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**53burb** · 04-14-2014, 04:06 PM

Need to monitor Short Term Fuel Trims with a scan tool, If they are way positive while idling then go down at part throttle.....90% chance of a vacuum leak.

I got a scan tool earlier today that reads live data. At idle (~700rpm), the STFT reads anwhere from 1.5 ot lower to 3.6 or higher. Most of the time it is around 3.1. At about 1500rpm, the STFT drops to about -.1 to -.5. Is this enough to indicate a vacuum leak? After changing the fuel pump, the codes come in at about 45 miles after resetting the computer.

04-14-2014, 04:06 PM	#10
53burb Registered User Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,004	Re: P0171 & P0174 codes Need to monitor Short Term Fuel Trims with a scan tool, If they are way positive while idling then go down at part throttle.....90% chance of a vacuum leak. I got a scan tool earlier today that reads live data. At idle (~700rpm), the STFT reads anwhere from 1.5 ot lower to 3.6 or higher. Most of the time it is around 3.1. At about 1500rpm, the STFT drops to about -.1 to -.5. Is this enough to indicate a vacuum leak? After changing the fuel pump, the codes come in at about 45 miles after resetting the computer.