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06 Kia Sorento is now back firing

My timing belt went out a few months ago and it damaged the heads so I’ve basically rebuilt the entire top end of the engine but now that I’ve got it back together it is backfiring when I give it gas. It idles just fine…no misses…just backfiring and has very little power. I have found what looks like honey comb material on the ground under the tail pipe. Am I looking at a bad converter or something else?

The first thing I would check is the timing.

Timing is fine already went back in to check that

You might need to check for an exhaust restriction; as in clogged converter. The easiest way to do this is with a vacuum gauge but you can also drop the header pipe connection and see if the backfire disappears.

Ran codes and the only one showing up now is mass air flow sensor low voltage. Car won’t start at all now. Can the maf cause this vehicle to not start at all? And if so can it be tested?

That honeycomb material is what’s left of the substrate for the catalytic converter. The backfiring broke up the substrate in the catalytic converter and the converter is now plugged. A plugged catalytic converter can prevent the engine from starting. To find out, bang on the converter with a rubber mallet. If you hear a rattling noise from the converter, the converter is shot.

Tester

Yup, except I would suggest that since you have some of the converter “guts” beneath the tailpipe pn the ground, you can skip the rubber hammer. The converter is definitely damaged. And probably plugged.