So I have a 2000 Z71 with the LM7 5.3. Having odd issues with misfires, cylinders 2,4, and 3 are missing. Have tried swapping coils and wires around, changes nothing, have codes P0332 (knock sensor low circuit bank 2) and P0174 (system too lean bank 2) and my bank 1 upstream O2 sensor has flat lined. All spark is good, compression is good, I'm leaning towards a fuel issue but I was curious if anyone else has had similar issues. It does idle rough on cold start but runs halfway smooth once warm but super gutless, i know these arent speed machines but it feels like i have maybe 75HP. Looking for advice.
Misfire mystery
- Thread starter dmcgaugh
- Start date
Welcome to the forum from Oregon.
Sounds like the knock sensors need addressed. Known weak spot for the 5.3's. Always use Genuine GM or AC Delco knock sensors and make sure you replace the wiring harness to them. Make sure plugs look good when reassemble. Can use GM gaskets or Fel Pro. Or, whatever you like best. Because of what has been spitting down the exhaust, may need the O2 sensors too.
Sounds like the knock sensors need addressed. Known weak spot for the 5.3's. Always use Genuine GM or AC Delco knock sensors and make sure you replace the wiring harness to them. Make sure plugs look good when reassemble. Can use GM gaskets or Fel Pro. Or, whatever you like best. Because of what has been spitting down the exhaust, may need the O2 sensors too.
stutaeng
Well-Known Member
Check fuel pressure with a gauge. Not common for low fuel pressure to ONLY affect one bank, but possible your O2 sensor on the other bank is not even reporting correctly (sounds like it.)
Usually low fuel pressure will affect both banks on the fuel trims, almost identical percentages.
BTW, what are your fuel trims? Do you have a scanner that can read live data?
Usually low fuel pressure will affect both banks on the fuel trims, almost identical percentages.
BTW, what are your fuel trims? Do you have a scanner that can read live data?
Checked the fuel pressure and it's within normal range, it does drop to around 42psi under load though.
INW-Iron-Steel
Well-Known Member
Sounds like you may have found your issue. Adding to this in case someone else is hunting a "mystery misfire". More specifically P0300 (random misfire) but it is general advice. Check the grounds. GMT800s are plagued with ground issues causing all sorts of electrical issues. Check the main fuel pump ground on the frame under the drivers door, the coil ground (g102) on the front driver side of the block, and the two main grounds at the back of the block. Passenger side rear block ground is main PCM ground, which can cause all sorts of weirdness.
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