My 1997 F150, 5.4L engine, has a CEL on and code scanner read 1131, lean bank 1, sensor 1. I have done a search in these forums on this code and many of the posts read something like this:

"I changed the O2 sensor and cleared codes. Light came back. Then I changed the DPFE sensor. Light came back on. Then I cleaned the MAF, then replaced the MAF, then the EGR valve, then the brake fluid, then the blinker fluid, the ashtray, the left tailight, and finally, the harmony balancer because I thought maybe the truck was out of harmony. It cost me $35,697, and I thought this was a bit much since its only worth about $5k. Light is still on. What should I do next?"

Ok, maybe that's a little exagerrated, but not too much. So I have questions about how to figure this out methodolically, without changing everything under the hood.

First, vacuum leaks. PCV elbow - would a leaking pcv elbow cause this? Seems that it would cause a problem in BOTH banks, not just one.

Second. I'll clean the MAF, but this also seems like it would cause it in BOTH banks.

Third. I am going to clean the TB and all EGR ports associated with that.

Are there vacuum lines that would cause problems with only one bank that might be leaking? The truck runs decent, but has terrible gas mileage (8-10). I will likely replace both front O2 sensors because the truck has 115k miles on it and it is probably time. But I want to do it for that reason, not because I am trying to solve the CEL by throwing a bunch of money at it.

It also seems to me that if it is in fact the O2 sensor that is bad, I should be able to swap my sensors - put bank 1 in bank 2, and vice versa - and I should then get a lean code, bank 2, sensor 2. Please confirm this is correct.

A couple months ago I had a different code - I don't recall the number - but it was "bank 1 O2 sensor, slow to respond," or something to that effect.

Thanks in advance for any advice you got (unless of course it is that I really must change the blinker fluid).

 

I would be looking at a fuel trim problem. Pay the money for a diagnostic scan in mode6 by someone who is familar with Fords.

 

Look at the code/s you now have. They/it may have changed and you don't know it.
If still a 1131 for one bank only,
consider the following: electrical short to VPWR in harness, open or shorted in OX sensor leads, damaged PCM, leaking fuel injectors on one bank, plus other assorted possabilties.
Shot gun approch spends money and unlikley to get the problem unless there is a high degree of luck.
Come see me. For headaches, I replace toes, then feet, fingers, then arms, ears etc.until you hurt so bad, you would be happy to just have a headache.

 

^^^^^^^^^^^^ gotta love the logic ^^^^^^^^^^^

 

For a P1131 (Bank 1) or a P1151 (Bank 2), it's usually (but not always) the upstream O2 sensor on that side. These two codes are usually pretty accurate on identifying slow, lazy, or wornout sensors.

I'd suggest going with the odds and replacing the upstream O2 sensor on the passenger side especially if your O2 sensors are original.

I doubt you'll need the blinker fluid or a new harmony balancer this time.

Steve

 

Seems like a search in these forums for code 1131 revealed one thing - most people FIRST replaced the upstream O2 sensor, and then within X miles (usually 5-20), the light came back with the same code. Just trying to avoid that scenario.

 

I don't think so.... You're likely confusing these two codes with the common "lean" codes".

However, since you seem to be inclined to do the least expensive stuff first (can't blame you), I'd suggest cleaning the MAF sensor and a thorough inspection of the PCV hose assembly, especially that elbow on the firewall side.

Do you happen to have the freeze frame data from the fault code(s)?

Steve

 

Cleaned the MAF sensor earlier tonight. Didn't really look like it had anything on it, but I did it anyways since others here have said it will have dirt on it even if you cannot see it. I also disconnected the battery for about 40 minutes so code should be clear. I also have a pcv elbow waiting for me at the dealership. This is more of a "I think it should be replaced" item than a "I hope this fixes all my problems" item. We'll go from there. If it is back, I'll have it read again, then maybe swap the O2 sensors with each other to see if goes over to the other bank.

 

Cleaned the MAF last night and disconnected the battery for about 40 minutes (sort of forgot about it, and then remembered to go back out and connect it).

Drove it to work this morning, no CEL. Usually it would come on pretty quick, so maybe a good sign. Or maybe I need to drive it a bit more than the 8 miles to work so it has a chance to cycle through, then give me a CEL again?