Duty Cycle stuck on 90% - 89 300SEL
 

I've been battling with finding the cause of this fault & have tried some tests found from searching BW without success. The car is an 89 M103, non-California car, so with my DMM plugged in ports 2&3, I should see 70%... but I do not.

My car reads 90.5% at all times from key on engine off, all the way thru running to 80* C. Flipping the poles in the diag port, i get 9.5% from KOEO thru running to full temp. The only time I get a fluctuation is upon throttle enrichment, where it moves to 60% then immediately back down to 90.5% upon liftoff. The car will start rough and die first attempt in the morning, but then starts to a normal idle of 750 during warm up phase & move to 1100-1200 rpm idle after reaching 80*C and stays there.

I've eliminated vac leaks & changed a ton of parts (list below). Hoping for a change, I unplugged the o2 sensor, deflected the air plate, tested voltage to IAC(11.7v)/potentiometer/EHA & all appeared to be well but did not see any change other than the CEL lighting up. No codes are stored when pulled with the code reader, just the 90.5% duty cycle (or 9.6%)...

The car is in what seems to be "limp home mode" & I'm looking to get out of it & adjust my duty cycle down to the 50% it should be at! I'm at the point where I've exhausted throwing parts at the problem, so what could I be overlooking which would correct this fault?


List of parts changed without success:

Brand new KAE OVPs (latest one 2 weeks old)
New Bosch 13925 o2 Sensor (last year)
New Potentiometer
New Fuel Pump & Filter
New Bosch Injectors & seals
Replaced IAC hoses
New Airflow meter boot
New throttle microswitch
Swapped throttle body+sensor with known working unit (new gasket)
Swapped EHA with a different unit
New Bosch Voltage Regulator
New Belt/Tensioner & associated parts
New Radiator (no impact expected)
Bosch Cap, Suppressor and rotor (1 year old)
Denso spark plugs (1 year old)
New 2-pin temp sensor (1 year old)
Swapped cracked hose from valve cover to breather tube on cyl head
New Bosch Coil
Replaced Fuel Pressure Regulator

Go through all of the tedious tests described in chapter 07.3-0121

Below is a link for a W124 300E - but there's a similar if not the same chapter in the W126 FSM that is also available on www.startekinfo.com

http://www.startekinfo.com/StarTek/outside/12264/Program/Engine/103/07.3-0121.pdf

For hints and tips to get that FSM to work see link in my sig...

I see you have been having 'fun' too !

Tons! Lol

Thanks for the link, I began a few tests before it got too dark. EHA wiring tested within spec at 19.5 on my DMM (under mA).

Idle control valve sees voltage at the connector, but unplugging/plugging the icv while car is running provides no change... Stuck at high idle.

I did find this fuse frail and cracked by the fuse box... Unsure what it controls but here's where I can start replacing...http://images.tapatalk-cdn.com/15/06...0af1464215.jpghttp://images.tapatalk-cdn.com/15/06...52fd2f0db3.jpg

I don't know what that fuse is for - possibly something big like AC?

From what I've read so far a disconnected air idle control valve should provide a high idle - connect it and it should work and the idle should drop (unless the car is in the warm up phase). Skip to the section for checking that valve - if you briefly apply 12V to the correct pins (check!) it should click...

On my 89 W126 KE-Jetronic, the duty cycle is supposed to be about 50% when warm. And I use a multimeter which has a duty cycle setting. I then need to reverse the leads as my multimeters reads % ON for Duty Cycle - Mercedes uses % OFF.

With that said, once I get an accurate duty cycle reading, the engine computer will be "stuck" at a certain duty cycle reading if there is a malfunction. This is similar to the duty cycle percentages in the following document. I don't know if this applies to your specific car? Here is that document... (See page 16.)

http://www.berlinasportivo.com/Technical/lancia/Thema832/Testing%20the%20KE%20Injection%20System.pdf

P.S. I just searched google for any old document which had the % readouts. I don't know which specific vehicle that document applies to, but may want to find a similar document in the factory service manual for your specific vehicle.

Also that fuse probably goes to the A/C / Heating blower motor inside the car.

Correct the fuse does go to blower motor. I believe it's mentioned on fuse card.

Sent from my SM-G900V using Tapatalk

I'm assuming that it is running rich?

Not sure if it is the same problem but I spent weeks trying to find a similar issue with my 82 380SL that turned out to be cracks in the air chamber which could not be seen and my duty cycle was at 90%. I only found it after doing a smoke test. The cracks were allowing additional air into the system which told the system to add more fuel. Unfortunately, I had replaced many unnecessary parts in the process. if you think there is a chance it is the same issue there are posts on this site with photos.

Did yours fluctuate at all, or was it permanently on 90% ? Mine is permanently on 90 (or 9% if poles are flipped), regardless if car is on or key on engine off.

