Partial Power-ALDA-HELP?
 

87-300D Turbo (603.96) (185K miles. owned since 10/96)

Over the last year or so, the thrust so to speak has been dwindling on the high end, I could drive 100mph+ sustained or pass with rocket like performance with no trouble, and as time has past over the last 12 months or so, I notice a "missing" like behavior early on during high load passing where acceleration was very brisk, and then I felt a missing like hesitation, though very slight as rpm and load climbed. This has given way to deteriorating performance on the high to midrange now, were 65 mph is a chore.

Interesting symptoms,

If you hold the throttle to the floor, it will go to the governor stop at 5250 rpm for about 3-5 seconds and decrease to around 3500-rpm and thats it. The colder the engine, the quicker the fade away is. Initial breakaway is brisk, but gives way to an underpowered situation.

I have boost. So far tested items inclued; system vacuum tight at about 20 inches, the EGR removed and checked, air recirculation valve on the turbo checked, turbo spins free, the mass airflow door hinges freely against it's spring, both switch/change over valves (Y29 & Y30 functionally tested and swapped) over boost switch checks open and has no effect on performance if it is connected or disconnected, as i have no way of testing it's operating pressure and with it disconnect, this would presume normal function. All pressure lines tested tight with no drop in pressure, some rubber connections replaced.

So, I have three guesses left, first one:

Has anyone had a main fuel filter (spin-on) gradually clog as it seems that given enough "recovery", initial throttle responses is normal and gives way to the underpowered situation? The clear filter has good flow through it. I would have changed it already but I'm out of stock and World Pac is closed till the 26th.

Along these lines, would a tired primer/lift/lowpressure fuel pump exhibit these symptoms?

Lastly, does the ALDA ever fail/stick/require a once over, etc? I am reluctant to mutts with this as it was working normally and as I understand it's function, it provides reference infromation and it works or it doesn't. Or does it???

Feedback would be really appreciated, I feel like Doc and Johnny on the tonight show with stump the band as I have beaten this to death and I'm still missing the fix.
-Mark

Sorry Brian, good question the trap has been gone since 98 and I have the new catalyst style installed parts free of charge by MB along with a new turbo as well. The head failed at 103K, in '97 trap still installed, overhauled replacement installed and followed by the complete exhaust and turbo one year later. Post exhaust replacement, performance was perfect until 12 months back as i mention above.

Does this vehicle have a catalyst in the exhaust system?

Does it still have the trap oxidizer in place, by chance?

I believe it has a catalyst ahead of the front muffler.

Yep, that's what I thought.

You have the signs of an exhaust restriction. Disconnect the downpipe from the turbo exit and run the engine without the exhaust connected. See if the problem is eliminated.

Report back, either way.

Edited:

If the catalyst is only seven years old, it's less likely to be plugged, but not impossible.

Definitely change the secondary fuel filter before bothering with the exhaust. That's a simple item that you can immediately rule out.

Sounds like it might be the spin on fuel filter that is clogging up and causing starvation. Also look at your primary filter for the black crap that tells of tank critters growing.

The primary fuel screen is clean and flowing nicely, which also frustrates me in that if the spin on or secondary is clogging, how did it get past the primary, unless of course we are talking about fine particulate contamination obviously sub 100 micron sized particles will flow through the screen and not the filter.

With regard to catalyst being clogged, and I don't doubt it could be, I would think the cold to warm transition in operation temperature and improvement in performance, i would guess that an exhaust restriction issue change regardless of operating temp but fuel would as a cold engine requires more fuel than a warm one, no?? Also, is the catalyst a "burn clean" device as the trap was?

Be glad if it is the secondary filter.
 

Be glad if it is the secondary filter.
Bad diesel is becoming more common every day.
I have learned the hard way.
My secondary filter is averaging seven to ten months, before performance loss alerts me to change it.

Exactly. Fine particles go right by the primary and clog the secondary.

Change the secondary and let's see what happens. It's cheap and fast.

Whoa, I think this might be tripping me up, I've dieseled since '84 and never jelled or clogged a filter, hence the lack of experience with lost performance. I''ve had plenty of loose or air leaking lines and filters but never the clogging. It's nice the primary turns color over time, thankfully it's clear to start with as it provides a gauge for replacement. --Thanks-MG

Big reason why I gutted the cat on my SDL when I had the chance. One less potential problem I could have to cause problems.

Hopefully it's just the filter. :)

Secondary Filter Partially Blocked
 

Well guys, and you specially you Mr. whunter, thanks a million, the spin-on filter was blocked, even to the point i ran the engine just before changing filters and as I removed the orifice bolt and the filter came loose, it hissed like a vacuum cleaner, the injection pump was trying like a dog to pull fuel past the element to the point of plenty of negative pressure. this also begs the question is my primer pump getting tired? I wonder if it would have helped overcome some of the back pressure if it were new? Anyway a million thanks to all!

Interesting other issue, the inner flat seal on the top of the filter was torn and deteriorating. there were some shreds of rubber in the orifice bolt when i removed it. Yes, the orifice bolt has two o ring seats vs. the newer style with only one. I bought a replacement about a year ago for my 95 124.131, the emergency shut off was leaking like a sieve and was over 80 bucks new, i replaced it with a straight bolt that was only 7, and it DID NOT have the lower or inter o-ring seat.

Filter time in service was 17,000 and 24.5 months. Mann WK817/3

Cheap and easy fix.

That's what we like.

BTW, the 603 does not have a primer pump like the older engines. You may be thinking of the lift pump that pulls fuel from the tank. It does not have infinite capacity to overcome a massive restriction in the secondary filter.

Help is what we do here.

Syntax
 

617 and earlier, I personally would call it a primer pump, 601 and later, a lift pump as it is engine/injeciton pump mounted and driven, you know how the germans are everything doesn't get translated cleanly, the parts catalogue called it a primer pump.

I opened the filter, the element material was jet black but there wasn't any noticeable quantity of particulate matter that was obviously obstructing flow. Light would not pass through it when i held it up to a bulb. This definitely gets an eight or nine on my weird-ometer.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1OY0MQ7B71P014E2AC&year=1987&make=MB&model=300-DT-002&category=All&part=Primer+Pump+Assembly

That's interesting. Definitely some strange terminology. It's the lift pump, for sure. Why they call it a primer pump???:confused:

How do you remove the cat from the exhaust pipe? The garage would not do it for me as it's against the law to remove the cat. I sure like to know. Thanks.