Lost, help appreciated.
Thread Starter
Teching In
Joined: Aug 2025
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Lost, help appreciated. moderator, if in the wrong spot please move but show me how to find it please.
First, I owned a 2001 suburban 6.0 LS and regret selling it and my 69 Camaro. Wish I would’ve married those two and been happy ever after. Wife love “her” suburban so recently we got a 2103 tahoe 5.3 ppv (police pursuit vehicle) at local auction and it’s killin me.
idk but think it’s LY5? It’s e85 compliant and has the dumb afm. I posted all this on a suburban/tahoe forum and only response was a moderator kicking me to the PPV section then crickets. Hoping there is some smart dudes here to help.
cylinder 3 random misifire, not constant. Not AFM, thats cylinders 1&7 this bank.
its over my head so took it to two different shops that both tried some and couldn’t go further so sent me down the road rather than rip me off. I used to be a mechanic in carburetor days then Mac tool guy for a few years, so know which shops around me aren’t thieves.
Bought at auction town next to Vegas with under 70k miles, obviously lot of idle time.
mechanical compression test good, relative compression shows something odd but can’t determine.
pulled valve cover: springs good, valve train operation good.
8 new spark plugs. Swapped coils w/#1. New spark wires 1&3 after coil swap. New injectors on this bank only. Everything done and the misfire is always only in #3. It is intermittent. Sometimes so mild you can’t feel it. Once was rough while driving @20mph enough I panic stopped and shut off engine, restarted and ran great. Next morning felt like 9.0 earthquake on start up, immediately shut off. Popped hood, all looked ok, attempted restart and never fired off. After work I recorded & cleared codes and tried again. Ran fine and drove to first shop.
All I can guess is wiring to that one coil? The mechanics checked that and found nothing. Oh yeah, when they put in the new injectors they even went in and swapped 2 of the new injectors just incase a new defective- always #3 fails but not always immediately.
Ok guys, fire away!
First, I owned a 2001 suburban 6.0 LS and regret selling it and my 69 Camaro. Wish I would’ve married those two and been happy ever after. Wife love “her” suburban so recently we got a 2103 tahoe 5.3 ppv (police pursuit vehicle) at local auction and it’s killin me.
idk but think it’s LY5? It’s e85 compliant and has the dumb afm. I posted all this on a suburban/tahoe forum and only response was a moderator kicking me to the PPV section then crickets. Hoping there is some smart dudes here to help.
cylinder 3 random misifire, not constant. Not AFM, thats cylinders 1&7 this bank.
its over my head so took it to two different shops that both tried some and couldn’t go further so sent me down the road rather than rip me off. I used to be a mechanic in carburetor days then Mac tool guy for a few years, so know which shops around me aren’t thieves.
Bought at auction town next to Vegas with under 70k miles, obviously lot of idle time.
mechanical compression test good, relative compression shows something odd but can’t determine.
pulled valve cover: springs good, valve train operation good.
8 new spark plugs. Swapped coils w/#1. New spark wires 1&3 after coil swap. New injectors on this bank only. Everything done and the misfire is always only in #3. It is intermittent. Sometimes so mild you can’t feel it. Once was rough while driving @20mph enough I panic stopped and shut off engine, restarted and ran great. Next morning felt like 9.0 earthquake on start up, immediately shut off. Popped hood, all looked ok, attempted restart and never fired off. After work I recorded & cleared codes and tried again. Ran fine and drove to first shop.
All I can guess is wiring to that one coil? The mechanics checked that and found nothing. Oh yeah, when they put in the new injectors they even went in and swapped 2 of the new injectors just incase a new defective- always #3 fails but not always immediately.
Ok guys, fire away!
