Winter/Spring Djet project - Mercedes-Benz Forum
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post #1 of 34 (permalink) Old 12-11-2015, 07:36 PM Thread Starter
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Winter/Spring Djet project

This past summer, I noticed that AFR was showing leaner mixture under load than it had and there was some loss of power when engine is hot. Also an occasional hesitation when cruising at mid range.

Nothing serious, but decided it might be time to do a lot of things. Starting with:
- Upgrade engine harness (under way)
- check injectors for equal flow (under way)
- replace plugs with BP6ES and check wires (under way)

Will post some pics and progress from time to time.

Plugs
Installed new NGK BPR6ES plugs in Spring 2008.
Timing set to about 27BTDC at 3000rpm.
Mixture on rich side at idle and approx to specs under load (using AFR gauge)

Today, took some pictures of plugs. Look OK, but some variation and maybe confirm running lean? Plugs too cold? Here are pics ( By the way, I had injectors 3 and 4 connections reversed. But on Djet, not sure how much that matters!)



Need to check plug gaps, but need to find or buy new feeler gauge set!

Last edited by MBGraham; 12-16-2017 at 02:29 PM.
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post #2 of 34 (permalink) Old 12-12-2015, 11:43 AM Thread Starter
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Progress:
- Finished installing BP6ES plugs.
- Made a diagram of harness.

Picture shows harness taped to broken down cardboard box. Marking and measuring lengths. White pieces are diagrams of wire location/color. Won't likely need this for harness upgrade, but "planning" on building a whole new harness later.


Last edited by MBGraham; 12-16-2017 at 02:30 PM.
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post #3 of 34 (permalink) Old 12-12-2015, 12:23 PM
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Nice work. Just curious, but what led you to the decision to change the engine harness? Just aging, or performance issues? Is it possible to source a complete engine harness, or do you have to build it yourself from scratch? The male/female plugs could be reused, I assume?

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post #4 of 34 (permalink) Old 12-12-2015, 01:57 PM
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For me, age has led to performance issues. I would be very pleased to have a wiring loom diagram so I could build a harness that would replace the original.
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post #5 of 34 (permalink) Old 12-12-2015, 02:39 PM Thread Starter
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Originally Posted by Ruindr View Post
Nice work. Just curious, but what led you to the decision to change the engine harness? Just aging, or performance issues? Is it possible to source a complete engine harness, or do you have to build it yourself from scratch? The male/female plugs could be reused, I assume?
It's partly Brad's fault (aka Cush). He started a thread on harnesses that got me looking at mine

Many of the boots were broken and because the plastic connectors housings were crimped on, could not be replaced without cutting the wires. The sleeves that are supposed to protect the wiring had become brittle and fell apart when bent. The wires near the connectors were therefore also toasted and insulation brittle. I think most old Djets would be similar.

On top of that I had a slight hesitation when driving. One possibility was a bad harness connection. When I started taking the plug ends apart, I found that some connectors had a loose fit on the injector/sensor spades. The design of the plugs is such that they can only be re-inserted a certain number of times. At 40+ years old, my harness was no doubt past it's best until date

You can (or at least could) buy complete new harnesses. I haven't priced them, but I think they are in the $800-$900 range. (Checked List $1129, Discounted $840)

So far as rebuilding a new harness is concerned, the only connectors that would likely be re-used, would be the ECU plug (Apparently unobtainable new), the relay plug, and the Thermo-Time switch plug. Not sure if the firewall grommet is available (It is: List $129, Discounted $96.75!) On most cars, it seems the housings of the plug ends have been heat fused making them unusable. Replacements can be purchased for low cost from same place in Germany that has the rubber boots. Or you could use the new style Audi/VW connectors Brad is keen on.

For most, a harness can be rejuvenated by installing new wire from connector back to the main harness. That is what I am going to do this winter (using the new style of plug that Brad has kindly sourced for me and has written about in his harness thread.)

