I would assume one should do this on a fully warmed up Engine as the Cold Start Valve is disconnected, and the Electrical Connector on the Cold Start Valve should be disconnected.

 

the cold start valve only work for a few seconds , so it has nothing to do after that .

 

For some time I have wondered how to check Fuel Pressure on my 560SL.
Ran across this exceptional YouTube video by Pierre Hedary on how to do this.

I made some notes from this video in preparation of the day that I obtain a KE Jetronic Fuel Pressure hose apparatus. On Ebay there is one for sale for approximately $100.
I have a generic Fuel Pressure Gauge but its not going to work.

In any case, this is a very interesting video.


Notes - Fuel Pressure Gauge Hookup - KE Jetronic ...

Video:

Preparation:
CIS KE Jetronic gauge/hose set
O-rings for EHA: 10mm OD, 6.2mm ID, 2mm Thick
2mm Allen Wrench
My EHA was mounted down with flat head screws, you might need an Allen Wrench

Setup Connections:
- remove 12mm plug right side of Fuel Distributor, connect to Gauge Hoses
(This is Control Pressure)
- remove at Cold Start Injector Port on Fuel Distributor, connect to Gauge Hoses
(This is Working Pressure)
- Disconnect Electrical Connector on EHA on Left side of Fuel Distributor
The Electrical connector is on the back side of the EHA.

Procedure:
EHA connection unpluged because you need your baseline fuel pressure
Start Engine with the Gauge Valve closed on the KE Jet hose set.
With the Gauge Valve closed, read number on gauge in bars, not psi - ex: 6.0 bar (Control Pressure)
Open Valve and read number on gauge in bars - ex 6.4 bar (Working Pressure)
Take difference between these 2 readings

Working Pressure vs Control Pressure:
Working Pressure (at the Cold Start connection) will always be higher than Control Pressure.
Working Pressure is the raw pressure from the Fuel Pump.
Control Pressure is the pressure modified from the EHA.

Goal:
The Goal is to get Working Pressure - Control Pressure = 0.4 bar with the EHA unplugged

Adjust EHA:
Remove EHA
Remove the brass protective screw on the back side with flat head screwdriver
Using a 2mm Allen wrench, if the difference is lower than 0.4 bar, turn CW 1/4 turn.
(lower than 0.4 bar is a lean condition)
Reinstall EHA and read Gauges again.

Notes:
Restart Engine with valve open
Renew O-rings behind EHA to prevent fuel leaks
This applies to all KE Jet CIS, but does not apply to earlier KE
Watch the video, Pierre mentions an adjustment you might need to make at the Air/Fuel metering on top of the Air Cleaner.

Control Pressure can be tapped in to here:
View attachment 2677020

View attachment 2677021


Tap into Working Pressure at the Cold Start valve:
View attachment 2677022

View attachment 2677023


EHA location:
View attachment 2677024


EHA O-rings:
View attachment 2677025

Interesting article. I guess this will apply to other engines with K jet.

 

Pierre mentioned that this does not apply to KE Engines.
I did note that there is a YouTube video of this being done on a KE Engine.

 

Hi Carl,

as you're an electronic expert maybe the following will be interesting. Instead of the traditional pressure gauge(s) you can use e.g. one (better two) automotive sensor from Bosch (BOSCH 0261230414) or a cheap Chinese thing.

New! Audi Q5 Bosch Fuel Pressure Sensor 0261230414 06H906051J | eBay

Press 'Read more' for more information.

www.ebay.com

Keep in mind that this is an absolute pressure device so you have to take care if you do measurements in Denver or on Mt. Eavens...

And in addition, it would be cool to have an adapter to connect the 2nd Sensor in line to the cold start valve
So you may be able to detect a leakage of this valve as well an can perform measurements during start, warmup and driving with full functionality.

Cheers Martin

mockup fuel pressures measurement device(s)

Design of the Adapter

Adapter...

...mounted on the FD

For fuel pressures see green dnd blue lines (blck= calculated differencew). With this scale no exiting fluctuations visible, but if you know where, you can detect the moment of fuel cutoff in overrun.

 

Martin, that is very interesting. Having an electronic device to continual monitor the two fuel pressures would be useful. Maybe the Chinese will come up with an inexpensive device that works.

 

if you want to test the basic fuel pressure , just disconnect the line at the cold start valve and connect there .a 100 psi gauge from your local hardware store , a piece of quality fuel hose that can handle the pressure , basic fittings , 2 clamps .fpr about $ 25 , you are done .read about 75 psi .

 

Hi Carl,

that's your "electronic device", based on a Raspberry PI. Prototype but just working fine. There is still there some improvement and debugging to do, as well on the GUI.

