87 300D had great power, today it's gone
 

Literally overnight, while parked power went "away" and this a.m. it felt like I was pulling an anchor and I was triple checking the e-brake was not engaged.

I know this car well, and have tuned and maintained its om603 to be a great runner over the period of two years. Following much from what I learned here. I've done my homework and searches and diagnostic trouble shooting list twice, brought it to my independent mechanic today and we are zeroing in on turbo. Tell me what you think, please.. maybe I'm missing something, that some test will tell...

The basics:

No strange noises, oil pressure 3 bar+, temp 80C cruising. Rolling resistance is not a problem, no brake drag (was my first thought), alignment is fresh and didn't hit a curb parking it, and throttle cable is working fine with full range and no resistance. Restricted fuel? Not likely, I have 2 tanks and can switch between the two and they have completely different filters. The odds of plugging all filters overnight? not a chance. No new fuel taken on board in a week. Clear lines show no air bubbles. Air filter is fine I checked. Air meter box is gone and is now a straight pipe into the turbo. Exhaust is blowing well out the right end, unrestricted, there is no trap ox, and catalytic is now a straight pipe. EGR is blocked, if you're counting. No strange smoke signals of any kind, on start up or running.

Driving characteristics:

Take off is slow to build up momentum from a stop. Boost is coming on slow, and I'm not seeing full boost under full pedal mash uphill anymore. I have interior mounted digital boost gauge with pressure take-off at the manifold. I can eventually gain speed on highway and the faster I go, the better the car gets and starts to feel like its old self around 70 mph. At 80 mph I get more boost responsiveness to pedal and it's almost strongish but won't get near the 0.9 bar peak it could pull yesterday. Maybe gets 0.7 bar. But I can pass cars if I needed to on the highway. City lights are a different story, I am embarrassed getting across the intersection, and avoid hills because it's takes full pedal to get up. Of course tranny is shifting poorly now because there is no power to match the vac signals and the bowden cable is untouched and fine (for a normal power curve). So as expected it is now shifting late [edit: not shifting early as stated previously] and then hard, but even if I hold it in lower gears it doesn't bring on the power to match [edit: until RPM are way up >3000].

Deeper points:

Turbo propeller spins with a finger, I'd say not free-wheeling but has some rolling drag (enough to bend a toothpick to get it going) but no slop in any direction. Wastegate actuator arm opens with pressure applied to its pod, and snaps shut when pressure removed. ALDA has been shimmed up a bit but not too crazy and is now directly connected to manifold pressure. Applying pressure to ALDA (with hand pump) while car running and revving it up produces black smoke like you think it should. Overboost protection solenoid vac lines and cruise fix vac plumbing all removed and not sadly missed. Tranny vac amplifier and plumbing intact and tuned with bowden cable set at the right points.

In a nutshell, the car has been running excellently for months with all the modifications and plumbing mentioned above, it could almost spin rubber on launch and didn't know it's own top end.

Today, a gutless slug - reminded me of when I first got the car with 2 bad injectors, broken ALDA shaft seal and IP timing was too retarded. Back then I thought "dead turbo".

What can make this happen during a park cycle? Why all of a sudden?

Wastegate hose, ALDA boost line, boost cut solenoid, ALDA...........
Did they use a MAF that early?

No MAF on 87 300D
 

I have seen an Injector Pump off by a bit produce the results that you describe but I have no idea how this could have happened at rest.

Also, you state that you have two tanks with distinct filters. What do you run in the additional tank? And would not even a seperate tank pass through the same spin on filter? If it plugs, you get reduced fuel to injector lines.

A bent tooth pic sounds like too much resistance in the turbo. I had the same turbo on a Saab years ago & I can remember that it would spin freely.
Maybe others will have other ideas.
When you shut it down just before you noticed this, how hard had the turbo been working? Maybe a bit of heat soak has occurred.

Check switchover valve on the firewall. Bypass it and see if the power comes back.

Check filters even if new.
 

You said you are running that grease oil fuel so maybe some lard froze in the filter. Power is not just going to disappear over night and the engine still starts and runs. I bet it is lard or something out of the tank blocking the filters.

BenzDiesel

Wastegate moves fine when pressurized through its own hose, and holds open until pressure released. Wastegate snaps shut when pressure released.

ALDA boost line is direct to manifold now. You know, that line could be plugged, that's one thing I didn't actually check - the 6 inch hose there. And it's a likely cause, doh!

Overboost solenoid and vac lines disconnected long ago. Still waiting for the once in a million years event to hear from anybody who can confirm their car has gone into dangerous overboost where that circuit actually kicked in and did its job.... assuming it wasn't plugged when it was needed ;-) My compensation was to install the interior boost gauge at eye-height with a bright blue LED that goes on at 1 bar.

MAF box deleted a while back. It's only purpose in 1987 was to control an emission pod that introduced air into exhaust. That path got deleted when MB did the trap ox re-fit with new exhaust pipe in its place so MAF box became a dead purpose. 3" straight pipe there now, 10 lbs lighter car.

Today's drive is making me think ALDA more and more.
Sloooow off the line... nothing under the pedal in the pre-boost zone <2000 RPM. The turbo isn't even normally in play at these levels so "fuel starved at low RPM" sounds more ALDA-ish and less turbo-ish.

And getting no smoke signals of any kind even at higher RPM and full pedal, I cannot get any amount of black smoke while driving. Sounds like when the ALDA was screwed on too tight before, that shimming fixed amazingly well. I actually replaced the original ALDA with a used one and shimmed that because the previous one's seal was broken (it rattled when shaken). Maybe this 2nd ALDA has had its seal go too, and/or it's line at manifold is plugged. Tho, it seems to be holding pressure when applied by hand.

