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08 1500 Cyl#7 misfire

08SILVERADO1500
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08SILVERADO1500 Enthusiast

08SILVERADO1500

Posted
Posted

Ok ya'll,  

I'll try to keep it short.

I have an 08 1500 5.3

over 300k miles

was a well maintained work truck. 

Had stuck lifter a while back pulled head replaced ran fine.

Ran for a long time with a exhaust leak on driver side @ the Y pipe to the manifold. 

I think it burnt out the sensors for running so long that way. 

replaced y pipe I got a rough idle and then CAT started rattling. 

new cats new 02's. 

swapped coil packs, wires, plugs and injectors, added some torque to the intake manifold . 

just have not check compression yet but will tomorrow. 

Please help!!!

08SILVERADO1500 Enthusiast

08SILVERADO1500

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  • Author
Posted
8 minutes ago, 08SILVERADO1500 said:

Ok ya'll,  

I'll try to keep it short.

I have an 08 1500 5.3

over 300k miles

was a well maintained work truck. 

Had stuck lifter a while back pulled head replaced ran fine.

Ran for a long time with a exhaust leak on driver side @ the Y pipe to the manifold. 

I think it burnt out the sensors for running so long that way. 

replaced y pipe I got a rough idle and then CAT started rattling. 

new cats new 02's. 

swapped coil packs, wires, plugs and injectors, added some torque to the intake manifold . 

just have not check compression yet but will tomorrow. 

Please help!!!

Does have AFM not sure it's working anymore. Has used oil lately. Also had every bolt loose on the valley pan when I did the intake manifold gaskets a while back. Which caused a major oil leak I thought the rear main seal so I pulled the tranny back and replaced it before I found the problem. Should I just try the AFM control delete module? 

Supreme Pizza Senior Enthusiast

Supreme Pizza

Posted
Posted
1 hour ago, 08SILVERADO1500 said:

CamGTP

What do you think I could find under the valve cover? 

Also, if I pull the wire to the coil pack, what voltage do I need to be getting to the coil?

 

 

Pulling the valve cover and then starting the engine will tell you of an AFM lifter has collapsed.

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

Right, if you pop the valve cover off and the rocker does not move when you crank the engine over or while it's running, then you know what the problem is.

 

The voltage at the harness should have battery voltage.

08SILVERADO1500 Enthusiast

08SILVERADO1500

Posted
  • Author
Posted

Ok, just pulled the plug and started the engine. Plenty of spark and sounds like a whole lotta compression. I've still gotta find my gauge to check the compression. 

 

Idk if I have stated before, i had a major missfire one time and could hear the ticking lifter and i believe it was on the same cylinder. I did yank the head and replace the bad lifter. 

Now it seems that maybe this has happened again. Same cylinder, brand new lifter. But I hear no rattle as to say I've got a stuck lifter. 

 

Thanks y'all for the input, I guess it's just time to pull the valve cover and see. 

 

 

asilverblazer Senior Enthusiast

asilverblazer

Posted
Posted

Compression? Maybe burnt valves. 

Try systematically swapping components to a known good cylinder, injector, spark plug, wire, coil. One at a time Eventually the misfire will follow one of those components. If it doesn't, its limited to a mechanical issue at cylinder 7, which a compression check should reveal.

Supreme Pizza Senior Enthusiast

Supreme Pizza

Posted
Posted
21 hours ago, 08SILVERADO1500 said:

Update: valve cover off, all rocker arms move especially the 2 on cyl #7

 

 

When you say the rockers move - do they move when you crank the motor over, or do they move when the engine is running?

 

Or both?

08SILVERADO1500 Enthusiast

08SILVERADO1500

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  • Author
Posted

Asilverblazer

 

I did check compression but I feel the gauge is way old and does not register correctly. 

So I feel that test is inconclusive. 

Especially, that it showed low compression and then removing the gauge thumps very loud from the spark plug port. 

Supreme Pizza Senior Enthusiast

Supreme Pizza

Posted
Posted (edited)

In order to check the lifters, you really need to start and run the engine with that valve cover off. It will run on the opposing bank just fine. After all, that's basically what AFM does, just using different cylinders. Anyway, if you have a bad lifter, it can cause the rocker to move when turning the motor by hand, and when cranking, but then when the engine actually starts, the lifter causes the rocker to stop moving. I know, because I had a bad lifter, and the compression test came back good. Then I cranked it over with the valve cover off, and everything looked fine and the rockers were moving. Then i started the engine, and bingo bongo - no rocker movement on #7 intake. Then I shut it off, and cranked the motor over without starting it - and the rocker started moving again.

 

When driving the rig, you could feel the missing cylinder kick in here and there and then cut out again.

Edited by Supreme Pizza

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