I am puzzled.

Rebuilt 2.9 has 33k on it. The #2 cylinder seems to be dead; engine vacuum
used to be 20, now it is 15. Using an infrared temperature gun, all other header
pipes show 350 degrees, #2 is 140.
Quicky compression test in #2 cylinder (throttle closed) was 125.
Voltage to fuel injector at idle was .5volts (same as #1 cylinder)
Spark plug wire is zapping good.

Replaced fuel injector. Replaced spark plug. No stored codes other than '32'
which concerns the EGR valve control. I disconnected the EGR diaphragm
vacuum line too.

#2 still seems dead.

Any ideas?!

Cheers, Jeff

 

stuck/leaking valve, either intake or exhaust. or burned exhaust valve.
weak or broken spring, stem slightly bent, push rod collapsed on end, lifter bad or a chunk of junk trapped on valve seat.

new cam or regrind?

check for valve leak wooshing sound in intake and exhaust while cranking over.

can try tapping the top of the valve stems with brass hammer to dislodge any debris.

 

Turns out it is the #4 cylinder (on my ancient GMC V6, it's #2).......

>stuck/leaking valve, either intake or exhaust. or burned exhaust valve.
>weak or broken spring, stem slightly bent, push rod collapsed on end, lifter bad >or a chunk of junk trapped on valve seat.

All looks good, cranking or running (running was brief, lots of oil!)
The stainless valves are adjusted properly, and make no noise.

>new cam or regrind?

Camshaft replaced on rebuild with Camcraft "rv" cam.

>check for valve leak wooshing sound in intake and exhaust while cranking over.

I haven't noticed this-- is it a easily noticeable sound?

>can try tapping the top of the valve stems with brass hammer to dislodge any >debris.

When the "dead" cylinder's fuel injector electrical connector is removed, the
engine changes VERY little (vacuum drop of 0.5"). The same on #1 cylinder
does a 2" drop.
I tested the fuel injectors, they all work identically.
The spark plugs fire reliably....a weakish yellow. Coil?
Compression is lower in #4: On first stroke, I get 75psi. 4 strokes= 120psi.
Cylinder #5 'next door' gets 100psi first stroke, 4 strokes= 150psi.

So it is a weaker cylinder, but not too far off Ford's 20% rule.

Oddest of all is the drop from 20" to 15". That is more than one cylinder
should effect the reading.
I may try a new coil as the spark looks weaker than I recall on my old points
type ignition even.

Any other ideas are welcome, otherwise I'll have to "Non-Op" it as it won't
be able to smog it before next tuesday's deadline... :-(

Cheers, Jeff

 

Well, took apart the engine finally.
The stainless exhaust valve heads could be moved laterally a 0.1" !
The intakes were fine. Looks like I had been running too lean.
In go bronze guides! Hopefully the end of this expensive problem.

Cheers, Jeff