problem with fuel trim

tom46 · February 2nd, 2012, 10:14 AM

i have a 2001 mustang gt with all the bolt ons. i have a fuel trim problem with a random missfire. fuel trim is -15% . all normal test performed and check out good. but when u take the oil cap off at idle. the fuel trim goes down to 1. i put a new pcv in it and checked for cloggs . nuthing no change in fuel trim. does anyone have an idea whats going on with my car. i do have the stock plastic intake manifold.

Tang Stang · February 2nd, 2012, 01:43 PM

Has the car been tuned? Opening the oil fill while the engine is running introduces un-metered air and will effect the fuel trims.

Is the list in your sig the complete extent of the mods done to the car? You haven't changed fuel injectors or the MAF without tuning, right? Have you cleaned the MAF recently?

tom46 · February 2nd, 2012, 11:47 PM

the MAF is reading right and i had a tune in it. the fuel trim was at 25% then i took the tune out and put it back to the stock setting and the fuel trim changed to -15%. i changed the pcv valve it droped to -10 %. the shop wanted to try somthing with the computer so they reloaded a stock setting on the car to make sure it was a true stock setting and then the fuel trim went to 5% and under. thats with no tune and long tube headers. im going to drive it for a week and if nuthing changes im going to retune the car and see what happens

bulloch27 · February 3rd, 2012, 02:32 AM

The fuel trim should be constantly changing with a target of 0. Rich conditions, as read by the O2 sensors, will result in a negative fuel trim value and lean conditions will result in a positive fuel trim value. If you're maintaining a negative fuel trim I would suggest looking at the output value of the O2 sensor for that bank of injectors with the negative value. You may find that you're not getting a proper reading out of that O2 sensor and that replacement may remedy the problem.

stal94gt · February 3rd, 2012, 04:45 AM

you may need a tune for your long tubes. relocating the o2 sensors down stream can require the heater ranges of the 02 sensors to be changed.

February 2nd, 2012, 10:14 AM	#1
tom46 Newbie 2001 mustang gt 14.0 Join Date: Nov 2010 Posts: 19 iTrader: 0 reviews	problem with fuel trim i have a 2001 mustang gt with all the bolt ons. i have a fuel trim problem with a random missfire. fuel trim is -15% . all normal test performed and check out good. but when u take the oil cap off at idle. the fuel trim goes down to 1. i put a new pcv in it and checked for cloggs . nuthing no change in fuel trim. does anyone have an idea whats going on with my car. i do have the stock plastic intake manifold. __________________ 2001 mustang GT --- 373 gears, pullys, 70mm throttle body, upper intake plenum, cold air intake system,bbk long tube headers, catless H-pipe to super 40 flowmasters, cobra R rims, sound system , HID headlights, grills

February 2nd, 2012, 01:43 PM	#2
Tang Stang Hardcore Enthusiast 2004 Mustang GT Join Date: Sep 2010 Location: Imperial, MO Posts: 1,961 iTrader: 2 reviews	Has the car been tuned? Opening the oil fill while the engine is running introduces un-metered air and will effect the fuel trims. Is the list in your sig the complete extent of the mods done to the car? You haven't changed fuel injectors or the MAF without tuning, right? Have you cleaned the MAF recently? __________________ Rod @ AzzKicker Cars 2004 Ford Mustang GT-The Driver-BBK CAI, PP TB & Inlet, Steeda UD's, SLP LM1, & 3.73's. 1990 Mercury Cougar XR7-The Meth Addict-5.0L DOHC Stroker w/2.1L KB SC. 1995 Ford F150-Mud Toy-5.0L, 4x4, 33's, & Warn 8274 Winch

February 2nd, 2012, 11:47 PM	#3
tom46 Newbie 2001 mustang gt 14.0 Join Date: Nov 2010 Posts: 19 iTrader: 0 reviews	the MAF is reading right and i had a tune in it. the fuel trim was at 25% then i took the tune out and put it back to the stock setting and the fuel trim changed to -15%. i changed the pcv valve it droped to -10 %. the shop wanted to try somthing with the computer so they reloaded a stock setting on the car to make sure it was a true stock setting and then the fuel trim went to 5% and under. thats with no tune and long tube headers. im going to drive it for a week and if nuthing changes im going to retune the car and see what happens __________________ 2001 mustang GT --- 373 gears, pullys, 70mm throttle body, upper intake plenum, cold air intake system,bbk long tube headers, catless H-pipe to super 40 flowmasters, cobra R rims, sound system , HID headlights, grills

February 3rd, 2012, 02:32 AM	#4
bulloch27 Hardcore Enthusiast 2003 Mustang Fauxbra N/T @ Fast Join Date: Jan 2011 Location: Statesboro, Ga Posts: 2,879 iTrader: 0 reviews	The fuel trim should be constantly changing with a target of 0. Rich conditions, as read by the O2 sensors, will result in a negative fuel trim value and lean conditions will result in a positive fuel trim value. If you're maintaining a negative fuel trim I would suggest looking at the output value of the O2 sensor for that bank of injectors with the negative value. You may find that you're not getting a proper reading out of that O2 sensor and that replacement may remedy the problem. __________________ All the typical bolt-ons, well a lot are welded on. Bone stock I tell ya. First time at the track, what do I do now? 03 Silver Fauxbra; 06 Legend Lime GT, 89 Outwlaw 10.5W Coupe, 93 Teal Cobra, 93 Red GT, 93 Teal LX - All Sold

February 3rd, 2012, 04:45 AM	#5
stal94gt I Post Entirely Way Too Much 2003 mustang v6 ;) slow Join Date: May 2010 Location: eglin afb florida Posts: 10,197 iTrader: 2 reviews	you may need a tune for your long tubes. relocating the o2 sensors down stream can require the heater ranges of the 02 sensors to be changed. __________________ bone stock from the factory!

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