I hate throwing parts at a problem too, I always want to figure out the root cause. I think there are some other ways you can diagnose a bad cat that you can find by googling it. The fact that it does it under power is probably the most convincing evidence that it is the cat.

 

So a bad Catalytic convert would cause misfires, and my truck to run lean? I suppose if the oxygen sensor is picking up a bad catalytic converter, it will cause the lean code, and in re-turn cause the the cylinders on bank 2 to misfire being that they aren't getting enough fuel to burn. The fact that my truck is throwing a lean code almost makes me believe its a fuel issue, but like you said I hate to replace the cat, if it ain't bad. It doesn't smell like rotten eggs, but my exhaust doesn't put out a lot of pressure though when its idling or at least it don't feel like it, so I suppose that could be a clogged cat.

I am just so confused.. those codes should of helped a bit. I guess I am gonna have to dish out 90 bucks and go to the ford dealership and make them diagnose exactly what it is... My thing is I could go to the muffler shop, and have a pressure check done on it.. If it is bad then I'll get it replaced, but I am just wondering if its just bad because its got 128k on it, or if its bad because something else is wrong. Would the cat be causing all these other issues? I mean misfiring cylinders, and the system to run lean on one side but not the other?

 

The misfiring happens because the exhaust isn't scavenging. I think the lean code would have to be the o2 sensor. I bet the dealer wouldn't even test drive it for $90. I'd rather go to the muffler shop for the pressure test.

 

YouTube - Ford F150 Heres a video of my truck in action.

 

Catalytic Converters are both fine. Muffler shop tested them for 15 bucks. He said the unburnt fuel going through the catalytic converter is whats causing that. I thought it was running to lean? Meaning it wasn't getting enough fuel? Can the COP's messing up cause a lean code like the one I am getting?

 

If the fuel is not burning completely it also means there is more oxygen in the exhaust stream than should be. The O2 sensor should pick that up as a lean condition sensing the higher O2. If the mixture is reach there is not enough O2 for all the fuel resulting in a lower O2 signal from the sensor.

I would pull each plug on that side and look at the electrodes. I might also try swapping COP's between banks.

 

What modifications do you have on your truck. I was able to watch the video but I really can't tell what's going on.

 

its breaking up in the higher rpm/load range from what i seen. this is the same thing mine did with the bad plug but i got misfire codes for that plug only and no lean codes.

 

One thing you should do is reset the PCM. Just disconnect the negative battery cable and let it sit for like 20 minutes or something. Reconnect it and take it out. If it doesn't happen I think that will rule out the o2 sensor.

 

No mods. Just an H-Pipe Dual Exhaust. They Y off into duals again half way down. I got no mufflers.. The resonators and cats are both still in place. That is it. I have reset the pcm... I didn't let it set for 20 mins I don't think... but I let it sit for 5 mins.

I just had my plugs replaced. I got two plugs misfiring, they are Cylinder 7 and 8. This last time only cylinder 7 was listed as one of the codes. The lean condition is what is concerning me. If I was 100% sure that it was a bad plug or cop that could cause a lean condition, then I'd be more apt to check it. As it stands the plugs on these trucks break off in the cylinder heads, and even if they are brand new I wouldn't wanna try and mess with it to much, unless I was for sure.

I am leaning towards a bad COP on those two cylinders, EXCEPT the lean code. See if a plug doesn't get enough fuel to it, would it not misfire as well? Causing a misfire and lean code? The lean code was listed first I am pretty sure.

I have inspected the truck for vacuum leaks. The main purpose of that video above is just the popping you can hear it. It is defiantly messing up in the high RPM ranger under a load. I can drive the truck and keep my foot half way down on it, and take off pretty quick without the misfire, or popping sound. Sometimes the popping doesn't even happen, but I can let off the gas after stomping it, press it hard again, and get the popping and sputtering. Sometimes its excessive, and happens until I take my foot up, and keeps happening, other times it does it for a minute, and goes right on ahead and runs. It doesn't matter if the motor is cold, hot or anything. It still does it.

This has got to be the most annoying thing ever. The truck will spin the tires from a dead stop, it has no loss of power. There is plenty of take off, and in fact taking off the popping and sputter hardly ever happens, even if I floor it. It only seems to happen whilst going and stomping it.

So here is the verdict I have come up with.

The dealership lied about changing the plugs, and forgot to do it.
The dealership did the plugs, and but the problem is within the COP's.
The intake gasket has a leak around cylinder 7 and 8 and is causing to much oxygen for the fuel its getting, causing my lean codes, and misfires.

The fact is spark plugs get dirty, and usually when they do they misfire at idle, every truck I've owned when it had a bad plug, it messed up at idle. It ran rough. This misfire isn't present very long at all. I don't know much about this engine..

My main question is, can bad plugs, or bad cops cause a lean code?

 

Swapped 7 an 8 around with each other. Did nothing at all. I even cleaned them. The COP's look brand new. I know on my expedition I had, I had a misfire once on a cylinder, and I pulled the plug wire off, and sprayed some electronics cleaner in it, and black **** came out, and I put it back on and the misfire was gone. I suppose its very possible that my plugs never were changed out, because the cops had dirt on them like they had never been removed. I am beginning to wonder. This motor is very interesting to me. Any vehicle I've ever owned when the plugs mess up, the motor idles rough. It doesn't sputter and pop only under a load. This seems more like a COP's issue or maybe something else entirely.

I wish someone could tell me if bad plugs or bad cops could make the engine give me a lean code on that bank?

I mean if the plugs weren't burning the fuel thrown at it good enough, wouldn't be to rich? Or maybe the plugs are burning it but its not good enough and its getting to much oxygen?

This is where I am confused. All these 5.4L's and no one really knows the answer to this. My thing is I don't see it being an injector, or fuel rail. I am utterly confused as to what to replace, because I don't know what it could be...

 

im with you on the bad plug causing a rich situation not lean and thats what was causing the popping on mine i think when the unburned gas would light in the exhaust. when mine was messing up before the plug change it would idle fine also. next time ask to get the old parts back after work has been done at the stealership.

 

they could have cracked a new plug going back it.

 

Well I have a lean situation. The PCM is throwing a code that clearly states its to lean on bank 2. If the plugs weren't working right, wouldn't they be the fuel be to rich? This almost seems like an oxygen issue. I am beginning to think I do have a in-take gasket leak. Which could also mess up under a load, maybe the seal is good enough to work at idle, in park.

I don't know what it is. I just know that the truck is running to lean according to the PCM. When it throws a code its usually Cylinder 7 or 8 misfire, or sometimes its multiple cylinder misfire, and then its a lean code on bank 2. Its only on bank 2. So its not a weak fuel pump, because then Bank 1 would be doing it as well.

It could be the plugs as you stated but every where I talk to tells me 3-4 different things.

 

i think you can spray brake or carb cleaner in the ? area and it should change the idle for a few seconds if it is leaking. ive done it on older engines and works fine but i dont know for shure on the mod motors