CB1100 Idle speed instability problem

[SportsterDoc]

Testing the IACV is described in the service manual pages 15-41 and 15-42, which are recapped in Post 775 of this thread

http://cb1100forum.com/forum/showthread....20&page=78

Fail safe operation of each sensor is described on page is 5-15 and 5–16 of the service manual, which are recapped in post 5 of this thread (already referenced by Max), see also posts 9, 11 & 22

[url=http://cb1100forum.com/forum/showthread.php?tid=12203&highlight=Dtc]http://cb1100forum.com/forum/showthread.php?tid=12203&highlight=Dtc

Max also listed the number of stepper motor pulses at start-up, etc.

This thread may also help

[url=http://cb1100forum.com/forum/showthread.php?tid=11893&page=3]http://cb1100forum.com/forum/showthread....893&page=3

[Speed_imp]

Speed, you are in very good hands (Lord Popgun & Max ) , therefore, there is no need to interfere from my side.

@ Lord Popgun, have no longer access to scope due to C-19

Speed, just out of curiosity:
* do you have any related electronic or mechanical mods on your bike?
* I can not read the DTC's , would like to know why?, as this should be one first step. This procedure is outlined in HSM on p. 5-13 -MSC INFORMATION, and I believe you have this book.

Here is some more info/threads about idling issue:

http://cb1100forum.com/forum/showthread....le+problem
http://cb1100forum.com/forum/showthread....le+problem
http://cb1100forum.com/forum/showthread....le+problem
http://cb1100forum.com/forum/showthread....le+problem
http://cb1100forum.com/forum/showthread....le+problem
http://cb1100forum.com/forum/showthread....le+problem
https://www.healtech-electronics.com/products/obd/
http://cb1100forum.com/forum/showthread....le+problem
http://cb1100forum.com/forum/showthread....le+problem

No modification made on the bike

Yes I have the service manual but no blinking codes can be retrieved

[Speed_imp]

The side stand method you posted is right. Also, no one with the problem reported any fault light or codes stored.

How exactly did you connect the probes to the wires? I know, sounds like I don’t have a clue, but if I check mine I want it to be like you did it.

I would appreciate if you could check that signal in a known good working one! I check the two coils of the valve separatedly as I only have one probe (so only one channel). I back probe the connector with two needles and connect there my probe, something like this (here the TP sensor, for the IACV same procedure but pins 1-4 or 3-2):



I checked the valve as per manual 5-41 and 5-42 and everything looks good, so I just wanted to see what the ECU tells the valve to do. On start up we have a PWM like signal for about 3 seconds (Ignition ON, engine not working yet)



Once we start the engine we have pulses I guess to control the valve position (I have not counted the number of pulses)



But then, with engine at normal temperature, out of the cold start phase, "sometimes" when opening throttle from fully closed this PWM signal appears again for less than a second. While I don't have the PWM on opening throttle from closed position the idle runs fine, when it starts appearing the idle starts going down (heavy traffic conditions, throttle from fully closed to opening and so on).



And this is what makes no sense to me, together with the fact that the signal goes from 12V to -12V. Of course I just can replace the IACV and then check if it works as designed again but I would hate to do all the job and... I think there is a member with same symptoms and IACV replacement did not help.

So Lord Popgun if I just could have a reference signal from your bike which is working ok I could rule out one component or another and go for a ECM (if you have different signal behaviour) or IACV (if you find same pattern) replacement with almost 100% success probability. (The theory always looks great )

[Lord Popgun]

OK, I see how you did the test. I'll look this later today (I just got up )

Hopefully it is not an ECM as they are expensive. And changing the IACV is a pain. I think the first step is disassemble entire motorcycle!

I wish I had that analog scope though. I love analog scopes and their instant response times. A Tektronix analog scope and a Simpson 260 and I'm in Heaven!

Thanks for the test setup. I wondered if you back probed or made up a test harness. I can make one up as I have pins and connectors, but would rather not.

[Houtman_imp]

All of this is over my head but it is very nice to see that some Forum Members are able and willing to help ! THANKS to all.

[SportsterDoc]

Popgun wiill likely be your best help with the oscilliscope, but the issue is less likely to be the ECM pulses to the stepper motor.

The problem is most likely the IACV stepper not moving in direct relation to the pulses. It has no feedback, unlike a servo motor with an encoder, hence no associated DTC for position error.

Steppers are very accurate, within torque limits. Above torque limits, there is no certainity of proper movement for each pulse. Thus, if the IACV piston is not free to move, position will be off. Winding resistance may be within spec, but there is no diagnostic in the service manual for IACV piston free travel.

https://www.amci.com/industrial-automati...-vs-servo/

In 1984, I was a regional sales rep for power transmission eqipment (clutches, brakes, gear reducers, motors, chain, belts, etc.) One of the lines was Superior. I got into the industrial automation business by accepting an employment offer from a client. When I retired, 35 years later, Kollmorgen was the ultimate.

https://www.kollmorgen.com/sites/default...tric_0.pdf

When I operated a motorcycle tuning shop in seventies and eighties, it was carbs and points, a few electronic ignitions (Martek 440 in my 1976 CB750); so most of my stepper/servo experience is industrial or automotive.

https://www.assemblymag.com/articles/918...aceability

I retired Feb 2017, then Calmation closed May 2017, so website info is all gone.

[Lord Popgun]

I’m no expert on stepper motors Doc, but I sure agree with you. I’m setting up to look at the pulses but I really don’t think he has an ECM problem either.

It will be interesting to see what they look like. I have to dig out some needles now as the connector kit I have doesn’t have IACV connectors/pins. So no test harness.

[SportsterDoc]

I’m no expert on stepper motors Doc, but I sure agree with you. I’m setting up to look at the pulses but I really don’t think he has an ECM problem either.

It will be interesting to see what they look like. I have to dig out some needles now as the connector kit I have doesn’t have IACV connectors/pins. So no test harness.

Not discounting the potential for ECM irregularities, or harness connection issues, just trying to emphasize the likelihood of an IACV issue when the windings are in spec.

Much earlier in this thread, a couple forum members were arguing against the IACV being the issue, but the replacement by Dave in San Diego verifed the conclusion documented in this thread. Unfortunately, it is a pain to change.

Thanks to you, Max and Peter for the collaboration.

I may have gotten too personal in post 1047, but wanted newcomers to understand that I am not giving "I think so" advice.

When I was fairly new to this forum, I made the mistake of too much background and caught some flack for it:

http://cb1100forum.com/forum/showthread....ght=Delete

[dave]

what i have never been able to work out is how much the difference between the piston and the cyl housing actually is, maybe Dave has an idea, i never asked him back then.
[/quote]
Hi Max. When I inspected my IACV upon removal the piston moved freely within the cylinder housing. If you remember, I even checked the movement of the old IACV versus the new IACV, and I didn't see any difference (checked by plugging it in to the bike normally and turning the ignition key off and on - while watching the piston movement with the IACV removed from the engine). My advice is just replace the IACV. By the way - replacing the IACV completely, 100% cured my idle instability issue, and it has never returned.

[SportsterDoc]

Dave
Thank you for your continued input.
Perhaps movement freedom was restricted when throttle body assembly was torqued into place?...and/or affected by thermal expansion?

Your bottom line advice is appreciated.