Zero throttle fuel usage?
02-10-2009, 11:22 AM
#11
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I also read somewhere that for some auto's it's not a good idea to coast in nuetral - something about damaging the tranny, since this reduces pump flow. Would this be true for the GM auto in our cars?
Sorry if I'm off topic
02-10-2009, 11:24 AM
#12
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Well, so far nobody has given the correct answer. 
Most of the newer engines today have what is called DFCO (Deceleration Fuel CutOff). When certain operating parameters are met, fuel is cut to the injectors. It helps with both mileage and emissions.
When the engine approaches idle, fuel resumes to prevent stalling.
I see it all the time with my wideband O2 sensor and during tuning data logs.
Whether manual or automatic, putting it into neutral will circumvent DCFO. So, for mileage, you are better off just leaving it in gear.
Hope that helps.
EDIT... Well pitbull answered right while I was typing.
Most of the newer engines today have what is called DFCO (Deceleration Fuel CutOff). When certain operating parameters are met, fuel is cut to the injectors. It helps with both mileage and emissions.
When the engine approaches idle, fuel resumes to prevent stalling.
I see it all the time with my wideband O2 sensor and during tuning data logs.
Whether manual or automatic, putting it into neutral will circumvent DCFO. So, for mileage, you are better off just leaving it in gear.
Hope that helps.
EDIT... Well pitbull answered right while I was typing.
02-10-2009, 11:28 AM
#14
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Missed yours as well pitbull. I need to learn to type faster.You are correct, I wasn't arguing, rather trying to use my own logic to explain why I didn't think I was saving fuel by using neutral.
Thanks to all for your input.
02-10-2009, 11:30 AM
#15
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Not that I agree with them but, when I used to be amember The "experts" @ cleanmpg.com recommended doing coasting at neutral.
I also read somewhere that for some auto's it's not a good idea to coast in nuetral - something about damaging the tranny, since this reduces pump flow. Would this be true for the GM auto in our cars?
Sorry if I'm off topic
I also read somewhere that for some auto's it's not a good idea to coast in nuetral - something about damaging the tranny, since this reduces pump flow. Would this be true for the GM auto in our cars?
Sorry if I'm off topic
Sounds like the "experts" are wrong in this case.
02-10-2009, 11:39 AM
#16
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coasting
you do not need any fuel to coast. but i have never seen any engine that was programed not to run while coasting. the engine needs to stay running while coasting to run the accessories- altenater - ac -power steering. they only way that is not getting any fuel would be if you turn the key off. my 08 hhr is always running , even if i coast for a mile , if it is running it is getting fuel. maybe the 09 is different , but i am sure that it is not because of the altenator . power steering is electric , but if cut off the key , you cut it off. it is dangerous to cut off the key ,while coasting , and probably illegal in some states. there may be some hybrids that cut off the fuel. hhr is not hybrid.
02-10-2009, 11:57 AM
#17
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you do not need any fuel to coast. but i have never seen any engine that was programed not to run while coasting. the engine needs to stay running while coasting to run the accessories- altenater - ac -power steering. they only way that is not getting any fuel would be if you turn the key off. my 08 hhr is always running , even if i coast for a mile , if it is running it is getting fuel. maybe the 09 is different , but i am sure that it is not because of the altenator . power steering is electric , but if cut off the key , you cut it off. it is dangerous to cut off the key ,while coasting , and probably illegal in some states. there may be some hybrids that cut off the fuel. hhr is not hybrid.
02-10-2009, 12:22 PM
#18
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JoeR, esmarkey and pitbull (and any others I missed) are correct. Joe and I debated this before and Joe was correct. 
Here is the prior thread on this subject. Joe posted some good information there.
https://www.chevyhhr.net/forums/2-4l-performance-tech-14/deceleration-fuel-cut-off-16957/
Here is the prior thread on this subject. Joe posted some good information there.https://www.chevyhhr.net/forums/2-4l-performance-tech-14/deceleration-fuel-cut-off-16957/
02-10-2009, 12:42 PM
#19
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DFCO is initiated in gear under deceleration, with a fairly tightly defined set of parameters. Coasting in neutral will show the same 99 MPG on the DIC, but you're not really in DFCO. The only way to tell the difference is to monitor wideband AFR (with a Dashhawk on the SS only) or monitor fuel g/hr. Under DFCO, the AFR will climb to a fairly high number, whereas coasting at idle will keep you at 14.7 give or take. The gal / hr parameter will also go below the normal idle value once you're in DFCO. Actually, rolling idle is higher than stationary idle because of the throttle cracker.
02-10-2009, 02:35 PM
#20
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JoeR, esmarkey and pitbull (and any others I missed) are correct. Joe and I debated this before and Joe was correct. Here is the prior thread on this subject. Joe posted some good information there.
https://www.chevyhhr.net/forums/showthread.php?t=16957
Here is the prior thread on this subject. Joe posted some good information there.https://www.chevyhhr.net/forums/showthread.php?t=16957
,and had the same skeptics back then It sounds like there is a fuel shutoff (DFCO) built into the programing so what I thought I was doing by coasting in N to save fuel was all wrong. (wasn't the 1st time and won't be the last)
Also, wasn't there a mileage or hyper-milling forum on this board before?