In reviewing the EFI Basics presentation it shows,

"Optimum AFR for cruise area is 13.4 - 13.6:1"

If this accurate why is my cruise area set at 14.2 after a dyno tune?

Thanks.

 

That question can really involved. Here are a few points to keep in mind.....

1) 02 sensors tend to be really accurate near 14.7 AFR. This holds true for both Narrow band and wide bands.

2) Narrow bands get really sketchy as an AFR measuring gauge as you get away from 14.7 AFR. This gets really huge as you get change exhaust temperature. 14.2 is really getting close to the outside edge, but until about a year ago, that was about the best you had available in the Harley world and still use the stock ECU to run closed loop so people did their best to ignore the downsides of narrow bands.

3) The motor will run great at 13.8 or so out of the high HP regions but narrow bands are useless at these AFRs. If you still have cats in the exhaust, these sorts of numbers will kill them quick. They really need to see an AFR change constantly from about 14.5 to 15 or so to stay healthy.

4) Having a really steady AFR without O2 feed back is almost impossible considering all the weather and fuel changes a motor has to deal with in the real world.

So tuner are stuck between a rock and a hard place. They either don't understand what is really going on in a motor, or they are trying to run stuff right up to the edge of workability. This all adds up to why the OEMs are often now converting to wide bands to get that silky smooth roll on power the 14.2 down to 13.8 provides but still deliver the 14.7 +/- .3 or so that the EPA and the cats want to see to remain healthy.

The big cheviot in all of this is the widebands that most of us can afford can very about .75 AFR when reading at 13 AFR that we really want to use at WOT. Add to that the fuel robbing that a Harley Y intake manifold and a "tuner" claiming their tune is perfect and 14.2 AFR is very optomistic at best.

Added: Most all of my motors are running closed loop with Dynojet Wideband2s. Most of them (with the exception of the Harley) are using the 0-5 volt outputs to drive other tuning hardware and software. I have found Dynojet pieces to be more reliable than other brands I have tried. At least on two occasions I can recall, I left the key in the ignition and the wide band sucked the battery to 0. Both sensors survived. That stunt would kill lots of other brands. I now wire all my widebands to only get power when the motor is spinning.

There are some other really promising devices coming to the aftermarket soon but time will tell.

Have fun tuning.

Andy

 

Dyno jet making their own sensors now Andy? Come on.

 

Gasoline produces three most power at 13.4- 13.6, it is most efficient at 14.6 - 14.7. Your tuner has you right in the middle which I'd fine for cruising, I like 14.4. What year is your bike? O2 sensors or not?

 

The sensors are Bosch, i have no clue who does the controller for them.

 

Thanks for the replies. The bike is a '07 Street Glide, 120" with street ported heads, T-man 662-1 cams, 10.8:1 CR, Drago 2:1 and HPI 58mm t/b.

Also have PV with Target Tune. Currently the map is 14.2 in the cruising range and runs fine. I did change the P.E. rpm/TPS to come on sooner which I think made a difference.

 

DDH from the AFR side, you are good to go on the fuel side of things if you fade to 13 at WOT. Say 90 KPA and above. Are your fuel trims running close to 100?

How does your timing look in the logs?

 

Yes, the motor fades to 12.8 at WOT. Not sure what is meant by fuel trims close to 100. Is that VE's?

At this point in my learning I have not delved into timing so I have no feel how the timing looks.

 

You need to post up a 45 min log driving in the twisties. Try avoid the highways. Get a log that includes the AFF front and rear and post up that data log.

 

The twisties are about 100 miles away, no problem but not sure its 45 minutes worth maybe turn around and head back.

Before I do anything I need to have a possible intake leak taken care of. I would do it myself but I have very little confidence in me doing it. In fact I was the one who installed the t/b after HPI rebuilt it. Not crazy about paying the dealership to do it but if I do it I have no idea if I can tell when I tighten the bolts if I did it correctly. Will have start it to see.