Vortec 350 Cylinder 4 Misfire

[Supercharged111]

A good, healthy leak near an O2 sensor will cause issues, it'll report a false lean condition and dump excess fuel.

 

[Schurkey]

And a spark plug that fouls in a day or two indicates either ignition problems on that cylinder; or wiped valve guides and/or rings. Possibly a failed intake gasket.

Need to diagnose that fouling #4 plug.

Mine doesn't miss as bad at idle as it does under pressure

Weak ignition coil? Test it using a spark tester calibrated for HEI.

Low fuel pressure?

Failing TPS? Failing MAP? Failing MAF? Did you ever verify all the sensors using the scan tool?

 

[Schurkey]

A good, healthy leak near an O2 sensor will cause issues

A leak like that would be neither "good" nor "healthy". It might be "large", though.

 

[Ty1er]

And a spark plug that fouls in a day or two indicates either ignition problems on that cylinder; or wiped valve guides and/or rings. Possibly a failed intake gasket.

Need to diagnose that fouling #4 plug.


Weak ignition coil? Test it using a spark tester calibrated for HEI.

Low fuel pressure?

Failing TPS? Failing MAP? Failing MAF? Did you ever verify all the sensors using the scan tool?

All sensors are good, since replacing fuel pump the pressure at the test port and behind fuel filter is right around 60psi and holding. I sprayed a can of starting fluid and carb cleaner around intake and no change in idle. Also no visible signs of a leak when I had the plenum off

 

[Ty1er]

I will have to get a spark tester...the only one I have is the in line light up type