the car is a 91 560 SEL. I have had these issues for a while now. I had the chance to do the following today. Would like to know what it all means and suggestions on how to proceed.

1. Hard Start when cold - When car is parked for a few hours or overnight, it takes a couple of cranks to get it started. The first crank about 4 seconds, adn the second crank starts right up. OVP is about 3 years old. I ahve the one with 2 fuses. Fuses are good. When ignition key is ON and engine is OFF, the voltage across the EHA wire harness is about 5V(open circuit - wire harness not connected to EHA) and the current is 0 (zero). I have read that there should be current flowing with the ignition switch ON and NEgine OFF? am I correct? Does this indicate a bad OVP? or Are there other things I need to check? NO Engine Light is observed. Water temp sensor and throttle switch checked-out okay using MBZ manual procedures.

2. High Idle at Park and Neutral - Idle sometimes stays at 750 but most of the time at 1000. In gear it is about 650-700. With Ignition switch ON and Engine OFF, the voltage accross the ICV wire harness fluctuates between 0.3 to 1.7V(open circuit - wire harness not conencted to ICV), and voltage stays at 0.3V with wire harness connected to ICV. With the engine running and in park, the voltage accross the ICV is about 5V, with the idle as stated above. Removing the wire harness while in idle and Park, would cause the idle to jump up to about 1500. Rough idle is obvservable but very negligible at this time... Any thoughts?

Thinking whether I am not measuring current correctly with the 2 above having measured as zero amps. But, current measurement is in series while voltage in parallel with the load being measured. Nothing much more, unless there is a something I am missing.

thx

my error on the current readings. I was not on the correct unfused terminal on my multimeter that was why i was reading zero amps.

anyway, for the EHA readings, it is 80milliAmps ( 0.08 on a 10Amp scale on my meter) when Ignition is ON and Engine is OFF. The reading goes down to 10milliamps at idle speed. readings do not appear to fluctuate.

For the ICV, I get 80milliamps when ignition is ON and Engine is OFF. The reading goes up to 1Amp at idle speed.

Are these normal readings? How should I proceed from here?

thx

i again worked on my hard start problem today and would like to check the duty cycle. however, i could not get my initial readings correctly.

At KOEO, I noticed the LED in X92 is continously on. Pressing the push button for 2-4 sec does not make a difference. I was trying to switch over to on/off ratio output mode and meassure duty cycle at X11. Nonetheless, when I measured X11 at pins2-3, I got 97.6% duty cycle ( using sears VM), and 1.9V. I am stuck here and cannot move forward with testing.

Can someone point out what I am doing wrong? and why the LED at X92 is continously on?

thx,
emmy

additional things i have learned:
1. The LED at X92 is ON continously at KOEO, but turns off when engine is running. At that time, I pressed the push button for 2-4sec and got a (1) flash. I pressed the button one more time and I got a continous ON LED. At this time, I got to on/off ratio test mode at X11.
2. Still not happy with my duty cycle readings, i decided to measure voltage instead at pin2-3. Engine was about 80 degrees. At idle( about 750RPM) I got an oscillating voltage from 2-3 volts at 12.93V battery voltage. This calculated to about 76% - 84% duty cycle which I thought are rather high. I revved-up to 2500 and measured 4.8-6V. This calculates to about 53%-63% duty cycle. At this point, i am not really sure what to do. With hard cold start as my original problem, now I think I am seeing one more problem with the duty cycle which may need mixture adjustment.

your thoughts would be appreciated.

Digging thru the archives, one sees many posts that attribute a hard cold start & high idle to a faulty OVP.

I realize yours is dual-fused and not that old, but....

Just for the heck of it, pull it off and shake it. Make sure the fuse flap is held down. If you hear anything rattling when you shake it, you have a bad OVP. There are theoretically other ways to test the circuits controlled by this gadget, but what I just described indicates a bad OVP.

It's simple to do and worth a shot.

__________________
'91 300-SEL

Thank you for the response. I checked my OVP and it is fine. No rattles, and both fuses are good. I am getting EHA current which tells me that my OVP is good.

However, the EHA current readings are not good. This is an update of a previous post. I think this is more accurate than what I had posted previosuly. At KOEO, and Cold engine, I measured 75MA. As I started the engine, I measured 12.6MA and monitored the current as the engine warms-up. The current readings dropped to about 0.5MA as the temp rose towards 80 degrees. But to my surprise, as the temp went higher above 80 and stabilizes at about 85-90 degrees, I noticed the current go up and was oscillating at 6MA-10MA. Current readings stayed and oscillated at this level whether in Park or in gear. Do I have a bad KE-Control module? or do I have a bad O2 sensor? How about the EHA?

thx

Was the O2 sensor disconnected when you were looking at EHA current - warmed up motor?

__________________
'91 300-SEL