[Steve86560sl]

My 1986 M117 duty cycle is same 48-50 idle and 2500RPM.

In H.D.s lambda tutorial he states "for years 86 & 87 M116/M117 mean value at idle should be 5-15% higher than the mean at 2500".

Can anyone tell me :
1)why for years 86 & 87 M116/M117 mean value at idle should be 5-15% higher than the mean at 2500.
BUT
2)why duty cycle should not differ more than +/- 10% for model years other than 86 & 87 M116/M117s
3)most important why am I getting same 48-50 duty cycle @ idle and 2500 on my car if idle should be 5-15% higher than @ 2500 RPM....is there something wrong??

4)Other than idle fluctuating 50RPM instead of a rock solid idle that H.D. says should be present if all OK my car runs great.

So......anyone help out with answers to 1, 2, 3 and 4.

Other than slight vacuum leak at throttle body shaft seal everything is OK ....only thing not replaced is EHA.


Help with 1-4 above pls.

Tx, Steve

 

[John350]

my car runs great.

Step away from the computer/phone and go for a drive.

The duty cycle is a reflection of how much "correction" from the mean is needed to get the O2 content of the exhaust into line. If your duty cycle remains in the middle of the range (but not rock steady, as in default value) then you're fine.

 

[Steve86560sl]

Hi John,
Tx for response.
AND more questions for John and All

As an engineer (nuclear submarines) I like to fully understand system design and operation so when there is a conflict between what I see with my car and what experts like H.D. have posted I want to understand the what and why.

John,I have been following your posts and seems for sure you well understand our cars so I appreciate your comments and look forward to yours and others responses to the following questions:

Questions:
A) 1)What is the purpose of comparing duty cycle at idle and 2500RPM? ..................
B) 1) Why ONLY for years 86 & 87 M116/M117 is mean duty cycle value at idle supposed to be 5-15% higher (note only states should be "higher") than the mean at 2500RPM.....................
Does the 5-15% higher @ idle mean want more fuel flow at idle than 2500RPM?..................
BUT
B) 2) General statement by H.D. for other than model years 86 & 87 states "the mean value at idle should not differ by more than +/- 10% from mean value at 2500RPM", note states can be +/- 10% so 2500 duty cycle can be higher or lower than idle by 10% and no need for different fuel flow idle vs 2500 ?
B) 3) What makes model years 86 & 87 different and why?...............
C) For my car (most important to me) why am I getting same 48-50 duty cycle @ idle and 2500 if according to H.D.'s lambda tutorial idle should be 5-15% higher than @ 2500 RPM....is there something wrong with my car?..................
D) Is the ECU sending unique/ different signals to the EHA for a 86 & 87 than other years, if so why?............................
AND if so but, I'm not getting difference idle to 2500 duty cycle is my repaired ECU really not repaired??....................
E) When measuring duty cycle @ 2500RPM which line in attached pic should be plugged?
I have been plugging line with red arrow that someone else "X'd" out as wrong. Should it be the line from the thermo valve to 78 purge valve that I have been using (red arrow) or line from the purge to intake per blue arrow or does it matter?

 

[Heikkif]

To find out the difference between model years you would have to compare part numbers of fuel distributors and air flow meter housings of different model years. When checking duty cycle you disconnect and plug the hose marked with blue arrow.

 

[Steve86560sl]

Heikkif,

Thanks for response as to correct hose to plug for 2500RPM DC test.

As far as your comment:"To find out the difference between model years you would have to compare part numbers of fuel distributors and air flow meter housings of different model years."

