EHA, 02 Sensor, Duty Cycle, ICV Testing

[stevenstevensteven]

In response to this old classic thread involving the Cap'n trying to get his 124 running, I decided to try to understand and go through all the tests discussed at this wonderful thread, found at:

http://www.peachparts.com/shopforum/showthread.php?t=53987

Here is a summary of my procedures & results (more detail page attached as PDF to this post):

02 Sensor @ Idle: .78V
02 Sensor w/ Computer side grounded: .82V (simulating too lean condition)
02 Sensor w/ 1V applied to computer side: Drops to 0V within 5sec (simulates too rich condition)

EHA @ KOEO: 19.75mA
EHA @ Engine Idle, O2 Sensor disconnected: 0mA
EHA @ Engine Idle, O2 Sensor disconnected, computer side of O2 sensor grounded: 13.69mA
EHA @ Engine Idle, O2 Sensor disconnected, 1V applied to computer side of O2 sensor: -10mA

ICV @ Engine Idle: 316mA

Duty Cycle @ Engine Idle: 41 - 45%
Duty Cycle @ 2000RPM: 42 - 49%

I readjusted duty cycle to make it slightly more lean after these tests were complete. Now duty cycle is 46 - 52%

I'm curious about the ICV value, as I thought it should be between 600-700mA at Idle.

Also, I would have thought O2 sensor would come close to .45V average. Not sure why it's tending toward .78V, but seems to respond very quickly to various inputs.

Anyone care to comment on these numbers?

[wbain5280]

EHA current should be around 9 ma. Something is amiss. Duty cycle should be 45 - 50, and is 1 - (observed duty cycle). So, it's a % of 'off' time, the reverse of a regular duty cycle 'on' time.

[stevenstevensteven]

Originally Posted by wbain5280

EHA current should be around 9 ma. Something is amiss. Duty cycle should be 45 - 50, and is 1 - (observed duty cycle). So, it's a % of 'off' time, the reverse of a regular duty cycle 'on' time.

I followed the directions on testing the EHA from the following discussion, where I understood that eha current should swing from +12mA to -12mA, depending on correction, but that steady state is 0mA.

Originally Posted by stevebfl

You must resolve the eHA current issue. 20ma is appropriate for key on, ENGINE off readings. The next step is to disconnect the O2 sensor. The ma reading should be zero with the engine running!!. If it is different this issue must be resolved.

If you have 0.0ma then try grounding the computer side of the O2 connection. This should cause the ma to slowly correct to the maximum which is about 12ma. Next place one hand on twelve volts and hold the computer side of the O2 connection with the other hand. (this applies a small >1v signal to the controller) You should slowly go to -12ma, full correction lean.

If the system has the ability to do this, the next step isn't so easy. The next step for testing would be to watch the differential pressure and to verify that it is .4bar and that it moves .1bar greater at 12ma and goes .1 bar less at -12ma.

Control is then working. See what you get with the O2 disconnected.

Did I miss something?

[bobterry99]

Originally Posted by wbain5280

EHA current should be around 9 ma.

According to Steve Brotherton's DIY article it should be 8mA for early 190Es and zero for other cars.

[mbdoc]

If duty cycle is around 50%, then current flow to EHA should be around 0ma with positive & negative fluctuations.

If that is correct...the electrical operation of the computer is correct & shouldn't cause excessive emissions.

[stevenstevensteven]

Originally Posted by M.B.DOC

If duty cycle is around 50%, then current flow to EHA should be around 0ma with positive & negative fluctuations.

If that is correct...the electrical operation of the computer is correct & shouldn't cause excessive emissions.

What I am most confused about is 02 Sensor @ Idle = .78V. From my extensive reading in this forum, I was under the impression that Sensor should be closer to .45V if everything else is setup correctly, which is appears to be from the values in my original post in this thread.