Cylinder 3 is misfiring and I'm starting to run out of theories

[fyyffky]

SO I picked up a 1998 Mazda B3000 4x4 3.0 with 165k miles pretty cheap to drive back and forth to Lowe's. Of course it has issues but this isn't my first Ranger and I'm fairly mechanically inclined. It is however my first 3.0 (the rest were 4.0's) I'm really confused about cylinder 3 which has to be my rough idle/misfire. It fires right up when I crank it but its definitely misfiring. I wish I would have compression tested it prior to doing the KOER test tonight. KOER test didn't give me much because I already knew the O2's which are from the gutted cat. Oh, no CEL, no stored codes, nothing.

So far and not necessarily in this order....

It already had new wires and pretty new plugs (Champion copper plus) BUT when I pulled the plugs to check them number 3 came out looking like it had just been installed but it did have a faint smell of fuel to it. Another had a crack in the insulator (probably from installation).

All 6 plugs were replaced with Autolite platinum.

Swapped out #3 plug wire with another which made 0 change.

Checked vacuum lines using carb cleaner (including throttle body gasket, intake gasket etc) and replaced the broken, cracked or ugly ones.

Cam synchronizer was obviously the original so I pulled it and swapped it out, per the majority of the instructions and videos out there and the same way I've ever swapped one really. This was the first time I used an alignment tool though but I wouldn't think that using that would throw it off.

New PCV

New air filter

Cleaned MAF

Cleaned IAC

Cleaned throttle body

Gutted the clogged cats

Coil primary and secondary test good.

No bubbles in the coolant

Nothing in the oil

Injectors test good on 1,2 and 3.

Hopefully Saturday I can test the compression and trying to fool the O2 with anti fowlers until I can get the time to weld at least one cat in. I'm not a fan of throwing parts at problems and the parts I have replaced probably would have been done misfire or not. I guess depending on what you guys think and what the compression test says maybe I'll pull the #3 injector and see if it looks like mud stuck to the end of it of something. I'm starting to run out of options!

I would love to hear what you guys think. I've trolled this site for reading material for years but this is my first time posting... or having an account.

 

[Cemeteryxgates]

Check for valve seat recession the 2005+ 3.0's were notorius for it but it way have happened on yours if it's been overheated

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[fyyffky]

Can recession be checked without removing the head? I assume that is going to cause low compression but is there anything specific that is going to say bingo that it right there!

 

[stmitch]

Injector failure isn't uncommon after a 3.0 gets past 150k. Go ahead and do the compression test and post the results though as it can help point us in the right direction. Also, I'd check for a broken valve spring before I bothered looking for an issue with the valve seat.

 

[Cemeteryxgates]

Can recession be checked without removing the head? I assume that is going to cause low compression but is there anything specific that is going to say bingo that it right there!

Leakdown test will show it it happens on the exhaust valve

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[fyyffky]

That's the plugs when I pulled them out and are not the plugs that are currently in it. I may try to test the compression after work tonight. I really appreciate the comments.

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[modelageek]

Sounds like it could be the burnt Exhaust valve issue. Does it come and go? Is it worse when idling and get better as you drive? Do you know if it's the original engine?

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[fyyffky]

It's always there, just feel it less as RPM increases. Pretty certain it's the original engine.

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[fyyffky]

Well I think I found the answer that I didn't want to find. 1 and 2 are right at 160 and 3... nothing. Not 80 not 50... as if I didn't even screw it in.

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[modelageek]

At least you figured it out. Hope you didn't pay too much for it?

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[fyyffky]

I've got about 650 in it. I assume if I swap the head out I'll be ok?

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[modelageek]

Well I think I found the answer that I didn't want to find. 1 and 2 are right at 160 and 3... nothing. Not 80 not 50... as if I didn't even screw it in.

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Any rust on the truck? Auto or 5 speed?

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[fyyffky]

Auto, 4x4 with the desirable vacuum hubs lol

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[modelageek]

Auto, 4x4 with the desirable vacuum hubs lol

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If you pull the heads you'll at least know without spending $$. I bought heads from Dover heads in Atlanta GA.

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[fyyffky]

There's a pretty good machine shop close to me I'm hoping their salvageable. What did they run you?

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