Having ongoing issues with this fault code on 2001 S10 Blazer and although there is a lot about this issue on the forum, nothing quite matches my problem.

When the fault first came up I replaced plugs, distributor cap and rotor. Plugs removed from bank 1 were carboned up and excessive gap. However this failed to resolve the issue.

Next step was to do a compression test, which was ok. Test signal to all injectors ok, checked ignition coil signal to all six cylinders ok.

When I removed the inlet manifold and injection spider found that it was pretty badly carboned up, so cleaned up manifold and unblocked injectors. Then tested the injectors for even spray and equal amount. Reassembled everything an on road test was initially running fine but misfire returned.

I then noticed bits of cat convertor coming out the exhaust, so cut out the old cat converter and welded in a section of pipe (which is legal in New Zealand). Once again the initial road test was fine and no fault codes. But shortly thereafter the misfire and P0300 error returned along with a new P0171 code.

The only other thing I have noticed is that there is a considerable voltage difference between the O2 sensors on banks 1 and 2. Although I doubt this is the cause of the misfire. All three O2 sensors were replaced 15,000 km ago.

So that is the summary of where I am at thus far, pretty much out of ideas so any suggestions appreciated.

 

Change wire set...old wires are leaking spark

 

P0171 is a lean condition on the left bank, (not enough fuel or too much air). It can be caused by a "lazy" or "dead" oxygen sensor. When an oxygen sensor is stuck lean, the PCM goes full rich trying to satisfy the sensor. This could explain the carbon fouled plugs only on the left bank. The P0171 pretty much eliminates the possibility of a leaky fuel injector or faulty secondary ignition part, (plugs, wires, cap, & rotor). When/if they fail, it causes a rich condition. Not to say there isn't a problem with them, BUT, the P0171 is covering it up if there is a problem. If P0300 is the only DTC, it's usually caused by a fault in secondary ignition, but in this case, the P0171 may have caused the plugs to foul setting the P0300 in the first place.

Following this flow chart will take you to the problem: https://blazerforum.com/forum/diagno...plained-35154/

If you don't have the equipment necessary to do all of the steps, you can monitor the left oxygen sensor voltage on a scan tool while spraying some carb cleaner in the throttle body. Voltage should shoot up to .9 volts like a rocket. If not, the sensor, or its wiring, is the problem.