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Discussion Starter #1
I have a 91 300d with I think over 500k miles on it and it seems to be running rich(lots of black unburnt fuel smoke) even under partial throttle loads.
I think older ALDA's have adjusting screws on the top of them which allowed Easy adjustment. Is this possible or how would you adjust fuel mixture.
I'm assuming it's not a lack of boost issue to the ALDA otherwise it would be a lean condition if I understand correctly how it works.

Any thoughts?
Thanks!
 

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Have you checked other stuff? Chain stretch may be an issue with 500k miles. Have the injectors ever been replaced? They don't last forever. Air filter?
You might need to adjust alda but I believe thay made it harder than on the earlier models.
 

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Discussion Starter #3
Have you checked other stuff? Chain stretch may be an issue with 500k miles. Have the injectors ever been replaced? They don't last forever. Air filter?
You might need to adjust alda but I believe thay made it harder than on the earlier models.
Thx,

Yes checked chain stretch and have it within spec. I have not done anything with the injectors, but have no idea what maint history the PO did I've owned it for the last 5 years and 40k miles. Guess it couldn't hurt to have them serviced, anyone have luck with that?
All filter changed regularly.
 

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I changed out all injectors onmy SDL two years ago at around 360k miles. Result has been a quieter engine, smoother engine and while I did not have a huge smoke plume exhaust, that too was reduced.

I have owned at least one MB diesel for the past 23 years, and adjusting the ALDA had never been an issue. Just have never needed or thought to do it.

What I have found is that these engines do much better when driven "like you stole it" at least on a regular basis. Puttering around town can lead to your condition.

Mobil 1 synthetic is also very theraputic. I change about every 8 to 10k miles

Have you used Lube Moly Diesel Purge? It could be a step before you elect to change out the injectors. Does an outstanding job.

One other thing to have checked is your turbo waste gate function. As these age, they can weaken, which effectively reduces the boost provided to the intake.

Sorry to ramble, but, I am just reticent to mess with the ALDA

Tom Scott
Richmond, Virginia
1987 300SDL 404k
1993 300D 306k
 

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Discussion Starter #5
I changed out all injectors onmy SDL two years ago at around 360k miles. Result has been a quieter engine, smoother engine and while I did not have a huge smoke plume exhaust, that too was reduced.

I have owned at least one MB diesel for the past 23 years, and adjusting the ALDA had never been an issue. Just have never needed or thought to do it.

What I have found is that these engines do much better when driven "like you stole it" at least on a regular basis. Puttering around town can lead to your condition.

Mobil 1 synthetic is also very theraputic. I change about every 8 to 10k miles

Have you used Lube Moly Diesel Purge? It could be a step before you elect to change out the injectors. Does an outstanding job.

One other thing to have checked is your turbo waste gate function. As these age, they can weaken, which effectively reduces the boost provided to the intake.

Sorry to ramble, but, I am just reticent to mess with the ALDA

Tom Scott
Richmond, Virginia
1987 300SDL 404k
1993 300D 306k

Thx Tom,
Makes sense. I'll look at injector service locally.
I do run the piss out of it on occasion like everything I own so that not an issue.
I do run Mobil 1 with similar intervals.
Have no idea what "Lube Moly Diesel Purge" is!

Waste gate/boost seem to be w/in limits.

DD
 

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What does it take to verify waste/gate limits? If I get down on it moves good..a light pedal and it move MUCH slower
 

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Another easy fix, often overlooked, is that of replacing vacuum line (rubber) and cleaning orifice at intake manifold as well as the one connector that is itself an orifice.

This one connector is colored differently that the "off orange / yellow" of the others. On the five cyl OM0602 it seems to be located between the intake orifice and the alda coonection.

Clean out these areas internally with brake cleaner (the intake maniflod orifice comes out with a 10mm deep socket) , make sure that all other rubber hose connections within the vacuum system, including the ones under the air cleaner housing, are sound. Just because a hose appears to be in one piece does not mean that it will hold a vacuum. If you do not have a mityvac, get one.

And then be surprised at the additional torque and power this engine will deliver.
 

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Good information Thanks so much..Is there a model number on the mityvac I need? There are a ton on there web site. Looks like one id for bleeding brakes, another to check radiator pressure and still another to check hoses like you mentioned and engine compression.
Thanks
 

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Don't recall. the base unit is the same. I think the differences are in the attachments. As I recall I got the base unit with a bunch of attachments for around $30 bucks. four or so years ago. Have never used most of the atachments, especially the brake fluid extraction thing.
 

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Discussion Starter #10
This one connector is colored differently that the "off orange / yellow" of the others. On the five cyl OM0602 it seems to be located between the intake orifice and the alda coonection.
I don't see a different color connector on mine.
MB 300d.jpg

I've bypassed the Over-Boost sensor as it was bad and causing loss of boost.
 

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Well, looking at your picture, that connector (orange / yellow) should have a very small orifice at its midpoint. In otherwords, if you hold it up to the light, it will not be a straight through constant diamenter cylinder.

