Black smoke on startup

[btoscano]

I've had this truck for about a month. Seems to generate a cloud of black smoke when I start it (usually worse when the engine is warm from what I've noticed). I'm not 100% sure what this means. I read in a search on black smoke startup that it could mean timing is retarded? It doesn't smoke visibly any other time. I do see some diesel exhaust under load at night in the rearview thru the headlights but not much.



Doesn't look like the valves have ever been adjusted. I replaced weeping valve cover gaskets this past week. If its retarded timing, what can I gain by advancing it? More MPG? What are the chances I'll make something worse?



Thanks,

Brian Toscano

'90 D250 ~128Kmi

 

[formula]

How big of a "cloud"? Is it more like a short puff just after you fire it up? Due to the design of the injector pump, it supplies a rather large quantity of fuel when cranking over the engine, which is quickly cut back as soon as the engine is near idle speed. This is the reason that the engine starts with a little "brap" and a puff of smoke. The smoke can be made worse by retarded timing and various other things. But I'd bet that what you're seeing is normal.



Cheers,

Sean

 

[paccool]

Mine does it and the timing is advanced to 1. 7. seems to be the norm with most of the trucks I've seen.

 

[btoscano]

Sean,



The smoke is large puff of black smoke. I call it large because I can see it and then it disapaits throughout the air. By comparison, the (small) puff from my Mercedes diesel can't be seen when I'm in the car.



If I advanced the timing, how much smaller would the puff become? What other things contribute?



Thanks,

Brian

 

[btoscano]

Stan,



You posted while I was replying to Sean. Glad to hear its normal





Thanks for the quick replies,

Brian

 

[BushWakr - RIP]

Brian,



The guys are right, the puff on start is normal, pretty much no matter what your initial timing is set at. Now, advancing the timing will help a bit to be sure. In fact when cold enough outside, the pump itself actually advances it own timing (via an electronic signal to the KSB solenoid. )

This temporary advance stays in place until the incoming air temp reaches a certain level and the 'sensor' tells the KSB to shut down.



As for timing settings, you can advance timing using two different methods of measurement.

One is the standard we are most familiar with, degrees advance, while the other is called "spill port timing" and is measured in millimeters of lift.

Generally you are pretty much safe to to advance your timing as much as 17* advance or roughly 1. 45-1. 5mm lift.

Going much beyond that "could" be hard on the headgasket.

Some have no problem, others do.

So advance timing addresses a number of things: first, smoke on cold start and with heavier fueling levels, also helps to lower EGT's slightly, provides more "responsiveness" in the throttle, generally better idle quality, is often necessary when installing uprated injectors.

The reason for that is the larger (higher HP rated) injectors often pop-off or, release the fuel charge, at a later time during the piston stroke due to that higher pressure release. That has the effect of "retarding the timing" from an injection/start of combustion perspective. Advancing the timing starts the injection process sooner and helps to compensate for that delayed reaction of injection/combustion.

The one issue with advanced timing goes back to the head gasket issue. Advanced timing results in higher cylinder pressures, and when combined with higher boost, results in stressing head gaskets, etc.



I hope that helps a bit... if I've gone off track anywere guys, please jump in and correct may mistakes... .



Bob.

 

[btoscano]

Thanks for the information.



One question still comes to mind - why doesn't the black puff occur all the time? For example this morning at cold start there was none, and after I stopped the engine for 1/2 hr and restarted there was none. Yesterday after I stopped the engine for 1/2 hr there was a black puff.



It may be that the black puff happens when its "warmer" out. Still collecting data.



Thanks,

Brian

 

[formula]

As BushWakr was mentioning, this is probably due to the KSB cold timing advance mechanism. It will shut itself off when the engine (intake charge, or perhaps the injector pump temperature in your case) is warm enough. Not sure exactly what that temp is on your year. As far as I know, the KSB on the non intercooled trucks used a wax motor type actuator for the KSB, so you can't override it with a jumper wire like can be done with the solenoid operated ones on the later trucks.



Sean

 

[paccool]

Mine happens EVERY time! There has been a couple of times where a good looking woman was beside my truck with the doors open and I have asked them to close the doors before I started up. Told them they would see why when I started. Didn't want to smoke up the cars.



Stan

 

[Bluebird]

Black Puff, at startup...

Mine happens at startup, thanks for confirming, it's normal...

Does fuel additive make any difference? Patrick.

 

[BushWakr - RIP]

Additive may help on the ' up and running' engine, but not for startup.

In the initial "start" phase, the pump is pretty well at near maximum "rich" fueling. That changes immediately after the engine reachs idle. Actually it changes on the way to "idle RPM" if I'm not mistaken, either way, the puff is pretty much always there depending on pump settings.



bob.

 

[JLEONARD]

The start-up "puff" from mine is not always noticable.

So I guess mine's acting like Brian's.

Maybe because we're pre-intercooled and our pumps are adjusted differently?

That means we can start-up in stealth mode... . oh forget that our engines are still loud enough to wake all the neighbors...







Jay

 

[btoscano]

BushWakr,



I think got a little off topic not that I mind This truck & engine is new to me so I'm learning as I go. When I get around to it, I'll find out about checking and adjusting the timing. Before I do that, I'm curious to do a valve adjustment.



Brian

 

[Tim1]

advanced timing and smoke

Brian, mine smoked at startup with the stock timing and injectors and smokes now with the advanced timing and pod's. The engine on my truck really smoothed out at idle with a change in timing, seemed like it was laboring to run before. Just move the top of the injecor pump in towards the engine 1\8" and you will be in the ball park. Good idea to adjust the valves also is quite easy to do. I would recommend a barring tool. although some have used the alternator to move the crank around. Check the search engine here for some very good info, thats where I got it. Tim

 

[formula]

Here's a link for instructions on performing the valve lash adjustment



http://www.dodgeram.org/tech/dsl/valve_adj/12_valve.html



Sean