I'm not trying to find out what differences are as we already know.
Per H.D. as reported from what he wrote in his "Lambda Post"
"The mean value at idle should not differ by more than +/- 10% from mean value at 2500RPM.
In case of engine M116/M117 of model years 86 & 87 the mean value at idle should be 5-15% higher than the mean value at 2500RPM"

I am trying to get the following questions answered as to the WHY and questioning my results that do not match what H.D. has advised what should be for my model car and model year (1986 560SL)

Questions:
A) 1)What is the purpose of comparing duty cycle at idle and 2500RPM? ..................
B) 1) Why ONLY for years 86 & 87 M116/M117 is mean duty cycle value at idle supposed to be 5-15% higher (note only states should be "higher") than the mean at 2500RPM.....................
Does the 5-15% higher @ idle mean want more fuel flow at idle than 2500RPM?..................
BUT
B) 2) General statement by H.D. for other than model years 86 & 87 states "the mean value at idle should not differ by more than +/- 10% from mean value at 2500RPM", note states can be +/- 10% so 2500 duty cycle can be higher or lower than idle by 10% and no need for different fuel flow idle vs 2500 ?
B) 3) What makes model years 86 & 87 different and why?...............
C) For my car (most important to me) why am I getting same 48-50 duty cycle @ idle and 2500 if according to H.D.'s lambda tutorial idle should be 5-15% higher than @ 2500 RPM....is there something wrong with my car?..................
D) Is the ECU sending unique/ different signals to the EHA for a 86 & 87 than other years, if so why?............................
AND if so but, I'm not getting difference idle to 2500 duty cycle is my repaired ECU really not repaired??....................
E) When measuring duty cycle @ 2500RPM which line in attached pic should be plugged?
I have been plugging line with red arrow that someone else "X'd" out as wrong. Should it be the line from the thermo valve to 78 purge valve that I have been using (red arrow) or line from the purge to intake per blue arrow or does it matter?
F) In addition I have a 50RPM dither at idle and from what I have read this is not supposed to be so trying to also figure out what might cause this.

In relation to all above please note I have pretty much replaced all elements of flex and fuel system as well as remanufacturing the IACU and ECU...only thing not replaced is the EHA...could my EHA be sticking and causing the duty cycle to be 48-50 both @ idle and 2500 when per H.D should have a lower duty cycle at idle than 2500 or is something else wrong????

Can you or someone please read in detail my questions A-E above and respond please.

Thanks, Steve

 

[Heikkif]

There are two things that can be mechanically adjusted and do affect differently fuel amount injected on the system. To check them both two air and fuel flow rates are needed.

 

[Kingorcus]

Heikkif,

Thanks for response as to correct hose to plug for 2500RPM DC test.

As far as your comment:"To find out the difference between model years you would have to compare part numbers of fuel distributors and air flow meter housings of different model years."

I'm not trying to find out what differences are as we already know.
Per H.D. as reported from what he wrote in his "Lambda Post"
"The mean value at idle should not differ by more than +/- 10% from mean value at 2500RPM.
In case of engine M116/M117 of model years 86 & 87 the mean value at idle should be 5-15% higher than the mean value at 2500RPM"

I am trying to get the following questions answered as to the WHY and questioning my results that do not match what H.D. has advised what should be for my model car and model year (1986 560SL)

Questions:
A) 1)What is the purpose of comparing duty cycle at idle and 2500RPM? ..................
B) 1) Why ONLY for years 86 & 87 M116/M117 is mean duty cycle value at idle supposed to be 5-15% higher (note only states should be "higher") than the mean at 2500RPM.....................
Does the 5-15% higher @ idle mean want more fuel flow at idle than 2500RPM?..................
BUT
B) 2) General statement by H.D. for other than model years 86 & 87 states "the mean value at idle should not differ by more than +/- 10% from mean value at 2500RPM", note states can be +/- 10% so 2500 duty cycle can be higher or lower than idle by 10% and no need for different fuel flow idle vs 2500 ?
B) 3) What makes model years 86 & 87 different and why?...............
C) For my car (most important to me) why am I getting same 48-50 duty cycle @ idle and 2500 if according to H.D.'s lambda tutorial idle should be 5-15% higher than @ 2500 RPM....is there something wrong with my car?..................
D) Is the ECU sending unique/ different signals to the EHA for a 86 & 87 than other years, if so why?............................
AND if so but, I'm not getting difference idle to 2500 duty cycle is my repaired ECU really not repaired??....................
E) When measuring duty cycle @ 2500RPM which line in attached pic should be plugged?
I have been plugging line with red arrow that someone else "X'd" out as wrong. Should it be the line from the thermo valve to 78 purge valve that I have been using (red arrow) or line from the purge to intake per blue arrow or does it matter?
F) In addition I have a 50RPM dither at idle and from what I have read this is not supposed to be so trying to also figure out what might cause this.

