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  #1  
Old 06-30-2003, 12:38 AM
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Unhappy 1987 300D lack of power :(

Hello all:

After playing around with our other 87 300D, I found out that indeed the ALDA holds pressure, though not vacuum. Beats me why. Anyway, it still seems to lack some power. So far I have:

Replaced ALL underhood vacuum lines and fittings
Replaced air filter, fuel filters and did diesel purge
Boost is 10 psi max and turbo spools up well
Cleaned ALDA fitting and manifold connector

I connected the line from the manifold directly to the ALDA, and there was no improvement. What frustrated me even MORE is that I disconnected the boost sensing line from the manifold of my other 300D (the fast one) and it drove JUST like this one - meaning that it feels like a non-turbo 603. It seems that the boost is getting sent to the ALDA but there isn't any extra fuel delivery going on here. Looks like I'll have to pull the manifold (not too fun) and dissect the ALDA. Thanks in advance for any help or suggestions.
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  #2  
Old 06-30-2003, 04:42 AM
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Dave M/gsxr says he pulls the ALDA without touching the intake manifold.

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  #3  
Old 06-30-2003, 09:50 AM
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Did you replace rthe air filter??
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  #4  
Old 06-30-2003, 11:28 PM
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It seems that the throttle is engaging properly - the engine revs up to 5000 RPM but definitely revs up slower compared to the silver 87. The boost signal is indeed reaching the ALDA (I ran a line direct from the manifold to it) but with no increase in power when the boost (10 psi) comes on. The ALDA has not been tweaked on either car, but it looks like that will have to change soon. Here's some tests I did today:

Test drive #1: Boost lines connected normally (through overboost sensor, etc) still slow - 0-60 in over 15 seconds
Test drive #2: Boost lines ran direct from manifold to ALDA - drove no different from test #1
Test drive #3: Boost line disconnected from the manifold (no boost reaching ALDA) yielded the SAME result as tests 1 and 2.
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  #5  
Old 06-30-2003, 11:37 PM
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Before you get yourself all tied into one solution make sure you check some other possible problems.

Do a leak down test on cylinders along with compression check

Do a valve job

While doing valve job check chain stretch

adjust timing if chain stretch exist?

(all these ideas from reading here not much hands nor seat of pants experience yet)
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  #6  
Old 06-30-2003, 11:42 PM
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First, you have a poopy turbo. You should be getting 13.9 psi at full throttle, not 10.

Second, you are not getting added fuel, and if the ALDA won't hold vac, I'd bet the diaphram is bad and not extending the pusher rod on the bottom.

You can remove it fairly easily by pulling the windsheild washer tank and using two medium adjustable wrenches -- one to hold the ALDA and one to turn the captive nut. Once the nut is free, unscrew it and tilt the ALDA over and it will come off.

Hook up the pressure outlet of the MitiVac and see if the round ended rod in the bottom moves out when you apply pressure. You can't use the gauge, but if you have some other low pressure gauge, the rod should stop moving at 15-16 psi, I think. If you get movement, adjust it.

If to doesn't move, the ALDA is shot, and you need a replacement. Probably have to get one from a diesel injection service, they aren't available from MB.

Peter
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  #7  
Old 06-30-2003, 11:58 PM
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psfred:

I think that even if the turbo is producing 3.9 less psi than it should, it shouldn't be THAT slow. My other 87 produces 10psi max and is one of the fastest 87 300D's I've driven - 0-60 in about 10 seconds without powerbraking.

What's bugging me is that when I disconnected the boost line from the manifold of my fast 87 300D, it drove EXACTLY like this one. I'm convinced that something is wrong with the ALDA.
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  #8  
Old 07-01-2003, 12:46 PM
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Quote:
Originally posted by coachgeo
Do a valve job
Assuming you mean valve adjustment, he's talking about an OM603 that has hydraulic tappets. So no adjustment is required.

