Injector fuel cut off

[ShadeTreeMech]

+1 on the DFCO on a modern car. I've noticed it on both my Villager and the Maxima; GPH goes to 0 when coasting with rpms above about 1200 or so.

I suspect not injecting fuel also helps to prevent backfire and the noise I hear from an older carbed car when going downhill; kind of a burbling noise while going downhill, especially if you downshift.

[comptiger5000]

What I find interesting is that my Jeep is significantly louder when IN fuel cut than out of fuel cut, particularly at high RPMs (downshift to stop at bottom of hill).

[texanidiot25]

Originally Posted by ShadeTreeMech

I suspect not injecting fuel also helps to prevent backfire and the noise I hear from an older carbed car when going downhill; kind of a burbling noise while going downhill, especially if you downshift.

Yup, the average carb doesn't cut fuel based on throttle position, it continues to draw as much fuel as the air pulling it requires. So you get a lot of unburnt fuel when coasting. My truck has a nice thundering coming off the freeway, with the occasional snap-crackle-pop when coming down from 3-4k rpm. I'm confident that if I had a spark plug in the pipes I could have a pretty wicked show coming off the freeway.

[ShadeTreeMech]

Originally Posted by texanidiot25

Yup, the average carb doesn't cut fuel based on throttle position, it continues to draw as much fuel as the air pulling it requires. So you get a lot of unburnt fuel when coasting. My truck has a nice thundering coming off the freeway, with the occasional snap-crackle-pop when coming down from 3-4k rpm. I'm confident that if I had a spark plug in the pipes I could have a pretty wicked show coming off the freeway.

My dad's 71 F-250 does that coming down the hill where we all lived as kids. You could be sitting in the house engrossed in whatever you were doing (or not supposed to be doing) and hear him coming from about a quarter mile away. And he had stock spec exhaust too! He says in his yonger days his buddies would put a spark plug in the exhaust and hook it to a coil for tailgaters. All it took was shutting off the ignition while rolling in gear for about 5 seconds, then lighting up that plug. I bet plenty of people pooed on themselves after the report and flash of fire from the exhaust!

[Nevyn]

I can report with near 100% certainty that my 2004 Elantra DOES, in fact, have some sort of DFCO. Kicks in at 2000 RPM, and out at 1200. I'll try to get video of it coming in and going out.

However, the SGII doesn't see it - I'm betting because it stays in closed loop as the computer "knows" it's going lean.

I wonder if I can program an Xgauge for my O2 sensor?

[EdKiefer]

Originally Posted by Nevyn

I can report with near 100% certainty that my 2004 Elantra DOES, in fact, have some sort of DFCO. Kicks in at 2000 RPM, and out at 1200. I'll try to get video of it coming in and going out.

However, the SGII doesn't see it - I'm betting because it stays in closed loop as the computer "knows" it's going lean.

I wonder if I can program an Xgauge for my O2 sensor?

Yes, O2 or A/F ratio should show it if it works on your vehicle (O2 and A/F are listed under standard Xgauge values not the enhanced (Ford/GM etc ) .
I don't have SGII but it says it does fuel rate , what exactly is that measuring ?
The best way would be pulse width length of the injectors, not sure if SGII can display this .

[ShadeTreeMech]

Originally Posted by Nevyn

I can report with near 100% certainty that my 2004 Elantra DOES, in fact, have some sort of DFCO. Kicks in at 2000 RPM, and out at 1200. I'll try to get video of it coming in and going out.

However, the SGII doesn't see it - I'm betting because it stays in closed loop as the computer "knows" it's going lean.

I wonder if I can program an Xgauge for my O2 sensor?

On my scanguage I can see the dfco kick in by the GPH reading (gallons per hour) because it will kick over to 0 fairly quickly when I let off the throttle. I suppose the o2 sensor would stay in closed loop if the ecu "knows" the o2 readings will go off the charts during dfco. Of course, the reaction of higher o2 readings is to spray more fuel, so if the injectors are cut off that can't exactly happen.

AFAIK there isn't a a/f ratio guage built in, I suppose it might be an xguage. I do know you can read up to 4 seperate banks of o2 sensors with the right xguage though.

[Nevyn]

Originally Posted by ShadeTreeMech

On my scanguage I can see the dfco kick in by the GPH reading (gallons per hour) because it will kick over to 0 fairly quickly when I let off the throttle. I suppose the o2 sensor would stay in closed loop if the ecu "knows" the o2 readings will go off the charts during dfco. Of course, the reaction of higher o2 readings is to spray more fuel, so if the injectors are cut off that can't exactly happen.

I can visually verify via tach that it's DFCO-ing. However, it stays in closed loop and my SGII doesn't go to 9999 MPG. I'm going to program O2 and AFR X-gauges here shortly and see what I see on my way home from work today.

AFAIK there isn't a a/f ratio guage built in, I suppose it might be an xguage. I do know you can read up to 4 seperate banks of o2 sensors with the right xguage though.

I know/knew they existed; I just hope that my specific car make/model reports the information.

[EdKiefer]

Originally Posted by Nevyn

I can visually verify via tach that it's DFCO-ing. However, it stays in closed loop and my SGII doesn't go to 9999 MPG. I'm going to program O2 and AFR X-gauges here shortly and see what I see on my way home from work today.


I know/knew they existed; I just hope that my specific car make/model reports the information.

I could see how scangauge could be not smart enough, the ECU can be in closed loop (monitoring O2 ) but still shutting down injectors during off throttle at specific rpm ranges .

[Nevyn]

Originally Posted by EdKiefer

I could see how scangauge could be not smart enough, the ECU can be in closed loop (monitoring O2 ) but still shutting down injectors during off throttle at specific rpm ranges .

I'll have a full report tomorrow for you all.