Since we both have 1G xBs, you can probably set your calibration to 13.5%, and be spot on. I use 21%, so my UG mpg display is pessimistic, and I'm not disappointed by my tank results. 13.5% is very accurate, in my experience.

The average mpg (general) is the average mpg since you reset the general average distances and mpg last. I reset it when I fill the tank, and I reset the trip parameters when I park the car after a drive. You could use your average mpg for the lifetime of the car, for all the driving you do in a month, for a quarter-year competition - whatever you want.

Timing advance relates closely to mpg. The more you mash the gas pedal, the more the ECU retards your timing, and the lower your mpg and timing go. The inverse is also true. So on a highway drive, as you're climbing a hill, your timing will drop into the twenties, and your mpg will drop into the teens or single digits. When you crest the hill and ease off the gas pedal on the downhill, your timing will climb into the 40s, and your mpg will shoot into the 200s. On level ground, you want to try to keep the timing in the high 30s or higher for best mpg. Unfortunately, it's hard to maintain speed when you keep ignition timing high.

BTW, I'll be in La Mesa later this week. PM me if you want to get together while I'm in SD.

 

Do you think the MPG calibration would be different if I have an auto? I know you use a manual. I will keep the 13% in mind.

K thanks for that information about the general mpg and timing advance, I will def use it!

I would love to but I dont know if I will have any time. Work and schoolwork is taking up the bulk of my time now that the semester is under way. Plus my box is in the body shop right now too, unfortunately. I will PM you if I find any time that opens up! Thanks for the help!

 

It's not looking good for me with spare time, either. Maybe another time.

Yes, I think the 13.5% calibration will be pretty close to perfect for your AT.

 

ok thanks sentra. Yeah definitely! I would love to get together! I am planning to head up to pleasanton in June so maybe a meet then? Who knows. TTYsoon

 

ok sentra, so i just took my first 30 minute run of the timing advance gauge.

1) when im traveling at a steady 65 MPH, my gauge reads between a 20 and 35, depending on road steepness variations. I can rarely reach up to 37. Havent seen a 40 reading yet. By the time I let up on the gas, the gauge drops way low, BUT the MPGs are in the 200s. I would say the timing advance drops back to the 20 range after releasing the pedal on freeway speeds.

2) On that note, when I travel at a steady CITY speed (i.e. 40MPH) and then let up on the gas pedal completely, my car goes into closed loop mode and then shows a reading in the single and sometimes negative digits! my car also has a slight hesitation in coasting (almost similar to engine braking) for a second or two following the release of the pedal. But just a split second later the gauge will read a normal value and the car proceeds to coast normally.

The annoyingness of my car always hesitating when I release the pedal is huge. It practically wants to slow down a full 5 MPH during that hesitation, making me never want to release the pedal. If I release the pedal at city speeds, my car wants to slow down!!! AGH! Although the hesitation is quick, it drastically reduces momentum and I find myself always reapplying the gas to make up for the lost momentum.

Any thoughts on all this? Remember, my car is auto.

 

It doesn't sound right to me. My MT xB, MT Sentra, & my wife's AT Elantra all show ignition timing advances when I lighten up on the throttle.

The first thing that comes to mind that might cause timing retardation is a defective knock sensor. If it signals knock, the ECU will retard your timing, causing the lower timing numbers you're seeing (and also causing lousy mpg, since retarded timing causes the engine to run rich).

Another thing that might be happening is deceleration fuel cutoff. DFCO cuts off the fuel to your fuel injectors, and would cause the UG to show 0 mpg (I think). I'm not sure what it does to ignition timing. DFCO would put your system into open loop, though.

ATs monitor some other stuff that MTs don't, like a brake switch that causes torque converter slippage.

Maybe someone else with an AT and an UG or SG can chime in with what they see when decelerating their AT xBs.

 

Yeah, if you're coming up to Pleasanton in June, maybe we can meet up then.

 

If I had a defective knock sensor would I be getting a CEL? Right now I have no CEL.

Also, the UG ONLY shows a 0.00MPG when idling at 0MPH. When I let up on the gas, I always go into open loop and my MPGs always skyrocket. In the 100s at city speeds and 200s at highway speeds.

Very interesting information, hopefully an AT UG user will come along. That might explain part of my bad fuel economy as seen on fuelly.com. haha :D

 

The CEL won't trigger on knock sensor signal unless the knock sensor continues uninterrupted for 10 seconds. The timing retardation corrects the knock, so the CEL doesn't trigger.

One of your earlier messages indicated you stay in closed loop when decelerating at city speeds. Apparently you go to open loop decelerating at highway speeds. If both are true, it indicates you're going into DFCO at highway deceleration. This is consistent with what I've observed when my MT goes into DFCO. It goes into DFCO when the engine speed is >1500 rpm and I'm in gear and the throttle position sensor drops to idle position. One way to prevent the sudden DFCO deceleration is to keep the TPS from dropping to idle - just a touch of throttle. I'd set TPS as a display gauge, learn what the TPS is at idle (9?), and keep it above idle (at 10 or 11?) when you decelerate. The other way to prevent DFCO is shift to neutral when you start coasting, and don't put it into drive again until you've lost enough speed that you need to accelerate. Try both those techniques, and let me know if that cures your deceleration issues at >40 mph speeds.

