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My '87 300SDL is a great car, with room, economy and comfort. I do think that something is not quite right about the turbo-boost performance, as the car only has a top speed of about 85 mph. It will run reasonably from 0-70, shifting at around 4800 rpms in each gear if it is ran 'on the floor'. Nothing fast at all, but it is as though the car needs either more fuel or additional boost. I have checked and replaced the fuel and air filters and noticed no change.

I have looked for instructions or a guide online to measure the turbo function, but cannot find one. The engine is the inline 6 m603 engine. The trap oxidizer has been removed. At 80 - 85 mph, the car just feels like it can produce no more power and kind of floats along. There are no fluid leaks of any kind, and the car is getting probably 30 mpg. I have heard that the car should easily reach over 110 mph. Is this true ?

The transmission shifts wonderfully through all 4 gears, and is very smooth. When 'passing gear' is dropped, there just isnt much power.

Any suggestions ? If the tubro is not working at all, what would be the symptoms ? I am looking at the alda valve, but would like guidance into what to start checking first. Like a checklist. thanks for any help,
 

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Yes, it should go faster. The ALDA is literally the last thing that you should play with for any performance problems. The most common problem of the ALDA "failing" is the hollow bolt that connects the ALDA pressure line to the manifold.

The line looks like a vacuum line, but holds pressure. Follow it from the alda to the intake manifold and you will find a brass bolt fitting. Remove the line, and the fitting. The line can be cleaned out with a shot of brake cleaner and the bolt can be cleaned out with a wire and brake cleaner. Make sure the the mating hole in the manifold is clear. This should clean out alot oof the crud that causes fuel starvation at higher RPMs.

If that is bad, then you may wish to look at the turbo side of the engine. Remove the cross-tube that tconnects the turbo to the manifold, being careful not to lose the manifold side gasket. The downpipe and EGR probably have similar gunk that you just cleaned out of the ALDA connection. This will severely limit airflow. It is not a bad idea to remove and clean out the whole assembly. This is very simple, so even if you have limited mechanical experience don't be afraid. Just be careful to not drop anything into the turbo housing. A rag stuffed into that area is good, so long as you remeber to remove it before assembly.

If all that is done, and you still don't have the performance you want, then follow up on this forum, and we can discuss the ALDA adjsutment.
 

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I guess that I really didn't answer your turbo prtion of the question. If the car is accelerating OK, then I would not suspect the turbo. Fuel starvation is a likely candidate, which is regulated by the ALDA and the airflow to it. Usually the airflow to the ALDA gets clogged, and the ALDA does not "know" to enrich the fuel. Hence, the procedure above.

To measure turbo output, a "T" fitting is put in the same place with the line to the alda, and a long line to a pressure gauge that is placed in the cabin, so that the air pressure (boost) can be seen while driving. Boost should be in the neighborhood of .8 bar (1bar=14.7 psi). Turbo adjustment is different for Airresearch and KKK turbos. You may have either.

I also failed to mention that the ALDA will typically have an 'overboost protection valve" inline with the ALDA and the manifold, mounted on the firewall. This valve can sometimes fail.

Good luck, and please follow up.
 

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Discussion Starter #4
Thank you Cracker.

You are very helpful - I will do as you suggest and post my results soon. Again, thanks. 8)
 

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Wow !!! Problem found and fixed !

First I cleaned out the hollow bolt - it was partially blocked but this did not seem to improve performance very much if at all. Next I removed the lines and blew them all out with cleaner and reinstalled. On my vehicle, there are rubber hoses with small clamps which attach each line. The line going into the manifold bolt seemed to be blocked solid, so I cut about 1/4 inch from the line and reinstalled it - there was plenty of 'slack'.

This time when I drove the car, I immediatley noticed greatly improved performance. The car literally feels 4 times more powerful, like going from half throttle to full !

I also noticed that the temperature gauge now goes closer to 100 degrees C, whereas before it stayed nearer 80 degrees. I suppose that this is to be expected, but is it normal ? I have only driven the car for a few miles, and the temp never exceeded 100 even when driving full throttle up-hill.
 

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Kind of like having a new car now, huh? :D

While 100C is not terrible, it is a little on the high side. I would not be afraid to drive it, but continue troubleshooting. It could be that there is still some fuel flow to free up before worrying about adjustments. Did you go ahead and clean the line in addition to clipping the end? If not, there could still be a restriction...

Also, it might be a good idea to run some injector cleaner through the engine. I recommend using Lubro-Moly's "Diesel Purge", using it straight, rather than diluting it in the fuel.

It is probably still worth continuing with cleaning the plumbing on the turbo side of the manifold as well. (Not that it would help the temperature issue).

FWIW, the fastest my '87 300D has gone is 125 MPH. Your SD might be able to come close to that.
 

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My thinking is that you were running so lean before that there simply was not enough fuel to burn hot enough to exceed the cooling capacity of your cooling system. That could mean that your cooling sysem needs a little service (a flush and a thermostat) or you are still running lean. Typically, running on the lean side cause the temps to run higher, while a richer mix causes a little cooler. Your engine running warmer kind of has me puzzled for that reason, so the previous posting and above is what I am guessing. I am assuming it is fairly cool weather right now wherever you are.

I did actually need to adjust my ALDA in my '93 and the engine did run a bit cooler after doing so. But, as you have experienced, there can be many other factors that affect your fuel mix and require attention instead of messing with the ALDA.
 

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Discussion Starter #8
Just a tad warmer really...

Drove the car a few hundred miles now, and it has not ever actually reached the 100 deg C mark, just a little closer to it than before. The initial test was a rather large local hill, and I ran the car 'on the floor', and it got as warm as it has gotten so far.

The car does run like a different one. I did blow out each of the lines, including the one that I cut.

I plan to do a cooling system flush soon, and Ill just watch the temp gauge to make sure it doesn't get any hotter. It is wintery here now.

Thanks for your help. BTW - do you know how to disable the factory alarm when replacing the Becker Grand Prix stereo ? I read posts in the "audio' section, but no answers. Thanks,
 

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It sounds as though there are no major concerns then, and you have a good grasp of what is going on with your engine.

I have removed the Beckers several times without the alarm system being an issue. The only issue that I have had with the Becker is making sure the access code is available to re-activate the radio itself. This should be on a card with your owner's manuals.

If the alarm system does need to be disabled, I am not certain where it is on the W126, but on my W124's, the alarm control module resides under the passenger floormat and can be unplugged.

HTH,

Neil
 
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