1975 107 D-Jet ECU Removal... - PeachParts Mercedes-Benz Forum

Jay Gibbs · #1 09-09-2012, 11:53 AM

In my never ending saga of slowly making my 75 450SL like new, I have gotten to replacement of the D-jet fuel injection harness...I have looked on the forums for an answer as to how to actually remove the unit and haven't found one?...I know that there is a "spring clip" that the ECU top slides into, and that there are two rubber "snubbers" on the back of the ECU that stick into the firewall. There seems to be something additional that I have not found that is holding it firmly to the firewall, but haven't found any kind of release mechanism...HELP!!

J.G.

rowdie · #2 09-09-2012, 01:02 PM

My '73 has a rubber plug on the top. The spring clip is on the bottom in the middle.

cushjbc · #3 09-09-2012, 05:30 PM

Jay,

When I removed my ECU the first time, I found corrosion from the battery tray had drained down and formed deposits which sort of crusted the ECU in place. I carefully unclipped the spring clip at the bottom then rocked the ECU out of its hangers.

I have removed 3 D-Jet engine harnesses from salvage cars. In addition to the ECU connector, there is a ground point and another 6 pole connector (only 5 wires present) mounted to a bracket that you will have to dissasemble at the shoe to pin points. You will also find the light blue with black hash wire that runs from the engine temp probe at the aft end of cylinder 4 (aft of right bank). This wire meets a single pole connector (push, twist, separate) which leads to the instrument cluster temp guage.

Are you replacing your harness with a new one? I have the MB published connectivity tests that you can perform if you don't have that.

Jay Gibbs · #4 09-09-2012, 10:33 PM

Quote:

Originally Posted by cushjbc

Jay,

When I removed my ECU the first time, I found corrosion from the battery tray had drained down and formed deposits which sort of crusted the ECU in place. I carefully unclipped the spring clip at the bottom then rocked the ECU out of its hangers.

I have removed 3 D-Jet engine harnesses from salvage cars. In addition to the ECU connector, there is a ground point and another 6 pole connector (only 5 wires present) mounted to a bracket that you will have to dissasemble at the shoe to pin points. You will also find the light blue with black hash wire that runs from the engine temp probe at the aft end of cylinder 4 (aft of right bank). This wire meets a single pole connector (push, twist, separate) which leads to the instrument cluster temp guage.

Are you replacing your harness with a new one? I have the MB published connectivity tests that you can perform if you don't have that.

Hey Guys-

Great info...thanks Brad for the mention about the temp gauge...guess I'll have to pull the cluster too...ugh. I knew this job was going to be a royal pain...not technically difficult, but tedious. I've been putting this job off for about a year and finally have about a month of free time and decided to bite the bullet. The harness is factory MB...got it from the Classic Center. I found my old harness had more than a few crispy connectors (hmmm...37 years old...ya think??!!) and rather than scattershot replacing individual connectors, I'd do the whole thing at once. For a part as important as this, I didn't want to go aftermarket. The harness looks pretty complete with all connectors seemingly attached to all the wires...ready to go out of the box. Once I rest my back a little and have a chance, I'll check behind the dash for the additional connectors and ground you referenced...

I'm combining the harness job with replacing all my fuel injectors and underhood fuel hoses. Got a nice set of salvage injectors and sent them out to WitchHunter Performance to be cleaned, rebuilt and flow tested. I really wanted to do these two jobs separately, but once I got all the fuel rails out I realized it would be a heck of alot easier in labor to do both while I had everything apart...

The connectivity tests would be great if you have them...I don't have them. PM me and I'll sent my e-mail address to you.

Many thanks!!

J.G.

cushjbc · #5 09-10-2012, 09:53 AM

Jay,

I explained it poorly. You do not have to pull the instrument cluster. You will find every thing in the vicinity of the ECU. The ground point and temp guage wire connector are behind and to the upper left of the ECU. You will also find a bracket in that area that holds the 6 pin connector (5 of 6 in use). This connector joins the engine harness to 3 relays:

1. ECU relay provides power to ECU pins 16 and 24 (black wires at pin 4 of connector)
2. Fuel pump relay - ground trigger from ECU pin 19 to control fuel pump circuit (tan and white wire at pin 1 of connector)
3. Starter Valve relay - ground trigger from Thermal Time Switch activates starter valve to enrich mixture via throttle body when < 35C. (all the other wires are some version of pink at pins 2,3 & 5 of the connector)

Did your classic center harness come with firewall grommetts. I trashed the first one I pulled but learned to be careful and preserved the other two. They are usually crusty and somewhat brittle but can be restored.

I have never installed a harness and am very interested in how this goes. Would you mind providing pictures? Did the new harness include the rubber protectors for the injector and throttle switch connections?

PM on the way