I am trying some more tests this evening & tracked down a newer idle control valve. The ICV which I have clicks, but testing my current unit seemed a bit off.

Elektri, the pdf file link you posted has a pretty major w124 error. It shows the O2 sensor at the right rear of the block. THAT is the location of the coolant temperature sensor.

My O2 sensor is screwed into the exhaust and the cts screws into the block

These M103's can be a nitemare to diagnose primarily due to all the different parts the factory threw at the motor.

Some of the coolant temperature sensors have an ohm reading of 3k+ while others have a sub 50 ohm reading, both values are on a cold motor as an example.

Some M103's require removing the valve cover to access the coolant temperature sensor, thankfully mine doesnt... the 22mm socket dropped right on.

Some ECU's or whatever does the adjustment allow for the Idle Air Valve in front of the fuel distributor to raise the idle when disconnected, my M103 on two different units dropped the idle speed by at least 500rpm at startup from cold.

Some EHA's have a 2mm set screw adjustment, others have a flat head screw.

The upshot is the controlling or adjusting the startup idle speed on this motor is greatly lacking in fun.

I've had a similar issue with my former '89 190E 2.6.

O2 sensor was causing chaos with the duty cycle, IIRC. Basically it rendered the adjustment non functional because there was no longer a loop/feedback from the sensor.

https://farm4.staticflickr.com/3782/...64500599_z.jpg

However, the EHA was also causing high idle at operating temperature. Bought a new Bosch unit and fixed the problem. The car is gone but I still have the EHA.

Even with a non-leaking EHA, if it was not good it would wreak havoc on the idle and throttle response.

thanks for the input! After some tests to the temp sensor/wiring, FPR, and ECU, I'm leaning toward replacing the actual EHA as you did above. I have a constant 90% duty cycle with absolutely no fluctuation, high idle after reaching operating temp and lacking in power toward the upper rpm range. I will try and track down a known working EHA to verify this is the root cause prior to taking the plunge and buying new.


Temp Sensor - .60k ua on the DMM & just under 5v at both connectors
Swapped in a different FPR with no changes (as expected)
Swapped in a different ECU with no change

I ran the car without an ECU plugged in & it ran exactly the same... just with the 100% duty cycle error. Car did not start once the original ECU was plugged back in... it was real low on gas upon the start of testing, so I'm thinking I ran it dry. Will refill & resume troubleshooting. FUN!

After some further testing yesterday evening, here's where I'm at today...

CIS Computer, Temp Sensor, Idle Control Valve, Throttle Microswitch all check out within spec & function as needed. The two EHAs I have are suspect, but wiring from CIS computer to plug is OK, so I decided to swap them again hoping for a change...

EHA 1 - Difficult start but car pulled strong off the line & idled around 1200-1300 rpm when warm. Constant error of 90% DC (neg on pin 2 & pos on pin 3)

EHA 2 - Car started every time to a smooth 750-800 idle, but stumbled pretty bad upon enrichment/acceleration. Once warm, would hover around 1k idle, fluctuating up and down 100 rpm. Constant error of 9.4% DC here (neg on pin 2 & pos on pin 3)

Progress... sort of. Assuming the 9% DC with EHA "2" is the 10% error (potentiometer/throttle pos switch), I swapped a new functioning replacement poetntiometer in to what I thought was within spec (.78v iirc). Idle remained around 1k rpm and no fluctuation off the 9.4% DC error.

Before I make the plunge on an EHA replacement & fuss around with throttle linkages, I want to have the X11 port show the 70% DC with key on Engine off... showing that there are no errors & allowing me to move forward with fuel adjustments.

Has anyone experienced the 10% DC error where the potentiometer was not the issue? If so, what steps were taken to correct your fault?

Check your coolant temperature sensor. CTS.
Almost against the firewall, right rear of motor.
Seems to be at least 2 versions.
One with the connectors pulled off should read under 50 ohms across the sensor
The other CTS seems to read about 4k ohms.

Both of these are two pin versions. I have no idea of the 4 pin sensor readings.

The under 50 ohm unit is a part number 0280130044

Test mode?
 

Are you putting the car into test mode to get the Duty Cycle? I don't see where you say you are going through the routine to put it into duty cycle mode. My 89 300SE is a California car even though it spent all its life in the Northwest, go figure. I have to turn on the ignition and press the button in the box for the 8 pole Diagnostic connector for 6 seconds, Let it show me any codes, then press it again for 6 seconds, then start the engine. The CIS then gives me the duty cycle that I can adjust. Otherwise I think it always shows 90% or some other constant number.

So do you have a button and red light in the box behind the 1st firewall to the right of the battery like in this picture?

no button nor redlight, by the box... non-California car. I thought I was following diag mode directions correctly, but will give it another go again using the makeshift code reader I have.

