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Discussion Starter · #1 ·
This all initially started off because I was having issues with the transmission flaring a bit. It turns out that the hose connecting to the EGR was disconnected and there was too much transmission fluid.

After reconnecting the hose to the EGR and removing the excess trans fluid it was shifting fine, but now after about a week there's essentially no power when accelerating.

I'll even attempt to floor it from a stop and it takes about 30 seconds to get up to cruising speed, all the while making a weird propeller-type noise and blowing tons of smoke out of the exhaust pipe. I can barely even get up a hill.

Anyone run into anything like this before, or have suggestions on what to look into first?
 

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1985 300CD, 1985.5 Porsche 944, 1969 Triumph TR6, 1998 Land Rover Discovery I, 1992 Volvo 240
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Does the motor respond "correctly" to giving it power manually under the hood? When doing so is there still smoke out of the tailpipe? What color is the smoke? Just trying to eliminate the motor/turbo being your issue. Is it a non turbo 300? Does sound transmission related.
 
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.................... ~'84 300D~~~~~~~~ ~~'85 300TD~~~~~~~ ~~~W123(s) Galore~~~
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As MSG asked above... how responsive is the throttle under the hood? what color is the smoke?
I wouldn't be to concerned about the tranny at the moment... you are checking the tranny fluid with the engine warmed up and running... correct? Also, is this an American '85? If yes, it has the Vacuum Transducer i.e., 'Blue Flying Saucer' on the left, driver side wheel well.

Black Smoke is your fuel/air mixture.
White Smoke is an issue... if you have this ...check your oil and coolant levels. Is the oil black or is it brownish? Is the oil over filled?

Additionally, lack of power may be the turbo, put together a cheap boost gauge and test the turbo. Personally, I delete the EGR (5 W123s so far). At 36+ years old the EGR does practically nothing for the environment however it does assist greatly in fowling your turbo & engine.

Have you done the following...

Have the oil, air and fuel (primary and secondary) filters been changed recently?
Have the valves been adjusted recently?
Checked the Timing (you do this when you adjust the valves)?
Pop-tested the injectors recently (if you do this... do a compression test at the same time)?
Do you have a boost gauge to test the turbo output?

edit: Without adding another post.... Ditto on the switchover valve Bypass or delete below... thank you 'Funkle'. Make sure the Banjo Bolt and Lines are Clean.
 
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06'E350 wgn,05'E320 CDI,04'E320 wgn,85'300CD,67'230SL
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+1 all the above ^^^^^. Plus...check the hose from manifold, to switchover valve, to ALDA on injection pump. If the line is plugged or any cracks or air leaks the turbo will not boost fuel.
I have to wonder if reconnecting the EGR has somehow pushed crud that's fouled this line, or the hose line (plastic tubing) has been disturbed.

Back in the day....we would bypass the switchover valve and run the tubing directly from the manifold to the ALDA to spool up the boost faster for better power response and smoother shifting. This may, or may not have been done already on your car. But you could eliminate the possibility of a bad switchover valve by doing this.

Just a suggestion.
 

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Discussion Starter · #6 ·
Does the motor respond "correctly" to giving it power manually under the hood? When doing so is there still smoke out of the tailpipe? What color is the smoke? Just trying to eliminate the motor/turbo being your issue. Is it a non turbo 300? Does sound transmission related.
As MSG asked above... how responsive is the throttle under the hood? what color is the smoke?
I wouldn't be to concerned about the tranny at the moment... you are checking the tranny fluid with the engine warmed up and running... correct? Also, is this an American '85? If yes, it has the Vacuum Transducer i.e., 'Blue Flying Saucer' on the left, driver side wheel well.

Black Smoke is your fuel/air mixture.
White Smoke is an issue... if you have this ...check your oil and coolant levels. Is the oil black or is it brownish? Is the oil over filled?

Additionally, lack of power may be the turbo, put together a cheap boost gauge and test the turbo. Personally, I delete the EGR (5 W123s so far). At 36+ years old the EGR does practically nothing for the environment however it does assist greatly in fowling your turbo & engine.

Have you done the following...

Have the oil, air and fuel (primary and secondary) filters been changed recently?
Have the valves been adjusted recently?
Checked the Timing (you do this when you adjust the valves)?
Pop-tested the injectors recently (if you do this... do a compression test at the same time)?
Do you have a boost gauge to test the turbo output?

edit: Without adding another post.... Ditto on the switchover valve Bypass or delete below... thank you 'Funkle'. Make sure the Banjo Bolt and Lines are Clean.
Thanks for all the input! I just recently purchased it a month or so back and it was running perfectly until I drove it to Joshua Tree through about 10 miles each way of bumpy roads (my own fault for not realizing what I was getting into).

