Poor gas mileage on a 929 -- is no o2 sensor to blame?

redcliffs · 01-19-2004, 11:16 PM

Hey all,

I'm a new 929 owner, and as I ride, have noticed some questions. One has to do with gas mileage -- or my lack of it... I'm getting just over 30mpg, which is a lot less than what I've heard about.

My bike is a CA bike, but my understanding from the previous owner is that all the CA stuff has been removed (wouldn't have been my choice, but there it is...) This includes the o2 sensor, which has been replaced by a Dynojet cutoff module...

My questions are this: is the removal of the o2 sensor, or the CA stuff in general, responsible for my poor gas mileage? Will the addition of a power commander remedy this problem? If so, will a pcIII work, or do I need a IIIr? Or is there some totally different problem here that I'm not seeing?

TIA!!!

djice929 · 01-20-2004, 1:38 AM

Quote:

Originally Posted by redcliffs

Hey all,

I'm a new 929 owner, and as I ride, have noticed some questions. One has to do with gas mileage -- or my lack of it... I'm getting just over 30mpg, which is a lot less than what I've heard about.

My bike is a CA bike, but my understanding from the previous owner is that all the CA stuff has been removed (wouldn't have been my choice, but there it is...) This includes the o2 sensor, which has been replaced by a Dynojet cutoff module...

My questions are this: is the removal of the o2 sensor, or the CA stuff in general, responsible for my poor gas mileage? Will the addition of a power commander remedy this problem? If so, will a pcIII work, or do I need a IIIr? Or is there some totally different problem here that I'm not seeing?

TIA!!!

i have a CA model with all the CA stuff removed, a PCIII and full exhaust.. i get about 35mpg city/hwy combined.. sometimes less depending on my mood

... check your air pressure in your tires at least weekly, that can make a difference too.

Latebraking · 01-20-2004, 2:07 AM

Quote:

Originally Posted by djice929

i have a CA model with all the CA stuff removed, a PCIII and full exhaust.. i get about 35mpg city/hwy combined.. sometimes less depending on my mood

... check your air pressure in your tires at least weekly, that can make a difference too.

If you're still running a stock exhaust, then it is safe to say that the lack of an O2 sensor is at least part of the problem. All of the OE stuff is designed to work together, especially when it comes to exhaust and intake tuning. Remove the flapper and nothing else - you've upset the balance of things in Honda's world. Remove the HTEV (by installing a full exhaust) and keep the flapper - same thing.

I have a full exhaust, no flapper and no O2 sensor (Ca. model) and my mileage varies from 32 - 39 mpg. I'm considering finding an O2 sensor and installing it (my system has a bung to install one) to see what the effect might be.

The O2 sensor on the stock bike leans out the mixture at part and steady throttle, which contributes to better mileage and lower emissions. I'm thinking that it may not play well with the Power Commander, though so I'll have to see.

Sure would be nice to get a few more mpgs back, though. I was getting 45+ until I went in search of more power / better throttle response. Gonna play?, you gotta pay...........

redcliffs · 01-20-2004, 2:11 AM

Quote:

Originally Posted by Latebraking

If you're still running a stock exhaust, then it is safe to say that the lack of an O2 sensor is at least part of the problem. All of the OE stuff is designed to work together, especially when it comes to exhaust and intake tuning. Remove the flapper and nothing else - you've upset the balance of things in Honda's world. Remove the HTEV (by installing a full exhaust) and keep the flapper - same thing.

I have a full exhaust, no flapper and no O2 sensor (Ca. model) and my mileage varies from 32 - 39 mpg. I'm considering finding an O2 sensor and installing it (my system has a bung to install one) to see what the effect might be.

The O2 sensor on the stock bike leans out the mixture at part and steady throttle, which contributes to better mileage and lower emissions. I'm thinking that it may not play well with the Power Commander, though so I'll have to see.

Sure would be nice to get a few more mpgs back, though. I was getting 45+ until I went in search of more power / better throttle response. Gonna play?, you gotta pay...........

I guess I forgot to mention that -- I do have a Jardine slip on, but I assume the flapper is still in place... Your explanation of the function of the o2 sensor makes sense, but I'm not now sure I understand the purpose of removing it, except maybe in a race environment...

so, then, that becomes another question I can tack on the originals (which I'd still like to hear more about): is replacing the o2 sensor a good idea?

