Poor acceleration 1985 300tdt

[rogersherwoodki]

Mercedes 300 tdt 1985 with automatic transmission.

This new old car has very slow acceleration especially when cold until about 30 or 35 mph and 2200 rpm where turbo must kick in because RPM picks up quickly and car accelerates well. Takes about 14 or 15 seconds to get to 60 mph so performance seems reasonable as long as it is being asked to accelerate the most. But at about 40 mph, car wants to slow down unless enough throttle is used to kick in turbo. Makes for a surge like ride for in town driving since can’t accelerate slowly – either almost not at all or fast with the turbo. Measured pressures are 17 in Hg vacuum and 12 psi pressure during acceleration peaking at about 14 momentarily during a shift. Would appreciate any suggestions.

Roger

[bgkast]

Calling Jimmy.

Is this a Cali '85? My old '85 cali was also very slow when cold. It could have something to do with the emissions stuff.

[Brian Carlton]

Diesels generally have poor performance when cold and also have less than desirable performace below boost levels when warm, unless the driver has lower expectations.

If you've never driven a diesel with higher mileage and few adjustments, your expectations might be tuned to a gasser.

Diesels are not for everybody. Patience is needed especially when cold.

What's the hurry, anyway..........trying to beat a gasser to the next stoplight??

[GRIESL]

Unless you're measuring pressure in the line that connects intake to alda, then you may want to check that banjo bolt and vacuum line. It gets gooped up and causes loss of low end power. Do a search on "banjo bolt" and "overboost protection solenoid", and you'll find a bunch of info. But I'd also agree that low rpm performance and especially cold performance is not good on these cars. I would even caution you against trying to accelerate too quickly on an ice cold engine. Good luck.

[rogersherwoodki]

This is a Cali '85. Will try to look into the emmissions controls.

Even when warm, it tends to not want to hold a constant speed in the 40 to 70 mph range. It either wants to slow down or speed up too much on more throttle. This also shows up as surging on cruise control.

Prior to posting the original message, I did check all of the banjo bolts and cleaned considerable crud from the one on the manifold. This seemed to help some but not as much as hoped for.

I may be spoiled by our 1991 350SD but it seems like the throttle control should be a little smoother. Thanks for all of the ideas and and more that may come.

Roger

[rogersherwoodki]

Forgot to say that vacuum was measured from the tap on the back of the manifold.

[Biodiesel300TD]

Might try a valve adjustment, and change the fuel filters. These cars a pretty sluggish until they get warm, especially in the winter time.

[rogersherwoodki]

Thank you. Fuel filters - this may be it as it seems worse at colder temperatures. Will do it and report back.

[bgkast]

Originally Posted by Brian Carlton

Diesels generally have poor performance when cold and also have less than desirable performace below boost levels when warm, unless the driver has lower expectations.

If you've never driven a diesel with higher mileage and few adjustments, your expectations might be tuned to a gasser.

Diesels are not for everybody. Patience is needed especially when cold.

What's the hurry, anyway..........trying to beat a gasser to the next stoplight??

I've driven a lot of these cars Brian, and this one was just SLOW when cold. I tried adjusting the valves, fuel filers, etc, but could never figgure it out...

[JimmyL]

Originally Posted by bgkast

Calling Jimmy.

OK, I'm finally here, and not a moment too soon.....

Originally Posted by rogersherwoodki

Mercedes 300 tdt 1985 with automatic transmission.

I think a good visual inspection of that badge on the left hand side of the rear hatch is in order....

[rogersherwoodki]

Emblem on back says 300TD.

[Brian Carlton]

Originally Posted by bgkast

I've driven a lot of these cars Brian, and this one was just SLOW when cold. I tried adjusting the valves, fuel filers, etc, but could never figgure it out...

If you drove it, then I defer to your opinion.

The only items remaining are the cam timing and IP timing. But, these items would also affect performance when fully warm.

Does it behave normally when warm...........or is it also slow?

FWIW, I've got similar problems with the '87............slow at all speeds/conditions.

[bob_98sr5]

Originally Posted by rogersherwoodki

Emblem on back says 300TD.

Roger,

Just ignore Jimmy. Hopefully he'll provide some tech knowledge not emblem knowledge.

Though we have different cars, here's a thread detailing how I got my 0 - 60 times up: How I got my 0-60 time down from 35 to 25 to 12

Some may be applicable. Key things are to change out all the vac hoses, rubber fittings that may be cracked, etc.

As others have mentioned, there's the banjo bolt coming out of the ALDA. At the junkyard yesterday, I saw one w/ the IP in there that they didn't remove. Curious, I unbolted the ALDA to see what this looked like. Lo and behold, the ALDA bolt was gummed up with stuff. I can see why the guys dispense this advice now on your 85.

You may also want to check your fuel system for any leaks. Of course, changing out all the filters including the tank screen (do 85s have them?) would help as well.

But as Brian said, expectations for diesels are usually akin to what other gas'r you drove before. I had to certainly lower mine!

[rogersherwoodki]

Thanks Bob, I will work through the 0-60 thread and see what happens.

[bgkast]

Originally Posted by Brian Carlton

If you drove it, then I defer to your opinion.

The only items remaining are the cam timing and IP timing. But, these items would also affect performance when fully warm.

Does it behave normally when warm...........or is it also slow?

FWIW, I've got similar problems with the '87............slow at all speeds/conditions.

Just to clarify I did not drive the OP's car, but I also had an '85 Cali that was very slow when cold, but was normal for a 300D Turbo when warm. It was very strange, when I would rev the engine in neutral when it was cold the engine would only slowly wind up. It was almost like the IP governor was what was limiting the engine.