The throttle seems to be responding correctly.
The smoke is both grey and white. Grey when I accelerate and then fizzles out into white.
The oil level is good, and just changed about 1k miles ago, and I just replaced the radiator hoses, flushed them out, and refilled the coolant.
The valves could probably use an adjustment. As good of care as the seller took of this, that's one thing I'm not sure if he did recently.
 

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Discussion Starter · #7 ·
+2 ^^^^^^^^

Is it hard to start ?
Does it idle smoothly ?
Can you rev the engine in neutral without issue or is it similarly sluggish even when there is no load

Is air being sucked in either side of the pump ?
Fuel Filters as above, PLUS tank strainer
It's starting up like a dream. No issues whatsoever with starting, and it idles very smoothly.
I can rev it in neutral and it seems normal, however, it's definitely spitting out grey and then white smoke.
 

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Discussion Starter · #8 ·
+1 all the above ^^^^^. Plus...check the hose from manifold, to switchover valve, to ALDA on injection pump. If the line is plugged or any cracks or air leaks the turbo will not boost fuel.
I have to wonder if reconnecting the EGR has somehow pushed crud that's fouled this line, or the hose line (plastic tubing) has been disturbed.

Back in the day....we would bypass the switchover valve and run the tubing directly from the manifold to the ALDA to spool up the boost faster for better power response and smoother shifting. This may, or may not have been done already on your car. But you could eliminate the possibility of a bad switchover valve by doing this.

Just a suggestion.
Being new to diesel I was very unfamiliar with the EGR but all I seem to see online are negative things about it. I wouldn't be surprised if having reconnected it caused these issues. It never made this propeller type noise before reconnecting it, but it was running fine for a bit after having done so. It's only now after about a week of sitting in my driveway that it's giving me this acceleration/lack of power issue, and that propeller noise is louder than ever. I've traced most of the lines and everything seems to be looking okay.
 

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Do you have a good independent MB tech near you familiar with these old diesels? Did you have someone do a pre-purchase inspection?
If not, it seems like you need to find one....quickly. Before a small problem becomes a big one.

The MB Club of America local branch could probably recommend someone near you. Once things are sorted, you can DIY a lot of routine maintenance on these cars. But I think you need a good starting point. Someone familiar can probably get to the bottom of these issues quickly. But very difficult over the internet.
 

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What color is the oil? And, is the oil overfilled? Good advise from Funkle... get it to a mechanic. While I cannot speak to the certitude of pi... White/Grayish smoke tends to mean coolant/water is leaking past the head gasket. It can also leak into your oil. Water/Coolant also causes friction and will deteriorate cylinder walls. You do not have to freak out... but, you do need to get it properly diagnosed asap.
 

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Discussion Starter · #11 ·
What color is the oil? And, is the oil overfilled? Good advise from Funkle... get it to a mechanic. While I cannot speak to the certitude of pi... White/Grayish smoke tends to mean coolant/water is leaking past the head gasket. It can also leak into your oil. Water/Coolant also causes friction and will deteriorate cylinder walls. You do not have to freak out... but, you do need to get it properly diagnosed asap.
Wait! That would actually make a lot of sense. Shorty after replacing the radiator hoses the bypass hose started to leak very badly, so I didn’t drive it for about a week until a MB mechanic could come by and replace it. Could that have possibly leaked into the oil? The oil’s definitely closer to black than brown btw.
 

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Discussion Starter · #12 ·
Do you have a good independent MB tech near you familiar with these old diesels? Did you have someone do a pre-purchase inspection?
If not, it seems like you need to find one....quickly. Before a small problem becomes a big one.

The MB Club of America local branch could probably recommend someone near you. Once things are sorted, you can DIY a lot of routine maintenance on these cars. But I think you need a good starting point. Someone familiar can probably get to the bottom of these issues quickly. But very difficult over the internet.
Yeah, I’ve got one coming by today. Probably a great idea before I start to attempt dabbling even more myself.
 

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Please keep us posted. Would like to know for future reference. The good thing about these old diesels is that there's very very few electronics. Most things are vacuum or electro-mechanical which are serviceable.

The 85's however, have a unique 'EGR Module' under the right side interior panels.They are known to go bad and replacements are nla. Only fix I know of is to bypass 'em. However, this doesn't sound like your current issue. But PO undoubtedly disconnected the EGR for a reason. ;)

Hopefully, yours is NOT a California model with the dreaded trap oxidizer that would shed pieces of ceramic and eventually destroy the turbo. I believe Mercedes replaced most of these under warranty.

I don't mean to add to your concerns. It's just info to know so you can address issues quickly before they become major problems.
 

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Discussion Starter · #14 ·
Please keep us posted. Would like to know for future reference. The good thing about these old diesels is that there's very very few electronics. Most things are vacuum or electro-mechanical which are serviceable.

