Misfire cylinder #4

[b454rat]

Can't seem to get rid of a misfire in my Yukon. I did full tune up, cap/rotor, plugs n wires. Plugs didn't look bad, but did em anyways. It has the miss at idle/low RPM, but smooths out the higher the RPM. It runs like a ****, so to me doesn't think it's a major issue. I was thinking it could be the spider, since PO had it since 01 or 02, (its a 99) and I had the upgraded spider from the last Yukon I had. Just got done putting it back together, and does the same ******' thing. I searched misfire, and says vacuum leak, but don't know where the leak would be around cylinder #4. I put a whole bottle of Seafoam in it, and it was sitting for a year maybe longer. But it fired right up when first looked at it. And think it's been cleaned out driving it up n down the road lol....

 

[L31MaxExpress]

Can't seem to get rid of a misfire in my Yukon. I did full tune up, cap/rotor, plugs n wires. Plugs didn't look bad, but did em anyways. It has the miss at idle/low RPM, but smooths out the higher the RPM. It runs like a ****, so to me doesn't think it's a major issue. I was thinking it could be the spider, since PO had it since 01 or 02, (its a 99) and I had the upgraded spider from the last Yukon I had. Just got done putting it back together, and does the same ******' thing. I searched misfire, and says vacuum leak, but don't know where the leak would be around cylinder #4. I put a whole bottle of Seafoam in it, and it was sitting for a year maybe longer. But it fired right up when first looked at it. And think it's been cleaned out driving it up n down the road lol....

Intake gaskets can cause a vacuum leak.

 

[b454rat]

And don't have any starter fluid. PO didn't say if they were replaced, maybe should go ahead and do it. Think I have a new set, but don't know if I feel like doing it lol.....thanks

 

[L31MaxExpress]

And don't have any starter fluid. PO didn't say if they were replaced, maybe should go ahead and do it. Think I have a new set, but don't know if I feel like doing it lol.....thanks

Vortec gaskets can leak from inside the engine as well. My 8.1L had been burning oil when I got it because the gaskets were shot. The gaskets were broken on almost every port and the oring had been sucked out of place allowing the engine to pull air and oil from the lifter valley into the intake ports.

 

[97Burban57]

My misfire with my #4 cylinder turned out to be a cracked head that very slowly leaked coolant into the cylinder . Took me 6000 miles of driving before i figured out what was causing the occasional misfire.

 

[b454rat]

This isn’t occasional, pretty much soon as the idle calms down after first start you can feel it. Smooths out while driving it. I don’t think the head/gasket is bad, coolant level hasn’t moved. Gonna get some either today n see if can find an external leak.

 

[DerekTheGreat]

For your viewing pleasure: (Althought I think part two is where diagnosis becomes solution. Spoiler: Intake gaskets):

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