Need help - Car Misfires
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Need help - Car Misfires
Need help figuring out what’s wrong with my car before spending money in diagnostic.
09 G37x with 213k miles.
Car “skips beat” then starts to shake and misfires. Engine light turns on gives code p0420, stored and p1721, p1815 OEM.
I reset battery (negative) and car returns to normal operation but then trips randomly.
New fuel injectors Spark plugs Coils Valve gasket Manifold air gasket
Checked Battery (2 years old) -good Alternator (only 2 years old)-good Oil- 2 months ago (steady no decrease) Coolant- steady but did top off 1 month ago Power steering fluid- no change
Can it be catalytic converters? I did have a hissing noise that was coming from the area for about a year ago but it’s no longer there. -original converters still on car. I live in New England so rust and weather play a factor. They are rusted but no visible holes.
Can it be a sensor? Would they give engine light codes if it was?
09 G37x with 213k miles.
Car “skips beat” then starts to shake and misfires. Engine light turns on gives code p0420, stored and p1721, p1815 OEM.
I reset battery (negative) and car returns to normal operation but then trips randomly.
New fuel injectors Spark plugs Coils Valve gasket Manifold air gasket
Checked Battery (2 years old) -good Alternator (only 2 years old)-good Oil- 2 months ago (steady no decrease) Coolant- steady but did top off 1 month ago Power steering fluid- no change
Can it be catalytic converters? I did have a hissing noise that was coming from the area for about a year ago but it’s no longer there. -original converters still on car. I live in New England so rust and weather play a factor. They are rusted but no visible holes.
Can it be a sensor? Would they give engine light codes if it was?
Last edited by jla_113; Aug 21, 2025 at 12:39 PM.
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Joined: Aug 2025
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Ive been playing with chatGPT and input your info.... it came back with the following... hope it may help
- Catalytic converter (P0420)
- At 213k, very likely your Bank 1 cat is weak. Even with new coils/injectors, a cat that’s lost efficiency will keep tripping P0420.
- Sometimes only noticeable under certain load/RPM conditions (like when you feel the “skip”).
- If it starts to clog, you’ll feel misfire-like shaking.
- At 213k, very likely your Bank 1 cat is weak. Even with new coils/injectors, a cat that’s lost efficiency will keep tripping P0420.
- Crankshaft or camshaft position sensor
- These can cause random engine stumbles/skips that feel like misfires but don’t always log a P030X code.
- On VQ engines (like yours), a failing crank sensor is a very common culprit for sudden hiccups and random codes.
- These can cause random engine stumbles/skips that feel like misfires but don’t always log a P030X code.
- Transmission/ECM communication (P1721 & P1815)
- These codes suggest the speed sensor / TCM-to-ECM communication is glitching.
- A weak/bad vehicle speed sensor or corroded connector can cause drivability hiccups that the ECU interprets as misfires.
- Double-check harness connectors on the transmission, and make sure your grounds are clean and tight (especially the one by the firewall and battery tray).
- These codes suggest the speed sensor / TCM-to-ECM communication is glitching.
- Exhaust leaks
- Even a small leak before the cat can throw O2 sensor readings off, trigger P0420, and make the ECU cut fuel/timing.
- Even a small leak before the cat can throw O2 sensor readings off, trigger P0420, and make the ECU cut fuel/timing.
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