2001 5.4L. Service Engine Soon light on. Code reader says both banks running lean. I have researched and worked this truck to death looking for the problem. MAF is good. DPFE is good. PCV is good. IAC is new. Upstream oxygen sensors are new. Sprayed starter fluid everywhere looking for an intake leak. Nothing. No vac line cracks or holes. Fuel filter & pump check good. When I put the new IAC in, I disconnected the battery to clear the code. I thought I had it fixed because no code. Then at 250 miles, it came back. I am at a loss. Any ideas? Arggg.

 

A common cause is the manifold seals & bolts. The leak could be in a spot that you can't get at with starter spray. I think Cometic Gaskets has a kit available. All seals, o rings etc. Since you're getting a lean code on both banks, its a good bet this is where your trouble is. Also how are your cats? they can start to clog up. I don't know if this would cause a lean cond.

 

I am told that if it was the cats, the code would somehow reflect to downstream oxy sensors. I hate to have to re-gasket the intake. Sounds like a lot of work. But I will google that kit. Thanks.

 

Are you running a CAI....with or without a tune? I had an issue with my old Titan running lean a lot because of my custom intake? Fried one cat, and I had a Jet chip as well. Headers, Mass Air flow sensor, etc.. Each time the check engine light came on it was like the left bank (cat)? I had a Ram Air setup....so, I had to put the lid back on the air box. Finally sold it and got a 14 F150.

 

No. My truck is all stock. Has 180,000 miles. Never had any problems until now.

 

Just sounds like to me the cats are just worn out. I think the shelf life is like 100k. So, new cats and or just sensors. :fingerscrossed:

 

But how could they both wear out within minutes of each other? The code says both banks are lean. That seems to me that it would be an upstream problem. But I'm no expert, that's why I'm asking.

 

I think the cats get plugged up and it messes up the ECU. You've got a lot miles on her, maybe take the cats off? I know it won't pass emissions....but could be fun. The Titan was like that at 90k. Had to cut her from the heard!-lol Or just shop around for the least price on the cats... :tossup:

 

I spent hours looking for a leak by spraying starter fluid around every nook and cranny I could find. Nothin. Going to take it to get smoke tested this Saturday. This is really baffling me.

 

The intake manifold gaskets (O-rings) basically are the most common cause and you likely can't find the leak because when the engine is first started but still cold they will suck air in for the 1st min or so of closed loop operation, that is where the code is coming from, once the engine warms up a little the plastic swells and seals the leak, I can't count how many of those I did working at the dealer for the very same reason.


Your cats will NEVER give a lean code nor will they cause one. Change your manifold gaskets as instructed above.