P0300 random misfire

[SupremeAboriginal]

2006 z71 Tahoe w/166k miles…no leaks…compression is good..spark plugs good…just swapped crankshaft position sensor. had it relearned as well. injectors good, grounding is good. everything checks out as normal. this is blowing my mind. tech says cylinder 5 is the issue. so it has been isolated to that. what else to do? a mechanic recommended a new engine. that’s last resort for me

 

[West 1]

Fire the mechanic. Compression is good says a lot. Internals are solid. Swap coil and plug wires with another cylinder and see if the problem moves with that coil and wire. Hook up a good scan tool and watch the mis fire count so see exactly what cylinder and how often the misfire happens. There are tests for the injectors etc. You just need a little help to figure it out.

 

[justirv]

2006 z71 Tahoe w/166k miles…no leaks…compression is good..spark plugs good…just swapped crankshaft position sensor. had it relearned as well. injectors good, grounding is good. everything checks out as normal. this is blowing my mind. tech says cylinder 5 is the issue. so it has been isolated to that. what else to do? a mechanic recommended a new engine. that’s last resort for me

Do you notice that its worse when engine is cold. If you have not replaced intake gaskets, look at spraying your choice of aerosol to see if there is any change. They tend to dry out and shrink over time.

 

[rockola1971]

Fire the mechanic. Compression is good says a lot. Internals are solid. Swap coil and plug wires with another cylinder and see if the problem moves with that coil and wire. Hook up a good scan tool and watch the mis fire count so see exactly what cylinder and how often the misfire happens. There are tests for the injectors etc. You just need a little help to figure it out.

Id do the the first immediately and tell that "mechanic" he isnt qualified to be a mechanic. I second swapping the coil or the spark plug wire to see if the problem moves. Its likely the plug wire if they are fairly old. In that case throw a new set on, they are cheap enough.

 

[Scottydoggs]

swapping coils wires and plugs is sound advice, when you have the plug out look for a black line in the porcelain, if you see that its a crack and will cause a misfire.

 

[West 1]

While swapping the coils you might swap them plug also. If a plug gets dropped at any point in its life from manufacture to you buying it they can break internally. Look fine but not fire well. Good to rule out a bad plug possibility.

 

[SupremeAboriginal]

mechanic checked compression...coils...even swapped plugs...isolated it to cylinder 5. they did all the tests needed before tearing major components down. I am at a crossroad.

 

[OBSandaNNBS]

mechanic checked compression...coils...even swapped plugs...isolated it to cylinder 5. they did all the tests needed before tearing major components down. I am at a crossroad.

Hmmm...check the wire harness and connectors at both the injector and coil for cylinder 5. Wiring is always high on my suspect list.

Also crankshaft and camshaft sensors work together, would be strange for a misfire to isolate to only one cylinder with the cam sensor bad. I think?? Might be worth it. Not trying to load up your parts cannon though.

 

[Fless]

Also crankshaft and camshaft sensors work together, would be strange for a misfire to isolate to only one cylinder with the cam sensor bad. I think?? Might be worth it. Not trying to load up your parts cannon though.

^^ This is worth a look-see. If it hasn't been done, do a quick CASE relearn so you're sure the cam and crank sensors are in sync.

 

[jetson22]

I am having a similar issue only isolating to cylinder 4. Did you find the solution

 

[Fless]

I am having a similar issue only isolating to cylinder 4. Did you find the solution

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