!987 260E
The car will not run with EHA plugged in. If I unplug the eha and tune the vehicle for best idle I can run it all day, as soon as I plug the eha back in the car stalls. If I tune it with the eha it idles fine but fouls out the plugs in less than 4 miles.
I've changed the FDU, eha, temp sender, idle motor,cap, rotor, wires, EZ unit and ovp. When I try to read the mil amps on the eha I get a constant .059 readout. Also I don't seem to get 10volts at the cold start injector. This is why I am now wondering if the cis-e ecu has gone bad, even though I get different results when I either plug the eha it in or unplug it.

Michael

I also purchased a fuel pressure tester for CIS and the pressures are correct as per the manual

bump

Did you ever try changing the O2? Perhaps just try unplugging the O2, see if that changes anything.

Jonathan

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I assume your reading is really .059 amps, which actually means 59 mA. So for some reason the brain thinks you really need enrichment. Could be the oxygen sensor or the coolant temp sensor. Does this engine have an airflow sensor?

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks for the input,
The 02 sensor is new. I have changed everthing except the ecu and I have the same problem of running rich. as I had with all of the original equipment. Nothing I have done so far has had any effect on the problem.
I could probably return all the original parts and still have an engine that will not run with the eha plugged in.
Here's what I don't understand, if the engine is tuned without the eha plugged in, why, when the eha is plugged back in does the system not just fine tune the motor, instead of stalling it?
Is the ecu on this vehicle a unit with a history of design problems or has it been fairly reliable?
I am not aware of a airflow sensor on this vehicle. The availability of shop manuals etc for this car seem hard to get. I subscribe to Mitchel on Line for this car, and even they don't have a vacuum diagram for the 260E.

Once again thanks for your input
Michael

With KE-Jet, the electronic-hydraulic actuator (EHA) on the FD doesn't just give the mixture a little bit of trim, like K-Jet with lambda. It provides the enrichment for warm up and acceleration as well. I think 59mA is nearly the max for enrichment. So when you plug it in, it's reducing the control pressure and drivng the mixture to extreme rich.

In the messing around I've done with both flavors of K-Jet since 1999, and reading stuff on web sites, I can't recall a confirmed case of a brain going bad.

One last thing to check. The throttle switch. Make sure it is not plugged in backwards or damage and sending a wide-open signal to the brain.

What mA reading do you get with key on? I believe you should see 25mA. This would be an indicator that the brain is still alive.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks Chuck,
2 new things to try. Throttle switch and 25mA at eha with key on. I'll check both of those tomorrow.
I'm excited two new things to try.
Michael

Note that when this happens, the O2 will foul in as little as 10 minutes. When you install the new or cleaned O2, does the car run ok for a little while, then go back to the "status quo"?

Although not on this motor I went through a nearly indentical problem on my 16V(also "KE")..turned out it was the ecu. However in the process, I messed up three O2 sensors....I was able to recover the last one by cleaning it on the bench and re-using it....what I did try was to disconnect the eha, then re-adjust the mixture, and ran the car tuned "manually". Although not perfect it allowed me to run semi normally over 2000 rpms.

Bottom line...we tried another ecu from a different car..and it solved the problem(after we retuned the air fuel mix..leaning it way back down to the correct readings with everything reconnected)...Actually we tried an ecu from a 2.6 W201, and guess what..the car runs fine with that too...strange.

MDE3
Thanks for joining the fray.

interesting input. As to the 02 sensor, the frustrating thing is nothing I have changed, swapped, replaced etc. has made any difference at all. That's why I am beginning to think ecu. I do want to check continuity on the 02 sensor green wire. The trouble with changing so many parts and testing is you're never sure if you have't pulled a wire out or broken some internal connection. I have no base line to judge anything by. Like you I have tuned the car without eha and it runs okay (hard to start) but that's not how I want to run it. I wish I could lay my hands on an ecu to just plug in and see if anything changes.

Michael

You can check the O2 with a DVM..basically if your car is like the 201's the connectors for the O2 are under the mat on the front passenger side. Just hook into the connection in parrellel using a small shunt inserted into one of the black connectors while leaving it connected (not the white ones as they are for the heater circuit) to which you attach the positive alligator clip...and then ground the black to frame(seat bolt or similar). With the motor warmed up, and held at about 2500 rpm's you should see the voltage fluctuate above and below .5V (Dvm set for 2v). If it is not functional, you will see a reading that stays below .5V.

If the condition you are seeing is similar to what I had, then your O2 may no longer be functional. They blind pretty quickly in a very rich air/fuel condition. At least mine ran well for a little while...so I knew the O2 was contributing to the problem...but the real cause was the failed ECU..creating the rich condition that was blinding the O2's.

We also had similar readings to yours at pin 3 when checking voltage with the eha disconnected and ignition on but motor not running before swapping ecu's...With the new ecu we got 11.9V, and then when running around 6.5 - 7 V once the air fuel mix was leaned back down (from memory..it was three years ago now). Now this was in a 16V, but I wager they are pretty similar readings for your car....dependant on the KE function.

Something new to report,
I removed the airflow sensor pot. and gently wiped the 2 tracks clean. Now I'm not sure that did anything, but I just reinstalled it without calibrating it and the rpms went up considerably, about 1500rpm idle with motor warm. Also the duty cycle seemed more active.
Tomorrow I will set the airflow pot. buy reading the voltage across pins
1 & 2, value I believe is .75v +/- .10v. May not mean anything but a change never the less.
I guess the airfow sensor is a kinda throttle position sensor.
I'll post the results after fine tuning.

Michael

Well I replaced the airflow sensor pot. and yesterday I set it .65v idle with motor warmed up.
The fact that there were changes in the running of the motor from removal to replacement leads me to believe that the sensor is working, so I guess I'm back to square one. I need to try a replacement ecu.
I'll check ebay etc. the Bosch number is 0280 800 212 and the MB number is 005 545 8032. If anyone out there has one for sale please let me know.

Thanks for all those who helped me.
Michael

there is a relay near the injection ecu, i think it has 2 circuit breakers on it, this controls the idle and start, try replacing it. if its faulty a new one will give u lovely pickup from idle and reduce ur fuel consumption.

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Thanks JayRash,
I think you mean the OVP relay. Mines appears good, from my reading of previous posts it powers part of the ABS circuit. Tell tail sign of a problem with OVP is ABS light on.
My start problem feels like the gas drains back to the tank and I have to wait for it to pump back up to the engine.
I will take another look at the OVP and thanks again for your input.
Michael