Misfire diagnosis

[97C1500TJ]

I’m troubleshooting a misfire on my 97 C1500 with the 350 Vortec 227K miles. I’ve got O2 sensor codes and a generic misfire code. I’m not wanting to throw parts at it but think it’s injector related but also running lean due to the fuel trim readings. Does anyone have any input to make sure I’m on the right track? The attached photos are of the live data when the truck is at idle.

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

 

[Schurkey]

Verify wire harness to O2 sensors. It is more likely to be the sensor than the harness or a computer problem, but that's never guaranteed.

You'll probably install all four O2 sensors to get rid of the three heater codes. No sense leaving the fourth sensor in place.

Short-term fuel trims look wonderful to me. 128 is "normal", your worst one is only three numbers away (131.)

Long term fuel trims show lean-command for Bank 2. I don't see the status of Bank 1 long-term fuel trim. That's telling you the computer is removing some fuel from Bank 2 in order to not over-fuel. May--may not be a big deal. Replace the O2 sensors, clear the codes, see what comes back.

What is your fuel pressure?

Is that scan tool capable of showing cylinder-by-cylinder misfire counts, or cylinder-specific misfire codes? Many consumer-grade tools LIE about misfires, they can't display cylinder-specific misfire codes so they display "random misfire" P0300 when the REAL code might be cylinder-specific (P0305 for example.)

 

[97C1500TJ]

Verify wire harness to O2 sensors. It is more likely to be the sensor than the harness or a computer problem, but that's never guaranteed.

You'll probably install all four O2 sensors to get rid of the three heater codes. No sense leaving the fourth sensor in place.

Short-term fuel trims look wonderful to me. 128 is "normal", your worst one is only three numbers away (131.)

Long term fuel trims show lean-command for Bank 2. I don't see the status of Bank 1 long-term fuel trim. That's telling you the computer is removing some fuel from Bank 2 in order to not over-fuel. May--may not be a big deal. Replace the O2 sensors, clear the codes, see what comes back.

What is your fuel pressure?

Is that scan tool capable of showing cylinder-by-cylinder misfire counts, or cylinder-specific misfire codes? Many consumer-grade tools LIE about misfires, they can't display cylinder-specific misfire codes so they display "random misfire" P0300 when the REAL code might be cylinder-specific (P0305 for example.)

Fuel pressure has not been checked with a gauge but I’m assuming it’s ok as I have no long cranking when cold or hot. As far as the scan tool, we have Autel scanners and I am new to them. I learned on the Snap On Zeus and everything is in a different place on the Autel. I believe it is capable of showing which cylinder is misfiring but couldn’t find it. I found the misfire counter bar graph and it was flat lined.