Another purpose to the pc, in my mind, would be to clean up the fi below 3500, which is pretty rough!

thanks again

Latebraking · 01-20-2004, 2:21 AM

Quote:

Originally Posted by redcliffs

I guess I forgot to mention that -- I do have a Jardine slip on, but I assume the flapper is still in place... Your explanation of the function of the o2 sensor makes sense, but I'm not now sure I understand the purpose of removing it, except maybe in a race environment...

so, then, that becomes another question I can tack on the originals (which I'd still like to hear more about): is replacing the o2 sensor a good idea?

Another purpose to the pc, in my mind, would be to clean up the fi below 3500, which is pretty rough!

thanks again

I use to run a half system with the PCIII, and could not get it to run clean below 3k. After I Put on a full exhaust, installed a map from dynojet and bada-bing, bada-boom, no more glitches below 3k.

The sensor would be fighting with the PCIII, I suspect - with it leaning the mixture, then the PCIII taking that signal and richening it (according to the fuel map loaded), so the O2 sensor may not have full effect, and the PCIII may not have full effect (in those situations) either.

An O2 sensor, the way Honda has it setup for OE running, only serves to placate the EPA, gas mileage is a pleasant side effect.

I can't say that repllacing it is a good or bad idea yet, I haven't been able to do it. I don't thing there would be any harm in doing so, but you may ecperience driveability issues. Then again, you may just get good gas mileage again...............

Holeshot · 01-20-2004, 6:30 AM

Back in the day.. I did some testing with a full system and O2 sensor eliminators on my Viffer. Man. The bike was upset with the full system and no other mods.

I tried the O2 eliminators and it made it worse, really rough on the lowend. I suspect you are suffering this same issue. The O2 eliminator puts a load across the heater circuit so the ECU thinks it is installed but without any lambda inputs from it the ECU is running openloop all the time and this tends to richen them up. Sometimes good but not always.

During extensive testing and discussions with Dynojet RE: PCII, O2 sensor eliminator and FI light issues one thing that came up was that they DO NOT suggest running the eliminators without a PC (well of course.. gotta sell those things, right) but I also found that when I removed them (while my PCII was in transit) it really cleaned up the lower-end mess. I just had to tape over the FI light and not worry about it for a few days.

Once the PC arrived I re-installed the eliminators (basically a resistor with a fancy factory plug) and starting tuning it and things were much better.

Try unplugging that bugger and see if that helps or hurts. Worst case is you get an FI light (it's running open-loop anyway).

Neat thing about the PC's are if you have a Plam computer you can load a bunch of different maps into it and re-tune the bike on the road (which I did a couple years ago with excellent results). Now, just try to re-jet a carburated bike at your next over-night hotel stop.

I did a bunch of seat-o-the-pants *dyno* work with my Viffer before I took it into the shop for some final tweaks on the dyno.. so if you run into any Dynojet Q's feel free to ask, I might be able to help.

- H

fivestar · 01-20-2004, 10:20 AM

I had a full exhaust on mine, with a PC. I averaged about 95 miles to a tank.

abtech · 01-20-2004, 10:34 AM

I should point out that 929s in race trim get nearly 6 mpg. These engines love to burn that fuel . . .

Holeshot · 01-20-2004, 1:58 PM

Quote:

Originally Posted by fivestar

I had a full exhaust on mine, with a PC. I averaged about 95 miles to a tank.

That's insane. I had just the Jardine RT-One on mine and I got 178 miles on one tank (yeah, I was sweating it but it did it).

Maybe you guys just have really crappy gas or someting... but that sounds way out of line to me.

- H

nedro · 01-20-2004, 2:45 PM

I got 128 miles per tank before the fuel light came on. With a full system, flapper out, pair valves blocked off, and mapped PCIIIr, I get 90 miles before the light comes on.

redcliffs · 01-20-2004, 4:42 PM

so then do I hear people saying that a PC will only make the problem worse, and that the way to recover gas mileage is to get an o2 sensor back on?

one thing that seems weird about this -- do 49 state bikes get much worse mileage because they don't have an o2 sensor to begin with? that seems unlikely...

abtech · 01-20-2004, 5:39 PM

Quote:

Originally Posted by redcliffs

so then do I hear people saying that a PC will only make the problem worse, and that the way to recover gas mileage is to get an o2 sensor back on?

one thing that seems weird about this -- do 49 state bikes get much worse mileage because they don't have an o2 sensor to begin with? that seems unlikely...

