Intermittent misfire at low RPMS

[AlphaZulu]

Hello all, I bought a 2017 Tahoe SSV recently with the 5.3L L83 engine. While towing a few months ago I began to get significant misfires and a P0303 code, but only when under load at less than 2,250 RPM. After finishing that trip by keeping the RPMs higher, I changed the oil and on my next trip I got misfires and a P0307 code consistently when under load at below 2,250 RPM.

What would you consider a good starting point for diagnostic? The vehicle has about 91k miles and had the transmission rebuilt at 53k.

Thank you for any assistance.

 

[AlphaZulu]

I guess since no one has any insights I'll just do plugs and wires and see if that helps. I was hoping to avoid the mindless loading of the parts canon, but 91k is probably fairly reasonable for the plugs and wires anyways.

 

[Tahoe14]

@Doubeleive, @Fless, @OR VietVet

 

[OR VietVet]

Because of the mileage and the known misfires on cylinders #3 and #7, I would say you are on the right track. I would remove all plugs and pay special attention to #3 and #7 and compare to the other plugs. I would replace with new plugs and wires. Post pics here of the plugs, close ups of the firing tips and pinpoint #3 and #7. How do the wires look, too. You likely have no idea how much idle time is on those plugs and wires, since it is an SSV.

https://www.rockauto.com/en/moreinfo.php?pk=13869485&cc=3434402&pt=7212&jsn=956

More Information for GM GENUINE 19431551

 

[Doubeleive]

at 91k add a induction service as well, this will help particularity with the direct injection motors

 

[OR VietVet]

at 91k add a induction service as well, this will help particularity with the direct injection motors

Like cleaning the MAF?

 

[Doubeleive]

Like cleaning the MAF?

well that's part of it but the induction service on the k2's involves cleaning the intake valves as well, carbon build up is a known problem usually shows up as a hesitation when accelerating, rough idle, etc. If it's time to do plugs and wires then it's time to do the service also.
this video shows what happens by 100k

 

[AlphaZulu]

Because of the mileage and the known misfires on cylinders #3 and #7, I would say you are on the right track. I would remove all plugs and pay special attention to #3 and #7 and compare to the other plugs. I would replace with new plugs and wires. Post pics here of the plugs, close ups of the firing tips and pinpoint #3 and #7. How do the wires look, too. You likely have no idea how much idle time is on those plugs and wires, since it is an SSV.

https://www.rockauto.com/en/moreinfo.php?pk=13869485&cc=3434402&pt=7212&jsn=956

More Information for GM GENUINE 19431551

Thank you for the reply. I ordered the plugs and wires and will report back on Saturday after I tackle the job.

 

[AlphaZulu]

Well, I got cylinders 1-7 done, and have enormous respect for anyone that can get #8. Worthy of note is that #7 had an aftermarket plug wire made by Packard with a 90° elbow on the plug end. This pushed the wire up against the exhaust manifold heat shield, and I believe this was the cause of my misfire. After changing (almost) all of the plugs and wires the vehicle runs smooth and strong.

Thanks again for the advice OR VietVet & Doubeleive

 

[Fless]

Hope the new plugs are the same, because the ones you removed are way mismatched. Nos. 1 & 5 were a different heat range than the others.

@Rocket Man shows the tool setup for the #8 plug:

spark plug change 5.3

So i decided to change my plugs on my 2008 Tahoe after a 125,000 miles, the driver side easy to do but the passenger side little more difficult. So i removed the inner wheel well liner and used my dewalt clamp to push the AC lines up to access the rear plug, see pic. Hope this helps someone.

www.tahoeyukonforum.com