# Misfire won’t go away



## Prashant8866 (Aug 30, 2015)

I have a code reading P0303 for misfire in cylinder 3. 
I changed the spark plugs, no change.
I replaced coil pack, no change.
I replaced fuel injector for #3, no change.

what would be next?


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## TDCruze (Sep 26, 2014)

It sounds like you have covered all the external parts swapping with no change.
I would do a Compression test to make sure that the cylinder in question is good or not.


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## Ravenkeeper (Sep 10, 2017)

Prashant8866 said:


> I have a code reading P0303 for misfire in cylinder 3.
> I changed the spark plugs, no change.
> I replaced coil pack, no change.
> I replaced fuel injector for #3, no change.
> ...


Bad wire in the harness to the coil pack, for Cylinder 3? Not sure how to troubleshoot that wire.


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## plano-doug (Jul 1, 2015)

Ravenkeeper said:


> Bad wire in the harness to the coil pack, for Cylinder 3? Not sure how to troubleshoot that wire.


I'd put an oscilloscope on it, but not everyone has one of those in their garage 

Some hi end automotive test equipment has similar features, but that's not available to most folks.

I was thinking along the same lines as you, but was wondering if the broken wire might be detected by inspection. I would look closely at the harness where it plugs into the ignition coil module to see if there's a damaged wire, or a pin has pulled loose.

For what it's worth, I looked at the schematic for the 1.8, and the ignition coil module for it is wired like four individual coil packs connected in parallel. The four units share a common +12V and common GND, with four individual triggers, as you indicate. So there's nothing special or exotic about it.

I assume the 1.4 is wired likewise.

Doug

.


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## RoninDusette (Aug 21, 2018)

TDCruze said:


> It sounds like you have covered all the external parts swapping with no change.
> I would do a Compression test to make sure that the cylinder in question is good or not.


+1 to that. You could just have a shi++y calibration from the factory on there too. Seems as though you have already covered your bases though. Where do you live at? Are there any other issues? Leaky or loose injector? Spark plus are torqued to spec and the threads aren't stripped? Any oil on the plug? Umm, just trying to think of things to check. Besides a bad ground or loose wire going to that coil or checking for proper compression doing a leak down or comp test... Idunno

Just for the hell of it check your cam and/or crank angle position sensor. I don't have a 1.8,but whatever is clocking the rotation of the engine should be checked for alignment too. Let us know what you find.


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## joes74challenger (Jan 9, 2017)

i had a misfire i couldn’t get rid of. took it to the dealer and they said the plugs were not tight enough. the plugs have to be 18 foot pounds. might be worth a re visit. 18 foot pounds with a torque wrench feels crazy tight but it solved my issue. 


Sent from my iPhone using Tapatalk


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## plano-doug (Jul 1, 2015)

joes74challenger said:


> i had a misfire i couldn’t get rid of. took it to the dealer and they said the plugs were not tight enough. the plugs have to be 18 foot pounds. might be worth a re visit. 18 foot pounds with a torque wrench feels crazy tight but it solved my issue.


Yes, in my limited wrenching experience on my Cruzes, I learned you need to get almost all the way to 18 ft-lbs in order to get the crush ring on the plugs all the way crushed (and hence, get the plug fully sealed in the head).

I thought ~13 ft-lbs felt plenty tight, but that didn't fully compact the ring.

The good part is, I have another bullet on my car repair resume  

Doug

.


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## Blasirl (Mar 31, 2015)

Prashant8866 said:


> I have a code reading P0303 for misfire in cylinder 3.
> I changed the spark plugs, no change.
> I replaced coil pack, no change.
> I replaced fuel injector for #3, no change.
> ...


A code P0303 may mean that one or more of the following has happened:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector 
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

Read more at: https://www.obd-codes.com/p0303


Remember to re-gap your plugs to .028, torque to 18 ft-lbs with no anti-seize on the threads of a stock type plug, ensure the boots have no rips / tears or holes in them, lightly coat them with dielectric / silicone grease and make sure the resister springs are clean and not caught up in the boots when you install them. Read _Hesitation Gone!_ if you need new plugs.

Just in case - Pull your coil pack, remove the plugs and send an endoscope into the bores. Look to see if the pistons are still good. Also if you see no carbon, i.e. pistons are clean or they are wet, you have an internal leak (bad head gasket).

Do a compression test
Bench test the O2 sensors





In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced.


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## sierracharlie65 (Mar 16, 2020)

Dude did you get it fixed? Im having the same problem.


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## RoninDusette (Aug 21, 2018)

Maybe I misread or missed it but what are your spark gapped to?


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