priming - I had an issue with mine not starting a few weeks ago after leaving it parked uphill (think fuel drained back to the tank due to leaky pump seals). Couldn't get it going with just cranking. Borrowed a little electric pump (old petrol Mini SU points pump) which REALLY struggled to pump anything (far too thick) but it worked just to force a bit of fuel into the IP. I then disconnected it and fed the IP inlet straight from a bottle held above the IP. Started straight away on that (even though it was a 1ltr bottle of Sunflower Oil). Let it run for a bit then plumbed the inlet back into the fuel filter and it was fine then.

[Jason]

I've been running mine disconnected for a while and the top end power is impressive. The difference of the extra timing and slight increase in fueling was suprising. I expect that the more your pump is turned up the more noticable the change will be. Many of the VE pump cummins guys run theirs' powered and have shown 30+ hp increase at the rear wheels with back to back dyno tests. Obviously if your not trying to push your car to the limit like I am, this may not be the best idea for you! Interestingly, on the 6bt cummins application, our high altitude corrector is used as a cold start device to aid with cold start ups by advancing injection timing. On the cummins pump the soleniod is wax pellet that heats up slowly so it takes a while to come down to normal as the engine is warming up. Why they didn't do a manual fast idle/pump timing advance lever like our engines have I couldnt' tell you. Just a little VE pump info I thought may be interesting to you guys.

Jason