Misfire after warm / hot restart??

Discussion in 'Engine Performance + Maintenance' started by SubWarrior, Jan 11, 2017.

  1. SubWarrior

    SubWarrior Newbie

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    1999 suburban 5.7 w/ 250k and an odd misfire problem. Starts up great and runs beautifully for 10, 20, 200 miles no problem. As soon as the motor is shut down and restarted the engine runs rough and misfires (typically cyl5). Scan tool reveals nothing remarkable on initial drive, but after restart fuel trim on bank 1 is 14 to 15% vs -2% on right bank.

    Codes are as follows po305 (cly 5 misfire), po430 (Cat below efficiency bank 2), po440 (evap system)

    At this point i'm thinking 02 sensor(s) or something electrical. Voltages on 02 sensors *seem* to be within normal limits. The rich fuel trim bank 1 w/ cat code on bank 2 is confusing me.

    Parts replaced in last 20k miles: Updated fuel spider, fuel pump and filter, plugs, wires, cap, rotor, coil and ignition module.

    Any ideas here? im kinda stumped and don't want to go crazy on replacing parts.
     
  2. SubWarrior

    SubWarrior Newbie

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    well I did some more testing and was able to find that I had an 02 sensor that was not responding correctly. I did end up replacing all of them and in the last 500 miles no codes have shown up so I believe that fixed the problem. There is a good chance that these are the original sensors with 245k on them so figured it one was bad the others are not that far behind.

    Here is the before and after diagnostic data in case anyone is interested. The high sustained high portion (post replacement data) was holding the engine at 2500 rpm.

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