leefire

I have a 2003 f-150 lariat and i'm having the same issue. mine started monday while driving in a heavy rain storm. I thought i just got a coil a little wet. It started running rough and missing. This morning I plugged it up and had these codes...(PO171 SYSTEM TOO LEAN "BANK 1"), (PO303 #3 MISIRE), (PO307 #7 MISFIRE) I cleared the codes and test drove it. The truck ran fine until it warmed up and then it started again. I'm thinking maybe coil packs #3,#7 , but after reading this forum I don't know anymore. What would cause the bank 1 too lean code? THANK YOU FOR YOUR HELP.......

livelifefreely

I have a 2004 but had the same problems. I changed everything over the last several months. New plugs, coils and catalytic converters (1200.00) and it didnt solve the problem. A new shop I went to tried something different. I was throwing PO305 and PO306 codes. They moved the plugs around and cleared the codes. Drove it for a day and no codes in 5 or 6 but new one in 1, so they determined it was the plugs. They also found TSB 08-25-4 that talked about the same problems that they were seeing. They changed the plugs to the recommended PZT-14F and it solved all of my problems.

echols85

I have a 2003 Ford f150 5.4l Triton fx4 it h as 330000 miles it had a 5&6 missile ,bad egr, & lean file mixture codes. So I have changed the egr valve,the coil,boot,&plug on 5&6 and it's still jumping and when it heats up it has a knocking sound coming from the exhaust. When I give it gas it sounds like it is sucking air. I am at my whits end and out of money to keep putting in it my next step is a new motor I need help

W00dy

I am aware the original post is antiquated but, I was curious what the outcome was. Fellow posters, please understand, I mean no disrespect to anyone, in any way. I hope to be of help to someone.

- (at least as a 'worst' case) blown/leaking head gasket(s)? It wasn't really mentioned much.
My take, I believe (purely speculation), a slight leak in head gasket(s), causing weak compression. At low RPM's, too much O₂ delivered to cylinder creating a lean condition/misfires/odd noises. When tach-ing up, a 'fuel dump' occurs, which seems to 'alleviate' the symptoms. Maybe, because the leak can't keep up with the accelerated demand. Just saying.

When hearing things like exhaust/vacuum leaks, I would consider a compression test.

Just more of my 2¢ worth (if I keep this up, I'll be in debt )..
As an electrician and generator technician (fleet 'mechanic' [more like, fleet parts changer]), when dealing with a real head-scratcher, I would also load test the cranking battery and check the charging system. Especially, if codes don't seen to 'match' each other (ie. random stuff).

Just a few notes
-flashing MIL = 'limp' home mode (ECM/PCM has shut down all affected cylinders' COP's and injectors).