How slow is a non-turbo 300td? - PeachParts Mercedes-Benz Forum

Mike Rancourt · #1 12-05-2007, 01:44 AM

This is my only experience with a non-turbo, so my question is, how slow is this thing supposed to be? What is normal?

I have a friend with a 1980 300td (wagon, nonturbo), and it's slow as f**k, so I have been working on it here and there to see what I can do.

It's got a ridiculous WVO "conversion" with a nest of hoses going everywhere, oozing (biodiesel) fuel lines (I have replaced most of them under the hood), a sh***y heat-exchanger for the veggie, a rather large Racor spin-on for the veggie, but everything also runs through the stock filter, and I think it has a looped fuel return, but there are crazy T connectors that make it impossible to trace the fuel supply and return paths according any form of logic I have come across in the 6 or so WVO vehicles I've played with over the years (probably 20 configurations on 6 vehicles because I like to try things). So, she runs biodiesel most of the time, but there's no difference in performance between that and WVO (she never runs petro-diesel).
One day, I changed the Racor and most of the supply lines under the hood and she saw a marked rise in performance, but it lasted only a few days and returned to normal.
Later, I changed the stock fuel filter, and it got a little better, but it still wouldn't make it above 45 mph in a half mile straight-away with a slight downward slope.
Today, I did some other things which require some back-story:
There was one 3/8" fuel hose connected to a 1/4" fitting on the stock filter!
There was one 5/16" hose connected to a 1/4" fitting on the stock filter!
There was one 3/8" hose connected to a 5/16" fitting in one of those mysterious T's I mentioned above, so I figured changing those things would help, and I think maybe it did a little, but I took the car on the freeway with my foot to the floor and couldn't get over 60 mph in two miles, dipping under that at the slightest hill.
This is my only experience with a non-turbo, so my question is, how slow is this thing supposed to be? What is normal?
I would also ask about the shifting. By the time I reach 25 mph, I am in 3rd gear and not accelerating very well - not that 1st and 2nd are that awesome, either. Is this normal shifting? When I go down to 2nd manually, I can get a little kick, but as soon as I go back to 3rd, it just sort of acts like it would rather have stayed in bed (this car doesn't drink coffee).
Yep.

pawoSD · #2 12-05-2007, 01:49 AM

It should not be as slow as you describe, but not as fast as a turbo. I ponder what damage has been done to the engine/injectors with all the "wvo" experimentation on it. Also, on biodiesel it won't have as much power either, as biodiesel has less energy in it than petro-diesel.

The shifting is wrong too. I'd check the vacuum to the tranny vac modulator, the bowden cable adjustment, and also the adjustment of the modulator itself on the tranny. All those things play into how it shifts. Fuel filters should be replaced, and the lines should all be properly hooked up like they are supposed to be. That engine puts out about 90ish hp when running properly.

kerry · #3 12-05-2007, 09:06 AM

Should be considerably faster. Could be as simple as a fuel delivery problem. To test for this, simply remove all the existing fuel lines, and attach a separate (pop bottle?) of fuel to the primary filter leading directly to the lift pump. Disconnect the return line which comes from the top of the secondary fuel filter and feed it back into the pop bottle. Now both feed and return are connected to the fresh clean diesel in the pop bottle. Secure the bottle under the hood and go for a drive. If performance does not improve, the problem lies outside the fuel delivery system, apart from the primary and secondary filters and lift pump which are still part of the jury rigged supply system.

BIGRED · #4 12-05-2007, 09:43 AM

Seems off the mark to me.

If it were my car, I would take all the $%#*#$ stuff out and get it back to proper "stock" running configuration to establish a performance baseline. "IF" it is going to be modified to run VWO then you can see the cause and affect.
Hows the smoke and the idle?

Performance will be impacted by
Fuel leaks (drawing air into the system)
Filters
Valves
Injectors

Good luck
Don

t walgamuth · #5 12-05-2007, 09:46 AM

teh 300d na should run and drive well. It should reach a cruising speed of 75 with no fuss. It will win no drag races unless paired with a 240d or an early beetle though.

They are perfectly nice driving cars when running correctly.

Tom W

pj67coll · #6 12-05-2007, 05:25 PM

Check the rubber thingy that sits on the firewall and connects the throttle linkage to the accelearator. If it's badly perished you might not be getting full throttle response even with the pedal to the floor.

- Peter.

truckinik · #7 12-05-2007, 08:37 PM

...(Very High Pitched)...BEEP BEEP BEEP BEEP BEEP!!

"Fries are up"

biobenz240d · #8 12-05-2007, 09:58 PM

when were the valves adjusted last?

turbobenz · #9 12-05-2007, 10:02 PM

air filter? When i got mine it would barely idle, new air filter and it ran fine

turbobenz · #10 12-05-2007, 10:04 PM

diesel purge?

Mike Rancourt · #11 12-10-2007, 11:34 PM

Quote:

Originally Posted by pj67coll

Check the rubber thingy that sits on the firewall and connects the throttle linkage to the accelearator. If it's badly perished you might not be getting full throttle response even with the pedal to the floor.

- Peter.

Yeah, that was it. What is that thing called? Other people might have a similar problem, so if you know the name of it and other common terms, you should post it here for others who might be searching in the future.
The fuel system is so crazy on this thing that I never would have thought about that, but it turned out to be an easy fix and free for now (my friend is not in a position to buy any more parts at the moment, so I stuck a plastic plumbing connector in the rubber ring to make the hole more narrow). It turned out the rubber space was too wide, so the throttle rod (that can't be the real name - I don't know it) would just flop around instead of anchoring to pull all the linkage as far as it needed to. The car performs much better now. I passed people going up hill at 65 mph and had to slow down for traffic. The car actually seems road-worthy now.
Thanks, all.

VWGuru&BenzFan · #12 12-11-2007, 12:57 AM

Coming from someone who drives a non-turbo 300D everyday, it's not really that slow at all.
The only time my car ever feels lacking for power is on long, steep hills such as mountain passes or what have you. Otherwise, I have no problem getting up to speed. I'm not saying that from a Benz apologist's standpoint either. My other car is a turbocharged Jetta with 200hp - I know what a relatively fast car feels like. The Benz isn't fast, but it's not dog slow. You also have to know how to drive these cars though - grannying them will make them seem dog slow.