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.



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.

 

I just checked the vacume and it's steady at 13 in/hg.

 

was it in any deep water or mud,lots of rain.look under the hood in the dark and check for any sparks.maybe you have water in the plug wire boot.unplug and spray all injector clips for water.check for bad plugs or plug wires.

 

Ne no water at all, i'll check for spark in the dark tonight. I sprayed the engine with carb cleaner yesterday and didn't hear a difference, I could do it again.

 

This my be a little out there but my 2000 z28 was having a similar issue and after changing out my plugs, wires, coil packs, and maf i finally changed out my 02's and Now it runs like a champ. The car never called the o2's. I just kept getting p0300. Good Luck!

 

Those misfire counts, at idle I assume, are not troubling.
A little lumpy. I would be inclined to blame closed loop
operation (O2 sensors) as well; the thing is, when they
get old (or cold), they get slow and when they get slow,
the fueling loop (trim and proportional fueling) "overtravels"
more as it tries to get the next sensor switching event.
New and hot, if you watch O2 voltages they never peg
high or low but bounce tight like 300-700mV; old / cold
you see them bury to 0mV and then swing up to 1V and
then back.

Upshot being your AFR (if you didn't filter the reading to
the point that you can't see real activity in-the-moment)
can swing 13-16 on a tight setup, and 10-20 on an aged
one. Which is going to stumble more?

You can test this by hot-idling for a minute, let it drop
to rest, and look at the NBO2s and misfires immediately,
and after a couple minutes' worth of cooldown. If things
start off happy and start bitching as it sits, pin the tail
on the O2s (or more probably the headers, but it's not
like most people will go backward; I think I'm a rare, if
happy, exception).

And I'd lose that TB spacer. Not because it causes any
misfiring, but because it's an insult to the motor and all
motorheads everywhere.

 

heres a hptuners log from tonight. its done in default metric.

 

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.

 

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.

 

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?

 

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?

 

Those misfire counts are normal... if you had a real misfire you would see the misfire counts jumping up every few seconds.

With the transmission installed, can you lift the engine to give you more room...?

 

The misfire that's in that video are from a different problem, the current misfires are in the tune. I wanted the video to show the current firing cylinder being all over the place. I don't think it even shows cylinder #8 and it shows a 0 for some cylinder. I'm going to leave the flex plate out and put a couple bolts in the tranny and lift and see. I tried befor and there wasn't enough room. Or that I could just disconnect the oil pick up tube as that's what looks to be hanging up.

 

I had to remove the pick up tube to get the pan out. Damn chinese cast ****, what I thought was metal flakes in the pan turns out to be slag.. but since I had the pan out I scraped the bottom with my finger and got a couple pics. It looks a silverish color. Where could it be from?

 

From your pic I can't tell flakes from bubbles...

do you have a closer close up without the flash (i.e. use daylight)...?

 

All those fakes/bubbles looking thingies are in the cast. What I was trying to show was the silverish color from scrapie the bottom with my finger(on left). I could try a pic in the daylight.

 

The grey sludge where you scraped your finger across the pan floor does not look like it has metallic sparkle from the pic, is due to water...

most likely from condensation that accumulates when engine is not run to operating temp for a sufficient amount of time.

How much of the grey sludge do you see...? If there's too much then the oil pump may suck it in.

 

Your misfire counters incrementing by 1 every 5 seconds is not a problem, that is normal.

They would be a problem if they incremented rapidly in a few seconds to say over 50 and kept incrementing.

 

Theres not much, just a few mm on the very bottom of the pan but you only see it if scraped. I still have the concern with the filings on the plug and where they might have come from, I wish I would have taken a pic. Its more than i've seen in that motor.

 

Ok I see, yeah the counts never went above 10 before I pulled the coil or injector and then they reset.