Thread Starter
Teching In
Joined: Aug 2025
Posts: 3
Likes: 0
p0303 cylinder 3 misfire
p0351 ignition Coil A Primary/Secondary CircuitThese were before it went into the shops. The codes were cleared multiple times when they worked on it and are not currently on, but at least the 303 I know he said returned multiple times.
a reminder coil 1&3 were swapped but problems continued at cylinder 3 so the coil should be fine.
they back probed power,ground, etc at the coil and everything was ok when they did (both shops said the probed the harness at the coil and at that time dismissed harness supply issues- but thats all I see as an intermittent possibility).
haha- oops I forgot.
p0303 cylinder 3 misfire
p0351 ignition Coil A Primary/Secondary CircuitThese were before it went into the shops. The codes were cleared multiple times when they worked on it and are not currently on, but at least the 303 I know he said returned multiple times.
a reminder coil 1&3 were swapped but problems continued at cylinder 3 so the coil should be fine.
they back probed power,ground, etc at the coil and everything was ok when they did (both shops said the probed the harness at the coil and at that time dismissed harness supply issues- but thats all I see as an intermittent possibility).
p0303 cylinder 3 misfire
p0351 ignition Coil A Primary/Secondary CircuitThese were before it went into the shops. The codes were cleared multiple times when they worked on it and are not currently on, but at least the 303 I know he said returned multiple times.
a reminder coil 1&3 were swapped but problems continued at cylinder 3 so the coil should be fine.
they back probed power,ground, etc at the coil and everything was ok when they did (both shops said the probed the harness at the coil and at that time dismissed harness supply issues- but thats all I see as an intermittent possibility).
P0351 is ignition Coil A Primary/Secondary Circuit for Cylinder Number 1
P0303 is obviously misfire detected on Cylinder Number 3
I wouldnt swap parts between 2 cylinders with issues, you could be adding to or band aiding something. Try swapping the coil currently on number 3 with number 5 and see if the issue remains.
You stated " mechanical compression test good, relative compression shows something odd but can’t determine." could you expand on that???
Thread Starter
Teching In
Joined: Aug 2025
Posts: 3
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Ahh, good point about why they used coil #1. Maybe thats why it got the new plug wire- they weren’t clear about that.
thank you for having me see that clearly. I’m at the point of cant see the forest through the trees right now.
the injectors replacement was basically firing the parts cannon. They were going to do all 8 and theory was an unknown amount of idle time being a cop car and all- maybe the injector was goofing up. And he said when the pull the rail it often messes up the other injectors with a clip & oring. Idk about these engines if thats true or not. But I didn’t see the need to mess with the bank that is working fine. I figure if the problem is solved and I keep the rig, I will pit in the other 4. If I sell it I will tell new owner what was done and why. I’m not a hide the truth kinda guy. I rather loose a couple bucks and look at my face in the mirror.
thank you for having me see that clearly. I’m at the point of cant see the forest through the trees right now.
the injectors replacement was basically firing the parts cannon. They were going to do all 8 and theory was an unknown amount of idle time being a cop car and all- maybe the injector was goofing up. And he said when the pull the rail it often messes up the other injectors with a clip & oring. Idk about these engines if thats true or not. But I didn’t see the need to mess with the bank that is working fine. I figure if the problem is solved and I keep the rig, I will pit in the other 4. If I sell it I will tell new owner what was done and why. I’m not a hide the truth kinda guy. I rather loose a couple bucks and look at my face in the mirror.
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Ahh, good point about why they used coil #1. Maybe thats why it got the new plug wire- they weren’t clear about that.
thank you for having me see that clearly. I’m at the point of cant see the forest through the trees right now.
the injectors replacement was basically firing the parts cannon. They were going to do all 8 and theory was an unknown amount of idle time being a cop car and all- maybe the injector was goofing up. And he said when the pull the rail it often messes up the other injectors with a clip & oring. Idk about these engines if thats true or not. But I didn’t see the need to mess with the bank that is working fine. I figure if the problem is solved and I keep the rig, I will pit in the other 4. If I sell it I will tell new owner what was done and why. I’m not a hide the truth kinda guy. I rather loose a couple bucks and look at my face in the mirror.
thank you for having me see that clearly. I’m at the point of cant see the forest through the trees right now.
the injectors replacement was basically firing the parts cannon. They were going to do all 8 and theory was an unknown amount of idle time being a cop car and all- maybe the injector was goofing up. And he said when the pull the rail it often messes up the other injectors with a clip & oring. Idk about these engines if thats true or not. But I didn’t see the need to mess with the bank that is working fine. I figure if the problem is solved and I keep the rig, I will pit in the other 4. If I sell it I will tell new owner what was done and why. I’m not a hide the truth kinda guy. I rather loose a couple bucks and look at my face in the mirror.