1985 300D - SLOW, won't accelerate past 75mph, foot to floor.

[85MB300D]

Not that I want to win races with it, but I thought these were faster than 75! It just seems to be really working hard at that speed. (Turns about 3500-4000rpm in top gear I think?)

Accelerates from a stop fine with your foot to the floor, but really starts slowing down at the top of third gear, but if you let off and make it shift to 4th sooner, it hits the boost/torque spot and is better until 70, then it just seems like it runs out of steam... Have never gotten it to go any faster than 75/80mph and that is REALLY pushing it! I can hear turbo spin, believe it to be working properly?

(BTW, car did not suddenly start doing this. It was purchased like this)

I had a '81 TD and it would do 85+ all day.

Going to do a valve adjustment this weekend, but is there anything else I should look at?

It NEVER smokes under acceleration, fuel and air filters have been changed. Tank screen not looked at yet.

Any ideas? I don't drive it like this all the time, but sometimes it's not fast enough to keep up with traffic ( won't go faster75-80mph)

WHY???


Thanks guys!

[kerry]

Check the accelerator linkage to make sure it is giving you full fuel.

[Skippy]

Sounds like a lack of fuel. Ideas:

Accelerator linkage-check to see that you are getting full travel at the injector pump when you floor it

Tank screen-could be clogged.

Tank vent-could be clogged. If the tank's not too full, try loosening the fuel cap for a test run and see if this helps.

My '83 will do 110 if you stay on it long enough. Yours should definately be going faster than it is.

[85MB300D]

Thanks guys for the quick replies, keep 'em coming!

99% sure throttle linkage travel is ok, but I'll check this weekend.

Where is the tank vent located? Pictures are always good. I'll try a search on here too, but if you see this and it wouldn't be too much trouble, by all means post location and/or picture.

I'll try these things this weekend, but if anyone else has any other ideas, post away!

-Brian

The performance should be much better than that. I agree that it sounds like fuel. Also, valve adjustment and IP timing should be verified.

[85MB300D]

Originally Posted by Craig

The performance should be much better than that. I agree that it sounds like fuel. Also, valve adjustment and IP timing should be verified.

I'm assuming a search for checking/adjusting/setting IP timing will yield results? If not, could you please post?

Thank you.

Originally Posted by 85MB300D

I'm assuming a search for checking/adjusting/setting IP timing will yield results? If not, could you please post?

Thank you.

There is a ton of discussion here on the best method for adjusting the IP timing, it's fairly complex to do it correctly. Personally, I just let my indy shop do it.

[85MB300D]

BTW, car did not suddenly start doing this. It was purchased this way.

Thanks.

Do you know when the valves were last adjusted? That's something that is often neglected.

BTW, is this a california car with a trap oxidizer?

[turbobenz]

I think its not shifting into 4th. I can get my 85 to shift into 4th at 75mph (about 4-4500 rpm). His rpm's shouldn't be that high, especially in an 85 model.


Proof:


http://www.youtube.com/watch?v=r4ZXQv9Toyo

[85MB300D]

Originally Posted by turbobenz

I think its not shifting into 4th. I can get my 85 to shift into 4th at 75mph (about 4-4500 rpm). His rpm's shouldn't be that high, especially in an 85 model.


Proof:


http://www.youtube.com/watch?v=r4ZXQv9Toyo

Wow, proof that they really do run 100!

I am almost 99% sure it is shifting into fourth, but again I'll check this weekend. These transmissions start in 2nd, right?

Originally Posted by 85MB300D

Wow, proof that they really do run 100!

I am almost 99% sure it is shifting into fourth, but again I'll check this weekend. These transmissions start in 2nd, right?

I believe yours starts in first. Just look at the rpm, you should be around 2500 rpm at 55-60 mph (more or less), if you're at 3500 or 4000 rpm it's stuck in third.

[85MB300D]

Originally Posted by Craig

I believe yours starts in first. Just look at the rpm, you should be around 2500 rpm at 55-60 mph (more or less), if you're at 3500 or 4000 rpm it's stuck in third.

Yep, I definitely see 25-2700 at 55-60mph. I'ts just when try to get to 80 there is just nothing there - extremely anemic/almost non-existant acceleration, and at that speed (if you can get it there) the tach is definitely over 3000, but again, just no accel/pull above like 65-75.

I wish I had the car here with me now... I'll have to get back to everyone after this weekend with the results of my efforts.

[vstech]

Originally Posted by 85MB300D

Wow, proof that they really do run 100!

I am almost 99% sure it is shifting into fourth, but again I'll check this weekend. These transmissions start in 2nd, right?

NO, the majority of turbo Diesels start in 1st. but to be positive, floor the car from a standstill, the button under the go pedal will force it into 1st if it was starting in 2nd.
if you are turning 4+KRPM, you are still in 3rd gear. rev limits around 4500RPM on these cars.
I think it's a few things, but certainly not getting out of 3rd gear.

[85MB300D]

Originally Posted by vstech

NO, the majority of turbo Diesels start in 1st. but to be positive, floor the car from a standstill, the button under the go pedal will force it into 1st if it was starting in 2nd.
if you are turning 4+KRPM, you are still in 3rd gear. rev limits around 4500RPM on these cars.
I think it's a few things, but certainly not getting out of 3rd gear.

I said I think it turns 3500-4000 at that speed (I was estimating), but I don't remember exactly. (I don't drive this car all the time, only on the weekends when I go out to my parent's place)

I do know/remember for sure that it turns approx. 2500 at 55-60, like Craig said in an above post. For this reason, I am 99% sure it is reaching top gear, but again from 60mph, with your foot to the floor it just will not pull/accelerate like its supposed to. There is nothing there (no power) after about 65mph.