Question on smoke at idle
 

On my new 240D, I have a situation where the car smokes considerably at idle but not under a load. Once I hit second gear under normal acceleration, the smoke disappears. And driving along at normal speeds I cannot detect smoke behind me. The car has plenty of power. Yet if I stop at a light, the poor person behind me.....(and this is written from a person who enjoys sending smoke from years of practice).
It appears to be a fuel related problem. At casual glance it looks like there is an ALDA setup similar to the 300's. My questions are as follows:

1. Could the ALDA help this situation?
2. Do I have an injector problem?
3. What other things could it possibly be?

Any suggestions would be appreciated as I hope to tear into it tomorrow.

diesel don,

I think these things actually have a vacuum in the manifold due to a governor plate, at idle. I had a 220D lose the vacuum pump diaphragm and at idle the car blew huge clouds of oil smoke. At running speed, it did not smoke much at all. The point is that you may have some bad valve seals and at idle, they leak more oil into the intake valves than at other speeds, or you may have a vacuum pump diaphragm beginning to fail.

Good Luck, Jim

Thanks Jim:

In combining your comments with the seller's comments I might start with the valve seals first.
How long did your starter malfunction before you fixed it? Mine spins about every other start attempt. It never spins twice in a row however.

Don

In order to deal with the smoke issue, you need to determine whether its oil smoke or unburned fuel smoke. Obviously they are two completely different problems.

Oil smoke is distinctly blue in color. Just about totally blue if its only oil being burned.

Unburned fuel is more of a light gray, perhaps with a touch of bluish tint. And it will clearly smell like diesel fuel.

Of course you could have combined problems and get combined smoke.

What I'd do is pull over when the problem happens, jump out and get a closer look & smell at the smoke.

I'd hate to see you redo the valve guide seals when its a dirty injector problem. Or something like that.

Ken300D

Diesel Don,

Ken300D points out something that should be considered, and that is to fix something you do actually have to make sure you have the problem identified. I made my observation based on the description you gave that the smoke goes away once you get past the idle speed on the motor. Most of the bad injectors I have encountered do not get better when you push more fuel through them. But I agree with Ken300D, you should make sure the problem is isolated before starting. Those rubber seals are getting close to twenty years old, and live in a really hostile environment. I am not sure how to prove it is valve seals until you either look into the manifold and see the signs of steady leakage (lots of black tarry or crusty deposits).

To answer your other question, when my starter chewed my ring gear, the frequency of failures to engage the pinion gear teeth in the ring gear quickly went to near 100% of the time. I actually used to get out of the car and push it a few feet in gear to get another spot for the teeth to mesh. This worked for me, and I rationalized it by theorizing the solenoid/pinion gear assembly had lost its ability to deflect if the teeth did not line up to mesh. My wife thought it was a totally unacceptable solution and made that clear.

But the problem was originally intermittent, and then became constant. I origninally suspected the pinion gear, but when I took the starter out it looked ok, and then the issue with the ring gear became clear.

Good Luck, and keep us posted on what you decide to do. Jim

The probability of a vacuum diaphragm leak is easy to check: Disconnect the line going to the intake manifold at the vacuum pump and look down into the fitting: If black oil, you have a leaking diaphragm---the line going to the intake manifold will also likely be coated inside with black oil.
Ken

Thanks Ken, Ken & Jim:

You've given me plenty to think through and look at. My friend Kirk (who went with me on the trip to purchase it), has a hunch that it is fuel related. The seller however had purchased valve stem seals and included them with the car.
Will check the vacuum line as well.

Jim: my starter is not messing with the pinion and ring gears. Rather, it just spins (whirs) freely on some 1st attempts. My 300TD on the other was slamming into the ring gear already in motion. That was a bad sound. This is something I can live with for a bit longer.

Thanks for the advice.

