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Discussion Starter #1
So I've been having a really bad miss in my 99 with the 5.3L vortec. It's also accompanied by a cough/very mild backfire when I let off the throttle. Took all my spark plugs out and discovered they are all burnt in the same small spot. All 8 of them. Took them to autozone, and the guy said it looks it's running lean, and he's never seen anything like this on a spark plug. He then said his guess would be a pre or post ignition problem or timing issue. Any body got any experience with this issue? Picture of spark plug below. All 8 look identical.
 

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Discussion Starter #3
These plugs are just a little over a year old, I put them in myself. And yes, the CEL is on, but it's on for multiple reasons. I.e. Torque converter code, O2 code, misfire code, etc.
 

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Discussion Starter #4
I realize they guy at autozone isn't a real mechanic, but I know he was right saying it's pointless to replace the plugs until I fix whatever the underlying problem is, because they will just burn up again.
 

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Check the fuel filter ? Fuel pressure? The white it looks like on the plugs does look lean. Do you have any exhaust leaks close the the engine ?
 

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Discussion Starter #6
Check the fuel filter ? Fuel pressure? The white it looks like on the plugs does look lean. Do you have any exhaust leaks close the the engine ?

Fuel filter isn't that old, I've replaced it in the last year or so, and it's probable that I do have a leak close to the manifold somewhere. Wouldn't surprise me. 260,000 on factory motor. Not sure how to check the fuel pressure though.
 

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Nerd a fp guage and there's a port on the fuel rail to hook up and see what you got. Sometimes if it had a exhaust leak close to the heads it could cause a mild backfire when letting off the gas or decelerating. May or may not have anything to do with it. But if it does have a exhaust leak before the 02 sensors it will throw the readings off and could be part of the lean problem ..

On all 8 cylinders it would lead me fueling problem
 

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A o2 sensor can cause it to run lean, if you got a goofy sensor it could make a lotif things go weird. Figure out why it's bad and start there, clean your mass air flow sensor as well. If your o2 and maf don't have good communication your just wasting money.
 

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Discussion Starter #9
Found an EVAP system leak under the hood today, seems to fix the miss when it is pinched shut, put I can't get the engine/intake cover off (bolt is stripped) to get to the hose to put a new one on. Also got a fishy AC problem going on. Truck is falling apart at 260,000 miles :( so my AC won't blow cold, I know it's full of freon because it wouldn't take any, and also I know it's not the blend door actuator because I took it off and opened it by hand. The air got a little cooler, but still not cold. Anybody got any ideas as or what the issue might be?
 
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