If not, I suspect someone prior to you had messed with it or replaced it thinking it was blocked. Instead it is little more than a pin hole.

Now I cannot direct you to a manual, all I can report is that on my two diesels, keeping this connector clean, as well as the fittin coming off of the intake manifold as well as the hoses makes a rather significant difference in power and shifting.
Do you leave the hose to the intake mainfold disconnected all of the time? If so, I wonder how the tranny get modulated to the engine force.
 

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Discussion Starter #12
New issue

Well I now have (just started one morning) a new issue.
Car starts instantly, but now has a miss and puts out large amounts of gray/white smoke. This is after sitting over night or at least 8 hrs, doesn't do it between shorter start cycles.
I've always wanted to replace the injectors so took this opportunity to install some new Monarch injector nozzles after running two full cans of Diesel Purge.
No real difference, I thought that maybe an injector went bad as was dripping fuel over night flooding whatever cyl.
I'm now thinking it might be Valve Stem Seals!
Engine smokes until it's fully warm and has been driven at least 10-15 min, then smoke stops.
I understand that earlier 2.5's can have their stem seals replaced w/o pulling head or valves, can this also be done on my engine??? :confused:
 

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Wiht regards to valve stem seals; I have owned three MB diesels so far. Never replaced valve stem seals. The first diesel was sold at 307k, still own the other two with 311k on the 2.5 and 411k on the SDL. I would be surprise if the seals were in need of replacement.

What is your oil consumption between oil changes, and do you have ANY engine oil leaks or seeps?

When replacing injectors it helps to be sure that they are balanced, that mean that they open at the same injection pressure. If not, there are shims to adjust. If you simply replaced the nozzles, you likely have a set of injectors that open at different pressures and that definitely could lead to rough idle and operation.

Likely contributes to your symptoms

My advice; Take the injectors to a diesel shop and pay they to balance the pressures. That will improve operation.
 

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Discussion Starter #14 (Edited)
Hey Tom, thanks as usual.

Turns out it was a bad Glow Plug (#2) causing the miss and most of the smoke. It had 42 ohms of resistance vs and avg. of 1.2 ohms on the others. The engine starts instantly and there is No initial smoke until 10-20 sec. then it starts smoking until the engine reaches full temp and or has run 15-20 min, then no real smoke. At full temp idle is super smooth.

I did run two cans of Diesel Purge through it before rebuilding the injectors installing new Monarch injector nozzles. I built a bench injector tester and was surprised just how balanced the factory injectors were. Factory spec is 1950 psi (turbo) and these ranged from 1935-1955 psi pop pressure.
I did have a problem with my tester after that and wasn't able to test all the rebuilt injectors, but considering just how precise injector nozzles are manufactured I can't imagine them being off much at all. It takes a shim change of 0.50mm to make 50-70 psi change to pop off pressure so I'm guessing that injectors are balanced at least w/in 100 psi maybe closer, but I have no numbers to back that up.

It does run better and I expect MPG's to also improve, but I would still love to eliminate that 15 min of smoking.
 

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DD

Good to hear.

As for the smoking, there shouldn't be much smoke at all after the initial start. A light smoke until it warms up maybe - thats for the first few miles of driving.

If you just let it idle, it will never warm up.
 

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Very slick tester!!!

I'm out'ta ideas or things to check. I was thinking that really cold weather can create smoking at start, but you aren't in a realy coil climate.
 

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Discussion Starter #19
OK after loosing a injector line(rupture) my car starts instantly with zero smoke and is quite. After 20-30 sec. the motor starts a heavy diesel rattle and begine to smoke(oil) and continues to blow a decent amout until engine is fully warm.
The fuel line was rubbing a bracket and failed, it was repaired with a oversized sleeve and reinstalled. Not sure if these lines are still avaiable???
Motor was very quite after recent injector nozzle replacement, but became loud after the line failure???
Maybe something was in repaired line and has a piece of trash in injector? Sounds like a different cyl. with knock though. Knock goes away around 2200 rpm>.

thx
 

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DD-
These engines will run on 4 cylinders. My daughter sprung a leak on fuel line to #5 several years ago. Couldn't fgure out where the leak came from, diagnosing long diwstance, so she drove from Lexington, Ky to Richmond, Virginia with the leak. Got real slow going up some of the WV grades.

Long and short, if the lines are not properly secured with the plastic brackets THEY WILL FRACTURE.

And, yes, replacement lines are available from the dealer at very reasonable cost. I would not go the route you have chosen. I recommentd getting a new replacement line for which ever cylinder yours failed, and get the plastic brackets as well.

As for your knocking, you could isolate each cylinder to determine which is knocking by loosening the fuel line at the top of the injector, one at a time, listen for canghe, retighten and move on to the next, until you find the cylinder that is knocking.

I can't tell you what to do after you isolate the cylinder other than to change out the injector with a spare, if you have one,to see what happens.

aldom
 
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