Hey guys. Im having trouble diagnosing a 2002 4.8. When the truck is warm it has a bad miss. It will not pull itself unless in power enrichment mode. It feels as if it wont take throttle, then backfires and takes off at about 90% throttle.

Fuel pressure checks good, maf and all sensors checked good. Short term fuel trips were at positive 50% and long terms were at poitive 25%.

When at idle i can change the commanded afr to around 10.8 and it smoothes the idle out. From what i saw on the scanner, the majority of the misfires were on the rear cylinders (7 and 8).

My best guess so far is that it might be the injectors. Anyone have any ideas of what to check.

 

If you have to comand more fuel it is probably running lean. This could be any thing from bad intake gaskets to Bad 02 sensors.

Are you getting and Codes??? can you post all the codes???

 

Only code is o2 lean and misfire. O2s are new. Maf and fuel pressure were good as far as i can tell

 

Which 02's are reading lean???

Is it only cylinders 7 and 8 that are miss firing???

 

Okay guys, it seems the problem begins when the engine warms up and kicks into closed loop. From the scan today it looks as if bank 2 is rich and bank 1 is lean. I want to believe the o2 sensors because they are brand new. I crawled under there to check out the connection and everything looked good. The only code it is throwing is engine misfire. Any ideas of what to check?

 

B2 S1 is only reading 9 MV and the other side is reading over 1000???
Watch the sensor's and see if there switching properly... if not its either bad or you have another issue else were.

The lower the number the computer see's it thinks it running lean and richens it up.

Same with the other side.

The higher the number and it thinks it running rich and tries to lean it out.

 

Okay it seems the o2 sensors are unresponsive to afr changes. I tried leaning the mixture and richening the mixture and neither o2 sensor changed. Could a bad ecm cause this? This truck is from the north and has some rust through out. The ecm connectors looked a little dirty. I plan to try a different o2 sensor and check the wiring in the next couple of hours.

 

PROBLEM SOLVED

So, the o2 sensors were new, but they were the wrong ones. I appreciate all the help everyone!