This started as a thread on Facebook, but I thought I would post it here for the true experts to put in their two cents:

Saturday June 29th:
Ok biodiesel afficianado's and mechanic friends ... I NEED YOUR HELP! The 300SD I bought a year ago today has been nothing but problems. The engine overheated last August, which I swapped with one from a wrecked donor car last Fall. When replacing the engine, I bumped the vacuum modulator on the transmission, which caused a big transmission leak.. So then invested in having a complete reseal kit installed on the transmission. After all that, I had a Diesel Benz with every engine and tranny gasket except the head gasket replaced and yet a major lack of power in the low end. I even took it to Nick's auto in San Diego, where they charged me~$400 to do a bunch of stuff that didn't seem to even be related to the actual problem and I still have a serious lack of power. I mean, when the engine was cold I had to put on the blinkers and it would only drive walking speed with the pedal to the floor. Strangely, it could eventually get up to highway speeds, 10 min later, and ran reasonably up at those speeds. I dedicated last weekendto get this problem solved once and for all so I could declare independence from this 4-door lemon before the 4th of July. I bought an auxiliary fuel tank I can temporarily put under the hood that connects to the fuel injector and fuel return. The idea was to isolate where I thought the problem was, the fuel tank and/or fuel line. If it ran fine with the aux fuel tank, I planned to go back to checking the screen again from the tank, and possibly looking at cleaning the tank and/or replacing the fuel line, which I am worried is going to be a royal pain in the rear...

My friend's suggestions on facebook: Get another car (most common and also useless suggestion), repaint the car and sell it, blow out lines with air, change filters (fuel and air).

What I did Saturday: Filters were already replaced. Fuel tank screen had already been checked and replaced. The hand pump on the lift pump had been replaced. Fresh fuel was put into the vehicle. I checked and replaced the fuel line from the hard metal fuel line to the lift pump and on the fuel return line as well. The air bubbles I then proceeded to use an auxiliary fuel tank to test the engine performance with fuel provided from something other than the hard fuel lines from the car's fuel tank. Low end performance did not improve. We also blew air through the fuel lines and actually got positive air pressure in the car's fuel tank.

The next day (Sunday):
After reading a lot of the forums on PeachParts Diesel Discussion, my new fav theory was that the vacuum from the intake manifold was not getting to the ALDA, possibly because the boost overpass valve was stuck open. Or the ALDA bolt was broken off on the injection pump that came with the donor engine. I had an old IP and turbo as a backup. I also had concern that the wastegate was stuck open on the turbo or was opening at too low of a pressure because it was worn out.

So I went forward with cleaning the banjo bolt (which was pretty dirty but not clogged) and cleaning of the line to the boost bypass valve. We even hooked this line directly to the injection pump in case the boost bypass valve was bad.. and the engine still ran the same. Also, the valve seemed to be fine because air could be blow through it. We then went forward with checking out the turbo. It certainly got spinning fine and didn't have much play in the bearing. We could apply pressure from an air supply to the hose going to the wastegate and hear it opening. We went ahead and swapped the turbo and wastegate with another that I had on hand because we couldn't be sure if it was opening prematurely without testing the manifold pressure, which was not as convenient at the time since we had the turbo on hand but no pressure guage and the correct fittings to connect it.

The engine still ran the same...

We finally broke down and did the last resort. We basically destroyed the cap trying to get to the screw on the ALDA. We then back it out a little, and the engine seemed to run better. We then backed it out completely, and it seemed to rev up MUCH better.... We went for a test drive and it definitely had plenty of low end power. Also, not too much smoke. However, it does still shift hard in the lower gears, which is weird because it shifted really nicely before all this engine swap/low end power problem started. Perhaps I need to have the transmission readjusted by the shop that installed the reseal kit?

I'm posting because I am not satisfied with this fix and have concern that what I did could somehow cause harm to the engine. I've told friends that I feel like a medical doctor because we somehow seemed to fix the symptoms, but never found the cause, and their could still be some side effects from the fix. I would be grateful for anyone's ideas and advice. Thank you.

The issue apparently developed after the engine change.

During the process of changing the engine, the linkages typically get misadjusted and the pedal might be on the floor but the arm on the IP is not all the way to the stop.

This has confounded many in the past.

Your adjustment of the ALDA provided more fuel at low rpm's which caused the vehicle to have a much better launch. However, the same result could have been done with the linkage if it is not fully opening the rack.

