p0300 2002 GMC Savana 3/4 ton 5.7L Gas p0300 random misfire

[smitty123]

Please see attached file for report.  Been dealing with this for a while.  Mechanics said they smoke tested and found no leaks.

Fuel pressure tested at 58.

Has random misfire code p0300 and lean code  p0171. Has installed new, Delco cap and Delco rotor and Delco Iridium plugs.  Last year tried Bosch plugs and new after market cap and rotor.   Still no difference.   Shows classic sign of vacuum leak as throttle increase causes fuel trims start to lower. 

What do you think?

SavannaReport08062022_0001.pdf

[Jsdirt]

Probably a combination of a few things. Could be lazy o2's - can't tell that on paper. Need to watch them live.

 

MAF reading is a bit high at idle - that could be failing, too.

 

Bank 1 is leaner - could be a leaking EVAP purge valve. That acts just like a vacuum leak once all the fumes are purged from the charcoal canister.

[smitty123]

3 hours ago, Jsdirt said:

Probably a combination of a few things. Could be lazy o2's - can't tell that on paper. Need to watch them live.

 

MAF reading is a bit high at idle - that could be failing, too.

 

Bank 1 is leaner - could be a leaking EVAP purge valve. That acts just like a vacuum leak once all the fumes are purged from the charcoal canister.

Thanks for the leads you gave me.

[Duelin]

I would also check for intake manifold gasket leak. Which is not an unusual problem with those engines.

Good Luck