[sharples8]

Decided to post new rather than follow up on previous post:

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1672644-rpm-mas-control-box-signal-flow.html

because the stalling problem is gone (fixed by replacing coil and EZL).

Now I'm stuck at not being able to adjust the lambda (duty cycle stuck at 90), due, I think, to a defective ECU or EHA valve, but I'm not sure which, or how to figure it out. The O2 seems to check OK with a voltmeter and scope (.87 volts rich, .2 volts lean, .45 on wire when first started cold), and the wiring also checks OK.

The EHA wiring to the ECU is fine too, perfect continuity, and the EHA internal resistance checks at around 19 ohms.

However the EHA current sits at 1.8 mils all the time and only changes for just a few 10th of a second if I really punch the engine. The 02 voltage sits at .87 all the time unless I induce a vacuum leak, then it drops to .2. So I guess the mixture is too rich most of the time.

If I disconnect the O2, the EHA current sits at 1.8 and never changes even if I punch the engine. BTW it sits at 1.8 even with engine off, once it's run at 80c.

I guess this could be either a bad EHA, or bad ECU. Any suggestions as to which one or how to determine? The codes say "illogical EHA and shorted O2, but I've already determined there's no short in the O2 line.

Update - this must be a California car due to the duty cycle at Pin 3. However, the http://www.landiss.com/mixture.htm procedure of holding down the test button for 6 seconds doesn't work - the LED does not stay on. Any other way to make this adjustment or read the duty cycle?

Thanks for any input,

Tom S.

 

[meinpanzer]

Your O2 is bad. It shouldn't be sitting at one voltage or the other, but fluctuating.

 

[sharples8]

Mixture rich?

Isn't it also possible, tho, that the mixture is really too rich all the time? It does fluctuate to the other state if I create a vacuum leak.

I have a replacement sensor, but just want to be damn sure before agravating my bad back to replace the thing

Your O2 is bad. It shouldn't be sitting at one voltage or the other, but fluctuating.

 

[meinpanzer]

Your O2 is bad. It shouldn't be sitting at one voltage or the other, but fluctuating.

 

[sharples8]

Replaced O2 sensor, still get EHA code 9 and 1.8 mils

I replaced the O2 sensor, but still seeing the same behavior from the EHA. The current just sits at around 1.8 mils unless I floor it, then it jumps for a half second and returns to 1.8.

Also can't seem to get Lamda waveform at pins 2 and 3. That is stuck at 90% no matter what. This may be a CA car fwiw, but holding down the code-reading button for an extended time, as suggested elsewhere, does not have the effect of changing pins 2/3 to Lambda mode (the code LED does not stay on either)

Any suggestions are welcome, thanks

Your O2 is bad. It shouldn't be sitting at one voltage or the other, but fluctuating.

 

[meinpanzer]

Have you taken off the air box and looked for a gas stain on the intake? or do you smell gas? Have you checked the engine temp sensors? one of mine had a bad solder joint on a connection tha looked fine until I touched it, was able to re-solder. Checked the contact surfaces of your plug wires?, cap and rotor? Do you leak coolant? Bad head gasket can produce whacky readings. That's what my 300 had, after changing everything else and going through 1 leaking EHA, and 1 that I tried to adjust.

 

[sharples8]

Checks performed

Hmm...well I have checked most of those things since this saga began a couple weeks ago. I did have the strong gas smell problem but that went away when I replaced the EZL and coil. I checked the coolant temp gauge and intake temp gauge, both test fine with a DVM. Disassembled, checked, and cleaned cap and rotor. Plugs are recent within the last 18 months. No coolant or EZL leak. The only "symptoms" at this point are the code 9 illogical EHA current (mostly sits at 1.8 mils) and the constant 90% duty cycle on pins 2 & 3.

I did notice improved responsiveness in the new O2 sensor, and I tried to tweak the mixture so that, at idle, the O2 sensor voltage would move above and below 4.5 volts equally. I got that tweaked in, but the sweet spot keeps changing.

I should also mention that after making the mixture tweak using the O2 sensor voltage, the engine seems to have a good bit more power.

Thanks,

Tom S.

Have you taken off the air box and looked for a gas stain on the intake? or do you smell gas? Have you checked the engine temp sensors? one of mine had a bad solder joint on a connection tha looked fine until I touched it, was able to re-solder. Checked the contact surfaces of your plug wires?, cap and rotor? Do you leak coolant? Bad head gasket can produce whacky readings. That's what my 300 had, after changing everything else and going through 1 leaking EHA, and 1 that I tried to adjust.