Don

Ken & Jim:

I just changed the fuel filters and observed smoke before and after. And all of this was on a warm engine.
The smoke is the same. It really smells of diesel fuel and is a grayish-color with perhaps a tint of blue. What continues to confuse me is that it seems to be non-existent when traveling down the road. Today was bright sunlight and I tried hard to see it. On occasion, I'd catch a glimpse of some but hardly any overall. I let it idle tonight at church and you'd thought the place was burning down. The car has great power and it started at 13 degrees tonight with a mere touch of the key. Best starting diesel I've ever owned.
Is the injector job large and complicated or is it straightforward? My Chilton's manual makes it look ok but they often leave out important stuff.

Thanks,

Don

Hmmmm. Well, I always like to try the easy and cheap things first.

- Pop the top off the air cleaner and see if it is clogged. Perhaps you can idle it for a little while this way to see if the smoke is reduced.

- Try some fuel injector cleaner. The most effective thing is diesel purge at full strength. A fairly effective thing is a full bottle of Red Line DFC.

- I don't think this is it, but if the valves haven't been adjusted in awhile, it is probably time to check on them. And also whether or not there is any timing chain stretch. (a search here on these topics will find a lot of information.)

---------------

So, the first two are really easy. The third is kinda hard in cold weather, and I'm not sure it would help - although it is something you need to do routinely on the car. Mercedes says every 15,000 miles - others here would say 20-30K.

I don't fully understand the fuel injection on diesels. But it seems to me if too much fuel were getting injected, it would simply speed up, not smoke. So for some reason you are not burning fuel correctly. This could be an air restriction - or maybe some kind of dirty injector problem.

Low compression comes to mind, but that's not consistent with good power otherwise and good cold starting.

Let us know what you find and maybe we'll think of other things to check.

Ken300D

My next step would be to remove the injectors and have them checked on test bench for spray pattern and opening pressure. If one nozzle is found to be bad I have shop replace all of them.
A defective spray pattern or low opening pressure can cause incomplete burning and smoke. Go to a shop that services Bosch injection equipment.
Ken

I second the notion about the injectors.
keep posting!

Thanks for the continuing advice. I've been following another post by Doug V who shares the same symptoms. Tonight I noticed black specks of dirt in the clear (90 degree) fuel filter even though I just changed it 3 days ago. If this car sat for awhile, the dirt might be affecting the injectors if the filter is collecting stuff that fast. Would you guys try to keep changing filters until that problem cleared up first before the more expensive injector issue?

I'm having fun with bringing the normal stuff up to good condition. Have had the car a couple of weeks and have done hood pad, alloy rims, tires, antenna, oil change, filters, vacuum locks, and a few other small things.

Other than the excessive smoke at idle this car is awesome. Can't wait to figure that one out.

Don

I'd like to hear your experience with the hood pad. I've got one ready to go in the 300D when it warms up some. What products did you use to clean the hood and what adhesive did you use?

Also, what kind of rims did you put on the car? I just put 15-hole alloy rims from a 1988 300SE on my 300D - looks nice.

While you may have some dirt, rust or algae in the fuel tank, I don't think fuel supply is your problem. You are getting enough fuel to run well at speed, for example. Your problem is one of proper fuel combustion. To do diesel purge at full strength you use extra fuel hoses to run the car off a jar filled with the product. Easier but less effective is to pour a full bottle of Red Line DFC in the tank (or a half tank). Diesel purge is surprisingly effective at cleaning injectors. And much easier than physical removal.

There is a supply of diesel purge on EBay right now at a good price.


Ken300D

ouch!
 

I am kicking myself for showing you that car instead of buying it myself! :eek:

It sounds like your pre-filter is doing it's job--I wouldn't think that those large specks are getting to your injectors. Remember that these indirect injection diesels DO NOT like to idle for long periods--they are too efficient. When sitting there idling they will not generate enough heat to prevent the pre-chambers from clogging with carbon, which leads to rough idle and smoke. So when it's cold outside, plug in the block heater for a couple of hours in the morning, then just get in and drive the thing without an extended idle 'warm-up' period.