Where did my fuel go?

Kha0S · 02-16-2006, 04:00 PM

I've been running on a pretty steady tune that's been keeping my AFRs in the neighborhood of 11.2-11.5:1. I arrived at that tune incrementally over the last six weeks or so.

Today, it's been about 20-30 degrees warmer than usual, and suddenly, I'm running about 0.7 AFR points leaner than normal. My short term fuel trims are at zero when wide open, and the long term trims are around -2.34% (where they've been pretty consistently).

What gives? The tune seems to be running leaner and leaner by the minute... it was running at virtually normal AFRs this morning, and has lost more than half a point of fuel in 20 miles of driving.

Any ideas?

/Andrew

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Kha0S · 02-16-2006, 04:03 PM

Note, idle and cruise are both centered happily around stoich, idle shows -3.13% LT trim, and cruise shows -0.78% LT trim.

Kha0S · 02-16-2006, 04:51 PM

... update... this might all be moot. I'm getting a new sensor for my wideband... it might have finally crapped out.

I made a plot of MAF g / injector duty %, and plotted it against RPM, with data from a few days ago versus now... the curves match. That makes me pretty sure that the same amount of fuel is going into the cylinders... it's not guaranteed, but I'll just go easy on the throttle tonight until I can get a new sensor in and check my AFRs in the morning.

/Andrew

mrbell · 02-16-2006, 05:08 PM

If the temp changed 30 degrees, it could be your coolant enrichments

Kha0S · 02-16-2006, 05:18 PM

Coolant temps have been virtually identical (180-190F). Good idea, though.

I found a local VW parts dealer that has the 7057 sensor for my wideband controller... I'm picking it up and putting it in tonight. Hopefully that'll assuage my fears.

x99percent · 02-16-2006, 05:38 PM

Tuned with...? Looks like AccessPort?

Did you happen to fill up with gas that has more ethanol content than you're used to?

Kha0S · 02-16-2006, 05:53 PM

Quote:

Originally Posted by x99percent

Tuned with...? Looks like AccessPort?

Did you happen to fill up with gas that has more ethanol content than you're used to?

Tuned with OpenECU tools. I ran one tankful of a different brand of gas last week and found that I was getting some incipient knock (due to the variances between regional additives for winterization). I'm back onto the same fuel that I have been using for the previously and the timing is back to full advance.

The gas uses MTBE, but I've been tuning against the same blend for a while now.

/Andrew

02-16-2006, 04:00 PM	#1
Kha0S Scooby Guru Member#: 8808 Join Date: Jul 2001 Chapter/Region: NESIC Location: Grantham, NH Vehicle: 2011 WRX (DGM 5D) 2002 WRX/2003 SVTF	Where did my fuel go? I've been running on a pretty steady tune that's been keeping my AFRs in the neighborhood of 11.2-11.5:1. I arrived at that tune incrementally over the last six weeks or so. Today, it's been about 20-30 degrees warmer than usual, and suddenly, I'm running about 0.7 AFR points leaner than normal. My short term fuel trims are at zero when wide open, and the long term trims are around -2.34% (where they've been pretty consistently). What gives? The tune seems to be running leaner and leaner by the minute... it was running at virtually normal AFRs this morning, and has lost more than half a point of fuel in 20 miles of driving. Any ideas? /Andrew * Registered users of the site do not see these ads.

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02-16-2006, 04:03 PM	#2
Kha0S Scooby Guru Member#: 8808 Join Date: Jul 2001 Chapter/Region: NESIC Location: Grantham, NH Vehicle: 2011 WRX (DGM 5D) 2002 WRX/2003 SVTF	Note, idle and cruise are both centered happily around stoich, idle shows -3.13% LT trim, and cruise shows -0.78% LT trim.

02-16-2006, 04:51 PM	#3
Kha0S Scooby Guru Member#: 8808 Join Date: Jul 2001 Chapter/Region: NESIC Location: Grantham, NH Vehicle: 2011 WRX (DGM 5D) 2002 WRX/2003 SVTF	... update... this might all be moot. I'm getting a new sensor for my wideband... it might have finally crapped out. I made a plot of MAF g / injector duty %, and plotted it against RPM, with data from a few days ago versus now... the curves match. That makes me pretty sure that the same amount of fuel is going into the cylinders... it's not guaranteed, but I'll just go easy on the throttle tonight until I can get a new sensor in and check my AFRs in the morning. /Andrew

02-16-2006, 05:08 PM	#4
mrbell Scooby Specialist Member#: 1871 Join Date: Jul 2000 Location: Salt Lake City, UT Vehicle: 2000 Impreza 2.5RS Blue Ridge Pearl	If the temp changed 30 degrees, it could be your coolant enrichments

02-16-2006, 05:18 PM	#5
Kha0S Scooby Guru Member#: 8808 Join Date: Jul 2001 Chapter/Region: NESIC Location: Grantham, NH Vehicle: 2011 WRX (DGM 5D) 2002 WRX/2003 SVTF	Coolant temps have been virtually identical (180-190F). Good idea, though. I found a local VW parts dealer that has the 7057 sensor for my wideband controller... I'm picking it up and putting it in tonight. Hopefully that'll assuage my fears.

02-16-2006, 05:38 PM	#6
x99percent Scooby Specialist Member#: 27108 Join Date: Oct 2002 Chapter/Region: MWSOC Location: Detroit-ish, MI Vehicle: 2004 STi 2004 A4	Tuned with...? Looks like AccessPort? Did you happen to fill up with gas that has more ethanol content than you're used to?