Oxygen Sensors
#11
04-06-2008, 11:00 PM
RE: Oxygen Sensors
ORIGINAL: Splatter
This can get lengthy ---
The PCIII is a "pulse stretcher." That is, it works by taking the signal from the ECU to the injectors and making it last longer, thus injecting extra fuel over and above what the ECU normally would. Since there's almost never a case where you'd want to cut back fuel from the stock map, they do what they're supposed to do.
The oxygen sensors on the 06 and up bikes are actually pretty cool. When the bike is running along at steady throttle or idling the oxygen sensors feed back to the ECU and tells it how complete a burn you're getting. So instead of giving you fuel based on an entry in a fuel map, the ECU adjusts the fuel so the burn is correct.
The problem that happens when you mix oxygen sensors with pulse stretchers is that the oxygen sensors just tell the ECU to cut back on the fuel until the effect of stretching the pulse is removed. So they can't co-exist.
Oxygen sensors come in two flavors -- wide band and narrow band. The ones on the bike are narrow band. They basically just tell the ECU "you're too lean," "you're OK" or "you're too rich." They are designed to keep the bike at a set (I think it's 14.7) air/fuel ratio. The ECU makes corrections until it gets the OK signal. It is an article of faith at the EPA that 14.7 is exactly right for all engines because it results in the theoretical perfect combustion and least emission. It is an article of faith among Harley riders that 14.7 is too lean and runs the engine too hot, which is why PCIII and such exist.Most such systems use oxygen sensor eliminators which are just simple resistors that fake an "OK" signal no matter what's going on.
The coolest oxygen sensors are wide band. They report back the actual air/fuel ratio, so you can set your ECU (not the stock one -- it doesn't know how to read wide band) to a particular AFR and the oxygen sensors will keep it there. The TMAX Autotune system does that -- you replace the whole ECU and the oxygen sensors and it keeps your bike at whatever AFR your faith believes in. I think there's at least one other system that does the same thing. There are also hybrid systems like the Innovate Motorsports LC-2 that let you hang wide-band sensors on a stock ECU and program them to impersonate narrow band sensors but have them report "OK" at the AFR of your choice.
Don't you wish you hadn't asked?
ORIGINAL: trevd
Is it just me, or is the PCIII a bit of a piece of spit? First I find out that it causes the slow starting issues, and now find out it has a work around the oxygen sensors. Did Dynojet just not modify their product to work with the oxygen sensors?
Are the oxygen sensors bad? I'm sure they're there for pollution control, but do they hinder performance?
Is it just me, or is the PCIII a bit of a piece of spit? First I find out that it causes the slow starting issues, and now find out it has a work around the oxygen sensors. Did Dynojet just not modify their product to work with the oxygen sensors?
Are the oxygen sensors bad? I'm sure they're there for pollution control, but do they hinder performance?
The PCIII is a "pulse stretcher." That is, it works by taking the signal from the ECU to the injectors and making it last longer, thus injecting extra fuel over and above what the ECU normally would. Since there's almost never a case where you'd want to cut back fuel from the stock map, they do what they're supposed to do.
The oxygen sensors on the 06 and up bikes are actually pretty cool. When the bike is running along at steady throttle or idling the oxygen sensors feed back to the ECU and tells it how complete a burn you're getting. So instead of giving you fuel based on an entry in a fuel map, the ECU adjusts the fuel so the burn is correct.
The problem that happens when you mix oxygen sensors with pulse stretchers is that the oxygen sensors just tell the ECU to cut back on the fuel until the effect of stretching the pulse is removed. So they can't co-exist.
Oxygen sensors come in two flavors -- wide band and narrow band. The ones on the bike are narrow band. They basically just tell the ECU "you're too lean," "you're OK" or "you're too rich." They are designed to keep the bike at a set (I think it's 14.7) air/fuel ratio. The ECU makes corrections until it gets the OK signal. It is an article of faith at the EPA that 14.7 is exactly right for all engines because it results in the theoretical perfect combustion and least emission. It is an article of faith among Harley riders that 14.7 is too lean and runs the engine too hot, which is why PCIII and such exist.Most such systems use oxygen sensor eliminators which are just simple resistors that fake an "OK" signal no matter what's going on.
The coolest oxygen sensors are wide band. They report back the actual air/fuel ratio, so you can set your ECU (not the stock one -- it doesn't know how to read wide band) to a particular AFR and the oxygen sensors will keep it there. The TMAX Autotune system does that -- you replace the whole ECU and the oxygen sensors and it keeps your bike at whatever AFR your faith believes in. I think there's at least one other system that does the same thing. There are also hybrid systems like the Innovate Motorsports LC-2 that let you hang wide-band sensors on a stock ECU and program them to impersonate narrow band sensors but have them report "OK" at the AFR of your choice.
Don't you wish you hadn't asked?
On the other hand the SERT actually changes the map program within the ECM.
The TFI, and similar units still make use of the 02 sensors in closed loop, and extend the opening of the injectors during open loop.
The TFI allows enrichment during a cruise mode, and another level of enrichment during Wide Open Throttle.
Of the benefits the PCIII and SERT is they both allow changes in timing control. The SERT allows you to tune by VE or AFR, and you can adjust front and rear cylinders independently.
It certainly gets more complex than this, and lots of arguements go on about the limitations and benefits of all the tuning devices.
DougJ
#14
04-07-2008, 01:22 PM
#15
04-07-2008, 07:00 PM
Banned
#16
04-07-2008, 09:39 PM
RE: Oxygen Sensors
ORIGINAL: DougsDyna
Pretty close............ The 02 sensors only work in closed loop part of the time. The rest the time the ECU works off a preprogrammed map.
Pretty close............ The 02 sensors only work in closed loop part of the time. The rest the time the ECU works off a preprogrammed map.
ORIGINAL: HDDyna2006
So If O2 sensors help adjust when is too lean, why 06 and later need PCIII or such deviceswhen you open up exhaust and change to hi flow intake?
So If O2 sensors help adjust when is too lean, why 06 and later need PCIII or such deviceswhen you open up exhaust and change to hi flow intake?
#17
04-08-2008, 09:00 AM
RE: Oxygen Sensors
My bike is at the dealership this week ('07 Street Bob) for routine maint. I put cobra pipes on it and I'm going to have them Dyno it to see how its running. I would think they can just remap the stock ECU to increase this "limited range of correction"but I will let everyone know what the outcome is. I too want to get to the bottom of this fact/myth debate of having to NEED a PCIII or aftermarket fuel management with a set of pipes.
I can't see why the stock computer with the O2 sensors won't do the trick if it's correctly mapped. Just give her a new set of codes.Why wouldthe stock computerbe designed with these restrictions? Especially when 90% of bikes sold get exhaust/intake upgrades first and foremost?? Makes no sense to me. I'd hope Harley would be smarter than that.
I can't see why the stock computer with the O2 sensors won't do the trick if it's correctly mapped. Just give her a new set of codes.Why wouldthe stock computerbe designed with these restrictions? Especially when 90% of bikes sold get exhaust/intake upgrades first and foremost?? Makes no sense to me. I'd hope Harley would be smarter than that.
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