I am posting this for my boss. He has a 86 300 SDL that has been giving him fits since he had to stomp on it a few months ago while getting on the highway. After getting to work it would not start up and he burned up the starter in the process. A shop used a high end diesel purge as well as replacing all the filters and draining the tank and the lines. It now has intermittent acceleration problems accompanied by billowing black smoke. What happens is when accelerating, it will be very sluggish accompanied with a lot of smoke, then all of a sudden it will take off with the smoke clearing and excellent acceleration. I am not a diesel person so I don't have a clue.
Thanks,
John

Is that model turbocharged?

It is a Turbo. His mechanic did take the exhaust off to check the turbo and everything seemed okay.

I know this sounds awfully obvious, but have they checked/cleaned the injectors?

It never hurts to check the line from the manifold to the overboost protection valve and from the valve to the ALDA.

You also might temporarily (ahem) disconnect the vacuum lines to the EGR valve and air recirculation valve, if equipped, to see if the problem lies in one of those systems.

Sixto
91 300SE
87 300SDL
83 300SD

I took a vacation to Montana back in August. On the way back across Wyoming I stopped for fuel in Cheyenne. Accelerating from a stop light, there was no boost and thick black smoke. This happened again at the next stop light. Drove across Nebraska without incident, but in Missouri at a traffic light I had no boost on take off (no smoke). Then back in Nashville it happened 2-3 times. Hasn't happened since, that was 4-5 months ago / 20,000 miles ago. Only guess I have is that I did idle it for 2-3 hrs while on vacation and maybe it was just cleaning itself out. Never had trouble starting it, though.

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Brian Toscano

I second sixtos advice about checking out the line from the manifold to the ALDA. On the same hand I would try to run some Diesel Purge through it AND check out the EGR valve real close. May want to plug the vacuum line to the EGR with a BB for testing purposes and see what happens.

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Jim

What is the ALDA? I'll see him tomorrow and I'd like to check it out. Thanks!

This sounds kinda-sorta like the way my '87 diesel wagon - same engine - runs when the air recirculating valve is activated. Power comes and goes as the valve modulates turbo boost. On hard acceleration - like getting onto the freeway - it'll bog down, smoke like crazy, then take off.

Disconnect the air recirculating valve and it'll run like a scalded cat all the time with only modest smoke. The ARV is located right next to the turbo. Look for a vacuum line running from the passenger side front of the engine compartment to the turbo. Should be obvious. Disconnect it wherever convenient and plug the line heading back to the front of the engine compartment - a golf tee works fine for testing purposes. Give it a test drive.

If that's not it, then I vote for an injector pump rebuild. There was a service bulletin that some of these cars suffered from premature wear of a bearing inside the injector pump. Result was too much fuel, lotsa smoke, and poor milage. What kind of fuel milage is this car delivering?

- Jim

The ALDA is an anaeroid (sp?) compensator; effectively a fuel enrichment device while under boost, but also a fuel leaning device at high altitude.

The ALDA is the flat square device about 8cm on a side and 2cm thick sitting at an angle on top of the injection pump. It'll have a tube connecting it to the overboost protection valve on the firewall ahead of the brake master cylinder. The valve will have a tube connecting to the intake manifold above the injection pump. Make sure both lines are clear and that you can blow air from the intake manifold connector to the ALDA connector.

If the line is clear, TEMPORARILY connect the ALDA directly to the intake manifold and see if that yields improvement. The risk is that you're running without protection against the wastegate sticking closed. You won't have any problems if you don't keep the pedal to the floor for extended periods. You shouldn't have any problems if you do but you have less of a margin of safety.

Sixto
91 300SE
87 300SDL
83 300SD

Well I screwed up. It's an 87. Located the ALDA and it's got a hose to the valve at the firewall and another hose going to a wire bundle at the left fender. Believe it or not, a can of Marvel Mystery Oil was added and it seemed to improve somewhat. Will keep you posted.

what that oil did is a MYSTERY to me

Let's approach this from the other end. On the intake manifold above the ALDA there's a pressure switch with one wire attached to it and just beside it is a nipple extending from the intake manifold. There should be a hose from this nipple to the vacuum switch on the firewall. That bit that goes into a bundle is the electrical hook up for the vacuum switch.

Sixto
91 300SE
87 300SDL
83 300SD