300D vs 300TD Performance Disparity
 

"It was the best of times, it was the worst of times." It sounds to me like Dickens owned two diesel Mercedes...

I've got the best of things and the worst of things: a 300D and a 300TD to compare to each other. Consequently, I'm perplexed at the differences in performance between these two cars.

Lilly, the 300D (265,000mi) , has real 'get-up-and-go,' she pulls well with her a/c on and gets 21-23 in the city and 24+ on the highway. I know that her timing chain has approximately 5°-6° of elongation and that at some point in her past, the IP was moved (probably to correct some lost performance issue) but, I do not know how much 'adjustment' was made.

OTOH, the lovely and charming Marlene, has always been 'stately' in her departure from traffic lights and can barely get out of her own way with the a/c running. Her economy is similar but she will occasionally pull a highway stint at 26-27mpg. Her cam timing is spot on (with a 4° offset key) and her IP has been adjusted accordingly but not checked by either drip timing or any other method.

I've always attributed these differences in performance and economy to different final drive ratios. I'd heard at some point that the wagon had a higher final drive than the sedan (2.88 as opposed to 3.07 or 3.56) and my experience in comparing the speed to the tach on the two cars seemed to bear this out. However, when we got TO's '85 wagon on the road, I discovered that it performed almost exactly like SWMBO's sedan which got me thinking that maybe Marlene wasn't living up to her part of the deal.

Then, one day I finally remembered to look at the final drive ratio stamp on the differential. Guess what? Both Marlene and Lilly have the same ratio: 3.07:1.

There just isn't that much difference in the weight of these two cars to account for the significant difference in performance.

What else could it be? All the usual stuff has been done: filters, oil change, throttle linkage etc...

I know the hydropnumatic pump pulls some power. When I move the level lever, I can hear the engine RPM go down when I raise the car. Just think about it, when you accelerate all the weight is thrown to the rear lowering it. The pump works to try and raise it to normal level and taking power to do so.

It might also be affectted by the difference in wear between the transmissions. Low compression, valve clearanve, the viscofan, poor oil circulation/pressure, and plugged exhaust system might also be sources of power zapping problems. I know the oil gauge pegs easy, but when the gauge only goes to 3 bar the top pressure is completely unknown.

My experience is exactly the opposite. Belinda, the 300TD, goes like a rocket. Sammy, the 300D, is like a slug out for a leisurely stroll. We attributed the difference to turbo vs non turbo.

Belinda was really slow out of the gate when we first got her, but it turned out to be a problem in the throttle linkage. This rubber component was torn. Could it be Marlene's problem?

Sorry, not much help. Maybe Marlene just needs a good scare. :p

Natalie

Have you checked your injector spray patterns/ pop off values and the little tiny holes in your precombustion chambers ?

1 Not boost signal to ALDA -- boost line is plugged, switchover valve is shot, line is busted, something.

2 If you don't know what the IP is set for, it needs to be set. Makes a HUGE difference.

3 Check throttle movement. The bushings on the firewall go bad and fall out, and a good deal of the rotary motion becomes sideways motion instead, leaving you will around half throttle at best. Check the links, too, you may have and ajdustable or spring loaded one set wrong. This was the case in the 75 300D my brother has. He was complaining about poor performance after we put it back together, and I discovered he only had about 1/4 throttle travel at the IP.....

Peter

I hate to harp on the throttle linkage when you said it was checked....
 

But, this was missed many inspections of the car, even by the mechanic we hired. You couldn't see it at all when it closed back up, then one day my husband just HAPPENED to be looking in the right spot and I HAPPENED to to be pressing on the accelerator, and viola , the truth was out. Here's the thread.

http://www.peachparts.com/shopforum/diesel-discussion/62642-wasnt-fuel-filter-wasnt-algae-wasnt-pinhole.html

Did this about 4 months ago; it was slightly clogged and after cleaning I did experience a slight improvement

I'll be sure to check this and set to specs.

With the throttle floored, the IP arm is about 1/16" from the full load stop. This linkage slop intermittently comes and goes depending on, I guess, how hard/fast you mash the throttle. My issues are with the first 1/3 of the throttle ie: the off-idle performance.

Not yet. Last Monday, I was going to take them all to Central Texas Injection and then there was this issue with Lilly's windshield...consequently, I'm driving Lilly while SWMBO drives the remaining car with a complete w/s.

R Leo,
I had the same problem on my 84 300DT, no off idle performance. I set the linkage per the book, cleaned the banjo fitting, line and switch (on the firewall) and cranked the ALDA 3/4 turn CCW. It now goes like a rocket, much better than my "new" 300TD which I am going to perform the same ritual on. Hope this helps, all of you have certainly helped me:D

Jerry

I'll second the ALDA adjustment -- if the timing is correct (no smoke, right?) and you have proper linkage movement, you aren't getting fuel delivery, and that is adjustable with either the screw on the ALDA or a thicker shim underneath it.

You should have 0-60 times of around 12 sec.

Peter

I diddled (3/4 turn CCW) with the ALDA (BTW, she was not a virgin either) a few days ago but was getting smoke on WFO acceleration and only a marginal increase in performance that was nothing like TO's or SWMBO's cars.

I'm going to do a drip time on this baby sometime over the weekend and eliminate that factor.

I wonder if the intake tract is gooed with EGR crud? I've disabled it (for off-roading only) but no telling what it's been through before now.