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Old 03-25-2012, 10:58 AM
Grubby Grubby is offline
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Default Altitude compensator solenoid stuck on ground.

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
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Old 03-25-2012, 03:23 PM
v8volvo v8volvo is offline
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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
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Old 03-25-2012, 04:11 PM
Grubby Grubby is offline
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Default Primer Bulb

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
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Old 03-25-2012, 04:49 PM
Grubby Grubby is offline
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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.
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Old 03-26-2012, 09:09 AM
Wren Wren is offline
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Quote:
Originally Posted by Grubby View Post
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

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Old 03-27-2012, 01:26 AM
ian2000t ian2000t is offline
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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.
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Old 03-27-2012, 06:34 PM
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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
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Old 03-29-2012, 11:15 AM
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Jason- you ran yours disconnected so its running full advance all the time? From what I understand (I don't know as much on the VE pumps as I should...) That has the same function as running your cold start activated aside from the high idle?
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Old 04-04-2012, 10:58 AM
v8volvo v8volvo is offline
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Based on what Jason said in the other thread (which I did not know before), it sounds like the roller cage has a limited range of movement... meaning that regardless of your starting point, e.g. whether you have the cold advance lever pulled forward, or the altitude compensation solenoid disconnected, etc, the resulting increase in advance only has effect at lower RPM, or until the pump's roller cage reaches the limit of its movement. The cage can be moved (resulting in timing advance from base static position) either mechanically by the CS lever, or hydraulically by the alt solenoid.... but in the case of the CS lever, the position that it bumps the cage up to is only so far, and above a certain RPM (I have heard something around 2500 from the 4cyl VW guys), the hydraulic dynamic advance takes over and moves the cage further than the CS lever had pushed it to anyway. Presumably when using the alt solenoid for advance instead, that shifts the entire advance curve rather than just altering the bottom half of it like the mechanical lever does (since the solenoid works by allowing some pressure to escape on one side of the advance piston in the bottom of the pump, and pump internal pressure is simply proportional to RPM). However, if I am understanding Jason's explanation correctly, even though the whole curve is shifted, at some point the advance still tops out at the same place regardless as the roller cages reaches the end of its range of motion. With the alt solenoid disconnected, it probably just reaches that max advance point at an earlier RPM and is more advanced than spec all the way there.

Of course, all this assumes that the pump's pressure regulator valve, advance piston, and front transfer pump are all working correctly -- if any or all are out of spec then that will throw off the whole dynamic advance curve and then all bets are off as to what happens when, and how.

The other thing I have wondered is just how much timing difference the altitude compensation solenoid difference makes. On other VE motors like the Cummins 6BT, the BMW M21 524td motor, and some VW industrial engines, the whole cold timing advance is accomplished using a similar solenoid. I have access to a diesel timing light that I have always wanted to play with... one of these days I will experiment and see what the solenoid does exactly. Since the Volvo cold start wax thermostats are getting harder to find now, it may someday come to the point where we will want to make manual (or thermoswitch-controlled automatic) cold advance systems electronically using the solenoid rather than the mechanical cold start setup.

Abe, if you just wire your 240 conversion so that the altitude compensation solenoid receives power at all times whenever the key is on, that will work fine... As Wren described, 700 series TD cars from 1985-on (and some very late 240 Diesels) have an altitude-sensitive switch mounted on the driver's inner fender that controls current flow to the solenoid, but presumably your gasser 240 body has no such switch and you probably didn't get one with your D24T engine ... and even if you did, you are better off eliminating it and powering the alt comp solenoid directly off the key. That's assuming your mechanical cold start system is functional and you don't want to use the alt comp solenoid to effect some kind of cold advance, as I was talking about above... but that is probably something you will not want to worry about until later on after you have gotten the car on the road.

George
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Old 04-05-2012, 06:37 PM
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George, you have it exactly right, all the lever will do is bump the timing initially, then once rpms and pump pressure increase the timing advances normally. Yes there is the limit of travel in the pump, however the pump may not necesarily reach its full advancement in stock form, especially with today's thinner ULSD, and pump wear. That can be accomidated by adjusting the preload pressure on the spring on the pump relief valve (the small tube from the alt solenoid runs up to it). With the pump pressure raised your getting the benefit of the most possible pump timing that the pump can deliver, along with a small increase in injection amount thanks to the higher internal pump pressure.

When I get my car dyno'd comming up here soon I will be doing a back to back run with it connected and disconnected. The butt dyno confirms that it pulls stronger around 2500rpms and up compaired to before though..

Jason
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