Hello, I have a 2006 3.0 that has a nagging misfire and o2 sensor problem. I have done all of the following:
New plugs
New wires
New coil pack
New O2 sensor
New fuel filter
New injectors
Compression test: cyl 6 @ 105

The o2 sensor keeps causing a solid check engine light, even though it's new. I have a crack in my driver's side exhaust manifold, but not sure if this is causing the misfire as well. I'm going to swap it out after tomorrow. I will update on if this resolved P2272 issue.
Regarding the misfire, I just had the heads replaced about a year ago. I don't expect this to be the issue. Also, I've had some recent shenanigans with the crash detector switch cutting off fuel to the engine for no apparent reason. I just need to reset the switch when it happens, then I'm good to go. Otherwise, I have a random flashing cel, things get shakey, I lose power, then give it some gas and it comes back to normal.
After replacing all of the parts listed above, the truck runs GREAT!!! I just cannot shake these codes.

Please let me know if I can provide any additional information. Thanks!

 

Welcome to the forum

Answered this at the other Ranger foruim

Do compression test for all 6 cylinders, cold engine test
If any are lower than the rest, then add oil to those cylinders then retest
If low cylinders do NOT come up to the average of the others then you have a valve issue in the lower cylinders

If your average compression is 140psi, then any cylinder lower than 126 is bad, 10% difference

2004 to 2006 Rangers with 3.0l Vulcan engines had recessed exhaust valve seat issues, causing intermittent compression issues

 

Thank you. I'll try that tomorrow and update.

 

So, compression tested all cylinders and 6 is low. Wet test showed a slight improvement in compression, but there is definitely an issue with #6.
I'm thinking about getting a brand new head for that side, but there are a lot of options. Can anyone offer advice on a reliable brand? Also, any brands I should avoid?
Thank you

 

Replace both heads or you will have problems with the other head before long, it was a parts issue, both heads got the same parts

No recommendation for a brand

 

Thanks @rond . When you say "was a parts issue" does that mean new heads will have resolved the issue from the past?

 

Yes, Ford engine assembly plant got undersized exhaust valve seats, as far as I know, these were used on 3.0l engines assembled in 2003 to 2005 so effected 2004 to 2006 Ranger model years, its not a 100% failure so no recall, just a TSB for service departments

Unless you buy USED heads from a 2004-2006 Ranger then I can't see an issue, it wasn't a design flaw it was a parts flaw
You can even have your heads rebuilt, basically a Valve job
It just takes longer to get truck back on the road

Usually when you buy heads there is a Core Charge, because they want the old heads to rebuilt and sell

 

I bought a NEW set for my wifes 1999 3.0 off eBay from the seller ispe661. They arrived fast and were a perfect swap. And no upfront core charge. They give 21 days to return your used heads.

 

Update: My last mechanic said he had both heads sent to be machined in 2018. He doesn't think it's the valves, he said it's probably the rings or hydraulic lifters. Does this sound accurate?

 

If the wet test showed only a slight increase then most likely it's valves. The wet test seals up the rings.
It is hard to say about the machine shop. If there is paperwork to show the valves and seats were checked and/or replaced that is one thing. It may even be a slightly bent valve for some reason. Unfortunately there is only one REAL way to figure it out and that is removing the heads. If you can afford the down time you can remove them and take then to a reputable machine shop and have them inspected. They usually charge about $100 to clean and inspect and pressure test.