Mercedes-Benz Forum banner

Winter/Spring Djet project

6K views 36 replies 11 participants last post by  107merc 
#1 · (Edited)
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!
 
See less See more
2
#2 · (Edited)
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.

 
#3 ·
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?
 
#5 · (Edited)
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)
 
#4 ·
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.
 
#6 ·
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!
 

Attachments

#13 · (Edited)
Have started on harness repair (Brad asked for pictures!)

Brad (cushjbc) kindly made up most of the new pigtails and supplied me with Audi style connector housings, double cantilever terminals, small uninsulated butt connectors and a supply of original color coded wire.

First of all, a picture of my hi-tech South Carolina work station :)


Sample of Brad's neatly marked pigtails


Two of my completed connectors (using Repro boots bought from Germany)



I ended up using this inexpensive crimper for both the JPT double cantilever terminals (20-16 upper right die) and for the uninsulated butt connectors (28-26 2nd from left top die). Used the middle lower die to crimp JPT tabs to wire insulation. I am sure there are better options.


JPT double cantilever terminal (see Brads Harness thread for more detail)


I am using silicone coated fibreglass wire sleeves bought from WireCare. This sleeving is strong, flexible and fire resistant. It shouldn't get heat baked and crack like the original pvc sleeves.
Pictures below show how 7awg sleeve butts against original pvc stub that I left in place (should have got it tighter before using heat shrink join) and 2awg that fits over the existing mps sleeve (will tape joint). 6 or 7 awg will fit into the injector boots and 2awg will fit the 4/5pole boots (from Repro).

 
#8 ·
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.
 
#9 · (Edited)
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.
 

Attachments

#12 ·
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.
The 6 pole male connector is called C103 in later ETMs. It contains the power leads for the ECU (terminals 16/24), the power lead for the start valve (terminal 18), and the switched ground for the fuel pump (terminal 19). In that harness pictured above, it also contains a simple series connection for the coolant temp gauge from the coolant temp sensor at cylinder 4.

Regarding what I said about other connections in the right footwell, I have seen ground connections mounted near the clip for C103 but it may have been on W116 harnesses. The point I was trying to make is that D-Jet engine harnesses have differences throughout the production of various MB models.
 
#14 · (Edited)
Well, got the harness done.
Summary:
- converted all connectors to the double cantilever type with pink Audi type housings that Cushjbc (Brad) researched and told us about in the Harness thread. (Brad made up most of the pigtails for me). Now I understand them better, these connectors make a far more positive connection than the original connectors do.
- Removed all the brittle PVC sleeving and replaced with silicone coated fibreglass. Used 7awg for 2 conductor wires and 2awg for 4 and 5 conductor wires. Also used 2awg on the grouped ground wires (fits over ring terminals)
- Used new rubber boots bought from Repro in Germany.
- Connected pigtails to main harness near main harness using small butt crimp connectors with heat shrink covering.
- tidied up main harness covering using hi temp self amalgamating tape.
- Final step will be to ring out each circuit from ECU connector to ensure everything goes to right place and resistances are minimal.

Some pictures below.
 

Attachments

#18 ·
- Final step will be to ring out each circuit from ECU connector to ensure everything goes to right place and resistances are minimal.
Just completed checkout and posting results here for future reference.

Measuring from ECU plug to each terminal - Digital meter goes back & forth between zero and 0.1ohms. Everything seems to go to the right place!

To try and get a better resistance reading, I plugged an old injector into each 2-pin plug (injectors, T1, T2, CSV) Overall resistance was same in all cases - 2.6ohms. Injector by itself 2.5ohms. So 0.1ohms for total return circuit.

I think that's it for harness until I get back home and re-install.
 
#16 ·
That looks great. Would you be in the mood to fab a few more for the less technically gifted?
 
#29 ·
Just to give credit where it is due. Brad (aka Cush) did all the research and found and supplied me with the double cantilever terminals, butt connectors and plug housings. He even made up most of the pigtails.

Brad is the go-to guy for anyone contemplating a similar project.
 
#30 · (Edited)
Today, I started to re-install the injectors.

I recall one owner having problems with seal leaks. Decided better way may be to first install top hat seals, then injectors, then rails (So that rails do not cause injectors to be misaligned.) Better than trying install injector to rail first.

In order to seat top hat seals in intake holes, I made this "tool" to ensure they were properly seated. Basically butt end of a drill slightly smaller than seal ID. Then slipped on a piece of plastic tube that was slightly larger than the drill. Used drill to align the seal, then pushed down on plastic tubing to push seal all way down. Worked great.


 
#31 · (Edited)
Just about done!

Work done since last Fall:

- New NGK non-resistor plugs
- Rebuilt injection harness using Brad/Cush's double cantilever connectors (see harness thread)
- Repaired corrosion found under battery tray and both sides of firewall. Painted tray and area with DOM16 (POR type paint)
- Relocated battery ground connection
- installed NEW trigger points!
- Replaced distributor cap and rotor
- Cleaned and tested injectors
- insulated injector rails
- new air cleaner to throttle body seal.

Started car today and took it for a short run. Idles smoothly and seems quite lively (mind you I have been driving our W123 300D!)

Still need to put passenger side lower dash back in. Otherwise done for now.

Really happy to have nice flexible leads and new style terminals on injectors and sensors. No more snap crackle & pop when working with harness!
 
#33 ·
I was really happy with way car ran.

Had no problem installing the new style plugs you obtained for me into the injectors and sensors. Getting the new boots on was a bit more difficult. Used needle nose pliers to help with some. I have the old-style trigger points - getting that boot on was not easy! I decided best way was to remove the distributor. Once out, I took opportunity to install new trigger points, cap and rotor. Managed to get dizzy back close to where it was, but I should double check timing.

Thanks for your help with the harness project!
 
Top