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BTW, you can also use your Engine Analyzer "dwell" meter in the 4-cyl mode to do another sanity check. That is if you have one.

And the dwell meter will give you the Mercedes definition duty cycle (because it measures the percent time the points are closed for the old style adjustable mechanical points, which is similar to the amount of time the diagnostic port signal is zero from the X11 - mercedes definition)
I have an old school dwell meter. How do I hook it up?

Same? Black on #2, Green (fr dwell meter) on #3.
 

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Yes.

Dwell meter hot (mine happens to be green, not sure if that is universal) on #3 -This is your signal
Dwell meter ground (Black) to #2 or battery/chassis ground
Dwell meter supply (red) to battery hot (+12 V)

It should work properly in the 4cyl mode. 8cyl mode would read half the value. 6cyl would be midway.

A dwell meter by definition is a duty cycle meter.

If yours is analog, it will read a nice steady duty cycle and will not jump around all over the place.
 

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Rather than trying to figure out the exact/correct dwell figure from an analog meter.....do the math formula for duty cycle using #2 & #3 in volts. Once you nail it, THEN put the dwell meter on and write down that number somewhere. Next time at bat, just hook up the dwell and adjust to that value. Of course, you have to set your analyzer to the appropriate number of cylinders your car has.

Kevin
 

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Rather than trying to figure out the exact/correct dwell figure from an analog meter.....do the math formula for duty cycle using #2 & #3 in volts. Once you nail it, THEN put the dwell meter on and write down that number somewhere. Next time at bat, just hook up the dwell and adjust to that value. Of course, you have to set your analyzer to the appropriate number of cylinders your car has.

Kevin
I can't wait to try this. I have an old school dwell meter and thought I'd never use it again. Cool!
 

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My Sears is nearly 40 years old Mike. I found it and wanted to double check my RPM's on the cluster with an independent analyzer.
That was a match, so I decided to try the dwell meter for duty cycle for extra credit. Sure enough, it works in 4cyl mode. It has to be a fraction of 90 degree which the 4 cyl is. 8cyl is 45 degree and 6cyl is 60 degree.

Try it! It works!

- Cheers!
 

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OK, decided to adjust my lambda as I never did after the EHA valve replacement 1 1/2 year ago. I knew it was running a little low (sub 40%) but had not bothered per HD's comments in the thread as I saw no ill effect.

Here is the before and after, using 2 meters and the Dwell meter. Also verified with DC voltage which is spot on with the DMM duty cycle as it should be.
Dwell is always registering about 2%-4% low because it is probably measuring the true ground level (points shorted) as opposed to the 50% mark as the signal is switching (in DMM voltage and duty cycle measurements)

Before Adjustment:

DMM - 37.3% (100-62.7% on meter)
Dwell meter - 35%

After Adjustment:

DMM- 47.5% (100-52.5% on meter)
Dwell Meter - 44%
DMM DC voltage= 7.2Volts DMM System voltage= 13.5Volts, Duty cycle= (1 - 7.2V/13.5V ) = 47.7%

Just demonstrating that it is always best to verify with multiple methods if in doubt.


Cheers!
 

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Hello, I need help, I myself am from Russia, if I write something wrong, sorry! in general, there is a car mercedes w124, 300e 4matic, a performance for the North American market, the problem is in oversized idling, on a hot one - 970 revolutions per minute. the sensors were checked, the metering adjustment was changed on the ECU, the wiring is new, nothing helps, the potentiometer is also good. on the machine, there is an ECU for 55 contacts, the MAS block, please respond, if possible, then in ICQ: 662 362 097, always online. we did not find any specialists who could help me deal with the problem, thank you!
 

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Hi,

I got a 10.1% reading of duty cycle from pin 3 of the X11 socket with ignition on, engine off and a warm engine. Any idea what this diagnosis result means?
(The meter actually shows 89.9%, but my meter measures the "ON" duty cycle)

Thanks!

M.K.
 

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varies some by year, but in 1990, 10% static duty cycle with engine off was "Throttle Valve Switch (S29/2) idle contact open"

diagnostics recommended involve ohm meter at N3 from pins 19-47, should be < 1 ohm, depress accelerator and should be open circuit, also test S29/2 directly, pins 1-2, should be same as above. if the switch si good, but the N3 values bad, its a wiring issue.
 

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I can't wait to try this. I have an old school dwell meter and thought I'd never use it again. Cool!
I wound up with three of them. My first one I built (Archerkit engine analyzer from RS) in the 70's and the last two are identical from Sears. One of the Sears analyzers came without a manual. I found a seller who was selling the same analyzer + manual and paid him to copy his manual. $23 later plus shipping I had a poor reproduction. Then the same analyzer came up again on eBay with a manual and I snagged it all for about $10 w/shipping....never been used.....lol. Lesson there in patience......

Kevin
 

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varies some by year, but in 1990, 10% static duty cycle with engine off was "Throttle Valve Switch (S29/2) idle contact open"

diagnostics recommended involve ohm meter at N3 from pins 19-47, should be < 1 ohm, depress accelerator and should be open circuit, also test S29/2 directly, pins 1-2, should be same as above. if the switch si good, but the N3 values bad, its a wiring issue.