In relation to all above please note I have pretty much replaced all elements of flex and fuel system as well as remanufacturing the IACU and ECU...only thing not replaced is the EHA...could my EHA be sticking and causing the duty cycle to be 48-50 both @ idle and 2500 when per H.D should have a lower duty cycle at idle than 2500 or is something else wrong????

Can you or someone please read in detail my questions A-E above and respond please.

Thanks, Steve

I have answered you earlier saying that the EHA can be tested and provided the video to do it.
Also the service manual has testing procedure as well.
Why not just test it and find out for sure instead of guessing and repeating the same question?

 

[isthenew]

I believe there are changes thru model years because there are changes thru model years. The same as there is some difference in the way the system of the m103 reacts to the air flow potentiometer vs how the v-8's react. For the specifics you're requesting, you need to speak to someone that made the differences.

As for E, I believe the point is to stop flow from the charcoal canister to the intake manifold. I believe you can disconnect and block the line at the thermo-vacuum valve or at the rejuvenation check valve. However, the thermo-vacuum valve is fragile. So blockage at the check valve is safer.

.. Additionally, have you taken DC% with the air filter in place? I understand that can change the % by 5 - 10%. And that may be your discrepancy,

 

[Steve86560sl]

Hi King,

Presently out of country/ not with the car but, I will test when back as you suggested/suggest.

BUT

No one seems to understand that I'm trying to not only diagnose my system (EHA likely issue ?) BUT, I want to understand the functioning of the system that according to H.D.s Lambda Post is different for a 86-88 M116/M117 than other years.

Really be great if someone would just read and respond to my questions A-F. If someone does I will learn a lot and maybe others as well.

So.....Can you/anyone respond to:

Questions:
A) 1)What is the purpose of comparing duty cycle at idle and 2500RPM? Basic question WHY is this done? I can't find anywhere an explanation of why we do this and what it means if not per what H.D. tells us it should be (see below)...................
B) 1) Why ONLY for years 86 & 87 M116/M117 is mean duty cycle value at idle supposed to be 5-15% higher (note only states should be "higher") than the mean at 2500RPM.....................
Does the 5-15% higher @ idle mean want more fuel flow at idle than 2500RPM and why so for just the 86-87 M116/M117 ?..................
BUT
B) 2) General statement by H.D. for other than model years 86 & 87 states "the mean value at idle should not differ by more than +/- 10% from mean value at 2500RPM", note states can be +/- 10% so 2500 duty cycle can be higher or lower than idle by 10% and no need for different fuel flow idle vs 2500 if car is not a 86-88 M116/M117 ?
So for a 88-89 M116/M117 don't need idle duty cycle higher than @ 2500RPM???? What's different in the 88-89 vs the 86-87???
B) 3) What makes model years 86 & 87 different and why?...............
C) For my car (most important to me) why am I getting same 48-50 duty cycle @ idle and 2500 if according to H.D.'s lambda tutorial idle should be 5-15% higher than @ 2500 RPM....is there something wrong with my car?..................
D) Is the ECU sending unique/ different signals to the EHA for a 86 & 87 than other years, if so why?............................
AND if so I'm not getting difference idle to 2500 duty cycle is my repaired ECU really not repaired??....................

F) In addition I have a 50RPM dither at idle and from what I have read this is not supposed to be so trying to also figure out what might cause this.

 

[Steve86560sl]

To isthenew,

Just saw your post...Tx for reply.

