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  #1  
Old 08-04-2003, 11:51 PM
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How Do I use My Fluke To Read Duty Cycle??

I have a Fluke 87III that I want to use for testing duty cycle to set my CO adjustment but I have no clue what I am testing.. Voltage, Current, Ohms, Hertz?????????? Can somebody enlighten me on the subject. I played with the CO screw when i was 18 now I want to correct my mistake.
Thanks!
Adam
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  #2  
Old 08-05-2003, 07:32 AM
LarryBible
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None of the scales you mentioned measure duty cycle. You need to read the manual for your particular model meter and see if it has a duty cycle scale and how to use it.

Not very many meters have this feature. Failing a duty cycle function, you can use dwell with a little simple math.

Good luck,
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  #3  
Old 08-05-2003, 08:40 AM
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Look at what georgehifi had to say in this post. You do not need a duty cycle VOM. More than one way to skin a cat.

Engine diagnostics 300E, lamda adjustment

and

Is it possible to adjust Lamda without a duty cycle meter???

Last edited by 1991300SEL; 08-05-2003 at 09:46 AM.
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  #4  
Old 08-05-2003, 11:07 AM
LarryBible
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Due to varying inherent capacitance and varying meter impedance from one meter to the next, making this adjustment using only a DVM on the DC scale is not a good idea IMHO.

You can buy a very good meter at Sears for less than $30 with a duty cycle scale. They have even been on sale for $19.95 at times.

You've heard the old adage, "use the right tool for the right job," this goes double for test equipment.

Good luck,
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  #5  
Old 08-05-2003, 11:07 AM
azhari
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Duty cycle

With your fluke dialled in to measure DC voltage, measure your battery voltage (V) with your engine running above 80 deg C.

Next, take the cap off the diagnostic port X11 (the round capped connector on the injection module).

Put the black probe of the meter to ground or battery negative and pit the red probe into pin 3 of the X11 port.

You should get a voltage (X) reading.

The duty cycle (%) is (X/V) x 100.

Eg. if your battery voltage is 13.8V (V) and the voltage at pin 3 (X) is 5.5V, then the duty cycle is (5.5/13.8) x 100 = 39.8% (slightly rich).

Cheers.
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  #6  
Old 08-05-2003, 11:30 AM
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Wells said Azhari - again - one does not need the $29.99 Sears duty cyle VOM.
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  #7  
Old 08-05-2003, 12:35 PM
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Question: so if 39.8% is slightly rich where should it be?

Haasman
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  #8  
Old 08-05-2003, 12:44 PM
azhari
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45% to 55%.
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  #9  
Old 08-06-2003, 01:47 AM
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Thanks For the info guys!
Here is what I have so far... I downloaded the manuals for my Fluke on the internet, ( It was purchased on Ebay, no manuals included). Just as I thought., It does measure duty cycle!! Here are the results from my examination:

Duty cycle with ignition at position 2, engine not running= 69.4%

Duty cycle while engine running pre operating temp. = 51.2%

Final duty cycle above 80C operating temp. = 18.1%

I attempted to adjust the idle adjustment screw but the duty cycle stayed the same the whole time!!! Yes, I did make sure I depressed the adjustment screw so that it was enguaged. I also waited the 10 seconds for the reading to correct itself......

Any suggestions??

Thanks for your help!!
Adam
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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320

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  #10  
Old 08-06-2003, 01:50 AM
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BTW: The engine runs great, You just have to wear a gas mask around it because it stinks!!!!! I am guessing because the mixture is rich....
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  #11  
Old 08-06-2003, 07:05 AM
LarryBible
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Now your cookin' using the right instrument for the job. Duty Cycle scale is usually some odd set up on the meter and the manual is usually necessary to figure it out.

Since the duty cycle is staying solid, this is most likely a trouble code. This being solid at near 20% duty cycle indicates a problem with the Full Load Contact circuit. This is the throttle valve switch.

I would start by disconnecting the cable to the throttle valve switch and put your ohmmeter probes across the switch. Move the throttle from closed to wide open throttle and make sure the switch makes and breaks. If it does not, correct it by adjustment or switch replacement whichever is necessary. If it does work, you will need to trace the wiring to look for an open circuit along the way.

Hope this helps,
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  #12  
Old 08-06-2003, 07:57 AM
azhari
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Adam

For your info, key on 70% indicates that yours is a federal car.85% would indicate it is a Calif car.These are indicators of the emission standards adopted for a particular car.

Engine cold 50% indicates that car is still in open loop ie O2 sensor not warmed up.

A duty cycle of 18% fluctuating at engine operating temps would indicate a very rich mixture.

Larry is right on the money.

A fixed duty cycle at operating temps indicates a fault code.

18% is assumed as 20% (as the fault codes are in increments of 10%).

The only code I know is a fixed 50% code at operating temps indicates a faulty O2 sensor.

Good luck!
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  #13  
Old 08-06-2003, 08:11 PM
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I know the fault codes for m103's that read 70% with the ign on (although it may vary from aust to us delivery)
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  #14  
Old 08-06-2003, 09:14 PM
azhari
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Andrew

Do you know the fault codes for M102 (Aust)?

Appreciate your help.
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  #15  
Old 08-07-2003, 05:46 PM
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Re: Duty cycle

Quote:
Originally posted by azhari
With your fluke dialled in to measure DC voltage, measure your battery voltage (V) with your engine running above 80 deg C.

Next, take the cap off the diagnostic port X11 (the round capped connector on the injection module).

Put the black probe of the meter to ground or battery negative and pit the red probe into pin 3 of the X11 port.

You should get a voltage (X) reading.

The duty cycle (%) is (X/V) x 100.

Eg. if your battery voltage is 13.8V (V) and the voltage at pin 3 (X) is 5.5V, then the duty cycle is (5.5/13.8) x 100 = 39.8% (slightly rich).

Cheers.

The formula above looks similar to the one at the following WEB site with a slight exception that affects the answer significantly.

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

When I have time, I'm going to get a reading using my Sears duty cycle VOM, then try the approach here using a standard VOM and formula provided; them use the standard VOM and the formula at the Landiss site.

In the end, I suspect it's simply easier to use a duty cycle VOM and leave the math to the engineers who invented the Bosch CIS-E system, but I am curious.
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Last edited by Mike Murrell; 08-07-2003 at 05:54 PM.
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Old 08-07-2003, 05:46 PM
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