85 300TD: Three-prong plug near monovalve? - PeachParts Mercedes-Benz Forum

andrewjtx · #1 09-20-2010, 10:59 PM

My '84 didn't have wiring routed up there around the monovalve.

Anyhow, I was cleaning up the engine bay on Puff this weekend and moved those wires out of the way to clear some debris. This round, 3-conductor connection literally falls apart in my hand. Tracing it down (roughly though a few harness junctions) I think it is for the A/C drier.

It's late and I don't have pics yet. Wanted to see if anyone knows what this is on description alone. I can plug it back together and the A/C still works, but it's no longer water tight. I guess I can wrap it in rubber tape, the kind that stretches and seals on itself. But is there a way to replace this connector?

andrewjtx · #2 09-21-2010, 02:04 PM

Here are the pics. Camera phone quality. But they get the point across.

winmutt · #3 09-21-2010, 07:42 PM

Tach sensor I believe.

4thesporty · #4 09-21-2010, 08:16 PM

Hard to tell from the pics but because it is right next to the wheel speed sensor (coax wire, round plug) it looks to be the brake pad wear sensor.

This is not the location it is in in my SD, but it looks the same.

toomany MBZ · #5 09-21-2010, 09:05 PM

I believe the two above responses are incorrect and sorry, I don't know what it is either.

The tach gets it's signal from the transmission on an 85. The socket that used to house the tach amp is simply a cover for the diagnostic port that gets the signal via a magnetic pick-up on the front of the crank (Hall effect sensor).

It's not the wear pad sensor wire either, (a two prong plug) perhaps the item below it.

4the... if he has ABS, that may be the wheel speed sensor.

andrewjtx · #6 09-21-2010, 10:53 PM

Quote:

Originally Posted by toomany MBZ

The tach gets it's signal from the transmission on an 85. The socket that used to house the tach amp is simply a cover for the diagnostic port that gets the signal via a magnetic pick-up on the front of the crank (Hall effect sensor).

It's not the wear pad sensor wire either, (a two prong plug) perhaps the item below it.

4the... if he has ABS, that may be the wheel speed sensor.

Good to know that tach gets it's reading from the trans. Didn't know that. I guess my '84 did as well, because the diag port on the driver's fender looked the same.

Definitely not the brake pad sensor, I know those are the two-prong flat connectors. Speaking of which I need to install the new harnesses I pulled from Betty.

ABS I do not have. Something I'm interested in having one day. Maybe if I find that 230TE in Denver again...

toomany MBZ · #7 09-22-2010, 09:13 AM

Yes, MB changed that (tach pick-up, tach instrument too) in 84.

The 85's have a few items older units don't.

I can't find anything on my car like that, or searching the epc.

Good luck, maybe with an electrical diagram you can figure it out.

DeliveryValve · #8 09-22-2010, 09:23 AM

The 3 prong round plug (top) is for the Rack Position Sensor located on the Injection Pump. The bottom prong rectangle plug (bottom) is for the RPM sensor, as noted by toomany, the sensor is located on the bellhousing and gets the signal from the teeth of the flywheel.

Both plugs lead to the so called EGR computer.

.

winmutt · #9 09-22-2010, 09:42 AM

Ah yes thanks, rack sensor. I knew it was something 85 specific

andrewjtx · #10 09-22-2010, 10:24 AM

Sweet. Thanks guys. Once you guys clued me to what it was, I was able to find more info. Good visual confirmation here: http://www.peachparts.com/shopforum/diesel-discussion/185572-1985-federal-300d-tachometer-repair.html#post1481907

Looks like this is a lot more junk I need to remove for EGR delete. It was sooo much easier on the '84...

DeliveryValve · #11 09-22-2010, 11:02 AM

Quote:

Originally Posted by andrewjtx

Sweet. Thanks guys. Once you guys clued me to what it was, I was able to find more info. Good visual confirmation here: http://www.peachparts.com/shopforum/showthread.php?p=1481907

Looks like this is a lot more junk I need to remove for EGR delete. It was sooo much easier on the '84...

If you want to remove the EGR, follow this thread and remove the stuff "X" out in the picture here.

EGR Delete/Remove

.

andrewjtx · #12 09-22-2010, 11:43 AM

Yeah, I've seen your diag on that as well.

I've yet to perform a full inspection of the vacuum on this car. There's definitely been some modifications of it, as the switchover valve was bypassed and I know there is a fuel filter put in line. Maybe this weekend I'll get a few hours to go over it all.

Car shifts fairly well once warmed up and all vacuum consumers work accordingly. So I don't have any obvious problems. Just need to sort out what I'm working with. I'll test plugging those two connections you recommend and see how it does.

-Andrew