I did take readings with evap line plugged AND the air cleaner installed. Got 48-50% @ idle AND same 48-50 oscillating @ 2500 RPM indicating lambda...not what H.D. per his Lambda Post says should be (he wants duty cycle to be 5-15% greater at idle than 2500 reading for a model yr 86-87 M116/ M117, not the +/- 10% OK for a 88-89 that I would be OK with in my case.

Yup I do understand different model yrs/diff models are different BUT, M116/M117 86-87 really same as 88-89 components so why difference ....well forget that BUT
I'd like basic question answered as to :
Why check duty cycle at idle and at 2500 RPM.....is it a check on EHA operation or ECU signals integrity to the EHA? Does anyone understand why and what differences mean?????

Trying to learn here.

THANKS

 

[Kingorcus]

To isthenew,

Just saw your post...Tx for reply.

I did take readings with evap line plugged AND the air cleaner installed. Got 48-50% @ idle AND same 48-50 oscillating @ 2500 RPM indicating lambda...not what H.D. per his Lambda Post says should be (he wants duty cycle to be 5-15% greater at idle than 2500 reading for a model yr 86-87 M116/ M117, not the +/- 10% OK for a 88-89 that I would be OK with in my case.

Yup I do understand different model yrs/diff models are different BUT, M116/M117 86-87 really same as 88-89 components so why difference ....well forget that BUT
I'd like basic question answered as to :
Why check duty cycle at idle and at 2500 RPM.....is it a check on EHA operation or ECU signals integrity to the EHA? Does anyone understand why and what differences mean?????

Trying to learn here.

THANKS

Maybe it is not oscillating .
48-50 is so close.
Maybe it's an error code.
I also suggested that you take raw voltage and not percentage to double check your results.

 

[Heikkif]

A) 1)What is the purpose of comparing duty cycle at idle and 2500RPM? Basic question WHY is this done?

There are two things that can be mechanically adjusted and do affect differently fuel amount injected on the system. To check them both two air and fuel flow rates are needed.

 

[Steve86560sl]

King,
I did see oscillations (using a professional ANALOG SnapOn MT471 duty cycle/RPM tester) so I felt was getting lambda.
In past always got varying voltage readings when I used digital multi meter in either V or duty cycle (reason I got the analog SnapOn meter) BUT, I will try again with the DVM in duty cycle and V when I'm back with the car.
Here is a video of what I see. This video from George same readings I get on my car using same SnapOn MT471; any comments???

King, Heikkif, isthenew,
No one answering WHY we take readings @ idle and 2500RPM and what differences if any mean?????
Can someone tell me why so I can learn

THANKS, Steve

 

[Heikkif]

King, Heikkif, isthenew,
No one answering WHY we take readings @ idle and 2500RPM and what differences if any mean?????
Can someone tell me why so I can learn

I tried to explain that in post 6. Read it trough carefully. It is not a very long explanation.

 

[Steve86560sl]

Hi Heikkif,

In your post 6 you are explaining what is done ("there are two things that can be mechanically adjusted and do affect differently fuel amount injected on the system. To check them both two air and fuel flow rates are needed.") I understand what you mean here.

BUT, not answering my question as to WHY we measure at idle and 2500RPM

 

[Heikkif]

BUT, not answering my question as to WHY we measure at idle and 2500RPM

To check the two adjustments with two different flow rates of air and fuel.

 

[John350]

There is no simple answer to all your questions. The simple answer would be "because that's the way it is."

The system is inherently mechanical. The airflow moves the air flow plate, which, through a mechanical linkage, moves the plunger in the fuel distributor, which meters fuel to the injectors. The amount of fuel actually delivered to the cylinders depends on the pressure and flow characteristics of the individual injectors (as well as the setup of the distributor.)

Once the fuel gets burned and enters the exhaust system, the O2 sensor measures the amount of O2 in the exhaust. From that the ECM can determine the ratio of fuel to air. It then adjusts the duty cycle which adjusts the differential pressure in the distributor which modifies the amount of fuel delivered relative to the measured airflow, to acheive the desired ratio.

