excessive smoke @ idle
 

Hi all ... new to the forum and have been reviewing threads about IP's, smoke, etc.

I have a 1993 300d 2.5 turbo just clocked 200k miles that put out quite a bit of black smoke at idle. The injectors were loud and I did a direct purge with no change. Bought 5 new Bosh injectors and install them this weekend. Injectors are much quiter and engine seems a bit smoother but .... still lots of black smoke @ idle.

At idle the engine will idle for 14 sec with little black smoke, drop a few rpm and chug black smoke for 14 sec, idle back up a bit and idle with little smoke for 14 sec, this continues.

I notice the most idle smoke when stopping for a traffic light, it's quite heavy

Can't see the black smoke while on the road unless drive the peddle down, then get some. Car runs smooth and avg 35 mpg.

Spoke with a diesel IP shop that rebuilds IP's and they think the governor is bad or idle spring, would not offer quote to repair.

Any ideas as what I can check before I go the IP shop route.

Thanks

The idle is electronically controlled. Check that out first. I'll mention an Italian tune up. Do a search here on it. Some are for it. Some are against it. Not sure what you mean by a lot of black smoke.
Could be timing chain stretch. Did you get maintenance records? Overall they're great cars.

There's are some resources are W124-zone dot com. Do a Google search.

I don't think you need to be jumping at the pump rebuild just yet. Could be a simple timing adjustment.

Bobo is correct, retarded timing can cause excessive smoke.

The cyclic idle thing bothers me, I guess it could be the idle control, not sure. Have you verified that all of your air intake is clear? Must be if the car will make power and highway speeds, and electronics control only the idle, EGR, and wastegate on your car IIRC, ... is it possible that the EGR is part of the problem?

If it were overfueling, it would not idle but run faster instead. If it were only a couple of cylinders, run rough. Seems like retarded timing is the most likely culprit of the black smoke portion (although I have a feeling that this is going to be one of those oddball solutions).

Line the 14* ATDC mark up with the balancer mark, open the timing port of the IP (oil will spill) and see if the timing/lock tang is in the center of the hole. Should take 5minutes and help diagnosis greatly.

Hey, is there a timing port on a 617 engine?

Interesting find this afternoon. Purchased a vac meter and there was no vac on the turbo side of the car. Replaced the vac line from the vac pump to the turbo side along with replacing a few line around the vac switches and got vac there now.

Does the temp sensor, single prong, possibly have na effect? My gauge is erratic, will peg at 120 for a few sec, drop to 85, etc. Generally holds at 85 while on the highway. When the gauge pegs at 120 I can hit the dash and it will drop to 85.

The car acclerates much better; however, the pesky smoke problem still exist.

It is strange ... the car idles fine with very little smoke for 14 to 15 sec and then drops a few rpm, no more than when the ac compressor would come on and a puff of dark black smoke comes out and continues for 14 to 15 sec and back to normal for 14 to 15 sec .... this pattern just continues.

I noticed today that the car smokes much more when in gear @ idle. Could this be an item to narrow down the smoke problem?

I stopped by the MB Dealer and while picking up a couple of parts for my SL and had an opportunity to talk with a MB Diesed Tech about the smoking problem..

The Tech said if not the ELR, which it doesn't appear to be, then he has seen on several cars, when smoking increases when in gear at idle, the the trans modulator valve is faulty and the car is sucking some trans fluid thru the vac line and into the intake.He also indicated that the reduced smoke when in nutral is another key, there is less esposure to trans fluid in nutral.

I will replace the modulator valve and post findings.

Fixed !!!! IP was 10 deg out of time. No injector nailing nor smoke now.

Another Score !
 

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