454 Vortec P0300 Multiple cylinder misfire code. Troubleshooting and solution.

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Ttoyota

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I should just swap wifes 6.2 with mine. Doubt she would know the difference.
 

Ttoyota

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So how do you know how many degrees of slop you have. Will i need to get degree tape made for h.balancer
 

Mangonesailor

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So how do you know how many degrees of slop you have. Will i need to get degree tape made for h.balancer

I have no idea, but that's how I found a bad chain on my bronco. I lost 7* of timing advance just from the swap in the chain. I checked the ignition advance when I started it back up.

You don't need a degree tape. There are marks already in the balancer. Just clean them with a wire brush/brillow pad and highlight the lines and numbers with a white paint pen.
 

GaryWB

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I wanted to let you guys know.

My brother has a 2000 Chevy 1 Ton with a 454 and about 145,000 miles on it. He uses the truck to pull a small travel trailer. So if the truck doesn't run right, he can't go camping.

He's been fighting the P0300 code and misfires for several years. He's taken his truck in to his shop to eliminate the issue several times. I'm not sure what all they did, but a lot. I know they pulled the heads, who knows what else. My brother said he spent over 12k with the shop. The misfire may have gone away temporarily, but came back.
He doesn't want to buy a new truck and was getting over the top frustrated with the whole thing.

So, I started doing some research trying to help him, see what I could come up with. I read several forums including "Mangonessailor's" very organized, methodical write up above.

I emailed this write up to my brother so he could compare what the shop had done previously and compare that to all the steps listed here.

He finally decided to take the truck back to the shop and just instructed them to install a new distributor.
That was several weeks ago. The truck has been running perfectly since, no codes, runs perfect.

Have a great day, stay safe.
Gary
 

Erik the Awful

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If he paid to have the misfire fixed, and they charged him without fixing it, he needs to take it back and have them fix it on their dime. They're throwing parts at it without diagnosis ON HIS DIME.

EDIT: Doh! Reading comprehension fail. I'm glad he got it fixed.
 
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Mangonesailor

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I wanted to let you guys know.
....


So, I started doing some research trying to help him, see what I could come up with. I read several forums including "Mangonessailor's" very organized, methodical write up above.

I emailed this write up to my brother so he could compare what the shop had done previously and compare that to all the steps listed here.

He finally decided to take the truck back to the shop and just instructed them to install a new distributor.
That was several weeks ago. The truck has been running perfectly since, no codes, runs perfect.

Have a great day, stay safe.
Gary


Glad I could help him out! Great to hear!
 

Supercharged111

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FWIW I did the gear on my 1500 and all that got me was CMPRET within spec. This has me thinking I should hip shoot the distributor. Mangone did you ever check for slop on yours?
 

8T7K5

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I'm chasing a similar issue on my 99 Suburban. Bought it last summer and it was in terrible condition, had multiple misfires. Figured I'd start with new injectors, new distributor, plugs, new ignition, new ICM, fuel pressure regulator, still didn't fix it. Kept showing misfires on 3 and 4. Compression was good, fuel pressure was good. Pulled 3 and 4 injectors and tested those, they're firing just fine. In the middle of all that it stopped cranking because the previous owner had screwed up a starter bolt hole, which caused the starter to screw up the flexplate. My plan now is to pull the whole engine, put a helicoil in the bunged up bolt hole, and do some other things I can't do with the engine in the truck.

Ultimately I'm planning on replacing the cap with one that has brass contacts and hope that fixes this problem.
 

Mangonesailor

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FWIW I did the gear on my 1500 and all that got me was CMPRET within spec. This has me thinking I should hip shoot the distributor. Mangone did you ever check for slop on yours?

I'll be honest, it didn't feel much tighter than before... I didn't put a dial mic on it. I just compared the teeth side by side, verified the rotor mount was square to the body, and stabbed it in.

However, the summit dizzy soon filled with aluminum oxide after 2yrs and I had to vacuum it out. I attempted to coat the innards with dielectric, and that apparently did not play well with the dizzy.

I got an auto-zone replacement, one of their duralast golds, which has brass terminals and a painted inside-and-out body. That has been on my truck for a couple years now with no problems... and I kept the receipt so when it's dizzy cap time I get a whole new dizzy.

And when the camshaft gear goes... the engine gets built.
 

Supercharged111

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I'll be honest, it didn't feel much tighter than before... I didn't put a dial mic on it. I just compared the teeth side by side, verified the rotor mount was square to the body, and stabbed it in.

However, the summit dizzy soon filled with aluminum oxide after 2yrs and I had to vacuum it out. I attempted to coat the innards with dielectric, and that apparently did not play well with the dizzy.

I got an auto-zone replacement, one of their duralast golds, which has brass terminals and a painted inside-and-out body. That has been on my truck for a couple years now with no problems... and I kept the receipt so when it's dizzy cap time I get a whole new dizzy.

And when the camshaft gear goes... the engine gets built.

I think those housings need to breathe to stay clean. My gear was WAY worse than yours, it was knife edged and I was physically unable to get CMPRET set better than 29 degrees. I've done a cam sensor and even run it unplugged with zero effect. My RPM logs are flawless so I have a hard time thinking it's the crank sensor.
 
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