Cheers Martin

 

@Martin_fromGermany, did you make that adapter yourself? I have looked long time for something like this to be able to have a fixed pressure meter in the engine bay.

 

Hi Bauke,

partly...We are a team of 3 but I'm not the mastermind ;-)
I only was responsible for the pressure/vacuum measurement, sensors, adapters and so on. The main electronic and programming work is done by another guy.
Up to now we have extension modules for fuel pressure and the O2-Sensor (you see them on the pic above), we are working now on a third module for vacuum measurement.
The main module (just to attach to the diagnostic socket) can analyze system voltages, duty cycle, ignition timing and dwell angle. The data is transferred via WIFI to a smartphone or laptop computer, no additional software required

When everything is working the way we want, I will present the result here, but this will take a couple of month more.

Cheers Martin

 

Hi Bauke,

partly...We are a team of 3 but I'm not the mastermind ;-)
I only was responsible for the pressure/vacuum measurement, sensors, adapters and so on. The main electronic and programming work is done by another guy.
Up to now we have extension modules for fuel pressure and the O2-Sensor (you see them on the pic above), we are working now on a third module for vacuum measurement.
The main module (just to attach to the diagnostic socket) can analyze system voltages, duty cycle, ignition timing and dwell angle. The data is transferred via WIFI to a smartphone or laptop computer, no additional software required

When everything is working the way we want, I will present the result here, but this will take a couple of month more.

Cheers Martin

View attachment 2677306

Where can I get the foam for the A/C line where your fuel lines are? The foam wrap (with sticker 107 476 0417) looks new.

 

Amazing. If we had some logger device that could easily be plugged in for this and a few other params it would super easy to debug all those mysterious gremlins we hit sometimes...

 

A user by the handle of “H.D.” In the w124 forum apparently has rubbed many people the wrong way and and critiqued Pierre’s video. I believe he was right about correcting Pierre on the terms of the FD. I believe that Pierre argues that the Control Pressure gets sent to the injectors when it does not and is the pressure that pushes down on the top of the piston. Higher control pressure means less fuel or leaner operation. System Pressure is the pressure provided in the bottom half of the distributor by the combination of the fuel pump and the fuel pressure regulator. I don’t know what “working pressure” refers to, and that may be my ignorance. I understand Pierre put a noble effort into this video, but he attacked H.D. for providing corrections and also not calling Pierre a professional (not cool, even if Pierre was wrong). Pierre’s thread called “exposing H.D.” Contained lots of w124 owners complaining about HD’s attitude. Although he supposedly was a MB or Bosch mechanic or engineer at the time of KE-jetronic and knows the system very well, apparently his attitude makes his valuable information fall on deaf ears. Last night the thread Pierre created was deleted, rightfully so. In that thread I attempted to provide technical info that’s in the videos below, but it’s gone now.

Anyway, I believe there is concern about someone we all believe to be wise and knowledgeable about the system using the incorrect terms. This thread is an example of how misinformation can be quickly proliferated on the internet. I’m not positive, but believe the incorrect terms proliferated here.

I believe that these two videos are a more reliable source of the terms that we should be using.

7-10 minutes, not the term system pressure around 8:55.
13:15-15:15 explains the control pressure

Maybe working pressure is the top half pressure above the membranes? But there could be a different pressure for each cylinder. It also can’t be measured. Only the pressure that goes to the injectors can.

I have yet to find an English speaking version of the below for KE-jetronic, but here is a Spanish speaking version:

Maybe someone can figure out how to download the Spanish transcript and translate it to English.

I’m not trying to cause any trouble, just information sharing. (And I’ve had calls on the phone with Pierre where I helped him understand things before. He is not Omniscient. What he does is very helpful to our community though.)

Edit: Texting Pierre now, he says I’m talking K-jet, not KE-jet. I went looking for additional sources and found this, which never mentions “control pressure” in it once. Lots of “system pressure” and “lower chamber pressure” though. Bosch KE-Jetronic Overview

the pressure above the membrane act on all cylinders equally .so to the control pressure on older cis . , the basic cis in 76 , had the warm up regulator to work the control pressure , it acted as a choke on a carburetor.then the oxy sensor came into view in 1980 , there the frequency valve did that at the lower fuel distributor , it did fine tuning from the ecu / oxy sensor .the WUR still work at the top of piston .then came the last one with the EHA , less parts , no more WUR or frequency valve .that was the best one .

 

We will!

I'll keep you informed. In addition to this tool the programming of a software for plotting the measurments is necessary as well. Doing this with Excel is not our goal and up to today I didn't found a free solution which is easy to use.
And finally the reading and displaying the fault memory for the California-models needs to be implemented as well.

Cheers Martin

 

Ran across this exceptional YouTube video by Pierre Hedary on how to do this.