The deceleration at city speeds is a different issue, indicating the torque converter isn't releasing from lockup. That one will require some diagnostic work by a knowledgeable transmission guy. You might try tapping on the brake quickly and lightly before letting up on the gas. That should decouple the TC and let you coast freely. Try that at city speeds. If you get good coasting by tapping the brake before easing up on the gas, then you'll need to find why the TC isn't releasing on normal deceleration.

 

I drove my wife's AT Elantra today, and checked what happens when I let off on the gas at freeway speeds. It pretty well matches your description. My ignition timing dropped to idle timing of 5, indicating it goes into DFCO. Instant mpg shot way up >100 mpg. Initially, DFCO didn't seem to affect coasting, but when I shifted to neutral, my coasting speed definitely improved. So, the solution seems to be shift to neutral to increase your glide speed and distance.

Her car has a Scangauge mounted, and I didn't have time to check open/closed loop, but the ignition timing drop to 5 tells me it goes into DFCO.

 

Ok thanks sentra for testing that out. that is exactly what happens with me. Now, I have heard a bunch of horror stories of shifting into neutral in an automatic then shifting back to drive.

Shifting into neutral definitely reduces resistance from the engine and allows for amazing coasting. I have searched online that the transmission hates it when shifting into neutral and then back into drive without first stopping. The claim is that the transmission has to get back into the proper coasting speed which causes more wear and tear on the auto tranny.

I go into open loop no matter what speed when coasting. Even at 10 MPH or at 75 MPH, I go into open loop. The open loop only lasts a max of 5-10 seconds and then goes back into closed loop even after continuous coasting.

Yeah, I do notice some freaky stuff with my torque converter. For example, it sometimes engages while slowing down approaching a signal. Or while rounding the top of a hill it will engage even if I am easing on the gas pedal. I think it does make sense that it could be causing issues too. For example, a steady 25MPH on flat road usually reads about 30-35 Instant MPGs. That seems pretty low to me. While traveling around a steady 25, my car seems to have the torque converter engaged. Also, I notice at those speeds that my car will never go into 4th gear! Why not go to the highest gear possible if there is flat road and its a steady speed?

 

I've done a lot of neutral coasting with shifting back into drive - three tankfuls worth on a rental AT Yaris, which I think has the same AT as the xB. Also 3600 miles of high speed P&G on a rental AT Kia Rio. No problems. The Yaris was smart enough to ignore two accidental shifts into reverse at forward speeds.

My wife's Elantra's AT gives an occasional unnerving clunk if I shift back into drive and give it gas immediately. If I just shift into drive with my foot off the gas, the TC slips and the 800 rpm idle speed shoots up to 2500 as the AT finds top gear. I just keep my foot off the gas until the rpms indicate normal operating rpm between 1500 and 2200 rpm. Then I can give it gas.

 

Ok, I might give the neutral coasting a go for now.

Also, I notice that coasting is always open loop UNTIL RPMs are under 1000, then I go into closed loop. Sometimes that takes a long time when at highway speeds. I have to be traveling relatively slow for that to occur.

 

Open loop indicates DFCO. On an AT, you're still pushing fluids, but your car doesn't slow as drastically as a MT car does. The reason it goes back into closed loop, is that DFCO starts when you decelerate from >1500 rpm in gear, but it ends when rpms drop to 1000 rpm. That's the same reason it doesn't happen in the city below 40 mph, because you're not >1500 rpm in top gear then.

Your car won't drop into DFCO when you shift to neutral, so you'll coast longer, but your engine will keep on idling. In DFCO, you use no fuel, but your coasting distances will suffer.

 

Ok thanks sentra, beasting up with all this knowledge. I will definitely be using it!

 

You're welcome. I think you're headed for much better fuel economy. Slowing down and conserving momentum account for 80% of my mpg gains. Take a look at this link. Every time you use your brakes to stop from 35 mph, you waste enough gas to do that. That's a LOT of wasted energy. Most drivers still have their foot on the gas half a block from stop signs and red lights. I start coasting to those stops 4 or 5 blocks away.

 

Drove my tc on a 26 hr round trip from Florida to Louisiana and back. Averaged 35mpg on the hwy @ or around 70mph. Boosted @ 10lbs on 93 octane and 255lph fuel pump with 3 people in the car and luggage. No complaints

 

Awesome! My SE-R only got 26 mpg @72 mph. Heck, my xB only gets 32 mpg @ 70 mph.

 

Thats darn good! Way to go!
Just think what you could attain if you were driving an xA

 

or a Yaris. They're both (the manual transmissions) geared to be buzz-bombs at highway speeds, unfortunately.