99.9% Duty Cycle - Mercedes-Benz Forum
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post #1 of 125 (permalink) Old 09-27-2018, 04:52 PM Thread Starter
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99.9% Duty Cycle

Hi,

I have been working on my 1989 mercedes 300se and have run into a problem. My duty cycle reading reads 99.9% all the time. It reads that with the key on accessory with the engine not running, when it should read 70%. It reads that with the engine running and cold, and with the engine running and warmed up. I am reading it at the X11 port pins 2 and 3.

I have replaced spark plugs, wires, cap and rotor, injectors and related seals, OVP, and had to replace the EHA due to it leaking. I have replaced the ICV hoses, CIS system rubber boot and the throttle gasket due to vacuum leaks. I have done a smoke test with no visible smoke anywhere.

Also, the car takes a few cranks to start after sitting for a few hours and over night. It idles at about 800/900 rpm in Park and Neutral, and 650 rpm in drive and reverse.

One more thing I have noticed is that in Park and Neutral, the economy gauge sits on the far left. In Drive and reverse it is sitting about 1/4 away from the left.

Does anyone have any ideas?
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post #2 of 125 (permalink) Old 09-27-2018, 07:07 PM
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Originally Posted by 89benz300se View Post
Hi,

I have been working on my 1989 mercedes 300se and have run into a problem. My duty cycle reading reads 99.9% all the time. It reads that with the key on accessory with the engine not running, when it should read 70%. It reads that with the engine running and cold, and with the engine running and warmed up. I am reading it at the X11 port pins 2 and 3.

I have replaced spark plugs, wires, cap and rotor, injectors and related seals, OVP, and had to replace the EHA due to it leaking. I have replaced the ICV hoses, CIS system rubber boot and the throttle gasket due to vacuum leaks. I have done a smoke test with no visible smoke anywhere.

Also, the car takes a few cranks to start after sitting for a few hours and over night. It idles at about 800/900 rpm in Park and Neutral, and 650 rpm in drive and reverse.

One more thing I have noticed is that in Park and Neutral, the economy gauge sits on the far left. In Drive and reverse it is sitting about 1/4 away from the left.

Does anyone have any ideas?
Based on trouble diagnostics by means of on off ratio and the work you've said that you did, it could be one of the following:
- Mixture set too lean (beyond EHA enrichment limit)
- Bad connection to X-11 unit or your meter sucks
- ECU not receiving power or not grounded
- O2 sensor signal implausible (shorted)

First verify your meter and the integrity of the X-11 by testing the meter with an assortment of batteries (AAA, 9V, the car battery, standard cells, whatever you got), then take voltage readout (or duty cycle, whichever you prefer for your DMM) between pin 3 of the X-11 and a chassis ground (the battery ground strap is a good place to go when in doubt).

The second thing I would check is oxygen sensor output. You should get fluctuating values from the O2 sensor ranging from 100 mV to 800 mV (should be 450 mV +-350mV with a 0.5 Hz 'refresh' rate), if your reading is continuously low then go and check EHA current as well to see if you're beyond the leaning limit. Hopefully someone can chime in on what the max EHA current will be if it's fully compensating for a lean condition because I'm blanking on the max value the ECU sends. If you're EHA current is maxed out and you have a lean condition you'll likely have to adjust the mixture and the EHA to obtain a duty cycle of 50% and a differential pressure of 0.4 bar between the upper and lower fuel distributor chambers. DO NOT GO AND FIDDLE WITH THE SCREW WITHOUT CONSULTATION, PREPARATION, AND MULTIPLE VERIFICATIONS THAT THE MIXTURE IS IN FACT PAST THE EHA ENRICHMENT LIMIT, I CANNOT STRESS THIS ENOUGH.

Car must be in closed loop, e.g. with O2 sensor providing feedback. If it doesn't or the O2 sensor does not have any voltage (no power) and you can't get voltage by grounding its wires then you'll have to check power supply to the ECU but we'll cross that bridge when it is determined that it is needed.

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Last edited by A.Cabral; 09-27-2018 at 07:18 PM.
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post #3 of 125 (permalink) Old 09-27-2018, 07:52 PM
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Before doing anything else electrical, I'd go clean all of the grounds in the car. The battery and all of the various ground wires under the hood.

I'd also make sure the duty cycle multi-meter you are using is actually working.

