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post #1 of (permalink) Old 05-24-2019 Thread Starter
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Misfire Diagnostics.

I've always had a weird misfire that would only occur at high RPM. Would only happen around 5,000+ and would Immediately clear up. But now It's starting to happen more. I was running errands last week and was just driving normally with the ac on but It felt kinda down on power but I figured It was because It was warm out. A heavily modded Silverado wanted to play and when I got on the SS I knew something was wrong, when It got to 5,500 RPM It started chugging until It shifted to second gear but still felt funny after that. Looked at misfire data and cylinder 5 was the culprit along with two other ones but 5 was the main one causing problems. I believe cylinders 3 and 4 were the other misfiring cylinders. But I swapped coils and cylinder 5 Is still doing It. I got some new misfires on 6 and 7 so I believe the coils I switched from 3 and 4 are bad. But 5 Is still the worst
doing It after multiple coil swaps. I even swapped the Injector from 5 to 1. It hasn't actually set a code yet for cylinder 5 after swapping Injectors but still the misfire counter Is still going up at high RPM but It hasn't chugged or lost power yet. But I haven't really been able to test It as It happens after you been on It for awhile. For example taking first or second gear to redline Is when It usually starts misfiring but then will clear right up. I'm at 156k think maybe the cam or crank sensor Is going out. Probably wouldn't be a bad Idea to replace them anyway as there not expensive. I also Installed all new OEM spark plugs and wires a few days ago. AcDelco plugs 41-162 and AcDelco wires. Cylinder 5 Isn't a DOD/AFM cylinder so I'm not sure. Please help thanks. LS4 V8 5.3
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post #2 of (permalink) Old 05-25-2019
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You can check fire on each cylinder with a light like this https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds.

I am not a mechanic, but if it were mine and all checked out good with ignition I would next be checking compression.

Given you have run e85 in a car/engine not designed to run it, you may be seeing possible progression of damage.

My 6 year constantly asks why. What adults can learn from 5 and 6 year olds, to listen with your ears and mind open. Hard to learn when you don't listen ......
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Quote:
Originally Posted by 12 lt View Post
You can check fire on each cylinder with a light like this https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds.

I am not a mechanic, but if it were mine and all checked out good with ignition I would next be checking compression.

Given you have run e85 in a car/engine not designed to run it, you may be seeing possible progression of damage.
Nah It's been happening long before I started running e85 It's just that It's happening a lot more now. So I'm gonna see If goes to cylinder 1 after the Injector swap and go from there If It stayson that cylinder I'll do a compression test and start looking at the heads.
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