2001 2500HD 4.8 v8 - 4 cylinder misfire
 

Hi folks. Im getting really stumped with this engine. Truck has 286K miles

Cylinders 1,5,6,8 are misfiring. Cylinder 1 misfires the most. All four misfire every second or two according to the Snap on Computer.

Plugs, Wires and Fuel Filter Replaced today.

So here is what I have done.

First Series of Tests
Seemed drivers side of engine was almost dead. Disconnected coils one by one and each one really didn't do much. Removed the O2 sensor from bank 1 (drivers side) before cat and it seem to run better(less restriction). So I figured I would drop the exhaust from the manifolds to rule out clogged cats. Helped a tiny bit so im still thinking at least the drivers cat is clogged up.

Second Test
Moved coil from cyl 7 to 1 and 1 to 7. To see if the misfire follows. Didn't follow. Still misfired on 1 and not on 7.

Third Test
Performed Injector Balance Test. Before each test the fuel system was primed via computer to 55 psi while fuel pump is running and rested at 52 psi when pump shuts off which is when I start the test. After the computer pulsates injectors for a specific amount of time, each injector bled the system 21 PSI. So according to that test, the injectors are flowing the same.

Forth Test
Compression Test. Only had time to test cylinders 1,3,5,7 (drivers side). All came back at 125 PSI. Had our charger on the battery and throttle open.

Even though the plugs and wires are new, tmro before I put the truck outside and bring something else in, I'll move plugs and wires around to see if I got a bad plug and/or wire set.

Mass Flow Sensor was disconnected at one point (not during tests) and truck ran the same...idled higher, but still misfired.

Questions:
Since compression test came back at a 125 PSI, wouldn't that also mean the valves and valve springs are working normal? Maybe bad cams?. Now what should the compression be? I started with Cyl 7 since that was not misfiring and am now led to believe the 125psi should create a working cylinder.

Could a bad Reluctor wheel cause this or crank sensor? I figure if the crank sensor? If the CS was bad I figure either the engine wouldn't start or the misfire would be random and not cylinder specific.

Any Ideas?