/
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post #4 of 125 (permalink) Old 09-27-2018, 09:18 PM
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... Hopefully someone can chime in on what the max EHA current will be if it's fully compensating for a lean condition ...
On the OP‘s engine it is +10 mA.

Reading post #2 ... I must say that it‘s really nice to see my “KE-Jetronic Lambda control” thread (https://www.benzworld.org/forums/w12...uty-cycle.html) obviously being read attentively every now and then. … BTW, thanks for your positive comments in that "weird" W201 forum thread I stopped posting to. …

H.D.

P.S.: regarding that 201 forum thread, btw … I do not recommend to remove the adjustment tower in that case … and there is a better & smarter way to get the engine to start again than suggested in that thread. ...
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Last edited by H.D.; 09-27-2018 at 11:02 PM.
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post #5 of 125 (permalink) Old 09-28-2018, 06:19 AM Thread Starter
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Quote:
Originally Posted by A.Cabral View Post
Based on trouble diagnostics by means of on off ratio and the work you've said that you did, it could be one of the following:
- Mixture set too lean (beyond EHA enrichment limit)
- Bad connection to X-11 unit or your meter sucks
- ECU not receiving power or not grounded
- O2 sensor signal implausible (shorted)

First verify your meter and the integrity of the X-11 by testing the meter with an assortment of batteries (AAA, 9V, the car battery, standard cells, whatever you got), then take voltage readout (or duty cycle, whichever you prefer for your DMM) between pin 3 of the X-11 and a chassis ground (the battery ground strap is a good place to go when in doubt).

The second thing I would check is oxygen sensor output. You should get fluctuating values from the O2 sensor ranging from 100 mV to 800 mV (should be 450 mV +-350mV with a 0.5 Hz 'refresh' rate), if your reading is continuously low then go and check EHA current as well to see if you're beyond the leaning limit. Hopefully someone can chime in on what the max EHA current will be if it's fully compensating for a lean condition because I'm blanking on the max value the ECU sends. If you're EHA current is maxed out and you have a lean condition you'll likely have to adjust the mixture and the EHA to obtain a duty cycle of 50% and a differential pressure of 0.4 bar between the upper and lower fuel distributor chambers. DO NOT GO AND FIDDLE WITH THE SCREW WITHOUT CONSULTATION, PREPARATION, AND MULTIPLE VERIFICATIONS THAT THE MIXTURE IS IN FACT PAST THE EHA ENRICHMENT LIMIT, I CANNOT STRESS THIS ENOUGH.

Car must be in closed loop, e.g. with O2 sensor providing feedback. If it doesn't or the O2 sensor does not have any voltage (no power) and you can't get voltage by grounding its wires then you'll have to check power supply to the ECU but we'll cross that bridge when it is determined that it is needed.
Thank you for the feedback. I will try what you have suggested and report back. I am thinking something is off with the mixture due to the problem arising after the EHA was replaced. Probably something mixture related was adjusted before we had acquired the car 11 years ago.
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post #6 of 125 (permalink) Old 09-28-2018, 09:52 PM
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Hello 89benz300se,

if, as you report, with the key turned to “ignition on“ (engine not running), you see a duty cycle of 99.9% (with a meter that reads the “off/on ratio“, not the “on/off ratio“ !) … and, with the engine at operating temperature, idle is 800/900 rpm in “P“ and 650 rpm in “D“ and “R“, the first thing I suggest to check is the fuse(s) on top of the OVP relay, respectively the OVP relay itself.

If, with the M103 engine idling at 650 rpm in “D“ and “R“, the needle of the economy gauge sits about 1/4 away from the left, there seems to be a small vacuum leak too.

I don‘t want to butt into other member‘s advice and I may be too busy for further detailed advice anyway, but with clear & concise info like in your initial post , I thought I should quickly post the above. …

H.D.
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post #7 of 125 (permalink) Old 09-29-2018, 06:18 AM
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Originally Posted by H.D. View Post
Hello 89benz300se,

if, as you report, with the key turned to “ignition on“ (engine not running), you see a duty cycle of 99.9% (with a meter that reads the “off/on ratio“, not the “on/off ratio“ !) … and, with the engine at operating temperature, idle is 800/900 rpm in “P“ and 650 rpm in “D“ and “R“, the first thing I suggest to check is the fuse(s) on top of the OVP relay, respectively the OVP relay itself.

