I recently replaced my 5.3ltr in my 06 envoy Denali. It seems to idle fine for a while then starts to idle rough. It seems every few minutes the computer straightens up problem but eventually goes back to rough idle. The vehicle seems to drive fine on flat land but going uphill under a load it is misfiring and dumping fuel until it won't go uphill anymore. If I turn off vehicle and restart I can go fine again momentarily. So far I have swapped throttle body and fuel rail, installed new plugs/wires, coil packs, and engine coolant sensor but it is still doing the same thing. Any thoughts or ideas as to my next step would be greatly appreciated!!
Random cylinder misfire, too lean/rich. Help!
- Thread starter TxMaverick75
- Start date
The cel blinks first then stays lit. Giving p0300 code so random and to rich/ lean but no sensor codes?
Yea I replaced engine coolant sensor today because that was my next guess and when I told a buddy he said that might be the reason but it's doing the exact same thing still? I'm not sure what my next step should be? Thanks
Had this on a 5.3 I swapped into a Firebird as a project car. Check to make sure the oxygen sensors are not reversed. The harnesses are just long enough to get reversed and will cause all kinds of havoc. It would explain recurring lean/rich issues. The PCM is attempting to straighten itself out based on O2 sensor readings but continually is not getting expected results.
88Ironduke
88Ironduke
linneje
Member
- Apr 26, 2012
- 404
Have you checked the air filter and MAF sensor? Looking at perhaps a problem with the air intake.
You really need some data with a live stream scan tool if you want to see exactly what is happening. The Torque app and a smartphone can do this if you are familiar with it. Or a friend with a high end scan tool.
Otherwise you are really just guessing (just like my WAG above
)
You really need some data with a live stream scan tool if you want to see exactly what is happening. The Torque app and a smartphone can do this if you are familiar with it. Or a friend with a high end scan tool.
Otherwise you are really just guessing (just like my WAG above
)Should have been a tad bit more specific, the O2 sensor harnesses should be checked for being plugged into their corresponding banks. Call it a WAG but the suspect area to be looking at is the engine swap itself. Even on a good day good mechanics can get two identical sensor plugs backwards, the sensor wire bundles are long enough to swap bank to bank. This problem plagued my Firebird for a few weeks until a mechanic from outside the loop suggested it. A simple check wire color codes will tell you if they are right. Mine were wrong. If I'm right the first time the engine is cranked up it will run and sound as it should. But its just a wag. 
88Ironduke
88Ironduke