171 , 174
Le Mans Master
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From: Charles Town WV
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P0171 and P0174? the first two digits matter. Also Year, Model, Motor configuration? Those would help us to diagnose.
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From: Cape Coral, Florida
Can you access “Freeze Frame Data” with your scan tool ??…post all the numbers for either the 0171 or 0174…ok, so you smoke tested but look at your fuel trims at idle anyway…if elevated (more than 10%) run the engine at 3000 RPM and see if the fuel trims decrease…if they decrease you have a vacuum leak..if fuel trims are good at idle but INCREASE under load you either have a fuel delivery issue (fuel pump) or a bad MAF sensor…with scan tool the MAF sensor should read in grams/second the liter displacement of the engine…in your case 7.0 grams/second hot idle…what you can also do is look at both upstream O2 sensors under WOT…they should go FULL RICH…pretty close to 1000mv’s…they normally oscillate between 200-800mv’s at idle.
Last edited by C5 Diag; Aug 28, 2024 at 01:34 PM.
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Joined: Aug 2024
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171 174 codes
Can you access “Freeze Frame Data” with your scan tool ??…post all the numbers for either the 0171 or 0174…ok, so you smoke tested but look at your fuel trims at idle anyway…if elevated (more than 10%) run the engine at 3000 RPM and see if the fuel trims decrease…if they decrease you have a vacuum leak..if fuel trims are good at idle but INCREASE under load you either have a fuel delivery issue (fuel pump) or a bad MAF sensor…with scan tool the MAF sensor should read in grams/second the liter displacement of the engine…in your case 7.0 grams/second hot idle…what you can also do is look at both upstream O2 sensors under WOT…they should go FULL RICH…pretty close to 1000mv’s…they normally oscillate between 200-800mv’s at idle.
Thread Starter
Navigator
Joined: Aug 2024
Posts: 9
Likes: 0
171 174 codes
Can you access “Freeze Frame Data” with your scan tool ??…post all the numbers for either the 0171 or 0174…ok, so you smoke tested but look at your fuel trims at idle anyway…if elevated (more than 10%) run the engine at 3000 RPM and see if the fuel trims decrease…if they decrease you have a vacuum leak..if fuel trims are good at idle but INCREASE under load you either have a fuel delivery issue (fuel pump) or a bad MAF sensor…with scan tool the MAF sensor should read in grams/second the liter displacement of the engine…in your case 7.0 grams/second hot idle…what you can also do is look at both upstream O2 sensors under WOT…they should go FULL RICH…pretty close to 1000mv’s…they normally oscillate between 200-800mv’s at idle.
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Joined: Sep 2013
Posts: 15,601
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From: Cape Coral, Florida
