tracking down P0174
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Senior User
Joined: Mar 2013
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From: Ocala FL
tracking down P0174
Trying to track this problem down. Truck is a 97 Expy 5.4. Code popped up yesterday right after I left for work about 1/2 mile from the house. Just got back last week from a road trip of probably around 1700 miles. I knew it had a minor exhaust leak on the driver side so fixed that today but that didn't take care of it. About 9,000 miles ago (when I bought it) I cleaned MAF, IAC, TB, checked all vacuum lines, new air and fuel filter, plugs, O2's, etc. Checked all vacuum lines again tonight but everything seems good. Checked LTFT on bank 2 and it's around +20. Bank 1 is normal. Truck runs and drives fine. I held the RPM in neutral around 1500 and noticed it would sputter a little bit randomly on the driver side (true duals). RPM in gear or park varies within 20 RPM on the scanner. I'm going to get the propane out tomorrow and check the manifold (hope that's not it!) but was looking for any other ideas. Everything I find online includes P0171. Thanks.
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From: Ocala FL
Thanks for the reply alloro yes I did remove that this morning and checked it and all is fine. I also tried the propane/carb cleaner around the intake manifold and vacuum lines with no change. Put a screwdriver up to the injectors and could hear them clicking. I was watching the fuel trims and although ltft was +20 stft was -20. Wondering if the fixing the exhaust leak fixed it (it was at collector) and it just hasn't gotten back to normal range yet. Should I disconnect the computer to reset the fuel trims and see what they read then?
Fleet Owner
Joined: Apr 2008
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Since you've confirmed there are no vacuum leaks then that random sputter out of the driver's side exhaust could indicate a slight misfire or a leaking exhaust valve. Either of these will also throw a lean code and also will throw off the fuel trim reading. You could next do a compression test on the driver's side and/or turn on the live data feature in your scan tool and go for a drive. The live data will count any misfires per cylinder and help narrow down where you need to focus.
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Senior User
Joined: Mar 2013
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From: Ocala FL
Ok I went ahead and reset the pcm and drove it about 20 minutes. So far fuel trims are all staying within 5%. The slight sputtering on the driver side at 1500 rpm seems to have stopped. I'll drive it around and keep an eye on the fuel trims and see what they're doing. Unfortunately I don't think my scanner shows a misfire count when showing live data. If it does I can't find it. Don't have time to do a compression test today but maybe can in a few days.
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