300 SDL Powertrain Problems / Questions - PeachParts Mercedes-Benz Forum

focuslnl · #1 01-09-2006, 10:00 PM

Hi
I just bought an 87 SDL. I expected to have issues to address, and so far they don't seem to bad at all - mostly maintenance. My primary concern so far is with regard to the engine and trans. I'm glad to see the head has been redone (number 22) and I assume it can't be too worn because it doesn't smoke and fires up instantly in the cold (teens F).

Here's the questionables.

Is about 62 MPH and 2500rpm normal for others.

I can't actually hear the turbo and I am not sure whether I can feel it. I know to a degree what a T-Diesel should feel like from driving my 6.0L Fords - granted very different animals. Ideally, I suppose, not feeling a Turbo "Kick In" means little to no lag - but I'm relatively sure that's not the case.

I see poor acceleration above 65MPH (won't accelerate in 4th and throttle pressure eventually leads to a kickdown to third.) In third I think it is screaming pretty good (about 4K +) but not really going anywhere or atleast going up slow. Is this normal. I could probably live with it but only if I am supposed to.

Shifts I know need to be addressed. From a stop with full throttle all gears go to about 4800 or 5K and shift hard. I might even be lifting a little to get the upshift. Many times, as well, I see a shift from 2nd straight to 4th if I do lift significantly.

So far the extent of my investigating/fixing is new filters and fluid all around and a quick look at the vacuum lines.

Anyone have thoughts, simple tests, etc.

Thanks in advance

Brian Carlton · #2 01-09-2006, 10:17 PM

Quote:

Originally Posted by focuslnl

Here's the questionables.

Is about 62 MPH and 2500rpm normal for others.

I can't actually hear the turbo and I am not sure whether I can feel it. I know to a degree what a T-Diesel should feel like from driving my 6.0L Fords - granted very different animals. Ideally, I suppose, not feeling a Turbo "Kick In" means little to no lag - but I'm relatively sure that's not the case.

I see poor acceleration above 65MPH (won't accelerate in 4th and throttle pressure eventually leads to a kickdown to third.) In third I think it is screaming pretty good (about 4K +) but not really going anywhere or atleast going up slow. Is this normal. I could probably live with it but only if I am supposed to.

Shifts I know need to be addressed. From a stop with full throttle all gears go to about 4800 or 5K and shift hard. I might even be lifting a little to get the upshift. Many times, as well, I see a shift from 2nd straight to 4th if I do lift significantly.

So far the extent of my investigating/fixing is new filters and fluid all around and a quick look at the vacuum lines.

Anyone have thoughts, simple tests, etc.

Thanks in advance

Welcome to the forum.

Congrats on purchasing the finest M/B that has ever been manufactured.

Yes, you've got a bit of a learning curve...........it's a bit of a complicated beast on many electrical issues.

62mph at 2500 rpm is right on the money.

You won't hear or feel the turbo on this vehicle. However, it should build power above 2500 rpm and the tach and speedo should climb faster than it did at lower rpm's. It does not sound like this is happening with yours.

Make a 0-60 time with it. The time should be about 11.5 seconds. Anything longer than this confirms a problem.

The usual culprit is the pressure line from the manifold to the overboost protection valve on the firewall. The line can get plugged with soot and you won't get any additional fuel from the boost pressure.

I'm assuming that you changed both primary and secondary fuel filters, already, correct?

If the problem persists, it's prudent to get a hold of a boost gauge so that you can see what the turbo is actually doing. The boost gauge can be T'd into the line to the ALDA (on the injection pump) and run into the cockpit so that you can observe it while you drive.

The vehicle should accelerate in 4th right up to 85 mph with ease. Between 85 and 105, the speed comes up slower, but the vehicle has no problem attaining 105 if in good tune.

At full throttle, the transmission should be shifting hard. That's the nature of the beast. However a quick 3-4 shift after the 2-3 is not normal and some investigation is needed here as well. Might be appropriate to suggest a transmission fluid and filter change since you have no idea when it was last performed.

A lot of good info on the first page under "DIY links". You can also read all about the vehicle if you do a search under "SDL".

They are fine vehicles when running properly, but can be a bit fickle.

Hit Man X · #3 01-09-2006, 10:52 PM

Your poor high speed power could be from that darn cat being plugged up on the downpipe.

I'd also make sure your throttle linkage is correct, giving full power at WOT. Those full throttle shift points seem fine.

CSchmidt · #4 01-09-2006, 10:53 PM

My old SDL had a plugged boost line. The boost goes through a small pressure line to the overpressure relief valve on the drivers inner fender well. From there it goes back to the alda - a unit that adds fuel as you add boost. This is right behind the IP and under a bit of the intake manifold. Do a search and there are lots of posts on this in the forum.

Check the pressure before and after the overpressure valve. Above 2500 rpm the acceleration should be noticable. It could be a plugged or cracked line, or a bad pressure valve,.. and maybe a bad alda.

When I had no extra fuel added, my stopwatch 0-60 was about 18-19 seconds, and it acted similar to yours. Lots of rpm - no zoom. Fixed the boost signal, and 0-60 in around 12 seconds ( with 220K on it at the time).

Good luck and you do have a great car.

Chuck

DslBnz · #5 01-09-2006, 11:07 PM

I still get 70 - 80 mph in third gear in about 6 seconds at WOT(speedo indicated, NOT GPS) with a plugged boost line, FWIW. at least in a simulation of a plugged boost line (ALDA connection to I-Manifold terminated, or, rotted off and leaked). However the ALDA was tweaked. With a 300SDL, ALDA tweaked, even with the turbo non-functional, performance around town is hardly hindered. The only noticeable difference is power at 3000 + rpm (up to where my TC slips in top gear at 40 mph)., and that extra sudden oomph. It is quite the difference though.

When the same thing happened to my 350SD, the topspeed became about 70 mph in 3rd gear, and about 85 mph in 4th. The acceleration was laughable, at the time. Can I get up this hill in time? Will I be able to reach highway speed?

I estimate 0-60 mph in that car at the time was at least 35 seconds. Gotta love the microcircuitry for later diesels.

Brian Carlton · #6 01-09-2006, 11:24 PM

Quote:

Originally Posted by DslBnz

I still get 70 - 80 mph in third gear in about 6 seconds at WOT(speedo indicated, NOT GPS) with a plugged boost line, FWIW.

Now, that's not a fair comparison and you know it.

Somebody has turned up the wick on that IP and all of your data ain't worth squat for a person with a stock vehicle.

DslBnz · #7 01-09-2006, 11:45 PM

Quote:

Originally Posted by Brian Carlton

Now, that's not a fair comparison and you know it.

Somebody has turned up the wick on that IP and all of your data ain't worth squat for a person with a stock vehicle.

Oh.......yeah.

focuslnl · #8 01-10-2006, 12:03 AM

Thanks all for jumping right in on the subject. I'll try some of this tomorrow and let you know.

It does seem like a great car. My first MB and I'm glad I did it. I bought it to keep my very hungry diesel truck off the road, but it has already grown on me. Can't wait to get comfortable that all's well and take a long trip. I paid $3500 and I'll bet if I put a couple thou into it I'll still have a bargain. Not so sure I'd even like a brand new one as much anyway. Something about a car with a quarter million miles on and running near perfect that I'll have to like.

Thanks again.

t walgamuth · #9 01-10-2006, 09:03 AM

to diesel benz world.

we'll have you all geeky in no time!

you have an excellent start.

tom w