Need to find a weekend to test it. Thanks for the advice.

I'll report the finding here.

M.K.
 

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Would like to thank H.D. - there is a lot of fantastic information here! I love it.

Forgive me, but I have been trying to read through and get everything I need to know but have a question.

If I am reading correctly, key on, and engine off, a Cali car should read 85%.
Mine seems to be reading 50% (49.9% to be precise). Is this correct of does this indicate an issue with my ECM or other component.

I read the values at operating temp after driving, at 2500rpm and got them to fluctuate from 46%-ish to 50%-ish. So from what I understand that should be right on.

Any help is appreciated, thanks!!
 

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according to my 1990 'introduction to service', 50% is 'all signals in order'. it mentions nothing of a special code for california cars. these codes vary with the model year.
Thanks, guess I must have misread the original post...

46-50% sound correct for a cali emissions car that you know? With everything I can possibly find in working order (but still with a slight stumble).
 

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Hi

I have a 1987 300E its just failed California Smog Emissions test

HC failed at 15 mph and 25 mph , NO failed at 15 mpg and passed at 25 mph. This vehicle does not have an EGR system.

Before I took the test I changed the plus, cap, rotor, and wires. I also changed the two idle air valve hoses and some of the vacuum hose fittings.

This time I put Bosch Platinum plugs in it. Do you think this could be the cause of the high HC? The test two years ago HC was fine.

I performed the check that this thread is based on.

I used a fluke digital volt meter and got the following results:

my vp6 was 13.5V

and my vp3 varied from first 3.8V - 4.4V then from 4V - 4.5V

I used a fluke digital voltmeter

this would give a range of of 67% to 72%

this is not right, I then tried with a Sears Craftsman analog / Volt / Dwell meter from the 80s and got the following.

according to the 6cyl scale the dwell read 33-35 degrees. Not sure if this is the same as duty cycle, but I think it is.

at idle there was very little fluctuation. as I brought the rpm up if move a bit more but not much.

I guess I should check it in the morning when it is cold.

ideas?
 

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Hi

I have a 1987 300E its just failed California Smog Emissions test

HC failed at 15 mph and 25 mph , NO failed at 15 mpg and passed at 25 mph. This vehicle does not have an EGR system.

Before I took the test I changed the plus, cap, rotor, and wires. I also changed the two idle air valve hoses and some of the vacuum hose fittings.

This time I put Bosch Platinum plugs in it. Do you think this could be the cause of the high HC? The test two years ago HC was fine.
those /are/ the wrong plugs, you want the old bosch super+ copper plugs on these cars, or the NGK equivalents.

but, failed smog is typically a O2 sensor and/or tired catalytic converter. the o2 sensor is a 60k mile replacement item on most all cars of that generation. I've had to replace the cats on several 300K+ mile cars that otherwise ran perfectly.
 

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those /are/ the wrong plugs, you want the old bosch super+ copper plugs on these cars, or the NGK equivalents.

but, failed smog is typically a O2 sensor and/or tired catalytic converter. the o2 sensor is a 60k mile replacement item on most all cars of that generation. I've had to replace the cats on several 300K+ mile cars that otherwise ran perfectly.
thanks, yes today I got thinking about the plugs.

I found some bosch 7978 that I am going to order, is this a good plug?

which cats did you replace? the two front cats in teh engine compartment or the rear cat under the car?
 

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Hi

I have a 1987 300E its just failed California Smog Emissions test

HC failed at 15 mph and 25 mph , NO failed at 15 mpg and passed at 25 mph. This vehicle does not have an EGR system.

Before I took the test I changed the plus, cap, rotor, and wires. I also changed the two idle air valve hoses and some of the vacuum hose fittings.

This time I put Bosch Platinum plugs in it. Do you think this could be the cause of the high HC? The test two years ago HC was fine.

I performed the check that this thread is based on.

I used a fluke digital volt meter and got the following results:

my vp6 was 13.5V

and my vp3 varied from first 3.8V - 4.4V then from 4V - 4.5V

I used a fluke digital voltmeter

this would give a range of of 67% to 72%

this is not right, I then tried with a Sears Craftsman analog / Volt / Dwell meter from the 80s and got the following.

according to the 6cyl scale the dwell read 33-35 degrees. Not sure if this is the same as duty cycle, but I think it is.

at idle there was very little fluctuation. as I brought the rpm up if move a bit more but not much.

I guess I should check it in the morning when it is cold.

ideas?


I just read the following

"""If you have terminal 3 in your diagnositic connector then check your lambda value first. 50% is normal for most engines but the 103 engine (which I presume you have) prefers to run at 30-40% (I put it on 35% during services), they run quite well at this mixture, 50% is too lean on acceleration from experience. You can check you EHA (if fitted) for operation by watching the lambda value fluctuate +-5%.""

So I guess my readings of 33-35 is ok
 
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