Not really. Since California has much more stringent air quality standards, bikes sold for this market run leaner than 49 state models. Leaner usually means less power, but also means more mpg. The AIR systems are usually the economy killers, but since both the California and 49 state models have the same system, this would have a negligable affect on economy figures between the two models. Also, since motorcycles usually use passive AIR systems (no engine driven pump), the overall hit on economy is pretty small.

luvtolean · 01-20-2004, 5:42 PM

Quote:

Originally Posted by redcliffs

so then do I hear people saying that a PC will only make the problem worse, and that the way to recover gas mileage is to get an o2 sensor back on?

That is quite probable.

redcliffs · 01-20-2004, 5:42 PM

what is the AIR system? please excuse my ignorance...

Quote:

Originally Posted by abtech

Not really. Since California has much more stringent air quality standards, bikes sold for this market run leaner than 49 state models. Leaner usually means less power, but also means more mpg. The AIR systems are usually the economy killers, but since both the California and 49 state models have the same system, this would have a negligable affect on economy figures between the two models. Also, since motorcycles usually use passive AIR systems (no engine driven pump), the overall hit on economy is pretty small.

abtech · 01-20-2004, 5:55 PM

Quote:

Originally Posted by redcliffs

what is the AIR system? please excuse my ignorance...

Air Injection Reactor (or Passive Air Injection Reactor for a PAIR system). On the Blade, it is a diaphragm and hose contraption that feeds fresh air (routed from the airbox) directly into the exhaust header to further burn the exhaust charge (lot's of unburned hydrocarbons in a reciprocating engine's exhaust). The PAIR system is activated by a pressure pulse from the crankcase that occurs almost immediately following the opening of the exhaust valves. On several cars, the system is active and utilizes a belt driven compressor to force fresh air into the exhaust manifold. Both of these systems play havoc with accurate o2 exhaust readings, so standard practice on performance engines is to disable or remove the system to accurately measure the engines Air/Fuel ratio.

redcliffs · 01-20-2004, 8:14 PM

Quote:

Originally Posted by abtech

Air Injection Reactor (or Passive Air Injection Reactor for a PAIR system). On the Blade, it is a diaphragm and hose contraption that feeds fresh air (routed from the airbox) directly into the exhaust header to further burn the exhaust charge (lot's of unburned hydrocarbons in a reciprocating engine's exhaust). The PAIR system is activated by a pressure pulse from the crankcase that occurs almost immediately following the opening of the exhaust valves. On several cars, the system is active and utilizes a belt driven compressor to force fresh air into the exhaust manifold. Both of these systems play havoc with accurate o2 exhaust readings, so standard practice on performance engines is to disable or remove the system to accurately measure the engines Air/Fuel ratio.

thanks for the explanation -- how would I tell if that is still on the bike? or is it not possible to remove from the 929?

abtech · 01-20-2004, 8:32 PM

Quote:

Originally Posted by redcliffs

thanks for the explanation -- how would I tell if that is still on the bike? or is it not possible to remove from the 929?

Removing the PAIR system on a 929 is about a 1 hour job. There was a KB article on the subject including pics, but it may have been lost during one of the Forum transitions. Perhaps someone would be kind enough to link to a more informative thread on removing the system.

CBR929Junkster · 03-04-2004, 10:55 AM

http://www.cbr929rr.com/pair.htm

The Sook · 03-04-2004, 8:00 PM

Just look at the right side of the airbox and see if there's a hose coming from it toward the front of the bike. If so, it's still there.
The bit above about the PC and 02' sensors is a little wrong. You need the 02 sensor blocked for mapping it as if you add fuel for instance, the 02 sensor will then lean that out, you'll add more, it'll lean it out again etc etc. You'll end up having a bike that will just have WAY too much fuel at low throttle etc (as the sensor isn't an instant thing. It senses, then starts leaning). AFTER you map it, it ain't gonna be a problem to remove it, as the PC doesn't change anything or sense anything. The amount of fuel the PC is telling the bike to get is set, so at partial throttle etc, the 02 sensor will just work how it used to. BUT overall it will prbably run better with it left in, so when you are cruising and say open the throttle, the fuel will be right (it may be a little lean withthe 02 sensor still working) Etc etc.