Slow revving startup/smoke

[SoyDriver Matt]

This is on my beater '83 300SD. When it starts in the morning it smokes, billowing whitish smoke, and no matter how much the accelerator is pushed the revs won't go above 800-900, then after about 30 seconds you can feel something "catch" is the only way I can describe it, it revs fully and the smoke stops. The rest of the day it starts and revs normaly with minimal smoke. Any ideas? Sticky valve or injector maybe? Something in the fuel rack in the I.P.?

[psfred]

Check injector spray pattern and opening pressure and injection timing -- bad nozzles will squirt a solid stream of fuel when cold, so you get very poor combustion all the time and white smoke with cold engine -- once the combustion chamber warms up, you will get much less smoke and more power.

Late injection timing will cause serious misfire cold because the fuel won't ignite. Burns much better when the combustion chamber temp comes up.

You could also have a stuck injection timer.

Peter

[SoyDriver Matt]

I'll be digging into it this week to do the valves and check the timing, but it doesn't feel like it's just waiting for the pre-combustion chambers to heat up with the way it suddenly revs and stays that way the rest of the day (usually). So what about this injector timer? Is it in the I.P. itself? Is it the kind of thing diesel purgeing it could help, or am I looking at I.P. removal and rebuild?

[psfred]

Matt:

You should also check for air leaks on the suction side fuel lines -- those fabric covered lines are notorious for going bad under the cloth, and sucking in air instead of fuel.

The result can be exactly what you have -- runs fine once you get enough fuel in the plungers. Eventually, the leak will get so bad the engine won't start.

It could also be the IP leaking down, in which case you will have fuel in the oil (crankcase or just the IP, depending on model).

The injection timer is driven by the timing chain behind the vac pump. It's a centrifugal device that in turn drives the IP, so that timing advances as rpm increases.

To inspect, you must remove the vac pump.

Peter

[SoyDriver Matt]

I had the vac pump off not too long ago (nothing to do with the slow rev start-up) , are you talking about removing the roller assambly that drives the piston in addition to the outer part?

[psfred]

Matt:

The part with the cam (which is driven by the timing chain) is the injection timing device. Works like a mechanical distributor advance.

I beleive it bolts to the shaft that drives the IP, but I'd have to check, it's been a while since I had one apart.

The important thing to check is whether or not the springs in it are compressed with the engine stopped. If so, it's stuck, and probably the injection timing is off.

Do a compression check too -- I'm betting your problem is a combination of incorrect injection timing, low compression, and worn out nozzles.

Peter

[SoyDriver Matt]

Thanks for the advice, unfortunatly I think you're right and it's a combination of 4 or 5 things that need fixing. The P.O. was not a maintainance guy I'm finding out. But just scored a cheap 300D to drive while I pull the SD for some catch-up on all the problems.

[dpbrowne]

Matt please keep us posted on the outcome. I also have a 83 300SD that is acting similar.