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obiwan
17th December 2006, 03:18
Fitted some V&H Straightshot slip-ons last week. The stockers were a pain to remove and I fear I might have damaged the gasket at the cylinder head. I'm getting some very slight popping on decel, but not all the time.

School of thought suggests that's either an exhaust leak or overly lean. Since I only changed the exhaust and not the intake could it really be too lean and how would that happen? Do the O2 sensors detect a free flowing exhaust and compensate somehow with more air? Doesn't sound logical I know but how else would it be lean?

Or is it more likely an exhaust leak? Don't want to go to the trouble of pulling down again and replacing all the gaskets if what I really need is a remap. I know I can put oil in the cylinders etc. and check for leaks but that's a messy pain as well.

How do the O2 sensors work, and is there any possibility of being too lean just from changing mufflers. If so how?

Appreciate your responses.

rharrison356
17th December 2006, 03:38
Fitted some V&H Straightshot slip-ons last week. The stockers were a pain to remove and I fear I might have damaged the gasket at the cylinder head. I'm getting some very slight popping on decel, but not all the time. I am getting some popping on decel after the same modification, and can hear some leaking from the front header gasket when the bike is cold. Once it warms up, it is fine. Yes, a leak will alter the O2 sensors...however, if that happens, the check engine light will come on. If it is not on, then they are compensating adequately.

decman
17th December 2006, 05:08
My first guess would be that you are hearing it now
because of the free flowing mufflers. Meaning the
popping was there before. You did say slight, right?

The O2 sensors should handle changes like that OK.

rharrison356
17th December 2006, 05:14
....Yes, a leak will alter the O2 sensors...however, if that happens, the check engine light will come on. If it is not on, then they are compensating adequately.Check out http://xlforum.net/vbportal/forums/showthread.php?t=18260

lagerdrinker
17th December 2006, 05:19
o2 sensors (oxygen sensor) detects oxygen in exhaust. simple
heat activates them and they generate a varying voltage signal based on oxygen level. a small leak will afect the signal, yes they are very sensitive.

obiwan
17th December 2006, 06:34
My first guess would be that you are hearing it now
because of the free flowing mufflers. Meaning the
popping was there before. You did say slight, right?

The O2 sensors should handle changes like that OK.
Great! Thanks guys.

As I understand it then -

1: the popping may have always been there but inaudible with the stock mufflers and
2: if there was a major exhaust leak it would register on the O2 sensors and trigger a check light

So nothing really much to worry about. Gotta love these new-fangled electronics. :clap

Gone
17th December 2006, 07:23
Yes, restrictive mufflers contain popping sounds pretty well.

Is winter over yet?

Moved On / My Own Choice
17th December 2006, 22:49
As I understand it 02 sensors actually generate a small (millivolt) signal based on the difference of the exhaust oxygen content with the content of oxygen in the air otherwise surrounding the rest of the sensor.

The sensor does not start working until it comes up to temperature, and that temperature is VERY hot (don't know how many hundreds of degree F off the top of my head).

That data is given to the ECM to let the ECM know how its fuel mapping is doing (in trying to approach an idea air-fuel mixture for maximum power and minimum emissions). As such the 02 sensor gives the ECM "feedback" on how well it is doing its job and the ECM can make adjustments accordingly.

That's why it is called closed-loop or feedback fuel control.

Kev

obiwan
19th December 2006, 12:33
Found a link to another interesting article on the O2 sensors:

The O2 sensors used in Harley's are fourwire narrow band sensors, which have a voltage output usually between 0 and 1.1 volts. A rich mixture will leave very little free oxygen and the reaction will send out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts ...


When the bike is operated at engine speeds between 2500 and 3500 rpm at road speeds in the 40 to 60 mph range under a steady light load (no down grades or steep upgrades, not decelerating or accelerating) for 30 or so seconds then, and only then, are you operating in "closed-loop" mode, and the O2 sensor inputs will cause a change to the ECU Map programming to attempt to obtain an A/F ratio at or near stoichiometric, or approximately 14.6 parts air to one part fuel. At all other times, the system is in "Open-loop" and the O2 sensors are not being used.
The whole article "Tuning Fuel Injected Harley'sŪ with the Power Commander PC-III-USB" can be found here:

http://www.jpcycles.com/Shell2.aspx?src=Tech/Articles/TuningFuelInjection.htm

:tour