IP question??

anders · #1 01-24-2012, 03:27 PM

The pump I have on my d24t in my 244 has a solenoid on the bottom middle of the pump, I believe for timing advance. My question is: If I apply power to it does it advance the timing? or just the opposite?

v8volvo · #2 01-24-2012, 04:58 PM

Just the opposite. The high altitude advance solenoid should have +12V applied to it at all times for best results. IP has normal timing when solenoid is powered, and runs in high advance mode when solenoid is not powered. Should be the other way around IMO, with the default mode being no advance, since if it comes accidentally unplugged the excessive advance could damage the engine... but that's the way it was designed. It moves the timing advance cage by altering the fluid pressure on that side of the advance piston in the bottom of the pump, rather than by mechanical means (like what the cold start advance lever does), and as such it affects timing across the entire RPM range, not just at lower RPM like the cold start does. Not a good thing if you are running with it unplugged accidentally, at high RPM and high load, on a hot day.... engine will not be happy.

Early D24 and D24T pumps did not have this advance solenoid, and had a simple block-off plate at that location instead. The altitude advance function was added in late 1984. (If you look at the pump on your new 1983 760, you will see that it does not have the solenoid.) They don't need the extra advance even at high altitude if the timing is set correctly, so I like the pumps better when they do not have the solenoid. You can remove the solenoid if you are able to get the appropriate block-off plate and the different case pressure regulator valve to go with it. Or, what I do is to jumper the connections at the altitude compensation switch (on the LH shock tower, a small tuna can shaped device with 2 spade terminals on it, that is closed at sea level and opens above ~3300 ft... if working correctly, that is). Once jumpered, this ensures that the altitude advance solenoid will be powered under all conditions. I like to make sure the connection there is good and tight too, and verify for sure with a circuit tester that there is battery voltage coming out of that wire whenever the key is on.

One time I bought a cheap and pretty solid 245 Diesel that was otherwise headed to the crusher because of a number of problems that its owners thought were very serious, but were actually fairly minor... one of the problems was that it ran extremely poorly and with lots of loud noise. What had happened was that at some point, a mechanic had replaced that car's injection pump with a pump off a later car. The new pump had the altitude advance solenoid on it, but the 1982 car that it was going into did not have altitude compensation and as a result the wiring was not there to connect the solenoid... so the mechanic just left it unplugged, and set the timing pretty far advanced too. Once I applied power to the solenoid, the engine quieted down and ran nicely.

On that one, to fix it permanently, I made a harness to power the advance solenoid off the same circuit that fed power to the main IP fuel cutoff solenoid, so that both would always be powered together. If this pump is in your 244, you might want to do something similar, since it probably doesn't have the altitude compensation wiring either.

ian2000t · #3 01-25-2012, 01:18 AM

Is this just a US thing? I'm quite sure my UK 1990 760 TD doesn't have the altitude compensation.

v8volvo · #4 01-25-2012, 10:14 AM

I don't know, but you could find out my taking a look at your pump. I can post pictures of the differences later today. The US had stronger emissions requirements for diesels than Europe in the 1980s which is why our Volvos had EGR and other such emissions-related functions long before Volvos on the Euro market did. We also have tall mountains here, which are also found on the Continent but not in the UK I suppose, so maybe for the UK market vehicles they figured may as well leave the high altitude equipment off.

anders · #5 01-26-2012, 11:27 AM

Well I ran the car with that unplugged for around 400 miles, It was running sweet. static timing set at .95. I re-set it to .85 because it rattled a bit. So last night I played with the solenoid, I applied 12v to it and the car started to miss, then cleared up. I drove it around and it did not have any engine breaking below 2200 rpm. Got it back home and it started to miss again at idle. Well I just pulled off the solenoid and pressure regulator and replaced it with parts from the pump on the original d24. It runs great now, but lacks the low end grunt it had with the full advanced timing.

v8volvo · #6 01-26-2012, 07:03 PM

If it were mine, I would set it to .95 again and leave the solenoid off. That should accomplish the best of all worlds.

anders · #7 01-27-2012, 05:18 AM

That's what I was thinking. Has any body here ran higher then .95? I have heard of some of the VW 1.6 guys running 1.10! I think that's too much, It must rattle like crazy but have some good low end. I think I will set it at .95, I'd rather have longer engine life and a less rattly engine then some more low end. I also found why my car had some hard starting issues. After it sat for awhile, cold or hot it would take some cranking to get it to start. It seemed it was loosing it's prime. I checked my fuel cap and it was not letting in air, so it was creating a vacuum in the fuel tank so it would suck fuel back to the tank when shut off.