- remove 12mm plug right side of Fuel Distributor, connect to Gauge Hoses
(This is Control Pressure)
- remove at Cold Start Injector Port on Fuel Distributor, connect to Gauge Hoses
(This is Working Pressure)

A user by the handle of “H.D.” In the w124 forum apparently has rubbed many people the wrong way and and critiqued Pierre’s video. I believe he was right about correcting Pierre on the terms of the FD. I believe that Pierre argues that the Control Pressure gets sent to the injectors when it does not and is the pressure that pushes down on the top of the piston. Higher control pressure means less fuel or leaner operation. System Pressure is the pressure provided in the bottom half of the distributor by the combination of the fuel pump and the fuel pressure regulator. I don’t know what “working pressure” refers to, and that may be my ignorance. I understand Pierre put a noble effort into this video, but he attacked H.D. for providing corrections and also ( EDIT Supposedly) not calling Pierre a professional (not cool, even if Pierre was wrong). (Edit HD sent me a Jan 2022 PM clarifying that he only called Pierre’s advice unprofessional, not Pierre himself). Pierre’s thread called “exposing H.D.” Contained lots of w124 owners complaining about HD’s attitude. Although he supposedly was a MB or Bosch mechanic or engineer at the time of KE-jetronic and knows the system very well, apparently his attitude makes his valuable information fall on deaf ears. Last night the thread Pierre created was deleted, rightfully so. In that thread I attempted to provide technical info that’s in the videos below, but it’s gone now.

Anyway, I believe there is concern about someone we all believe to be wise and knowledgeable about the system using the incorrect terms. This thread is an example of how misinformation can be quickly proliferated on the internet. I’m not positive, but believe the incorrect terms proliferated here.

I believe that these two videos are a more reliable source of the terms that we should be using.

7-10 minutes, not the term system pressure around 8:55.
13:15-15:15 explains the control pressure

Maybe working pressure is the top half pressure above the membranes? But there could be a different pressure for each cylinder. It also can’t be measured. Only the pressure that goes to the injectors can.

I have yet to find an English speaking version of the below for KE-jetronic, but here is a Spanish speaking version:

Maybe someone can figure out how to download the Spanish transcript and translate it to English.

I’m not trying to cause any trouble, just information sharing. (And I’ve had calls on the phone with Pierre where I helped him understand things before. He is not Omniscient. What he does is very helpful to our community though.)

Edit: Texting Pierre now, he says I’m talking K-jet, not KE-jet. I went looking for additional sources and found this, which never mentions “control pressure” in it once. Lots of “system pressure” and “lower chamber pressure” though. Bosch KE-Jetronic Overview

 

I saw Pierre's Youtube video responding about this.

 

I have yet to find another source referring to control pressure on a KE-jet. Semantics and terminology. You can call red black and black red, and it doesn’t matter if everyone uses the same terms. It’s just that they don’t.

I’m not sure I’m correct. That’s one thing I’m sure about.

 

Your outline was infinitely better than Pierre’s video. Good job

 

Hi RiconinAZ,

I prepared the part with heat shrink tubing and then just wrapped it with Neoprene (4mm). Only the sticker is new (a reproduction).

Cheers Martin

That was the first attempt...

 

This came out great. Looks factory. Thanks for sharing.

 

Only thing I would add to Carl's great write up in post #1 for safety is to:

A) So not difficult to start with the line to the CSV disconnected as will be needed during test I suggest to start the car before connecting any lines for just a few minutes; therefore easier to start vs a really cold start.
B) Shut engine off have some rags handy and disconnect the line to the CSV and the 12mm plug at the FDU collecting any fuel drips with cloths
C) Connect appropriate connectors to the FDU connections at the CSV and 12mm FDU plug and then the hoses of the pressure tester to the connections
D) Turn ignition key to start but, not cranking to prime the FDU and lines....check for leaks then repeat if none or fix leaks.
E) Turn ignition key to start but, not cranking one more time and this time bleed the fuel gauge and lines (assuming you have a gauge set up with a bleeder) to remove trapped air to insure a good reading.

After above proceed with Carl's excellent write up.

 

Hi Carl,

that's your "electronic device", based on a Raspberry PI. Prototype but just working fine. There is still there some improvement and debugging to do, as well on the GUI.

Cheers Martin

View attachment 2677162

Martin did you en up manufacturing this tool

Hi Carl,

that's your "electronic device", based on a Raspberry PI. Prototype but just working fine. There is still there some improvement and debugging to do, as well on the GUI.

Cheers Martin

View attachment 2677162

Martin did you end up manufacturing this tool?

 

Hi Elmar,

sorry, no progress...
The guys are working on an updated version, but we still don't know how we want to continue with this,

Cheers Martin