Yes, it definitely sounds like an ALDA problem. Since you have two of the same year and model, why not try swapping the ALDAs? Not trivial timewise I sure, but at least it won't cost anything.
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  #9  
Old 07-01-2003, 01:31 PM
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Yep, I'd swap ALDA's. Some cars will require loosening the rear three metal injection lines to allow the ALDA to come up & off the IP (some cars don't need this - each is different). If the car runs great with the "good" ALDA, you've found the problem, and just need to buy a used ALDA from a 617 or 602/603 (~1980-87). While you're doing that, try tweaking the ALDA, turning the setscrew about 0.5-1.5 turns CCW. The car should jump off the line pretty strong, and you should NOT feel any "hit" of power as boost builds - it should be smooth & seamless (strong enough off idle that there is no "hit" when the turbo spools.) Only turn it up enough so you get the power gain, go further and MPG will suffer.

About the boost pressure. 10psi is a little low, but it could be a weak wastegate. Spec is 0.85-0.95 bar, which is 12.3-13.8 psi. No ALDA enrichment can cause low boost too. Also, as Speedy said, 10psi can make for a plenty fast car if everything is perfect. My 1984 only makes 10psi, and cranking up the boost to 15psi gave ZERO power gain. More boost does not always mean more power...!




HTH,
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  #10  
Old 09-02-2003, 01:52 AM
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Hey guys...

I just brought my 1987 300D home from Oklahoma and it is SLOW! I cannot seem to tell if the turbo is working or not and I need some help. Anyone have any ideas of where I should start looking? My former 300D was MUCH faster and I cannot begin to understand why this thing is so much slower. It had a tough time climbing any hills and I always had to drop it into 3rd and crawl up even the slightest incline. Any ideas?

Thanks.
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  #11  
Old 09-02-2003, 03:10 AM
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newbie alert!!!

Ok, I'll start right out with the dumb question. What is an ALDA?

I just bought an 85 300TD and actually thought that the performance was "just diesel". I haven't done _anything_ to it but drive it home so far, and it is my first diesel car so I know next to nothing.

I had intended to change oil and filter, air filter, and fuel filters. But it looks like I need to read up on ALDAs.

Thanks for your help!

kma
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  #12  
Old 09-02-2003, 04:44 AM
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Dear kashbaugh:

An ALDA is a device that controls the amount of fuel enrichment based on the pressure output from the turbocharger. If the turbocharger increases the turbo pressure boost, the ALDA will accordingly trigger the injection pump to inject more diesel into the pre-combustion chambers, thus providing a better stoichiometric balance of turbocharger-induced air pressure and diesel fuel, leading to a boost in power.

Eric
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  #13  
Old 09-02-2003, 10:08 AM
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Sounds like I'll have to be reading up on how to check its operation and such. Gee, I didn't know!

My 300TD has trouble holding highway speeds - 65 to 75 - on almost any grade, and when I take off it is s l o w! I will try to time a 0-60 today so I have a benchmark.

I had figured - lack of knowledge showing through here - that I would change the timing chain. The engine has 230k and the seller had not changed it in the two years he owned it, so I figured it was probably just time. I thought that was about all I could "do" for performance.

As usual, looks like I wuz rong.

Thanks for the info.
kma
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  #14  
Old 09-02-2003, 01:53 PM
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The ALDA rarely fails. You need to check the signal line (small plastic tube) from the intake manifold to the ALDA. It often gets plugged with soot, effectively reducing power to non-turbo levels. It routes through a switchover valve, so make sure you can blow through that as well. This cures most complaints of low power. If the power is still weak off the line (off idle), where the car is a slug until "the turbo kicks in at ~2500rpm", then you may need to richen the fuel delivery curve by adjusting the ALDA base setting. This cures the off-idle power complaint most of the time. Sometimes the power loss can be due to other things though, like plugged fuel filters, etc. Photos of the ALDA on a 1987 300D are here:

http://www.meimann.com/images/mercedes/OM603_injection/



HTH,
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1997 E420 - 155kmi (Bugeyes)
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1993 500E - 193kmi (Lollipop)
1992 400E - 189kmi (Stinky Dirty)
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  #15  
Old 09-08-2003, 04:36 PM
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I found that I couldn't blow through the switchover valve and I have a replacement on order. I'm very anxious to see if this cures my low power problem.
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