EHA Current Measurement Results - Evaluation?
 

My 1986 300E has an intermittent rough idle and stalling problem. It usually occurs shortly after reaching operating temperature. It may suddenly die at idle, be hard to restart, and then miss under load at lower RPM. Or it will start missing under load, refuse to idle, etc. These episodes may go on for half an hour and persist if the car is shut off and restarted. Then it will clear up and run well for some time.

Under normal conditions, the car also has a slightly rough and slightly surging idle.

At idle, the on/off ratio fluctuates around 50%. But it will drop as the idle decreases and then increase as the idle speed increases. I cannot tell which is the cause and which is the effect.

I have rounded up the usual suspects: cap, rotor, and plugs are new, and the plug wires were replaced about 20K miles ago.

A couple of days ago, my EHA test harness arrived, so today I installed it and hooked it up to a DMM with extended leads so I could watch it while driving. I was hoping to catch it in the act, but no luck. But I did observe the readings - in all cases there was constant fluctuation:

Idle: -.6 to +.4 warmup, -2.1 to -1.2 hot idle with AC on

Normal driving, including highway: -2 to .8

Hard acceleration +8

Full deceleration -64

Is there anything in these readings to suggest what the problem might be? Any other driving conditions to be tested?

TIA.

Chuck:

I know this has been beat to death here - thought I'd throw it in anyway.

http://www.peachparts.com/shopforum/showthread.php?threadid=45190&highlight=EHA

Chuck:

Did some more digging. Steve Brotherton provided a way to eliminate the OVP in the following thread. You'll use the harness you just bought - key on - engine off - 20Ma. If you have that, the OVP is not the problem.

http://www.peachparts.com/shopforum/showthread.php?threadid=8707&highlight=EHA

Thanks - I missed that post. The OVP is two years old, and I have not had any ABS issues, though.

Checked the current with ignition on: 19.5 mA.

Where are the experts on this problem?

Chuck:

You are very close to spec -- you want 0 mA plus or minus 1 mA at idle, and it should run near 0 at steady throttle. 20 mA on startup (key on, engine off). The very negative number is for fuel shutoff on closed throttle. Unless the EHA itself is bad, everything is working, unless the O2 sensor is going and giving bad readings.

Verification would be to drive it with the EHA unplugged -- this will make it run on mechanical only, no electronic corrections. If the rough idle persists, you KNOW it is fuel distributor, injectors, or ignition.

Your idle problems probably aren't fuel related unless you have a dripping injector -- this will make one cylinder run over-rich, and the EHA will then obligingly run the rest slightly lean, and it rumbles. I think this is part of the problem with the TE, but I've not managed to find the time to dig into it yet.

Peter

Chuck,
The readings you got are almost perfect!

Stalling on CIS-E cars is usually caused by an incorrect sensor imput to the CIS computer & then the computer cuts the power to the idle control valve, then the engine stalls.
Finding that bad sensor is the trick. The sensors that can cause that problem are air-flow position sensor, throttle valve switch, & decel switch. Also the hall-effect speed sensor on the speedo(cruise) can cause stalling problems as well.

Truer words were never spoken!!! In addition you might mention sensor signal , since a shortage can drive you mad! (like it did me)

My EHA current with ignition is 10mA.

Is this correct?

However, I remember seeing a post about the largest group of cars showing 20mA, while the second largest group show 10mA.

Can anyone confirm?

Ignition-on EHA current
 

My EHA current with ignition is 10mA.

I remember seeing a post by Steve Brotherton that touched on this.

You should look up the proper key on engine off current in the CD. The large majority run 20ma. the next largest group run 10ma.

I'm just curious why the values would vary with certain cars.

Coz I might have a faulty OVP or EHA for all I know.:confused:

I know how frustrating a stalling problem can be from my experience. People will finger you and say "look even mercedes can brake" or something like that. It is also unsafe to be stuck in the center lane of a highway or at the traffic light and wait for a tow car.
My car used to suddenly stall and be hard to restart too. I used to wait for 30 minutes to be able to restart it. First time when this problem happened it turned out to be a bad connector leg at fuel pump relay. I resoldiered it to the relay's inner board at no cost to me and everything was fine for 6 months and then the problem reoccured.
The car again would suddenly stall or have a very low idle for some time and then suddenly would be running fine. This time problem turned out to be a fuel pressure regulator. I bought one from the junk yard for $30 and that solved the problem. Then the car ran fine for 3 months.
You would be surprised to hear that a low idle problem revisited me a month ago. I then added a bottle of injector cleaner and got a smooth idle. Right now my car is running smooth and has no idle or stalling problems(nock on wood).
What I am trying to say here is that the answer to your problem might be anything. If the idle computer will get any bad signal from the sensor such as air mass meter then it will switch to limp home mode or might even shut down the car. If you can get some free advise from local mechanics about this problem that might be helpful. Good luck.

Hurshi

I'm just curious why the values would vary with certain cars.

Coz I might have a faulty OVP or EHA for all I know.


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well if you read the article it states the 2.3 have one reading and the 2.6 run at a different reading 2.3 run 8ma on the eha reading where the 2.6 runs 0ma or +1-1

mine did everything mention stalling rought running
foul smell culprit=fuel distributor