loss of boost until key recycled
 

we have a 1995 s 350. car has plenty of turbo boost for about a mile of driving then loses boost. as soon as you turn the key off and on we have boost again for another mile or so then the cycle repeats. recent work is injection pump rebuilt by gus at pacific fuel injection and a new engine wire harness. no engine fault codes. unable to pull any tranny codes as both of are scanners for some reason are not being able to get in. any ideas? thanks in advance.
paul

Something has to be hooked up wrong in the harness or something done wrong with the pump. Since it goes away when the system is cycled I'm leaning towards a Sensor or wiring error. if you did the job yourself, go back over with a schematic and see if anything is hooked up wrong.

You might get away with a simpler scan tool like this - http://www.k6jrf.com/MB_X11.html

It's probably something like a bad EGR valve or whatever sensor confirms EGR is flowing when it should (temp sensor, airflow sensor, etc.).

Do this and never worry about it again.


Sixto
87 300D

Sixto - Are there dual vacuum transducers that control the wastegate and egr valve like the 606 has? If so, I'd start with swaping those units and checking vacuum and electrical connections.

gus at pac fuel injection is the man. he's been doing pumps for me for 20 years. i can probably rule that out. the wire harness is nothing like the 104s or 119s. it's cake. there's only eight sensor plugs, takes 10 minutes to replace. yes there is dual transducers. both have been changed and switchover and vac checked. thanks for you replies. just thought someone might have had same problem with easy answer.
paul

The 140 engine vacuum system is simple for its vintage - http://www.peachparts.com/shopforum/2636770-post123.html

One vacuum amp for EGR and one for boost control, as you said. It doesn't make sense to swap them for diagnosis because a bad one in either location will disable boost.

There isn't much in the archives about sorting this situation. IIRC how it works is EDS opens the EGR valve and expects to see a drop in airflow through the MAF. It's a pre-OBD system so you can't just hook up any old scanner to see read codes or log values. On the other hand, there are only 3 things to replace - vacuum amp, EGR valve and MAF. It's easier and cheaper to replace the vacuum boost actuator with a pressure boost actuator. And more gratifying :)

Sixto
87 300D

By the way, yes, I had the same problem in my 93 SD.

Have you cleaned the EGR valve?

Your car is of the vintage that MB used prematurely disintegrating wiring harnesses. Maybe there a bad connection to the MAF.

Sixto
87 300D

Overboosting?

Could be but who has an EDS interface device to know for sure? The 603.971 doesn't have an overboost protection solenoid to monitor with a test light. It has a [Nippondenso!] MAP sensor which EDS uses to manage boost through the vacuum wastegate actuator.

Sixto
87 300D

You are far more expireinced with the W140 than I..... On the W210, you can swap the tranducers around. The fault parameters for the EGR seem to be more "generous" than the wastegate, so if the wastegate transducer is faulting/failing and the egr transducer isn't, swapping them will oftentimes result in both being happy....

Oh right. P2... and not ODB :(....

Yes you will need to do the X11. Def sounds like limp mode..

Yes, Terry, but you are far more experienced with transducers than I :) I only know how to put them in a box in the garage. My 87 doesn't even have a BFS. You, however, have smog checks to worry about :P

Sixto
87 300D