ok folks so 3 weeks ago I bought a 99 4.0 4x4 ranger that had some issues... so here’s the run down

issues when purchased
1. Would not reach operating temp at all
2. Check engine light. Mis fire codes and both banks lean
3. 4wd not working

to address these issues this is where i started after reading ever possible thing I could find

i replaced the thermostat and flushed the coolant system - this fixed the temp issue

found out that the auto hubs are bad - need to replace auto hubs. Gunna put manual hubs on it.

now for the cels.... I did a plug and wire change and found the 2 plugs had cracked porcelain around the center conductor... once new plugs where in I put K-Seal in the coolant figuring it’s a blown head gasket.. motor hasn’t thrown a misfire code since and isn’t loosing coolant.

the lean codes I have addressed as this- I put an upstream bank 1 o2 sensor In it. Then cleaned the maf sensor. Put a new iac Motor on it. Check the fuel pressure which is perfect. And have checked all vacuum lines for leaks. I also replace the upper egr tube gasket and o-ring and while doing that I vacuum checked the egr valve it’s self and it is good.

motor runs great and when on a live time scan tool the short term trims are great when your driving the truck... the trim values are high (meaning it’s sensing a lean condition) when the truck is at idle.

i think I have covered everything I have done and I’m beating my head agains the wall trying to figure this out... the one thing I haven’t done is the intake gaskets but I do not like throwing parts at a vehicle... other then propane or carb cleaner I haven’t figured out any other ways to check for leaks in the intake gasket.

any suggestions on a direction to head?

What’s making me think that it has/had a blown head gasket is when I did plugs and wires on it.. it had 2 plugs that the porcilane around the center conductor was cracked... so I figured coolant got in there and cracked them because of the temp difference... also the short temp fuel trims are now only out when the truck idols and I get a random misfire code when it’s cold out and I’m letting the truck warm up.. once it’s about warm it will get a rough idol and stall...

do a compression test. If you have two low cylinders side-by-side, you have a bad HG. If you have one or two cylinders low, it could be a HG leak into a water jacket, but that will take some more diagnostics to confirm. I’d also pressure test the cooling system to check for leaks, were you loosing coolant? Were the broken plugs really clean, like "steam cleaned" clean?

sparkplug damage could be from carbon build up, or even just fatigue from age and/or use

The plugs looked super clean like the motor was running lean... not sure when he last did a tune up and lol I will do a compression check... other then having bad STFT outta wack when idoling the truck runs great... just drive it 270 miles and it got 18mpg on the highway