I made a previous thread about how my 93 190E 2.6 acted like it was running lean. I went and got a spare EHA valve from a friend and swapped them out. Car runs ALOT better now, but still runs slower than usual and coolant temps are slightly on the higher side.

I went and measured the duty cycle at X11 on pins 2 (red positive DMM lead), and 3 (black negative DMM lead)

It was interesting to get the duty cycle working on my car, so I will post it here so someone in the future can follow these steps.

Getting Duty Cycle Working:
I've read that to get the duty cycle readings to show up on pins 2 and 3, I have to do key on, engine off and I should see 85% for a california car. However, I got 50%, each time I took the key out and put it back in the switch.. Then I also read that I had to press the X92 led button for 4 seconds, release, and repeat again to have the red led on constantly. That didn't work either. When I cranked the car to start it up, it showed 70% while cranking, then went straight to 50%. I thought the O2 sensor broke, since thats what everyone was saying. I spent some time reading the O2 sensor voltages, but the O2 sensor was working properly with heater wires at battery voltage and fluctuation in the signal wire. I went back to the X92 port, plugged my leads in (2 - red positive, 3 - black negative since people were saying Mercedes runs the opposite duty cycle) and to my surprise, I was getting something other than 50% and was fluctuating. So then I figured out that the engine needed to be running for at least 30 seconds at operating temperatures for the duty cycle to appear on my DMM.

anyway, I replaced the EHA valve and wanted to make sure it was adjusted right for correct fuel mixtures. at idle i am getting around 34% with fluctuation, and at 2500rpm it is nearly 50% with fluctuation.

are these acceptable values? i still feel like my car is running lean. I am going to tweak the EHA valve a 1/4 of a turn and read the duty cycle again to see if anything changed. any thoughts?

Try 1/8 of a turn first. If you do a search, I think you'll find that's the recommended amount. The function of the EHA is to bleed off some fuel pressure based on the O2 sensor readings.

Personally, given the age of these components, it might be best to get a complete replacement from BOSCH because the air flap potentiometer on the side is also wearing out as is the rubber diaphram in the fuel distributor.

Or, swap over to Megasquirt.

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

thats the thing, I might be doing megasquirt in the future, so I'd rather not fork out the monies to get brand new factory stuff.

If ur going to read out the duty cycle you must check between pin no.1 with negative (black) lead and pin no 3 with the positive (red) lead

O.k at least here in europe it's so, i may be wrong

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