My First Post. 94 S350
 

Ive spent many days looking over this forum. Ive had the car for 2 years. Mint condition. 140000 miles. started to have boost cut off and with key cycle it would start again to boost. Now no boost ever. Have new pressure acuator on way. My tach and ac doesnt work at idle an intermittent tach at around 2000 rpm. Id really like to know what this could be. I cant find any repair info for this. please help
TJ
Also any info regarding testing vacuume pump would be great
I measured the signal from ring gear it was 3volt ac at idle. Car idles great. if i disconnect the speed sensor it idles very low.

welcome to a great site

you will get way better results by posting separate problems in other separate threads

i see about 4 diff issues in your post

ok, thank you, i will try to do that

ok, thank you, i will try to do that, i really dont know where to start, feel like giving up,

one problem

sounds like the above prob may be related but might be 2 separate issues and i doubt related to the first turbo issue


#3

When troubleshooting, best to start with knowns and dealing with the easiest and (ideally) cheap issues first

thank you

what`s the story on the actuator?

how`s the wiring? mb used a biodegradable setup that i think your car falls under

i re insulated the wires with shrink wrap. actuator is on its way,

Not sure what you mean by pressure actuator. If you mean this - http://www.peachparts.com/shopforum/diesel-discussion/212097-wastegate-actuator-swap-om602-962-a.html - I'm glad you see the light :)

Turbo boost is controlled by vacuum; vacuum is supplied by the engine vacuum pump, modulated by a vacuum transducer then put to use by vacuum actuator attached to the turbo. If the brakes work as expected, the transmission shifts smoothly and the engine shuts off when you turn the key to OFF, the engine vacuum pump is fine. Check the vacuum lines especially the connectors and bends from the engine vacuum pump to the turbo and EGR transducers and continue to the actuators. Hook up a voltage gauge to the turbo actuator connectors and check for voltage when you expect boost but it isn't available. If voltage drops corresponding to a drop in boost, EDS detects a fault. Diagnosis isn't easy because there's little written about the subject and/or you need fancy diagnostic equipment. If voltage doesn't drop when you lose boost, check the vacuum system again. You might temporarily swap the EGR and turbo transducers but EDS won't allow boost if the EGR system is faulty.

EDS relies on an engine rpm signal shared with the tach, AC and cruise control. Since you've tested for voltage at idle, check that the voltage increases proportionately with rpm and doesn't fade when you lose boost. My 140.134 days are long ago so I don't remember but if that model has an OVP relay, that's something else to check.

Sixto
87 300D

ok, here is what i found last night, 20+ on vacuum, but the vacuum transducers dont let the vacuum go to egr or turbo. it lets a little you can see the actuator try to pul(have actuator off turbo and vacuum gauge on egr line) there is 12volt going to all three valves behing headlight. and i found the egr actuator lets air pass (i think diapram is busted)

Are you checking for voltage between a transducer wire and ground or across particular transducer wires? If the transducers might have constant 12V and a regulated ground from EDS in which case seeing 12V at one wire doesn't mean the transducer is getting a signal from EDS.

MB EGR actuator failures are rare. This might be the first one I read about. If yours won't hold vacuum, that could be the root problem. EDS expects to see a drop in airflow through the MAF sensor corresponding to 'sootflow' through the EGR valve when it directs the EGR valve to open. If the MAF doesn't register a drop, EDS denies boost until you cycle the key or fix the problem.

[soapbox] I'm surprised anyone spends time trying to figure out vacuum wastegate acuator problems. Hugging a porcupine is more rewarding. [/soapbox]

Sixto
87 300D

yes 12yolt across the connector wires,

the transducers say made in usa, maybe thats the problem

y31/6 is working, y31/1 and y31/4 seem to be dead