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Old 05-05-2017, 06:22 PM   #1 (permalink)
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Fuel Cut off on lower RPM then before!!! What does it mean??

Hello all!

Has the title say something strange start to happen on my SGII readings...
So when coasting in gear downhill the SGII always show me 0,00 lt/100km under 1800 rpms. Above that it shoes 1,2 lt/100km or more...
I know that very well because I always try to maintain under so I can get better mpg...
About a week or so ago, it only shows 0,00 lt/100 under 1500rpms!!!
And above 1500 rpms shows 1,2 or more...
What in the hell just happen to change the fuel cutoff from 1800 rpms to 1500 rpm when coasting in gear???

Should it be the SGII that is giving bad information? (the readings are matching with onboard computer...)

Or should it be someting with the car??
It's a 2007 european hatch civic with the 1.8 i-vtec R18 engine.
It has an EGR, a MAP sensor, and a drive by wire throttle with eletric butterfly intake...
The SGII scans no ecu errors...
Maby EGR needs a cleaning although doesnt usually get to dirty on petrol engines ?!
Or MAP sensor misreading?!
Or the intake butterfly doesnt close entirely and needs cleaning?
Or maby I shouls reset the ECU?
Or injectors? (I dump a bottle of Wynns Injector cleaning on this tank to see if it makes any difference...)

Does this happen with any of you?

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Old 07-18-2017, 10:16 AM   #2 (permalink)
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Thanks for the replies...

Anyway, for the benefit of others:

- The bottle of injector cleaner did nothing.
- I reset the Ecu by disconnecting negative battery cable for half an hour. It went worst! Start to show 0 consumption under 1200 rpms! Meaning that with engine on is almost always burning fuel!! Throttle, or no throttle!
- So, take it to dealership to clean eletronic throttle body, that was very dirty by the way, and after the cleaning it needed some TPS and idle calibration with HDS (Honda software) connected by the OBDII...
Success!!
Now it shows zero consumption from under 2.5k rpm... But will test higher to see upper limit... Also the engine is now smoother and refined... SGII was reading right...

My guess was right, a dirty throttle body don't completely close letting some air pass it, and the ecu compensate it by burning some extra fuel....

It's a preventive maintenance worth doing, because not only can improve gas milleage, as it prevents a faulty throttle body with excess of carbon on it, and I tell you: electronic throttle body AIN'T CHEAP!
Cost me an hour labour...
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Old 07-18-2017, 11:05 AM   #3 (permalink)
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Thanks for the update. I did not know that after certain rpms dfco was deactivating. Good to know.
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Old 07-18-2017, 12:13 PM   #4 (permalink)
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My ScanGauge shows zero fuel use ABOVE 1800 rpm when coasting in gear, then starts to burn fuel below that engine speed. I thought that was the way it was supposed to work?
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Old 07-18-2017, 12:22 PM   #5 (permalink)
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Quote:
Originally Posted by JockoT View Post
My ScanGauge shows zero fuel use ABOVE 1800 rpm when coasting in gear, then starts to burn fuel below that engine speed. I thought that was the way it was supposed to work?
Ditto.
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Old 07-18-2017, 01:27 PM   #6 (permalink)
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Would like to know what gear you were in, and maybe ambient temperature makes a difference. My Insight won't cutoff at any speed when the engine is still cold - and it is a hybrid!

My old Nissan Almera had the fuel cutoff at higher RPM, which made itself felt as hard engine braking. Then at say 1500 RPM it fired up again and more or less coasted down more gradually until the idle actually pushed the car forward.

Instead of using FCO I preferred to kill the engine and coasted down in top gear, clutch to the floor but ready to engage to restart when needed or when the speed got to say 20 km/h (half a turn of the crank would already do it even at very low speed)
Could coast maybe 3 times as long that way.
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Old 07-18-2017, 03:08 PM   #7 (permalink)
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Quote:
Originally Posted by RedDevil View Post
ambient temperature makes a difference. My Insight won't cutoff at any speed when the engine is still cold
My Jazz won't cut off until engine is up to temperature. I think it needs to be in closed loop mode.
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Old 07-18-2017, 04:44 PM   #8 (permalink)
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My Civic is kind of odd with fuel cutoff. Its really not super consistent and I haven't been able to peg down when it will or won't do it.
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Old 07-19-2017, 01:28 PM   #9 (permalink)
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Quote:
Originally Posted by JockoT View Post
My ScanGauge shows zero fuel use ABOVE 1800 rpm when coasting in gear, then starts to burn fuel below that engine speed. I thought that was the way it was supposed to work?
Maby you need a throttle cleaning too...

I bought my 2007 civic 4 years ago, when it had 6 years old, and the FCO was always under 1800-2000 rpms...
So at highway speeds (above 2000 rpms) it always shows some consumption...

I'm talking about SGII values here, because Onboard computer always shows zero when off the throttle...

But some months ago it start to FCO under 1500 rpm only...
That caught my attention...
After a reset it got worst, under 1200 rpms or so...

Now after the throttle clean and calibration, even above 2000 rpms it shows zero!!
Maby it's supost to be like this since new! Once it had already 6 years when I bought it, it should have already some dirt on throttle body...

Really happy with results, because it's smoother, it looks like it acelarates better, and this few days looks like I'm getting more mpg in daily commute...

Advise everyone doing that clean every 60k miles!
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Old 07-19-2017, 02:04 PM   #10 (permalink)
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What you are describing seems counter intuitive to me.

It is supposed to cut off at higher rpms. There is a minimum , after that thr engine needs to inject fuel to keep running.

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