PO300 random multiple misfires?

2007 CADILLAC ESCALADE ESV
150,000 MILES • AUTOMATIC
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FREERIDER78
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  • 28 POSTS
Truck is sluggish to accelerate then engine light flashes. Read codes and it's PO300 or specifically PO307. Coil swap with 5, code stays with 7. Live data running rpms very little to no change when disconnecting coil feeds on all cylinders, same with injector feed on 7. Removed spark plug wires on driver's bank and all coils giving strong spark. Was going to run injector pulse test before swapping an injector. Haven't checked plug but it seems like 7 is firing along with the rest. Any suggestions on next steps in diagnosis?
Jul 22, 2026 at 11:43 PM

What to check next

Diagnostic guidance. Suggested checks and possible repairs are separate from the owner's reported results.

The reported repair is the useful starting point: inspect plug condition and connection security before assuming an injector failed. If symptoms return, record current codes and cylinder-specific misfire activity, then test the affected ignition circuit using the matching service information. The worn gap mentioned in the thread is an observation, not the replacement-plug specification.

Guidance references and applicability

Source discussion: question 1713069 https://2carpros.com/questions/po300-random-multiple-misfires--1713069 Supports the reported history and outcome only. Follow-up guidance is editorial synthesis; unverified specifications and diagnoses are not adopted. HELLA: Ignition-coil diagnosis https://www.hella.com/techworld/uk/technical/car-electronics-and-electrics/check-ignition-coil/ General ignition diagnostic background; example-vehicle values are not specifications for this question.

Read the replies · Discussion summary and reported outcome

AI-ASSISTED GUIDANCE · REVIEWED BY 2CARPROS
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BENNETTLYLEEEEE
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The injector on cylinder 7 might be clogged or stuck. You could try swapping it with the one next to it to see if the misfire follows.
Jul 23, 2026 at 2:43 AM
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STRAILER
  • ✓Experienced Mechanic
  • 55,579 POSTS
I would check the spark plugs first, they might have never been changed at 150k. So the code is a p0307 correct? lets concentrate on that cylinder then. Go for the spark plug first, upload an image of it so I can see. Also, here is a guide to help as well

https://www.2carpros.com/articles/engine-misfires-or-runs-rough/

Let me know how it goes.
Jul 23, 2026 at 7:37 AM
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FREERIDER78
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Turns out the boot on #7 plug was loosely attached. The plug itself was worn to a .065 gap with the ground strap heavily worn. All the plugs were in the same condition. Replaced with AC Delco iridium and no more misfire. I think just pushing the boot on firmly would have fixed it but the plugs needed changing.
Jul 24, 2026 at 7:38 PM
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STRAILER
  • ✓Experienced Mechanic
  • 55,579 POSTS
Glad you could get it fixed, thanks for letting us know. Please use 2CarPros anytime we are here to help.
Jul 25, 2026 at 7:42 AM
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Discussion summary

PO300 random multiple misfires?

The owner reported sluggish acceleration, a flashing engine light and misfire codes including P0307. Swapping the cylinder-seven coil with cylinder five did not move the fault. Inspection then found a loosely attached cylinder-seven plug boot and heavily worn spark plugs. The owner replaced the plugs and reported that the misfire stopped.

Reported outcome: The owner reported no further misfire after replacing the spark plugs and addressing the loose boot.

The owner thought tightening the boot alone might have helped, but that was not tested separately. The two identical outcome replies describe one repair, not two independent confirmations.

Read the original discussion

AI-ASSISTED SUMMARY · REVIEWED BY 2CARPROS
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