Duty Cycle readings vs voltage readings

[xp190]

Hi Everyone

Haven't posted in a while, but now that school is coming back I can drop the extra hours of work and get back to doing what I love, reaserch

I have a rather technical question, and I know someone out there knows what I will be talking about, so here goes.

The car is still my 1985 190E 2.3L 8vlv. Since I fixed my hesitation problem some 8 months ago, I come to realize that my car is burning too much gas. I can only get about 350km per tank on city streets, and around 450 on pure highway driving.

I wanted to test the duty cycle reading, but my tests were inconclusive and I came to believe that my car will not show a duty cycle reading simply because it is a very eraly model. I checked the manual and nowhere does it show a % reading for engine controls on the diagnostic port, just voltage.

Fair enough, I will stick with voltage. This is what I did.

I hooked up my MM to pin #2 and #3 on the disgnostic port X11 on the driver side fender and I took the car for a ride.

With ignition on, the reading was 4.03V, sure enough the manual states it should be between 2.1-4.8V so I'm all good here. Once the engine was started the reading remained the same, and stayed there for a good five minutes. Since this was not a very long drive I was curious to find out when the readings will start changing, and they did a good minute or two after the engine warmped up.

Here is what I observed, for a short moment, the readings would fluctuate as I accelerated and decelerated. When I left go off the gas, reading went back to 4.03 V, when accelerating, it peeked at 7.30V.

After about a minute of this fluctuation, the reading stuck at 7.30V and remianed there for the rest of the trip.

I shut the car off, went to do some shopping, came back started her up again, almost the same thing except now the small one minute window of fluctuation was completely gone.

The car went from 4.03V stragiht to 7.30V after running for 5 minutes and no variation was visible.

I should also mention that netiher of these two recorded voltage fluctuated the required 0.8V like the manual states.

Now some additional information. Originally, to fix the hesitation, I had to adjust the eha current by manipulating the fuel mixture screw on top of the air filter. I had to turn it quite a bit since whoever replaced the engine in my car did not know that the reading has a mid point at 8ma and not 0ma. After I did this the car showed me what it is really capable of and has not given me any problems since.

Observing the EHA current, I do believe that Closed Loop is achieved since it will fluctuated just like it should when accelerating and decelerating, unplugging the O2 will put it at 8ma and keep it there no matter what.

If this is correct however, why wont the reading on the diagnostic port change?

I know I am missing something from this equation, and finding it will let me get the gasmilage that the car should have.

I should also mention that I had to let the car run rich since at the perfect setting of the mixture, it would not start, this I have to figure out as well but I have a feeling these two are related.

Any help will be greatly appreciated.

Regards

xp

P.S. I'm sorry I wrote so much

A fixed voltage at pin 3 X11 at warm idle would indicate a fault code.

The fault code is calculated as 1 - (v/V) x 100, ie v = voltage at pin 3 and V is battery voltage.

So your fault code would be (assuming your battery voltage is 13V, please check) 1 - (4.03/13) x 100 = 70%

I have been looking for the fault codes (for readings taken off pin 3 X11) for my car which is a 1991 190e 1.8 Euro RHD without any luck.

Someone out there should have the fault codes for your car.

Good luck.

[xp190]

Thanx a lot Azhari, but I do wonder how you found this information, would you care to share?


and yes, anyone with the fault codes for a 1985 190E 2.3 or any other 190E please post them!!!

would very much appreciate it.

xp

I've come across this information once too often on this forum but can't find anything for my car.If I remember correctly, it was Benzmac who had the duty cycle fault codes though I also forgot the car he was discussing, 124 or 201...

You could get luckier coz your car is similiar to the ones in the US so the guys on this forum may be able to help.

My model is similar to the Aussie and UK version so I guess I should search in those areas.

Good luck, buddy.

[xp190]

I found a webpage with that exat info and some more, but no definition of which duty cycle reading means what.

here is the link in case anyone is interested

http://www.landiss.com/mixture.htm

but I still can't find what 70% duty cycle means on my car.

xp

[sjsfiji]

Hi,

First off, I'm not sure how much this applies to you, but here what I get from my CD (W124, '87 260E).

Since you're getting KOEO, Duty Cycle approx. 70% (4.03 V), you have ON/OFF Ratio Fault Recognition...

Duty = 70% {I think it has to be lingering at 70 & not fluctuating)

Possible causes of fault = No TD/TN signal. Open circuit in wiring at KE control unit.

Test Scope = Test TD/TN signal.

I'm not sure what TD/TN signal means but it's a start...

good luck,



Remedy/Test step