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Trying to help a neighbor out with his 02 z06. Car is basically bone stock besides intake and cat back exhaust.
Started having super rough idle and threw code for p0300. He has a nice snap on obdII reader and showed cylinders 5 and 7 were missing.
Car has 50k miles and he’s never done plugs or wires so obviously started there. No help.
Next we took coils from my working z06 and swapped them on. No difference.
Swapped injectors around and still showed 5 and 7 were missing. Now the odd thing is cylinders 6 and 8 are almost cold to the touch on the exhaust manifold. Idk of the knock sensor is just reading the wrong side of the motor??
Took off valve cover to inspect springs and they seem to be all good. Even bumped the motor over to see if they were in working order.
Also sprayed around intake manifold while running to see if it was leaking no change.
I’d check for injector pulse on 5 and 7 if you haven’t done that yet and as Pounder said check for chaffing at the rear of the fuel rail...disconnect 5 and 7 injector connector and with 12 volt test light connected to battery positive see if the test light blinks when probing the “control” wire of the injector (striped wire) circuit...I’d also see if you have a 12 volt feed with key ON on the other injector wire !!
Sometimes a misfire will show on other cylinders that are not misfiring...my “diagnostic process” for misfires is 1) cam/crank relationship 2) fuel 3) ignition 4) mechanical. I’ve recently gotten into using an “in cylinder pressure transducer” with my scope and this is the way to go for diagnosing the mechanical end of a diagnosis...leaky valves, worn cam lobes and timing issues !!...you can check 6 and 8 too !!...keep us advised !!...these misfires can sometimes be elusive without the “heavy equipment” !!...another thing...what do your fuel trims look like ??
I’d check for injector pulse on 5 and 7 if you haven’t done that yet and as Pounder said check for chaffing at the rear of the fuel rail...disconnect 5 and 7 injector connector and with 12 volt test light connected to battery positive see if the test light blinks when probing the “control” wire of the injector (striped wire) circuit...I’d also see if you have a 12 volt feed with key ON on the other injector wire !!
ok so with test light on negative and car in on position all injectors plugs light up. Switching to the positive I see the pulse you were mentioning. All injectors pulse the same so they are getting juice and do not believe it to be a wiring issue.
With car running and pulling injector plugs individually the car would bog down as it should since it is not firing that injector.
When you pull 6 and 8 there is no notable difference as if they are not working at all yet test light shows it is getting power! And still computer says 5 and 7 are the one miss firing
If you can get your hands on another scan tool I'd see if it's picking up 6 and 8 instead of 5 and 7...what model Snappy scanner were you using ??...a Verus D10 ??...if you did a cylinder drop test on 6 and 8 and no change in RPM maybe you should chase down those 2 cylinders...they are not contributing !!...you can do the "swaptronics" again with injectors and coil packs...99.9% of the time the coil packs are not the problem...do you have a strong spark when you pull the plug wires a the coil packs ??...you not only have to swap out those components but also check it's wiring...it's best to current ramp injectors and check the voltage on the control side to see if the injector is actually opening and closing (pictured below) but you need a scope for this which your normal DIY'er doesn't have !!...I would also OHM out those injectors...keep us updated !!
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P0300 code engine misfire