I can get black smoke while parked, by putting direct hand pumped pressure into the ALDA while free revving parked - whoosh a black cloud. Doing this gives faster upward swing of RPM too. But these are "dry" RPM and produce no great boost numbers because there is no load... but she revs up quicker. On the road, I have not repeated this manually applied pressure to ALDA, I think I should.

Altho the turbine is not as free wheeling as I'd like to see, it is still contributing boost starting at where it used to begin (2000 RPM) and builds under load, just slower and not up to its old maximum... see my next post on turbine comparo with a known good.

I think I'll pop the ALDA off again and see if she responds like it did before when I first discovered the magic of no ALDA.

I'll also try restricting / pinching the fuel return line from the IP to make sure it's not bleeding too much pressure out its rear end.

..it helps to talk it through, thanks for listening.

I have a slow drive into my neighborhood and driveway is long. Lot's of turbo cool down time there.

I have a spare turbo on the bench, known good working from the car I took it off also sitting in my garage... and I compared spin factors.. Yes it spins more freely. Even has a bit more radial play than mine. But it also stops spinning when my finger comes off. It does not bend the toothpick nearly as much to get it going. Blowing a stream of compressed air into the turbine turns it, whereas air does not turn the one in my car...

This was all done at 0C/32F in my garage and that spare turbo has been pulled for about 2 years and sitting there. And it spins like this. The one in my car was still warm from a drive when compared.

So I know my turbo is not top-notch. But shot?

The car goes 80+ mph, starts on first crank and is not sucking any air into the IP. In high RPM range starts working like a song and is very responsive to pedal, power starts to appear again - I can pass cars doing 90 mph. Blocked filter wouldn't allow that kind of flow.

Trouble is below 3000 RPM off the line.

check throttle linkage travel and verify the IP is getting full to stop range of motion.
what fuels are you running in the two tanks?

Cable and linkage work. Full travel.

Finger pulling throttle at IP to full stop while parked shows same whimpy response, slow rise RPM. So it's not slack.

I run whatever fuels are most readily available. Winter diesel, D2, bio, canola... 2nd tank is a fully heated system. Lard in there would have the consistency of water by time it reaches the injector, but I don't run lard. 2nd tank fuels are cleaned, dried, and tested before it goes in the car... to sub 10-micron.

Alda is my guess. Did you try removing it yet?

ALDA is not off yet and I can hardly wait to try it tonight, if I had a 27mm wrench I'd probably try doing it a lunch on the street.

I re-read some of my own advice from almost a year ago, jeez I was really into ALDA then and had it all figured out. Good thing I was posting because I forgot a great bit of this content:

http://www.peachparts.com/shopforum/diesel-discussion/247067-alda-fuel-delivery-air-fuel-ratio-boost-3.html?highlight=alda+piston

After taking this all in again, if my problem is ALDA related, my guess is one of those aneroid capsules in the ALDA has fatigued and ruptured at a seam, so it no longer compresses under pressure. The rupture probably relaxed the capsule (expanding it) so the plunger got pushed down a bit more into the IP, further restricting fuel - at low RPM and for the whole delivery curve. And since it no longer compresses under pressure, the plunger is either going nowhere (if both aneroids in the ALDA are shot) or is doing half as much travel (if the other aneroid in the ALDA is still good). This all assumes a good ALDA shaft seal.

If the seal was shot the ALDA would not hold pressure when tested, and it would push the plunger down when boost is applied. The ALDA was observed to hold pressure, and it's working somewhat by allowing enrichment (while parked and revved), but as the indie commented "still not enough". Supports one out of two aneroids shot.

This makes sense on paper, and a fatigue rupture like this could happen overnight randomly and show its effect the next day. Truth will tell when I pull the part and have a look / drive. Al least the theory fits my observed driving conditions. (Anything but a turbo pull would make my day!) Can you tell I'm really hoping!

Now the power is back!
 

ALDA is off now. And the power instantly returned.

So if this disappearing power thing ever happens to you, the answer is "yes" it is possible for an ALDA to go phfpbbttt! overnight, all by itself. And when it does, you drive a sled the next day. This was ALDA number 2 on this car... I think I'll just do without now. My overboost solenoid has already been bypassed for a long time... I'll (not) miss you ALDA!


Removing the ALDA addressed my problem. I might do another ALDA teardown to see if my theory of one ruptured aneroid capsule was right... the seal seems to be OK with a blow test. It holds "mouth" pressure even with me pushing the plunger up into the ALDA body. Up to a point.. if I push and wiggle a bit the ALDA will release the pressure


I also learned a few things about my turbo and wastgate in the process. The wastegate spring must be getting a little soft / opening too early because I could only pull around 0.7 bar (absolute manifold pressure) under full load. That's a bit on the so-so side for turbo pressure. At the altitude of where I live my gauge shows typically -0.1 bar absolute manifold with the car OFF. (So this means the turbo was providing about 0.8 bar boost maximum.)

With ALDA off and full pedal, I could blow a little black again, a good sign the car was not starving for fuel ;)

I installed a manual boost controller spliced into the wastegate line, and adjusted it to get about 0.9 bar absolute pressure from the turbo under full load (about 12.8 psi). She spools up a bit faster too, because the wastegate is held shut longer ...until something much closer to its pop pressure is reached.

The extra air sooner cleans up some black smoke at WOT! A manual boost controller ($20) is a great mod to go hand in hand with ALDA removal.

Ahhh... the driving experience with ALDA off, gives me all that power early in the pedal. I have to get used to that feeling again... very very addictive.

Right now I'm fish tailing up hills and squealing around corners again!

keywords to help future searches
OM603.960
w124.133