Need help '04 5.4 3v running lean
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Joined: Apr 2004
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Need help '04 5.4 3v running lean
I've got an '04 f150 5.4 3v that I was told needed new cats and had code p0420. I replaced all 4 cats and put 4 new o2 sensors on. When I first test drove the truck it ran fine until underload in overdrive, then it would buck and start to miss. From here I watched the live data on my scan tool and it looked my MAF wasn't reading the right lbs/s so I replaced that along with the dirty air filter and fuel filter. On my next test drive the truck responded the same way. I can get the truck to throw a pending code of p0171 and also just got a p0302 so it seems my problem is on the passenger side. My short term fuel trims look good at idle and I sprayed looking for any vacuum leaks but found nothing. My last thoughts were possibly a bad injector, bad plugs or coil pack. Any help is greatly appreciated.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Gee, what a huge amount of pi$$ed away money on wasted parts. You'd have been better off taking it somewhere for a professional diagnosis in the first place.
You do NOT have an engine running lean, you have an engine that is running rich plus has a misfire. Spraying and listening doesn't work, the computer is too fast.
Fix the misfire first.
You do NOT have an engine running lean, you have an engine that is running rich plus has a misfire. Spraying and listening doesn't work, the computer is too fast.
Fix the misfire first.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
Zero in on the #2 misfire first.
Are all cylinders misfiring or just #2?
If just #2, easy test for bad COP is swap it with #1.
The coil is probably good, how are the boot/spring?
How many miles since the boots/springs been changed?
Are you getting 12v thru the coil and injector lines to the PCM.
The PCM is going to ground the 12v power for the coils and injectors so the 12v should go all the way to the PCM connector input pins.
Are all cylinders misfiring or just #2?
If just #2, easy test for bad COP is swap it with #1.
The coil is probably good, how are the boot/spring?
How many miles since the boots/springs been changed?
Are you getting 12v thru the coil and injector lines to the PCM.
The PCM is going to ground the 12v power for the coils and injectors so the 12v should go all the way to the PCM connector input pins.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
The quality of the responses you get are going to be directly proportional to the quality of the information you provide. If you provide lousy or incomplete information, guess what type of response you're likely to get....
Fleet Mechanic
Joined: Aug 2002
Posts: 1,899
Likes: 29
From: Raleigh USA
A misfire can cause lean codes. The O2 sensor picks up the unburned oxygen and the PCM interprets that as running lean. O2 sensors read oxygen, not fuel. Lean=leftover oxygen in the exhaust that didnt get burned, rich=no oxygen in the exhaust from total burn.
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