Brad likes doing this sort of work and is THE man on this forum if you feel your harness needs an upgrade and you don't want to tackle it yourself. Harnesses are easy to remove - just need to tag all the branches so you can put it back correctly (although wires are color coded)

Last edited by MBGraham; 12-12-2015 at 04:10 PM.
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post #6 of 34 (permalink) Old 12-12-2015, 02:57 PM Thread Starter
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Originally Posted by redghost View Post
For me, age has led to performance issues. I would be very pleased to have a wiring loom diagram so I could build a harness that would replace the original.
You too eh? It's affected my car too

The wiring diagram is in the manual. Partly in Section 07.4 (see attachment)and partly in the Chassis manual overall diagram. It provides the wire colors and size and of what goes where. But is hard to read!

The diagram I am making, is for my 72 350SL. Your 74 would be slightly different. Really what I am doing, is making a routing diagram along with the lengths between branches and length of branches to plugs. It probably would be about the same for most V-8 D-jets. I may be able to make up a table of some sort. At the moment, it is just scribbles!
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File Type: pdf 074-040.pdf (1.18 MB, 126 views)
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post #7 of 34 (permalink) Old 12-13-2015, 02:56 PM Thread Starter
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For what it's worth:
-pic of full size harness layout
-pdf with wire color coding, branch lengths and distances between branch nodes.
This for 1972 350SL 4.L
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Last edited by MBGraham; 12-13-2015 at 04:58 PM.
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post #8 of 34 (permalink) Old 12-13-2015, 11:50 PM
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Quote:
For me, age has led to performance issues. I would be very pleased to have a wiring loom diagram so I could build a harness that would replace the original.
Sometime in 1973, MB changed the harness split for the MPS to a point near injector 8 (MPS wires contained in fabric weave around the entire fuel loop - longest in the harness). Sometime in 1974, the coolant temp gauge lead was included in the engine harness and an additional hot start relay was added. This hot start relay changed the coolant temp (T2) circuit and the aux fan circuit. MB did not sit on changes until a new model year as Rowdie has pointed out numerous times in this forum.

I rebuilt a 1975 450 SLC harness that had all these provisions - still sitting on it as I thought about incorporating that hot start relay with a different trigger in my car. I'm not as interested in that now that I've solved my engine cooling problems with other measures.
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post #9 of 34 (permalink) Old 12-14-2015, 07:18 AM Thread Starter
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Originally Posted by cushjbc View Post
Sometime in 1973, MB changed the harness split for the MPS to a point near injector 8 (MPS wires contained in fabric weave around the entire fuel loop - longest in the harness). Sometime in 1974, the coolant temp gauge lead was included in the engine harness and an additional hot start relay was added. This hot start relay changed the coolant temp (T2) circuit and the aux fan circuit. MB did not sit on changes until a new model year as Rowdie has pointed out numerous times in this forum.

I rebuilt a 1975 450 SLC harness that had all these provisions - still sitting on it as I thought about incorporating that hot start relay with a different trigger in my car. I'm not as interested in that now that I've solved my engine cooling problems with other measures.
Brad, I saw an ended eBay auction for a 72/73 harness off a 1973 450slc w107 Mercedes 450SL 450SLC 72 73 Engine Wire Harness 107 540 0509 D Jet Jetronic | eBay. It looked almost same as my early 72 with the old style trigger points connector. It had same part number as shown in EPC, except with KS at end and was 1972 original. 1075400509KS. It would be interesting to know just which harness you get when ordering the part number on EPC (1075400509) Of course, we don't have that problem

This one had a green lead coming out of the relay plug that I do not have. Is that the line going to the temperature gauge?

I seem to recall you mentioning that there was one other thing that had to be disconnected under dash when removing harness (perhaps a ground?) I only had to disconnect the ECU and Relay plugs.
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Last edited by MBGraham; 12-14-2015 at 07:32 AM.
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post #10 of 34 (permalink) Old 12-14-2015, 09:39 AM
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So a updated report on the wire harness 107 540 05 09. I had Mercedes Valencia Ca check, I called CABLE FUEL INJECTION | Genuine Mercedes-Benz | 107-540-05-09 in Naperville, and had the classic center Irvine check. All of them report back as NLA.
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