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2003 chevy trailblazer_ls
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4 Posts
Discussion Starter #1
Hi, so I recently bought a 2006 Trailblazer 5.3 4wd with 176000 miles on it. I get it to my house and it is throwing a P0301 code (cylinder 1 misfire). Okay, no problem. Changed the spark plug, no result. Swapped the spark plug wires, no result. Swapped the coil pack. No result. Changed the fuel injector, no result. I'm so confused on what I could be! It does have the AFM (DOD) system so I swapped the valve cover to the upgraded design but that didnt do anything either. Now, I'm looking at the real time data and I have misfires on 1, 2, 3, 4, 5, 7, and 8. Although 1 and 8 are by far the worst, 2 is concerning, and 3, 4, 5, and 7 are running one misfire for every thousand misfires on 1. I am pretty sure compression is good but I have no idea if the torque app can actually give an accurate reading for that nor what it should be. Has anyone run into this? I mean this is getting ridiculous and is starting to make me feel like I really got screwed by buying this truck. Everything but the engine is in great condition though. This is really urgent as I need the truck to be in good running order ASAP!
 

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2004 gmc envoy_slt
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2,320 Posts
Compression can only be measured using an air pressure gauge. This must be you next step. Stop shot gunning.
 

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2003 chevy trailblazer_ls
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4 Posts
Discussion Starter #3
Well I didnt think I was shotgunning. The problem is the code P0301 is so unspecific it leaves a lot of possibilities. I will be checking for vacuum leaks next. Any cheap/easy way to do it myself or will I need to take it somewhere?
 

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2004 chevy trailblazer_lt
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72 Posts
:m2: Possibles > Low fuel pressure (pump failing and / or fuel regulator} can cause a random misfire as well as your fuel filter could be plugged giving reduced fuel delivery.

Pressure Check Within Specs ?
 

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2003 chevy trailblazer_ls
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4 Posts
Discussion Starter #5
Update! Was able to borrow a compression tester from my grandpa and got around to actually swapping all 8 of the spark plugs. Now I have no misfires on cylinders 3-7. Cylinder 1 still has a consistent misfire and its compression read 25 (the rest of the cylinders read 125). What could be the cause of this? Cylinders 2 and 8 have good compression but misfire at idle (not under throttle). What could cause this?
 

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25 PSI indicates a problem. Does it make noise? #1 cylinder is an AFM cylinder, right? Next you need to disassemble/pull left valve cover and see if both rocker arms are opening and closing valves. If they are then remove rockers so both valves are closed and slowly feed air into cylinder, you'll need to modify your compression gauge and have access to an air compressor. Or have an air compressor and a cylinder leak down tester. In any event, slowly feeding air in will show where your compression is going, if air in intake=intake valve, air in exhaust=exhaust valve. Hearing some air in crankcase is normal but excessive =rings/pistons(not likely).
 
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