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Discussion Starter · #1 ·
05 LJ stick shift. So I have a few odd things. I have a p0306 code but it's cylinder 1 that is dead. Also have codes for all 4 o2 sensors. I've tried moving fuel injectors, moving spark plugs, different coil rail, and did a compression check which was good. I put a test light on the injector harness and it's firing, I can also feel the injector clicking. I know the o2 sensor codes point to a bad PCM, but could a bad PCM also cause a misfire?
 

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About the only way the PCM could kill one cylinder would be if it was not firing the injector for that cylinder. Maybe a bad driver. Since you have checked the injectors they are apparently all firing so the PCM should be ruled out.

Is the cylinder completely dead or just weak enough to set the code? How do you know it is #1?

Since #1 & #6 are paired cylinders meaning they both fire from the same coil & are 180° apart in the firing order it might be possible to confuse the PCM if the OPDA is set 180° out. That would mean when the holes line up you are on #6 compression, not #1. The PCM would not “know that” & be counting the cylinders 180° off.(?)

And yes, I have read where they are 180° out & still run, apparently pretty well too.
 

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All cam sensor is used for at least on pre 05 is to get the fuel injectors timed right and since intake valve opening really times air/fuel entry to cylinder it could run ok with with cam sensor timing off as lots of earlier efi engines fired injectors in batches


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What specific exhaust sensor codes are you getting
If all four are either heater circuit high voltage or all four are heater circuit low voltage and the ground for sensor heater is ok most likely those codes are due to heat sensitive pcm failure


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Discussion Starter · #5 ·
Heater control circuit high is the o2 codes. I verified the opda position to tdc and it is correct. I know the plugs for 1 and 6 are tied together l, but are the injectors also? Or are 1 and 6 injector controlled independently?
 

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Yep six different injector pulsing ground triggers on 6 different wires from pcm

The coil rail only gets three pulsing ground triggers from pcm
One for 1&6 one for 2&5 one for 3&4

The coil rail has one constant plus 12 as do all six injectors one common constant plus 12


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Discussion Starter · #7 ·
Yep six different injector pulsing ground triggers on 6 different wires from pcm

The coil rail only gets three pulsing ground triggers from pcm
One for 1&6 one for 2&5 one for 3&4

The coil rail has one constant plus 12 as do all six injectors one common constant plus 12


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Ok. I verified spark on 1 and 6. Also put a test light on the #1 injector and could see it flashing. I wonder if the PCM going bad could mess with the pulse width or timing of that #1 injector. At this point I don't see what else it could be but I'm open to ideas.
 

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Carefully exam the harness where it passes near rear battery hold down bolt and around back of engine as abrasion there can interrupt or ground a single injector trigger wire


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Discussion Starter · #9 ·
Wiring harness checks out fine. The injector is getting 12v hot and the ground pulses. New PCM from WranglerFix fixed the o2 codes but it's still missing on #1. Compression tested again at 140psi, verified the opda timing is correct also. I'm kind of at a loss now.
 
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