Air Fuel Ratio Question
Road Warrior
Joined: Apr 2007
Posts: 1,952
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From: Senoia, Ga., by way of Miami, Fl..
All I can add is that I think the location may be your problem. In typical automotive applications, the O2 is calibrated for the location. With a single O2 reading about a foot further away from the front cyl, than from the rear, the mixture from the front cyl will have time to burn off before it reaches the sensor.. So, if you are running a "perfect" ratio, it could be showing rich because the front cyl burnt more oxygen in the front pipe before getting to the sensor. As to why you're lean, not so sure, but I think Graham is on to something with the imbalance.. I recently swapped my '95 to carb because of the tenability of this system.. What programmer/module are you using?
Club Member
Joined: Jun 2007
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From: Bedford UK
As with all EFI bikes my Buell and Sportster have two sensors, one close to each head. On my Glide, with a carb, I have a set of EFI pipes with sensor holes in the same locations, which my dyno man used when setting it up. There are blanks in the holes now.
So while you have chosen a convenient location for your sensor, it seems bound to be giving you false readings. Not all the exhaust from the rear cylinder is passing the sensor, for example and as Greg points out, the gases in the exhaust continue to burn as they pass down the pipes.
I suspect you will need to make a variety of small adjustments, but using your meter readings for interest, rather than as a reliable guide to things being just so.
So while you have chosen a convenient location for your sensor, it seems bound to be giving you false readings. Not all the exhaust from the rear cylinder is passing the sensor, for example and as Greg points out, the gases in the exhaust continue to burn as they pass down the pipes.
I suspect you will need to make a variety of small adjustments, but using your meter readings for interest, rather than as a reliable guide to things being just so.
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Stellar HDF Member
Joined: Aug 2013
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From: Texas
I talked to the AEM tech, and he said to put the sensor 36 inches from the head, and that is where I put it, at least as close to 36" as I could, but I do think that I may be getting a false reading at idle because I can add fuel until it is running rich enough to smell the gas, and it will still show lean on the gauge. I still have a lean spot at 2500 rpms, with about 40% throttle, around 15.4 AF, but just for a second, and then it drops back to high 13s.
I will keep changing the map until that is gone. The bike is running great, I just need to take a rode trip to see how it runs on the interstate. My gas mileage has gone from 34 mpg to 43 since I got the bike last year, from me adjusting the map.
I got a email from power commander
When I get the new exhaust it will have the bungs closer to the head.
I will keep changing the map until that is gone. The bike is running great, I just need to take a rode trip to see how it runs on the interstate. My gas mileage has gone from 34 mpg to 43 since I got the bike last year, from me adjusting the map.
I got a email from power commander
Good Morning Bob,
Thank you for your inquiry and support of Dynojet products, it sounds as though you have your O2 sensor too far back in the exhaust and you are getting some extra air past the sensor, either because of an exhaust leak, or fresh air from the end of the tail pipe (Reversion) which is skewing your readings, the bike is not and would not idle at 17.5 true AFR, we would recommend checking the system for exhaust leaks or possibly relocating the O2 sensor closer to the heads for a cleaner sample, if the rest of the AFR under load looks good and the bike is running ok, you may just want to add some fuel at idle or have the bike dyno tuned to optimize performance, thank you, ride safe.
Thank you for your inquiry and support of Dynojet products, it sounds as though you have your O2 sensor too far back in the exhaust and you are getting some extra air past the sensor, either because of an exhaust leak, or fresh air from the end of the tail pipe (Reversion) which is skewing your readings, the bike is not and would not idle at 17.5 true AFR, we would recommend checking the system for exhaust leaks or possibly relocating the O2 sensor closer to the heads for a cleaner sample, if the rest of the AFR under load looks good and the bike is running ok, you may just want to add some fuel at idle or have the bike dyno tuned to optimize performance, thank you, ride safe.
When I get the new exhaust it will have the bungs closer to the head.
Last edited by RLH3175; Sep 29, 2014 at 01:07 PM.
Club Member
Joined: Jun 2007
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From: Bedford UK
It sounds as if the PC chap doesn't know his Harleys! Placed where you have your sensor you have the header from the rear cylinder coming in. On a system with only one final pipe his suggestion would probably work, but our comments above are indirectly confirmed IMHO. His comments about ensuring there are no leaks is valid.
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Stellar HDF Member
Joined: Aug 2013
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From: Texas
I ordered the 2 into 1 exhaust today, it has the bungs already in the pipes. I will just ride it like it is until I get the new exhaust installed.
Thanks to all for all the information.....
Thanks to all for all the information.....
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,081
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From: Ohio
Reversion is messing with you my friend, that is why when tuning you want the O2 as close to the head as possible, Harley pulls air back in making the O2 read lean. When building maps with a data recording system, you have to pull the clutch in on decel or reversion blends in and records a lean condition although the AFR's are good.
When you add timing you also will find it will slightly lean that area on the map and if you are doing a Power Commander format, a -5 in the 0 throttle area will kill any popping thru the exhaust on decal, sometimes it takes a -10 to work but you are adding fuel to cool the exhaust down. Good Luck, you have some sleepless nights ahead of you
When you add timing you also will find it will slightly lean that area on the map and if you are doing a Power Commander format, a -5 in the 0 throttle area will kill any popping thru the exhaust on decal, sometimes it takes a -10 to work but you are adding fuel to cool the exhaust down. Good Luck, you have some sleepless nights ahead of you
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