About 300k its misfiring pretty bad. Rough idle, sluggish, doesnt want to really go down the road. Inspection and registration is due this month
@TexomaExplorer
From your first post, it didn't sound bad; I figured you were just burning some oil.
The low compression in Cyl #4 can be expected due to the fact that you were getting a HOT coolant & water mixture into that cylinder, which was "steam cleaning" off the protective oil barrier in the cylinder, thus slowly killing the compression ring as there was basically contact of metal compression ring to metal bore of the block - BOTH of which had no protective oil on their surface...
Moving on; I can only assume that since getting the misfire condition, you have checked the wires are connected to the correct plugs.
NOTE: So I'm just spitballin' here; EARLY explorers with the original coil pack had the corresponding cylinder printed next to the spark plug wire port.
AND the original early OEM/Factory coil pack (if you're still running it) had two (2) of the ports are numbered different from the later coil packs.
It was common, early on, when guys pulled all the plug wires, and refitted them ACCORDING A MANUAL (meaning without checking the coil pack) they got the firing order wrong.
So if you're running an original coil pack, check the spark plug port numbering.
How about this; just throwing it out there. Have you ever changed the Camshaft Position Sensor Assembly (kind of pricy and a pain in the butt to change - but you'd get a chirping sound from under the hood if it was going bad) or the Crankshaft Position Sensor (really cheap and easy - plus the "pick up magnet" in the aftermarket offering is WAY STRONGER than the factory oem sensor. Due to their location, these frequently go bad due to heat, vibration, and road grime/weather - $12 - 14 bucks at Rock Auto for a Standard Motor Products offering. Many times these go bad WITHOUT giving a Check Engine Light. Due to the low price, and ease of replacement (maybe 10 minutes underneath) it's worth a shot.
Another thing I'm thinking is if everything ran A-OK after your head swap, meaning no misfiring, and then later down the line - say two-three months - your engine started misfiring (without you changing any parts) I would start wondering if you have a coolant leak.
Regarding the head swap operation: It's essential that your "work surfaces" (heads and block) were properly prepped (completely removing the old gasket material from the block surface, and then the block surface cleaned with a polishing wheel, followed up with a wipe-down of Acetone) As well as wiping down the gasket surface of the new head with Acetone. Also, there is the Torque To Yield head bolts and the extra 45 degree tighten down.
Also, the aluminum intake is held down with 8 bolts at a relatively low torque. The corresponding holes in the top of the block block should have been cleaned out of oil with compressed air, and q-tips dipped in acetone, followed up again with compressed air. Then, when installing the intake, using Loc-Tight Blue on all 8 bolts. The final thing to do is to witness mark the top of the bolt to a spot on the intake manifold, so over the long haul you can visually see if the bolts are loosening up.
Anyways - all this is the long way to say that you should make a witness mark on your overflow tank, and carefully watch for coolant use.
But the way it sounds from your 2nd post - your Ex is basically not able to drive any distance or?
Seriously - I'm having to do a LOT of speculating in my post because I don't have a lot of info to go on from the two posts.
I'm hoping to get you running and passing your upcoming inspection