As long as the duty cycle called for is within the range of "adjustability" the engine will run at the correct air/fuel ratio. If that value is outside the expected range that indicates that something in the system (or the engine) is not performing up to expectations. If the value is one of the ends of the range (zero or 100%) that indicates the system cannot achieve the desired air/fuel ratio.

Attempted answers:
A. You can adjust the system to get the desired reading at idle (or at 2500 RPM) but if it doesn't give you the correct readings at both then something is amiss.
B. There is a mechanical difference between the components used in the early cars vs. the later ones.
C. Good question. Maybe you've got mixed and matched parts, or some issue with the engine mechanics.
D. The ECU sends signals based on the measured O2 in the exhaust. It's only the messenger. It doesn't evaluate the driving conditions and decide they call for a particular duty cycle. It measures the O2 in the exhaust and determines the change in duty cycle necessary to bring it to the desired level.
E. Answered in post 4.
F. Could be any of a number of things: Vacuum leak, sticky valve, bad valve compensator, valve timing, injector, hysteresis in one of the components...

 

[Steve86560sl]

John,
As usual great response.
I do fully understand your 1'st 4 paragraphs.

Some additional questions/comments and responses to what you wrote.

H.D.'s Lambda Thread states:
The mean value at idle should not differ by more than +/- 10% from the mean value @ 2500rpm BUT, in case of engine M116/M117 of model years '86 & 89" the mean value at idle should be 5-15% higher than the mean value @ 2500rpm"

I am out of the country but, went back and checked my readings and found:
At idle I'm 48-50 oscillating (mean 49) and @ 2500 rpm I'm 49-51 oscillating (mean 50)
See video in post 13 above.

According to H.D.for a model yr 86-87 M116/M117 If I'm 50 mean @ 2500 I should be 52 to 58 @ idle but, I'm a mean of 49 so out of range of 52-58

BUT, If I was a model yr 88-89 M116/M117 calling for idle not to differ more than +/- 10% from the mean @ 2500 (55-45%) I would be fine @ 49%well w/in 45-55%


BTW: FWIW:
My car had a DC of 62-64 @ idle and 53-55 @ 2500 before I corrected a too large spark plug gap : went from a gap of .035 to .0315
The plug gap only thing done

Thoughts?


Still looking for answers to why we measure duty cycle at both idle and 2500 RPM; is it to identify problems that occur at one but not the other?

 

[John350]

Still looking for answers to why we measure duty cycle at both idle and 2500 RPM; is it to identify problems that occur at one but not the other?

A. You can adjust the system to get the desired reading at idle (or at 2500 RPM) but if it doesn't give you the correct readings at both then something is amiss.

Like I said, you can adjust the air flow meter to give you any reading you want under a specific set of conditions (e.g. idle), but if it doesn't track as expected for other circumstances (e.g. 2500 RPM) then you know something is amiss.

My car had a DC of 62-64 @ idle and 53-55 @ 2500 before I corrected a too large spark plug gap

That "something" could be ignition related.

 

[Steve86560sl]

Editing above Post:

Only other thing done in addition to spark plug gap is that the air cleaner was installed with new duty cycle test showing 49 mean/idle and 50 mean/2500 rpm vs

Just re-read all posts above and noted in post #8 above "isthenew" said the duty cycle can change by 5-10% with the air cleaner installed so.....would the addition of the air cleaner reduce my original numbers of 63 mean @ idle and 54 mean @ 2500 or what???

And note that my original numbers with wider plug gap and no air cleaner showed a higher duty cycle @ idle as H.D.'s instructions required (63 @ idle almost perfect for 5-15% higher at idle than the 54 @ 2500)

I'm REALLY CONFUSED !

Am I correctly interpreting how to relate the duty cycle numbers to H.D.s instructions, why is a higher duty cycle wanted at idle than at 2500 rpms???