Misfires 2,4,6,8 and now 7

[ashleyfetter]

I have a 2007 Tahoe LT 4x4. The check engine light has been on for several months. The code was P420. It did not miss or run bad until recently. Now while idling and driving down the road at constant rpms it surges. When it starts this there is a hum that comes thru the radio speakers.. the hum continues until the surges stop. I had a computer hooked to it and it showed the worst cylinder miss was on 6. Yesterday it popped another code p307. So now cylinder 7 is missing enough to throw a code. If I accelerate it stops surging and will run and pull fine. It has plenty of power. I don't think the cats are stopped up because it is very powerful. Anyone had any similar issues or anyone know what a possible cause would be.

 

[bladenbullet]

is the vehicle driven regularly?...or does it sit for long periods?....

the p0420 (catalyst efficiency) was probably a result of misfires if you've been experiencing them all along....

have you had a flashing ses lamp during any of this time?...this would indicate a catalyst damaging misfire...

waiting with a concern like this could cause quite a bit of expensive damage...

the "so now 7 is misfiring enough to throw a code" is a bit confusing....are the other cylinders still misfiring or is it just number 7?...

you really need to get someone who knows what theyre reading to look at it....

the hum is an interesting symptom...looking forward to hearing more about this one...an ignition breakdown could be causing radio interference...get the truck to someone who can perform a diagnosis...

 

[ashleyfetter]

Yes now 2,4,6,8 and 7 are missing. The p420 code was on for a few months never had a problem with power or surges... Had tranny put in and then the misses started. Sorry I left that out. Bad ground or pinched wire from tranny being installed? Taking Tuesday to have looked at again hopefully they can diagnose and or fix! Could O2 sensors cause anything like this? When I had it checked a few weeks ago cylinder 6 was worst misfire with over 2000 2,4,8 had under 400 each. All was on bank 2. Now the p307 code came up. Not sure bout rest of bank 1. Will no for sure Tuesday hopefully.

 

[ashleyfetter]

Yea it's driven regularly. At least a few hundred miles a week

 

[bladenbullet]

looking forward to hearing what they found...

 

[ashleyfetter]

Ok well the misfire problem is fixed. Also the surging is fixed. The misfire was fixed with plugs and wires. The previous owners put regular plugs in and they were bad. The surging problem makes me feel dumb but I would have never thought it was in the tranny. When the transmission was fixed I didn't allow for an empty cooler. It was low of transmission fluid and was not allowing it to shift out right. Any way it was a cheap fix. Runs great but the check engine light came back on and is showing the great P0420 code. Probably gonna by pass the ole cats soon.