IP advance arm / timing

[rockbender]

Like everyone else, I am always in search of that extra MPG and have been going through my van slowly but surely learning more about the IDI engine. I recently replaced my injectors (thanks type4!) and got all my up pipe leaks taken care of so now the turbo is spooling like it should. My next quest will be to get the timing dialed in.

I was curious if the advance arm actually moved or was perhaps seized up so yesterday while the engine was running I pushed it in a little bit and hit the throttle. With the advance arm pushed in, the throttle response seemed a little crisper and the engine quieted down A LOT. It also put out a lot of black smoke too. Pushing in on the advance arm should be 'advancing' the timing, is this correct? I am curious as to why the diesel / PSD rattle mellowed out when advanced? I thought that retarded timing typically didn't have that rattle.

Two other related notes - the advance arm plunger/seal seems like it is weeping a little bit. Since this application is a van, I am not super excited to get started pulling the IP but I assume that I may want to put it on my winter list to either replace that seal or do a new IP.

Second, I don't think I am getting power to my cold start advance. I haven't hot wired it yet to see if the solenoid itself works. It would be interesting to see what the sound difference is - from what I've read, it advances the timing about 2.4 degrees at 1400 RPM.

I didn't have a mirror handy to check any alignment marks on the IP, but I'm not sure that I want to spend any time moving the pump around guessing at timing until I have a meter to do it right.

I haven't driven another IDI for probably 20 years so have no reference point, but I'd sure like to have it with the quiet sound if possible - so much nicer!

 

[icanfixall]

Well if the plunger seal is leaking its just about time to replace the injection pump. As the leak gets worse the pump will loose its fuel prime. Then hard starts can cause the starter to leak out all the smoke... Or it burns up from long cranks. These engines should fire off at the smallest of crank movement. That only happens if the fuel system is tight and not leaking out. A couple of 10 second cranking will ruin the starter is short order. We really only see this slow cranking AFTER we replace the starter. Its tuff to actually see the starters slowing down . It happens over time. Thats why its hard to notice happening. How many miles are on the injection pump. If its around 125,000 miles or more its due for a replacement.

 

[Black dawg]

pushing in on that plunger will retard timing. Internal pressure advances timing with engine speed. That lever retards timing with load (more throttle takes away timing)

 

[rockbender]

Thanks Black dawg - that is certainly how it was behaving so I was confused to think that it was making it advance. Makes sense noise wise too - when I put my foot in it going up a grade or accelerating it doesn't have nearly the engine noise/cackle as when I am just cruising along.

The pump I am sure is due for replacement based on mileage - probably right around that 125k mark. As long as it has a decent glow plug cycle it fires up cold without too much trouble and always lights right off when warm. I'll probably do the IP this winter but it seems to be doing fine for now. This isn't a daily driver, just the family fun rig that doesn't get a ton of miles put on it. I do want to treat it as well as I can though.

 

[Black dawg]

if it gets more quite under throttle than cruise, advance the pump a little at a time till the sound stays the same (from cruise to near full throttle.

 

[Agnem]

That arm only affects the lower RPM band. At higher speeds the internal advance plunger regulates the timing. Both work together to keep the timing where it needs to be for the RPM's you are turning. This is the reason why our engines have to be pulse timed at 2000 RPM. At that speed the lever on the side is out of the picture. It is also the reason why pulse is superior to lumy when it comes to timing. At 2000 RPM, the optical pickup method is just too unreliable, so running the engine at 1400 RPM is really a huge compromise.

 

[Black dawg]

I dont know what rpm the arm wont retard timing at, but I do know that at 2k it can still take away alot of timing.