misfire problem that I need help with. (Page 1/1)
Tweeder FEB 17, 01:10 PM
The truck: 2000 silverado 5.3 Z71 RCSB 4X4, 2005 caddy conversion, 4L80E, 6" BDS lift, 3" body lift, torsion bar keys, 36" super swamper TSL SX, throttlebody spacer, headers, 3" magnaflow hi flow cats and mufflers, lingenfelter high volume oil pump, double roller timing chain, comp cams 265 extreme, GMPP yellow springs, chromolly pushrods, 44lb. injectors, ported 317 heads, e-fans, Intercooled Powerdyne BD-11A, HP Tuners, Detroit tru-trac. The problem: I have it hooked up to hptuners and did a scan with my misfire cfg and it showes multiple misfires in cylinders 4,5,6. I just replaced the fuel filter and checked the plugs. So one by one to disconnected each coil pack at the harness.
1 missfired 8
2 missfired 6
3 missfired 3 and sometimes 1
4 missfired 4+3
5 missfired 4+5 and sometimes 6
6 missfired 6 and sometimes 5
7 missfired 2+7
8 missfired sometimes 7+6

Any idears? I had a p0300 code but once cleared it hasn't come back but stumbles so bad to the point its not driveable. Also for the current cylinder firing its random and I don't recall seeing cylinder 8. Heres a vid of last year, ignore the misfire on that one as I found out it was a cad coil and a loose inhector harness. Concentrate on the current firing cylinder.

http://www.youtube.com/watch?v=8N7bH0TDcRY

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86 GT Convertable 3800

Tweeder FEB 17, 05:10 PM
I unplugged the maf and that changed nothing. Unplugged each injector individually, the engine stumbled when disconnected so they're all working. I temped all cylinders 2,4,6,8 I couldn't get a reading on as the machine only goes to 320. On 1,4,7 3-320 but on 3 it barely hit 200. In drive, I foot braked it and floored it and it barely makes it past 2000rpms.

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86 GT Convertable 3800

Raydar FEB 17, 05:39 PM
This is a complete shot in the dark, but have you done anything with the crank sensor, recently? (Or might it be failing?)
Replacement of the crank sensor usually (always?) requires a procedure called a CASE learn. It calibrates the PCM to the particular crank sensor that is installed. (And yes, they're supposed to be *that* picky.)
Seems like I remember that the failure to perform this procedure produces a bunch of random misfires.

I hope someone else can elaborate on this, since all I've done is read about it.
Or maybe just Google "CASE learn", along with your vehicle or engine.
Tweeder FEB 17, 05:50 PM

quote
Originally posted by Raydar:

This is a complete shot in the dark, but have you done anything with the crank sensor, recently? (Or might it be failing?)
Replacement of the crank sensor usually (always?) requires a procedure called a CASE learn. It calibrates the PCM to the particular crank sensor that is installed. (And yes, they're supposed to be *that* picky.)
Seems like I remember that the failure to perform this procedure produces a bunch of random misfires.

I hope someone else can elaborate on this, since all I've done is read about it.
Or maybe just Google "CASE learn", along with your vehicle or engine.



No haven't touched it, the only codes I have are the p0300 and p0141, the heater part I'm not worried about it just takes longer to get an accurate reading. But that's been like that for well over a year and this problem just started last week. I also checked the vacume and it's steady at 13 in/hg.

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86 GT Convertable 3800

Tweeder FEB 20, 09:57 PM
I might have found out the problem, I checked cylinder #3 as it temped colder. I stuck my bore scope in there and I thought I seen a chunk of something right under the spark plug hole. So I cranked it till the piston was lower and looked again, it looks like a small chunk off one side. I put a compression tester and got just over 100 cold and it wouldn't hold pressure. Guess I gotta pull the heads and see.

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86 GT Convertable 3800

Tweeder FEB 23, 03:19 PM
Well that didn't solve anything. I have the drivers side head off and the #3 cylinder looks normal, I must have been looking at carbon or something. But that doesn't explain the low temp and compression reading. I looked at the intake gasket and that cylinder looks normal. I have one thats questionable with a little wave in it on cylinder #1. Should I pull the other head? I didn't compression test any other than #3. I also bought ARP head bolt kit years ago and never had a chance to put them on. Its a LS6 kit #134-3610. Looking at the bolts there's 2 sizes, large and small. On my truck I have 2 different lengths on the larger bolts, this kit has all the same length for the larger. What do I do about that? I can't reuse the bolts I just pulled out. I also noticed when I drained the oil, the magnet was full of filings.

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86 GT Convertable 3800

Tweeder FEB 24, 11:51 PM
I got the other head off and as with the other side, I see nothing wrong in the cylinders.
I have the pan loose and sitting on the crossmember. I thought I could get it out as the flex plate was in the way, so I disconnected the tranny and slid it back enough to take off the flex plate. I still can't get the pan out, it looks like its catching on the pick up tube. Any suggestions on that feat?

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86 GT Convertable 3800