Help with random & cylinder 4 misfires

[Ti44]

New to this forum and looking for some help and guidance. I have a 1998 Chevy K1500 Z71 with the 5.7 vortec V8 that has a cylinder 4 misfire and a random misfire. The random misfire has been going on since August of last year, and the cylinder 4 misfire started after fixing a cylinder 5 misfire (bad plug on that one). Here is a list of what I have fixed and done so far:

Fuel injectors

Fuel filter

Fuel pump

Spark plugs

Spark plug wires

Distributor

Cap & rotor

EGR

Cam Sensor

Crank Sensor

Timing Chain and gear (verified)

Air filter

PCV

Exhaust Manifold Gaskets

Adjusted valves (verified)

Coil

Catalytic Converter

Bank 2 Sensor 1 Oxygen Sensor

Throttle position sensor

Tested for intake leaks multiple times, nothing found.

Seafoam treatments

Lucas Fuel system cleaner

 

As you can see, I am at my wits end here and completely stumped. After adjusting the valves yesterday (second time since we made a mistake the first time last week) it seems to be less noticeable, though it is still there. So my question is, what else is there that can cause these issues, separate or together? Any hints or tests that can help? Thanks.

[Justin101714]

Time to check mechanical stuff. If you have access to a vacuum gauge, install it in the brake booster hose and start the engine, if the needle isn't dead solid on a number, I'm gonna say around 15 inHg, as in, it's bouncing around even the slightest while the engine is running, you have a mechanical problem. Check compression for that cylinder, dry and wet and check running compression of the bad cylinder and a known good cylinder. Let us know what the results are

 

 

Sent from my iPhone using Tapatalk

[Swimmer8366]

I would do a crank relearn if it hasn't been performed than do compression tests.

 

Sent from my Z981 using Tapatalk

[dcheeseman]

Check intake Manifold gasket, Chevy's are bad for that. Spray some water around the intake ports to see if it sucks in the water.

 

Daniel

[Swimmer8366]

What is the fuel pressure at?

 

Sent from my Z981 using Tapatalk