I'd like to set the open loop fuel mixture on my distributor and was refering to the Steve Brotherton article in the DIY section. He states that -3ma is slightly rich. I'd like to have a slightly rich open loop mixture for WOT and cold start operation. Is -3ma ideal?

How do I get the correct measurement. I have my multimeter "amp" port connected to the black wire at the plug and my multimeter "common" port connected to the brown wire at the plug. With this set up will -3ma reflect a slightly rich open loop mixture?

Also I checked the altenator brushes and found that they protrude about 1/4" from their holder. Is this acceptable or should they be replaced?

Thanks
Jorg

-3 mA will give you what you want. Sounds like your hookup is correct.

You'll be needing to replace those brushes soon. Sounds like they're about 75% gone.

__________________
2012 E350
2006 Callaway SC560

Just checked the current with my multimeter connected as described above but I get +13.7 ma.
When I try to adjust in either direction it starts to run rough. Am I doing something wrong? I'e got the multimeter connected to the plug that normaly connects to the EHA.

Help!

Jorg

Before relying on test data one should always verify one's calibration. There are a couple fixed situations that should measure out before trusting your readings. If you disconnect the O2 sensor you should get 0.0ma EHA. If you turn the key on, engine off, the current should be 20ma on most KE systems.

To measure current one must place the meter into the circuit. A premade harness is the easiest way but what must happen IN THEORY is that one of the two wires must be cut and the two ends hooked to each of the leads such that current flows into and out of the gauge to make the circuit.

Don't cut the wires but without a made up harness you will need three jumper wires. Pull the plug. Jumper one side to the EHA pin it was meant to be on. Place a second jumper from the connector to one meter lead, place the last jumper from the other meter lead to the EHA.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve,

I've made a harness and connected as you suggested. Key on Engine off is 20ma
and running with the O2 sensor disconnected is 0.1ma (close enough?). Other than a small studder when I connect the O2 sensor the car runs smooth throughout. I guess I should check the O2 sensor next?

Jorg

Not necessarily. What are your EHA readings when the O2 sensor is CONNECTED?

__________________
2012 E350
2006 Callaway SC560

+ 13.7ma, steady. Any attempt at adjusting the mechanical mixture results in rough operation and no change in current. Am I trying to adjust the mixture too quickly?

Jorg

Just rigging up a harness to try the O2 to ground and power through Capt'n method I found in previous posts.


Jorg

OK, here's my take.

You have a bad O2 sensor. Actually a shorted O2 sensor (OR WIRE). I state all this because of your stated conditions.

1 - You are at the maximum lean correction. The lambda control basically is from about -12ma to +12ma. I assume you to be at the +stop on your system. A plus correction means MORE fuel and is a correction for a lean mixture OR low O2 sensor voltage (short to ground is as low as it goes)

2 - I base that on the fact that you read 0.0ma with lambda (O2sensor) disconnected. If other erroneous inputs had altered fuel correction, then the value wouldn't have been zero.

3 - you made mixture changes from good to bad in both directions (rich and lean)without controller output change (always at full lean correction. This part is conclusive and based on stated observation.

This of course is a normal car and you have made correct and full observations. You will of course understand that once one has proven a case the law of automotive entropy suggests other possibilities.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

My head hurts!

If I'm at max. lean correction shouldn't running with 0amps (O2 disconnected) have made the motor quit since it is now running rich, or are we talking very fine calibration, well within the range of smooth running?

Can I check continuity on the 02 sensor or output voltage while running hot as a test of the sensor?

I will probably run out and get a Mustang sensor later and try to straighten this out before I have the dubious pleasure of watching McLaren get spanked tonight.

Jorg

The engine should not quit with the O2 sensor disconnected...it should run just fine. The whole closed-loop system is only for fine tuning.

0 mA at the EHA means that no correction is being made at all.

You should see a varying mA reading at the EHA, not fixed.

Why not try reading the pin 2-3 duty-cycle output on the round diagnostic socket? It may confirm the problem. I believe 10% fixed would confirm Steve's diagnosis of a bad O2 sensor.

What voltage is the O2 sensor putting out when the engine is running?

__________________
2012 E350
2006 Callaway SC560

Either your understanding of the system or my understanding of your last statement need help.

You have a mechanical/hydraulic fuel metering system with a electronic mixture correction. The whole of the electronic system is to be placed over the top of the mechanical system with the system adjusted to roughly the mixture you are going to try and feedback home in on.

Properly set up with .5 -1.0% CO as an exhaust gas reading. The electronic lambda capabilitiy of -12ma to +12ma will not make the car run poorly except at the nds of range and probably then only on the lean end. The O2 sensor only gives accurate readings in the range of 0-1% CO. The car will run about the same from .25% to about 6% CO. Obviously the area of control only represents a small portion of all the mixtures that will perform good. The best running cars froma performance stand point are usually out of that control range.

You can read the sensor voltage with the sensor disconnected. If you disconnect the O2 sensor the wire going to the controller will have somewhere around .5v on it when not hooked to the sensor. It should also have the same voltage when hooked to a cold sensor. When hot the voltage of the sensor dominates the the high resistance output from the controller.

If left disconnected, the voltage on the lead from the sensor should vary from 0.0v to around 1.0v as one passes through the range of control mentioned above 0 -1% CO. If you are adjusting at the airflow meter you will run across this range somewhere between running rich and then running lean.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

brewtoo,

I didn't try reading at the diagnostic plug because I don't have duty cycle on my multimeter, nor do I have a dwell meter. I guess I shlould look for one in future. I tested the 02 sensor and it had failed. I relaced it with the Mustang sensor and all is well.

Steve,

I guess I didn't understand the accuracy of the mechanical injection. I assumed that since they removed the control system from the all mechanical injection and replaced it with the EHA system that only very crude mechanical injection was left in place. Now that I have the new O2 sensor in place and get to watch the system in action I am very impressed at how accurate the mechanical system is, at least at the conditions that I have observed it at.

I watched the EHA current go from +10ma on cold start slowly move to -7ma when warm an adjusted to approx. -3ma. My concern is that I do in fact have the open circuit running slightly rich. I assume that at cold start the mix was lean and the EHA current (+10ma) was richening the default setting. As the engine reached operating temperature the default mix became rich and the EHA was sent -7ma to lean it out. Therefore setting to -3ma ensures a slightly rich default setting (open circuit) for WOT operation. Is this correct?

ps. Thank you both for all your help. I have a lot to learn and so far am enjoying it immensly.

Jorg

This is the best overview of this issue I've seen yet on the various forums. It should be made into a sticky.