Hey all, I have a 95 w124 wagon, an e320 I did a C36 swap on. Speedtuning did the reprogram on my stock ECU and it runs fine. I just swapped in a manual 5 speed and I need to figure out what the coding number should be for the ecu to tell it it's a manual transmission.

Here are a few reasons why this is important,
1. idle control, the car things it's always on park. Unless you know for sure because you've been deep in the ECU maps, I don't know having the ecu think it's always on parkesses with timing and emission controls. The manual trans cars have a clutch switch input, connector 1 pin 22 which should directly effect idle speed and also kill the cruise control when the clutch is pressed.

2. The transmission overload switch. The 722.3 had this switch and it retards timing when the transmission would be under heavy load just before or during a shift to help as a torque management solution. It only activates sometimes and there is some kind of logic built into the ecu to detect if it's working. I'm the HFM manual it even states of there is a high speed missfire, check this switch. So it effects timing and it cannotnkisy be jumped to bypass it, I've been down this road. Setting the ECU to know it's a manual transmission will ignore this Input.

I have a USA car with a cat, cruise, no asr and a 5 speed. There is no coding info I can find for the USA car. I found this combo for a euro eur and it would not take the coding number, HGMscan would report coding failed. Also the euro cars I think all had a CO pot to adjust fuel mixture, which no USA car has. There was also only one other HFM car that know of that was manual and that was a euro c280.

So what can I do here? Not having this set right is effecting performance.

 

On the HFM W124, the engine ECU does not communicate with the transmission in any way so it has no way of knowing whether the transmission is in Park or not, so there should be no issue from an idle perspective. But, another big issue that you are going to have is that the US cars have a transmission hold 2nd gear mechanism (vacuum solenoid valve) to warm up the car when the engine is cold. The ECU contains an algorithm that detects if this is working (RPM vs temp vs Mass Airflow, etc.) and with a manual trans, this will throw a check engine light. Maybe you should get a manual ECU from Europe and see if you can code that?

 

I've had no issues with 5 spd swap into stock M103 300E (87) and M104 E320 (94). Trans pressure switch cable not connected to anything, capped vacuum line to the shift delay solenoid. Believe issues are due to the C36 engine/electronics swap

 

The ECU does see if the car is in park or neutral or drive. It's right there on the live data using hfm scan. And if you manually bypass the neutral switch the idle speed changes slightly. So yes, the ECU knows if it's in gear or not.

Second, In the HFM manual it tells you exactly what the overload protection switch does, and how it effects drivability when failed. And when disconnected or bypassed it is assumed failed because a fault sets in the ECU. It has to see that switch open and close when your driving. I don't know how the fault logic is setup, but it is there and it pulls timing.

There is nothing fancy about the wiring for the 3.6. it's the same engine as what was in there before, an M104. The only thing that was done was the ECU flash for fuel and timing maps, everything else about operation of the engine is exactly the same and any m104.

The shift delay solonoid is the least of the issues, because all you do is remove the vacuum line, cap it and leave the solenoid plugged in.

If you research that overload protection switch you'll find out exactly what it does. It's a huge misnomer that you can just unplug it or try and bypass it and not effect top end drivability. It's just the the SLS shocks. Everyone seems to think the rear accumulators control ride quality. But in reality the SLS shocks are regular shocks that do wear out...difference is they have the ability to be raised and lowered with hydraulic pressure. The accumulator is there to be a resavoiur for the non compressible fluid when you go over bumps, the fluid it has to have a place to go. But as far as ride quality and control, the shocks are shocks. Unless the accumulator fails. Then you get a hard harsh ride. If not attended to soon enough, that hard ride works the valving in the shocks tod and you will get a floaty ride like an old American car. This is exactly how my wagon was when I bought it. New SLS shocks made it ride hard and stiff, it was then obvious the accumulators failed, and they were ignored till the shocks wore out.

For now I connected the overload switch to the clutch switch. So the ECU is seeing it open and close. When my foot it off the clutch, that would be the normal state of the switch. I'll see how it goes after a few weeks and I'll know if that will be enough to keep the ECU happy. But so far, I've felt no issues at high rpm high load like I had before.

 

Theoverload protection switch causes the ECU to retard timing during full throttle shifts. It does not need to cycle for normal operation. Leaving it disconnected has no effect (at least in my small statistical sample). Connecting the circuit to the clutch switch may make it easier to shift smoothly.

Unaware of how the ECU knows if in park or not except for the NSS which I believe only interrupts the starter circuit. No other connections. Is it an engine load/unload condition? If not in park or neutral it's closed. Jumpering the proper terminals should make no difference.

