E500 Engine Wiring Harness Install - PeachParts Mercedes-Benz Forum

#1 01-21-2003, 04:24 PM

Just got my car back on Fri with a new PS pump to help keep my garage floor clean!

Before I picked it up, the owner of the shop told me the car was not idling right. "Its surging" was his comment. He said the wiring harness needs to be replaced as its the likely culprit. Moving crispy wires around isn't good for it. He wanted $800-and-some to do it. I told him I'd pick it up and do it myself.

I got the harness Sat. from one of our local Dallas dealers for $336

which is the cheapest I could find including Partshop. Its a pretty cool looking part - I have it on the kitchen table and I admire it every time I walk past!

So, long story short I will install hopefully tonight or tomorrow and report back. I think its pretty straightforwrd? Any gotchas appreciated.

Randy
'94 E500

#2 01-21-2003, 08:13 PM

No words of wisdom to give but I do have a request.

If it's not to late, can you take detailed notes and pic's to document the job? Maybe one of our industrious members can turn the job into a "How to" page.

Good Luck.

run.exe · #3 01-21-2003, 08:22 PM

sounds familiar... but I doubt the wiring harness will fix your surging... though i hope it does.

PS - which wiring harness (there are 2)?

rainmaker · #4 01-22-2003, 01:16 AM

No gotchas or any surprises...

...just make sure that you study how the old one was connected so that install goes a lot smoother. It's all pretty straightforward.

I suspect you're replacing the engine harness, P/N 124 440 20 06, the one that connects to the temp sensors. The other one, , which connects to the alternator is more than $1000! I suspect mine is about to go soon as interior lights are beginning to exhibit strange behavior...

Good luck...

#5 01-22-2003, 10:29 AM

Hey all,

Its the harness for the injectors and sensors. I was wondering how it would solve this surging problem too but the car had a rock steady idle when I brought it in and all he did was the PS pump. I know he wrecked the connection at the driver's side cam sensor and he spliced back together best he could. I'm hoping maybe its a temp sensor. If I have the same problem then its on his nickel to find!

Last night I decided to replace breather hoses, vacuum lines, etc. while I'm in there. I pulled the MAS and TB and made a list of parts that goes like this:

Small hose inside intake below TB
TB to intake gasket
MAS to TB rubber coupler
big multi-jointed breather from TB to rear PS cam cover
various vaccum lines and connectors

I also need something to re-wrap all the lines that run close to the engine on the DS. The stuff on there originally has deteriorated. Would be nice to get something that would be heat resistance. Any ideas?

There is also a breather line right on top of everything that runs from the front of the DS cam cover then does a "Y" with one leg running to the middle of the PS intake, the other leg running to the middel of the DS intake and another hose back by the "Y" that loops under the intake back to the front and then runs under the DS rotor to then be connected to something over on the DS fenderwell. This stuff all looks expen$ive and its still OK and would be easy to replace later so I will price it and decide.

The original harness is still in place so I can see how to route the new one. I have no digital camera so I cannot take pics but nothing is that difficult anyways. It took me awhile to get the MAS off b/c the coupler below it was basically baked onto it. I also see no reason to pull the intake - I don't think there are any other hoses hiding in there and I don't think I have any leaks at the intake/head connection.

Is there anything out there thay could shine up my valve covers? They are celan (no oil leaks) but just dull grey.

Thanks for any input,

Randy
'94 E500

rainmaker · #6 01-22-2003, 12:56 PM

Quote:

Originally posted by Randall Grubbs
Its the harness for the injectors and sensors. I was wondering how it would solve this surging problem too but the car had a rock steady idle when I brought it in and all he did was the PS pump. I know he wrecked the connection at the driver's side cam sensor and he spliced back together best he could. I'm hoping maybe its a temp sensor. If I have the same problem then its on his nickel to find!

That reminds me, right before I replaced my wiring harness, I took the car to my body shop for clearcoating. They cleaned the engine as well and they seemed to have inadvertently jiggled the connection to the temp sensor (the blue one). I remember the engine surging between somewhere around 500 to 1500 at idle and it didn't smooth out until above 2k rpm. I went on the shoulder and yanked the connection to the temp sensor. Car idled fine, but the aux fan was permanently on. Changed the harness soon after that...