If, with the M103 engine idling at 650 rpm in “D“ and “R“, the needle of the economy gauge sits about 1/4 away from the left, there seems to be a small vacuum leak too.

I don‘t want to butt into other member‘s advice and I may be too busy for further detailed advice anyway, but with clear & concise info like in your initial post , I thought I should quickly post the above. …

H.D.
Don't worry about butting in, I appreciate the interjection as at the end of the day we have a responsibility to provide credible and complete advice if we're going to post potential path forwards for someone to solve a problem. The reason I did not suggest the OVP is because the OP said he had just replaced it, now I suppose that the replacement could be bad or have a blown fuse but I feel that is rare, unless if it's a KAE branded relay. There is a standard procedure to testing the OVP which is posted on the W201 forum, just ignore the wiring diagrams if there's an interruption as they are W201 diagrams and the W126 diagrams may be different.

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post #8 of 125 (permalink) Old 09-29-2018, 08:13 AM
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Originally Posted by A.Cabral View Post
... we have a responsibility to provide credible and complete advice if we're going to post potential path forwards for someone to solve a problem. ...
Good policy! …

Quote:
Originally Posted by A.Cabral View Post
... The reason I did not suggest the OVP is because the OP said he had just replaced it, now I suppose that the replacement could be bad or have a blown fuse but I feel that is rare ...
Right … don‘t let that replacement overawe your logic. …

Note that (in post 6) I said “with a meter that reads the “off/on ratio“, not the “on/off ratio“ ! … Whether a duty cycle meter reads the “off/on ratio“ or the “on/off ratio“ can be checked very easily with a voltmeter according to the instructions I posted under “Measuring device“ in this thread:

https://www.benzworld.org/forums/w12...uty-cycle.html

IF, with “ignition on“ the right kind of a duty cycle meter reads 99.9% … and, warm idle is 800/900 rpm in “P“ & “N“ and 650 rpm in “D“ & “R“, checking power supply from the OVP is the first thing that should be done. …

BTW, sensors / switches / relays should always first be checked at the connector of the control unit / component that processes / uses their input ! … The sensor / switch / relay itself may be in order, but there might be a problem with the socket it sits in, or with the plug connected to it, or with the connector of the control unit / component that‘s supposed to receive its input, or with the wires, etc. … That way all these potential problems are covered in the test. …

H.D.
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post #9 of 125 (permalink) Old 10-01-2018, 04:56 PM Thread Starter
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Originally Posted by A.Cabral View Post
Don't worry about butting in, I appreciate the interjection as at the end of the day we have a responsibility to provide credible and complete advice if we're going to post potential path forwards for someone to solve a problem. The reason I did not suggest the OVP is because the OP said he had just replaced it, now I suppose that the replacement could be bad or have a blown fuse but I feel that is rare, unless if it's a KAE branded relay. There is a standard procedure to testing the OVP which is posted on the W201 forum, just ignore the wiring diagrams if there's an interruption as they are W201 diagrams and the W126 diagrams may be different.

It was a KAE OVP that I put in. Maybe it is bad?
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post #10 of 125 (permalink) Old 10-01-2018, 05:00 PM Thread Starter
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Originally Posted by H.D. View Post
Good policy! …


Right … don‘t let that replacement overawe your logic. …

Note that (in post 6) I said “with a meter that reads the “off/on ratio“, not the “on/off ratio“ ! … Whether a duty cycle meter reads the “off/on ratio“ or the “on/off ratio“ can be checked very easily with a voltmeter according to the instructions I posted under “Measuring device“ in this thread:

https://www.benzworld.org/forums/w12...uty-cycle.html

IF, with “ignition on“ the right kind of a duty cycle meter reads 99.9% … and, warm idle is 800/900 rpm in “P“ & “N“ and 650 rpm in “D“ & “R“, checking power supply from the OVP is the first thing that should be done. …

BTW, sensors / switches / relays should always first be checked at the connector of the control unit / component that processes / uses their input ! … The sensor / switch / relay itself may be in order, but there might be a problem with the socket it sits in, or with the plug connected to it, or with the connector of the control unit / component that‘s supposed to receive its input, or with the wires, etc. … That way all these potential problems are covered in the test. …

H.D.
So I guess I should check the OVP socket. I need to do some more research. Only if someone is willing to post here how to do check that socket.
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