 

This is copied right from the HFM manual. It's not as simple as everyone states. And the ECU does see if the car is in gear. I dunno why I have to say it again, it's in the live data, engine speed is adjusted if it's in great or not. The wiring diagram also shows it connected to the ECU. I would suggest finding and studying the HFM design and function manual. It may be the first EFI system Mercedes used (not talking about Djet). But it's much more advanced than you think

If the HFM control unit does not receive a shift signal
from the automatic transmission when the car is
being driven, whether as a result of a fault at the
transmission overload protection switch (S65), brake
B1, or at the wiring, the HFM control unit switches
into the emergency running mode. The
transmission overload protection continues
operating only to a restricted extent in the
emergency running mode.
If no shift signal is sent by the automatic
transmission, the HFM control unit recognizes the
start of a gearshift as a result of a change in engine
speed within a defined level.
When the transmission overload protection is
operating in the emergency running mode, this may
be noticable as a result of the temporary retardation
of ignition timing at high speed.
M
In dealing with the complaint "Misfiring at high
speed", it is then necessary to check the
transmission overload protection switch (S65) and
also the wiring.


A transmission overload protection is integrated in
the HFM control unit in order to protect the shift
elements of the automatic transmission from
excessive thermal stresses during load shifts at
higher revs.
The HFM control unit processes the following
information for this purpose:
 Signal from transmission overload protection
switch (S65)
 Engine speed
 Air mass
As a result of the transmission overload protection
function the ignition timing is retarded to 5° CA
before TDC (reduced engine torque) for about 400
ms during
1-2 and 2-3 upshifts.
As this retardation of the ignition timing also
improves the gearshift smoothness during the
shifting phase, this measure is also used for 3-2 full
throttle downshifts.



Here is your selector lever position Info

k) Selector lever position (AG only)
The starter lockout switch (S16/3) is used for
recognizing selector lever positions P/N and also 2/3
for the HFM control unit.
The selector lever position is required in the HFM
control unit for the following functions:
 Fuel injection
- Post-start enrichment
 Catalytic converter heating
 Transmission shiftpoint retard
 Camshaft adjustment
 Governing maximum engine speed

 

Good morning! The HFM may be addressing features available in later or other models but the 95 E320 in USA market doesn't have the above. What market is yours?

 

It's a 95 e320 USA model

 

Interesting. I have always thought the connection to the ECU was so that it would know when the engine was being cranked (which it probably still does). Looking carefully at the schematics, it is possible that with a pull up resistor in the idle speed controller connection, in theory it would be possible to sense whether the signal was be grounded by the starter solenoid via the NSS. Thus one could detect P/N or not P/N (but no way to know which gear the trans is in). But this strikes me as a somewhat flaky, un-mercedes like circuit design and more like something you might see on an old British sports car. Is the overload switch sending a D, 3, 2, 1 or R signal? Do you have a source for the HFM manual you are quoting from? Thanks!

 

Gonna put a relay in the starting circuit similar to what I had with the 722.6 I had in there previous to the 5 speed manual. Im pretty sure as long as I can have the start wires separated then the ECU will show its in gear. I haven't had a min to play with it.

The overload protection switch is a pressure switch that's activated by a valve that it actuated by the b1 band mechanically. So under a full throttle 1-2 shift or other conditions when the b1 bad is loaded right the valve is actuated and then the overload switch. This retards timing 5 deg for 400ms. It's torque management. I'm not sure how the ECU logic is setup to determine if it's working other than wanting to see it open and closing, maybe there is a resistor value in there too so it never sits open or closed. I don't know how far the logic goes, if it looks for switch activation above certain throttle positions and what not. I did hook it to the clutch switch so the ecu would see it open and closing. Closed would be clutch pressed and switch activated, so if it retards timing it won't matter really. It seems to run better at high speeds, but I need to look at the data to see what's going on and see if it's set a code. Right now I have to deal with a driveshaft vibration issue lol.

 

It seems to me that if the circuit behaves as I have speculated, all one would need to do is disconnect the appropriate connection from the starter circuit and the car will think is is in gear. If you want to get fancy, use the clutch switch and/or appropriate relay to tell the ECU that it is in gear when the clutch is engaged and in neutral when the clutch is disengaged.

 

Hey!. Did you resolve the S65 trans pressure switch and P/N condition with timing retard etc?. linking the Starter circuit between the ECU and EA/CC module via the starter lockout switch is what tells it its in gear.
I have installed the system, but wondering if I should put the pressure switch on the clutch or if that still causes the ECU to fault in certain conditions?.
The selection for Park/Neutral-Drive probably needs to be automated on a short timer - ie 1-2 seconds after start it goes into Drive.
None of the manual coding options work on the C36 ECU, tried the early and later coding too.
People suggest using the C280 manual ECU and retune, but its not an easy option for me down here.

 

No I didn't. No coding would work right as you said. I ended up just leaving it jumped together I think. In the end I was never happy with the tuning of the ECU, the whole time i had the car. The timing it would pull due to intake temp, then coolant temps, it was stupid. But it was what most manufactures did in the 90s. Drive the car in 90 deg weather with the ac on in traffic it becomes quite a dog. The car always had a weird thing at the top of the room range where it felt like it was messing with timing. Not always, but a lot of the time. I sold the car when the market started to go crazy on the wagons, and I was getting tired of dealing with 124 quirks. I needed a daily I didn't have to touch. I wish I could have kept it, cause I loved it. But if I did I probably would have done a halter ECU or something at some point. Good luck!

Mark