The 85's however, have a unique 'EGR Module' under the right side interior panels.They are known to go bad and replacements are nla. Only fix I know of is to bypass 'em. However, this doesn't sound like your current issue. But PO undoubtedly disconnected the EGR for a reason. ;)

Hopefully, yours is NOT a California model with the dreaded trap oxidizer that would shed pieces of ceramic and eventually destroy the turbo. I believe Mercedes replaced most of these under warranty.

I don't mean to add to your concerns. It's just info to know so you can address issues quickly before they become major problems.
Yeah, at first I had assumed maybe it got disconnected accidentally when he got the fluids changed before my purchase, but after all the research it definitely would seem intentional. I’m pretty sure it’s Federal since it said it says it conforms to USEPA regulations. Thanks for all the input, btw!
 

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Yeah, at first I had assumed maybe it got disconnected accidentally when he got the fluids changed before my purchase, but after all the research it definitely would seem intentional. I’m pretty sure it’s Federal since it said it says it conforms to USEPA regulations. Thanks for all the input, btw!
It would be good to run a free vin# lookup to see what options it was shipped with; and if equipped with 'California compliant' code that's above and beyond the Fed USEPA. The CA models had the trap oxidizer; which was so problematic Mercedes agreed to fix 'em.

Between my 123's and 126 with that wonderfully durable OM617A engine I've probably put on well over 700,000 miles. I still have an 85 300CD (non-CA) that reminds me why I own Mercedes.

Once sorted; these are solid cars destined to run forever if properly maintained. Unfortunatly, in the wrong mechanic's hands not familiar with the old ways....they can get pretty screwed up. Not un-fixable; just needing proper attention.
There's a guy in Titusville FL, Pierre Hedary that really knows these cars, and has a pretty informative U-Tube channel. Have you seen it?
 

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Discussion Starter · #16 ·
I’ve got my guy here now working on it. He says there’s no trap oxidizer so I guess that’s a good thing. He’s thinking there’s a problem with the vacuum lines and they’re potentially switched up. I was searching for diagrams myself and everyone I seem to find is such low quality that I can’t tell which colors are supposed to go where.

I’ll definitely check out that Youtube channel. Thanks for the tip!
 

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FYI - As part of the warranty, MB replaced the trap oxidizers with a different system. You have to check vin# to see if it was originally a CA emissions car. The same thing happened on the W124 87 300D and early 6 cyl W126 SD's circa 1986 that came with trap oxidizer.

The 'propeller sound', was while car was moving/accelerating? Check the driveshaft and motor/trans mounts. Fan shroud? Your guy should find source. You'll get familiarized with the car in the process. 😁
 

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Discussion Starter · #18 ·
FYI - As part of the warranty, MB replaced the trap oxidizers with a different system. You have to check vin# to see if it was originally a CA emissions car. The same thing happened on the W124 87 300D and early 6 cyl W126 SD's circa 1986 that came with trap oxidizer.

The 'propeller sound', was while car was moving/accelerating? Check the driveshaft and motor/trans mounts. Fan shroud? Your guy should find source. You'll get familiarized with the car in the process. 😁
It’s funny you say that because he’s replacing both the motor/trans mounts as we speak. Definitely learning a lot.
 

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Is this readable? Block Off the EGR crap (red Xs). You can temporarily block off #123 (blue flying saucer) & 125 & 126 (switchover valves). It will still run beautifully and shift perfectly (even with 123 & 125 & 126 blocked off). Run the Banjo Bolt (just above the number 110) line directly to the ALDA. Run the transmission modulator (#100) directly to the top of the VCV (vacuum to the top, add dash-pot). The Brown lines go to the shutoff valve... 1 line goes through the fire wall to the ignition the other comes out of the fire wall to the shutoff valve. Yellow goes to the doors... Green goes to climate control. There is a black line from the fire wall that is purely 'atmospheric' (no vacuum, no pressure)... connect it to the bottom of the VCV Correct me if I'm mistaken guys.

You are insane if you do not own a MITY-VAC (and, 20 golf tees) and you own one of these vehicles.

1985_617_VacuumDiagram_FED_CalElimi.jpg
 

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Is this readable? Block Off the EGR crap (red Xs). You can temporarily block off #123 (blue flying saucer) & 125 & 126 (switchover valves). It will still run beautifully and shift perfectly (even with 123 & 125 & 126 blocked off). Run the Banjo Bolt (just above the number 110) line directly to the ALDA.


View attachment 2695940
+1 ^^^^^ yes! And it's a good idea to use a new piece of tubing, and make sure the orifice in banjo bolt and manifold is clean and clear; or you'll get zero boost and wimpy power because the ALDA won't increase your fuel! Once started a compression ignition engine just needs two things to create power...More Air and More Fuel. ;)

I once drove my 300D 1,000 miles from NC to NH with no alternator and a dead battery. I had to manually STOP the fuel supply lever to shut it off!
 
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