Might be the same thing with yours...

Ashman · #7 01-22-2003, 01:34 PM

interesting post. If you want to polish up the valve covers, try flitz. Works well on metal and plastics.

Alon

Sterling Gee · #8 01-22-2003, 05:04 PM

Randy,
I did this on my 92 400e, and it was a snap. Took less than an hour. I removed the old one and started at the computer and worked my way forward. I think you will need an allen socket for the harness bracket where it bolts to the passenger side cam cover. The MAF will need to come out, and so I'd make sure to have a new rubber boot, as when I did mine it broke, and I had to duct tape it together until the dealer was open again. THe boot I'm referring to is what holds the MAF to the throttle body.

#9 01-22-2003, 05:10 PM

Sterling,

What's going on? I see you've been trading vehicles again! I decided while doing the harness to do the rubber hoses and bits. I took everything out last night (including MAF and TB) and got all the parts at lunch today. The MAF doesn't need to come out to do the harness - maybe your 400 was different.

Need to get together soon. Talk to you later.

Randy

Sterling Gee · #10 01-22-2003, 05:11 PM

I probably could have left the MAF in, but the harness for the MAF was up agains the intake and I couldn't unplug it.... yep I traded cars again... a 98 e430 this time.... very nice...

#11 01-22-2003, 05:15 PM

Sterling,

That's the 3 valve engine right? I love the 500 in the new S. It is the smoothest, sweetest, flattest power band engine I have driven. You can't even tell when its running its so smooth.

I think the 500 and the 400 had different intakes maybe? b/c the plug on the MAF in the 500 is a simple reach down and turn and pull off with plenty of room. First time they ever made anything easy!

Randy

#12 01-23-2003, 10:37 PM

Just an update on the project.

I found what is most likely the culprit for the surge at idle. The small white plastic vacuum line that runs from the rear of the lower intake then by the TB/MAF and then out the front and under the DS rotor and over to the control module on the DS fender was busted right under the DS rotor where you can't see it. I broke this line by the TB and I could then see it was broken right where the tech was working by the PS pump. Can't believe he didn't think of this b/c we all know how leaking vacuum lines can totally screw up the idle.

I'll report back after I get it buttoned up this weekend.

Randy
'94 E500

run.exe · #13 01-23-2003, 10:43 PM

may prove to be Theseus-laid...

My fingers are crossed, in hopes it may contribute to the solution to my own surging/stalling problems.

helmutvonschet · #14 01-24-2003, 12:43 AM

b/c we all know how leaking vacuum lines can totally screw up the idle.

HUH!?!

If "we all knew" why didn't anyone come up with that besides you?

Just giving you crap. Your mechanic should have looked for that. Classic amatuer screwup.

#15 01-24-2003, 09:53 AM

I have to get another vac line today at the dealer so hopefully I get this thing done this weekend. BTW, when I say surging, its really more of a stalling problem. When I hit a light I needed to supply a little throttle. Ran fine though. I think the control unit on the DS fender controls idle as well as limp home and probably a few other things. It has a vac line going to it as well as a larger line off a breather hose (thats the one I broke last night).

I don't know how many of you are familiar with the 928 engine and its myriad vacuum lines and breather hoses that you can't even see. The 928 has a huge intake and nothing under it is visible. At some point when hoses start to fail, you need to pull the intake and replace anything rubber or plastic. On a 928 its about $500 in parts from at aftermarket prices (more at dealer) but you cannot just poke around replacing this and that b/c something will always end up leaking.

This is why I decided to replace all the lines in the E and believe me they are all very brittle. I got stuff in there snapping like spaghetti. It ran great, but its just a matter of time before problems start popping up. On the E everything is easy to get to once you pull the TB. I don't think you need to pull the intake unless its leaking which doesn't seem to be an issue.

Also, I was also going to pull my injectors and have them cleaned and balanced but I think I'll try the service where the shop runs cleaner through the system and its supposed to also clean valves etc. Anybody done this?

Randy
'94 E500