Coolant temp Wiring checked out OK, as did the sensor (2 pin)... the troubleshooting continues.

I'm afraid to say that it is just a constant trudge through that list in the FSM...

Tested the throttle position switch & idle/WOT check out...

Installed a new Air Flow Pot sensor & set to 0.74v...

Tested EHA values:
-Unplugged with KOEO plug terminals showed 19.5mA
-Plugged into EHA but KOEO showed 18.1mA
-Car idling at 80deg #s would start at 0 mA but would slowly climb to -9.1mA!!!
-Revving engine/producing load would bring it back down closer to 0mA, & back to the idle reading

I could've sworn I had the +/- terminals on the correct probes while testing, but regardless, something seems suspect with those numbers... Has anyone experienced such drastic changes with their EHA readings?

Stick with the basics.

Spark plugs every 16k miles
Cap and rotor? Make sure they are genuine, or at least Bosch
Wires? Go for genuine
Check for 12v at the cold start valve on a cold engine. Check with a LIGHT tester, not a voltage tester. You can have "12v" and not have enough to actually pull a load. I had similar crazy issues, ended up being a tune up and a loose ground.

Cis is difficult to understand, due to the simplicity of it all. There are only a hand full of inputs, and once it gets all the inputs, and power, voilà! It will right itself.

Tune up piece is complete. I took off the ground located on the battery, gave contacts a good cleaning & reinstalled. The braided ground strap from the coil to fuel distributor was corroded and weak, so I replaced it with some 8awg wire I had lying around... no changes resulted from either. Not sure if/where there's another ground connection which may contribute to these issues for the w126 M103, but I'm hoping to find the issue by week's end.

Trace the upper engine harness as it makes its way to the ac compressor you will see a ground to the intake. That is the one that did it for me. Let me know what happens when you check the voltage.

That ground from the upper harness appeared to be OK, but took a wire brush to it and reinstalled. The groundstrap from the coil also bolts to this location, so I cleaned & replaced that (as mentioned prior)...

Did not get power to the cold start valve, but car was outside for a bit prior to first start... Unsure if that rise in temp from a 90deg day has bearing on cold start activation/voltage.

Did a few more tests with O2 and EHA while I wait on my CIS fuel pressure tester to arrive. Unplugging the O2 did not change the hard coded 9.3% at the diagnostic port. Ran out of sunlight and forgot to record O2 voltages but will do that on lunch along with retesting the cold start plug.

http://images.tapatalk-cdn.com/15/07...85ebd324be.jpghttp://images.tapatalk-cdn.com/15/07...01eb231df4.jpg

To update... O2 voltage began at .49v from a cold start. Once car was warmed up, voltage constantly fluctuated from .09v to 0.84v and everywhere in between... So that seems to be functioning properly.

With all these new/replaced sensors, I feel I should be closer to a perfect running car than where I'm currently at, regardless off differential pressure from EHA. Since all grounds I could find in the bay were cleaned and inspected, I decided to troubleshoot some areas again.

Starting with the O2 sensor, tests performs exactly as expected... No change since last testing.

Next was the potentiometer. Now with neg on pin 1 and pos on pin 2 I was getting a range of -11v to -5.9v (changed as the sensor moved). The SG motors ports tutorial states to use these pins when adjusting the potentiometer... Obviously I can't achieve the proper 0.7 voltage here. Moving the positive probe to pin 3 however, I was able to get "0.7v"... High idle remained though. I accidentally grounded the negative probe and idle settled down. This is a brand new sensor FYI.

Something is off here. BtW, duty cycle error is 90.6% now, not 9.3%.

I feel lost again... More frustrated :(

figured out the issue upon going thru the troubleshooting manual... the wires leading into the coolant temp sensor (two prong) were split and shorting right at the plastic connector. This was difficult to see since it was partially covered by rubber sleeves. I ordered replacement leads from the local dealer and after soldering them in, I now have a fluctuating readout on my DMM!.

Prior to finding this wiring issue, polarity at the air pot was way off, EHA readings were off & essentially did not allow the ECU to function properly. Some slight adjustments to the EHA & tower were required to reverse any previous changes... so now duty cycle fluctuates between 45-52%, air pot is adjusted to 0.71v & EHA appears to be within the .4bar spec. Idle is back to ~700rpm in park & 550 in D.

Going to fill up and give it some good driving throughout the week to ensure all remains well.

Do you happen to have the part number for those replacement leads? Mine are brittle and perished. Thanks for the write up, very informative.

I think I've got to concentrate on my EHA...

...building up the courage as I type!

When you say the duty cycle fluctuates - do you mean at different rev ranges / temperatures it has different values or do you mean it always fluctuates and you don't get a steady reading?

on my particular car, duty cycle fluctuates at idle as in no "steady" reading.

similar to what's shown on this vid...
https://www.youtube.com/watch?v=zahcIRGZZwY