So I had my CEL come on the other day, and the truck continued to run perfectly. I immediately thought oxygen sensor is bad. I pulled into my nearest auto parts store and had them pull the code. I mentioned as the guy was going through the scanner while it was hooked to the truck that I thought it was an oxygen sensor. Anyways, right after I got "sensor" out of my mouth, he said "yep your right" and unplugged the scanner. I asked which one, and he said both. I did not get the actual codes that it pulled up. I left and got on rockauto.com when I got home to order the sensors, and realized that they have an upstream and downstream sensor. I replaced one of these on my old GMC truck a few years back, and I seem to remember it having 4 O2 sensors (upstream and downstream on both sides). I may be totally way off on this, but I've only had to replace one at a time before and have always assumed that there were an upstream and downstream on both banks. Do these trucks only have two? If I have to, i'll go get the exact codes and change them accordingly, but I figured I would check on here first to make sure that there weren't just two of them. If so, I will just replace them both and be on my way.

Thanks in advance

 

first thing to do is clear the codes, and see if they come back. there a 4 O2 sensors, one before the cat on each side, and one in the cat on each side.
and they are not cheap either.
if i remember correctly, it was close to $350 for the 4 motorcraft O2 sensors two years ago.

DY1193, ford part # 8F9Z9F472J upstream, before the cat
DY1181, ford part # BL3Z9G444B downstream in the cat.

and don't be surprised if the codes come back after replacing the sensors. if the truck needs spark plugs, it will load the cats up with unburnt fuel burning them out which will cause the O2 sensors to turn the CEL on.

 

 

Not under .100k. I'm sure it needs spark plugs. Looks like I have some work and money ahead of me.

 

plugs are not that bad to do if you have the time and patience. the lower rears are the worst, it is easier to access them through the wheel wells.
i changed plugs at 93,000 miles, and only has one firing 100%.if i remember correctly the others were 3 at 60% 8 at 50 %, 4 between 20 and 40%, and 2 that were completely dead.
luckily i had at least one semi working plug in each cylinder.

 

Yeah, the truck doesn't seem to be having any issues. Runs like a sewing machine, so I'm sure the plugs aren't that bad, but I am going to change them anyways. The CEL light went back off today. It is snowing here right now, so I won't be doing anything to it this weekend. Drove it 37 miles to work in this ice/snow mess, and it ran great. 4x4 worked flawlessly, etc. I'm not too overly worried about changing the plugs. I've done it on tons of vehicles. Some of them were real bears to get out, so I have all the tools/extensions to remove them. I do need to go get the codes pulled again when the CEL comes back on so that I can figure out which O2sensor is bad.

 

mine purred like a swiss sewing machine too.
that was why i was so amazed when i hooked up auto enginuity and saw over 400,000 misfires detected.

it runs even better with the new plugs and cats.

 

there is supposed to be a way to use some of the better scanners to read live data to determine cat problems and stuff

 

if you get PO420 and PO 430, or maybe it is 421 and 431. that is low catalyst efficiency, which means the cats are bad.

 

I'll keep that in mind. I usually only drive it on Friday's (drive my beater most days), so if the CEL is back on when I drive it, I will take it and get the codes pulled again and get the numbers this time.

 

This time don't tell the guy what you think the problem is. Wait until he tells you what the codes are.

 

Here's how this plays out ...
You can guess or you can know.
Guessing is up to you; most people are really good an taking a SWAG. Doesn't always end up well, though.
Knowing means investigating and researching; many folks end up not wanting to put the time into this approach.

Get the actual codes, and clear them. If they reoccur soon, it's likely that you'll need to replace items very soon.

Here's what happens and why. The 6.2L engine is an "over-square" engine; it's bore is larger than the stroke. Much larger in fact. That's why it revs so easily. And over-square engines have lower stress for the total displacement because they have lower piston velocity contrasted to other designs. Lower piston speeds means lower stress on the pistons, con-rods, crank and all those bearings. The one downside is that a large-bore/short-stroke engine does not have a very even flame front propagation. To improve this, these engines often have two spark plugs to get a better combustion effect. As those plugs wear down with use, they lose efficiency. That in turn makes for a less complete burn. That results in more un-burned or incompletely burned fuel going down the exhaust. Way back 50 years ago, over-square engines didn't have cats to worry about, so this fuel effect didn't matter. But nowadays it does. So the cats today get an overdose of hydrocarbons when the combustion is less than optimum. That also results in O2 sensors getting dumped on. It's all inter-related.

I am not a fan of over-maintaining stuff. Doing stuff more often than necessary is a waste of time and money. But in this case, Ford's recommended 100k mile plug changes are probably not set to an interval that makes good sense. Whereas the plugs themselves might last to 100k miles, their degraded state can cause other issues down stream. This is one time where changing plugs more often than the OEM spec is probably a good idea.

If you think 16 plugs and 4 O2 sensors are expensive, wait to you get the bill for the cats !!!! If you change the plugs and O2 sensors now, you might just save yourself the cost of the cats, if you're lucky.

Keeping the plugs in top working order will safe the cats and O2s from abuse. 16 plugs are a lot cheaper than the other items. I have no data (no proof) of what is an appropriate interval, but somewhere between 50k-75k miles would be a good place to start for plug changes. And make sure to buy the best you can afford; get double-plat or even iridium if you can as they will resist degradation longer.

 

cats can cost $300 for high flow, to $2300 for the proper ford units.
99% of aftermarket cats will not meet ford specifications and will throw a low Catalyst efficiency code.
same with the high flow cats. the only way to turn off a low efficiency code is to have a tuner write a tune to compensate for the aftermarket cat.

 

I really don't think it is having problems with the cats. If that were the case, I feel like the O2 sensors would be giving faulty readings all the time hence constant CEL. I've done my research, and know how to change the plugs and the O2 sensors. Neither of which seem to be ridiculously expensive (60-70 for 16 motorcraft plugs, 40-50 a piece for O2 sensors). I don't mind working on it, I just would like to get the exact codes before I start throwing parts at it. Like I said, it has only came on two or three times since I have owned the truck. I just have not had a chance to catch it in the act with a scanner until the other day which was short lived because the CEL is now back off. I will get the exact codes the next time it comes on which could be quite a while since I don't drive it that much. In the meantime, I will go ahead and throw some plugs in it, because I am sure it needs them (doubt they have ever been changed), and lay in wait for the CEL to come back on and get a scanner hooked back to it to see what the codes are.

I appreciate your information about 6.2L engine and about it being "over square" (i did not know anything about all that). Everyone just always seems to go straight to the worst case scenario on this forum when it comes to troubleshooting...LOL.

 

I have used non-foulers on Dodge Chargers for the aft cats O2 sensors and the codes go away and stay away.
The 0420/0430 on mine have been gone a while now.

The non-foulers put the sensors out of the exhaust stream and no more codes.
Not sure on FoMoCo stuff though.

Griz