Remember a diesel only needs air and fuel. If you don't give it enough fuel, for whatever reason, it won't do any work for you. If you give it too much fuel for any reason, it will smoke. Simple as that.

Thank you for the suggestion.

So we did check that... I sat in the driver's seat and pressed the pedal to the floor. My buddy checked and the linkage could not go any further. Is it possible that the linkage could be adjusted in a way to provide more fuel beyond its current maximum?

Anyone ever look at the camshaft timing or the IP timing?

Weak low end power is also a classic sign of late timing caused by an elongated chain. Some of them are 10° late and they can't get out of their own way.


I presume you have checked and readjusted the valves on the replaced engine?

You should also pull the brown line off the vacuum shut off valve as an only partially releasing vacuum will limit fuel to the IP.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

We did adjust the valves. I am interested in getting the timing adjusted on the injection pump, but I'm not sure where I would have that done. The Mercedes shop I took it to last, Nick's Auto, seemed to be clueless about adjusting the injection pump.

I'm a little torn about whether to keep pursuing it now that it runs reasonably well. I really want to just get this vehicle sold so I can focus on my 83' 300CD restoration. Unfortunately, I've already got almost 5k invested in this car and I estimate it is only worth ~$3500 whether or not I get the injection pump timing adjusted...

If this were the case, would the car have trouble shutting down? Currently, it is shutting down fine.

I have an "83 SD the symptoms you describe are similar to mine
i traced the low power issue to a leaking vacuum switch, it would shut down fine
but i had to wait a few minutes for the car to want to start and then it would be exessively sedate. so as a test i pulled the line to the vacuum shutoff (between the ip and the oilfilter housing), found the source of the problem. It ran with much more power and was no longer sedate. replaced the vacuum switch on the key switch problem solved.

Kerry wants you to try this as a test.

If the power increases dramatically, you've got a vacuum leak to the shutoff valve that is partially closing it during operation.

Clearly, leaving the hose permanently disconnected is not the final solution.

Thank you Brian for the clarification. I just didn't understand that a little vacuum leaking from this line could decrease the fuel supply.

First, I screwed the ALDA bolt back down until I felt resistance. The reason I did this is because loosening this screw seemed to give us enough fuel to alleviate whatever the real problem was/is. I wanted to put the ALDA back in the "orginal" position to best test the affect of the brown vacuum line independently, aka without the compensation of the ALDA being wide open. Any suggestions on how to properly adjust the ALDA? Since I'm afraid of "breaking off" this adjustment bolt on the ALDA, I was very cautious when screwing it back in.

Then, I detached the brown line going to the fuel injector, plugged it with a bolt, and took the 300SD for a ride. It had tons of power and shifted REALLY nicely.

There is a business park by my house that has no traffic on holidays and weekends and a big long hill ending in a cul de sac. I drove down to the bottom of the hill at the cul de sac and then reattached the brown vacuum line. Oddly, the car still had plenty of low end power with the line reattached AND the ALDA screwed back in the bottom It possibly may have been shifting a little harder in the lower gears with the line reattached to the IP. With the line detached, I turned the ignition switch off and could feel plenty of vacuum, and obviously the car kept running until I reattached it. With the car running, I could not feel any vacuum coming from this line.

My best guess now is that when we swapped the turbo with the more recently rebuilt one, it may have fixed the problem. This could be because the wastegate was opening too early (at lower than proper manifold pressure) and the one we replaced it with is operating properly. I wanted to test drive it immediately after swapping the turbo before messing with the ALDA bolt, because I wanted to test one variable at a time. However, the friend I was working with swore that the engine sounded the same when we revved it in park with the new turbo and didn't want to waste time test driving it before also trying to (un)screw with the ALDA.

One other little bit of data is that before I replaced the blown out engine, all the vacuum-powered door locks would go down when locking the car. Now, mostly only the drivers door lock goes down, sometimes one or two of the others. This seems to be telling me that something is still arye with the vacuum. Thanks again for the help.

The vac to the door locks works from the pump in the trunk. It does not affect the way the engine runs, shuts off, or shifts at all. Different problem. Pull the carpet on the front passenger side and use a mityvac to trace out vac leaks inside the cabin for door, trunk, and gas tank door locks. Again does not affect engine performance or tranny shifting in an SD. If it is the regulator (forget if that is the name) in one of the doors it is simple and costs about $25 each.