2.9 sudden vacuum drop, misfire

[capridude]

Trying to smog '87 Bronco II 2.9 5speed 4x4.
The engine is self-rebuilt with 33k miles. Replaced/renewed almost everything.

The idle vacuum is 15", steady. Used to be 20". Even-misfire at tailpipe.
Ignition timing is correct. Valves are quiet, seem to operate fine, lots of oil.
Fuel injectors all work fine. #4 cylinder has lower exhaust temperature (210)
than the others (300-400). Removing #4 fuel injector electrical connector has
VERY little effect of engine running, maybe a drop of 0.5" vacuum. That cylinder gets same spark as other cylinders (but they all seem a weak yellow).
#4 compression is 75/120psi (first pulse/fourth pulse), while neighbor cylinder
#5's compression is 100/150psi.
My only ECU code is 32 (Egr valve not opening enough-- egr valve disconnected for the troubleshooting anyway)

It seems unlikely that one lower cylinder would cause a 5" vacuum drop.

I have two ideas left: failing coil/ignition; and mechanical timing jumped a
tooth on the cam. If it jumped a tooth, would the computer be able to compensate to get a correct ignition timing?

Anybody have any other ideas?!

Cheers, Jeff

 

[WildSide]

The chain would not jump if fairly new unless you messed up royaly. Whip another coil on there and do a leakdown test for leaky valves.

 

[IMenriched]

Yeap..think'n that the #4 is abit too low, just barely within 20% of the others....compression leak down...& or check for exhuast gasses in the coolant.