Misfire on #8 at 5000rpm help

[vsellens]

07 ls2 corvette edelbrock eforce blower, stock everything else. At about 5000 rpm #8 cyl misfires about 18-35 times. By the time it gets to 5300 it quits misfiring and begins to build power again. I have swaped plugs, wires, coils, injectors, inspected the crank relucter ring, rerouted the fuel system to feed the fuel rails better, heck I've even replaced valve springs to no avail.

[vsellens]

heres a dyno sheet. and logs run 12 goes with misfire1 config anr run 3 goes with 07ef config

[vsellens]

Compression test and cylinder leak down test are both good. Does any body have any ideas of other things to check?

[10_SS]

Is there any way the spark plug electrode direction play a part in this? Or could it be too rich/lean and that cyl is affected the most?

Or maybe fuel pressure is low and the injectors not able to atomize properly?

Next time let it miss fire and shut the engine off and pull the plug see what it looks like.

My scanner isnt showing your 02 readings so maybe it's too rich or lean?

[vsellens]

The fuel pressure never drops below 56 psi and its running 12 to 1 afr. The plugs don't look lean. I tried shrinking the gap a little more down to .022" it didn't help. The last test I did is watch the injector waveform on a scope at 5000 rpm. It does something kind of strange so I'm leaning towards an injector driver in the ecu.

[realcanuk]

can you post the tune. Maybe by comparing I can spot something off.

[vsellens]

I'll post the tune in the morning its at work.

[IDRIVEAG8GT]

I know you said you swapped plugs, but I'm willing to bet the plug is cracked. 12:1 is too lean. Turn it down to 11.5:1 AFR.

[IDRIVEAG8GT]

What injectors are you running by the way?

[realcanuk]

One more thing to check. This happened to me and a few others and trust me, it was a nightmare to diagnose. The coil pack harness can get crushed and a wire damaged when reinstalling.
some info here

http://forums.corvetteforum.com/c6-f...e-force-2.html

[10_SS]

WB's cant always be trusted either. I would richen it up a bit and see how it feels then do the opposite if it gets worse.

[vsellens]

What injectors are you running by the way?

zr1 injectors, the ones that come with the kit. I richened it up a bit and leaned it out it didnt seam to make a difference. I've installed about 20 to 30 of these kits on everything from an ls2 to an ls7 and this is the first time I've had an issue. I think edelbrock sized the injectors waaaay too small for this aplication. my duty cycle is at about 95%. Most of the kits I have installed were on cars with cams and heads or all out built motors. On those aplications I sized my own injectors. I have inspected all the coil harness and the injector harness no pinched wires. thanks for your help. I've also checked the cats their good.
heres the tune

thanks again for your help

[vsellens]

I know you said you swapped plugs, but I'm willing to bet the plug is cracked. 12:1 is too lean. Turn it down to 11.5:1 AFR.

I not only swaped plugs I replaced the whole set. I cant get much richer nthan 12:1 Im at 95% dutycycle. I also noticed on the before pull on the dyno that the problem was already there. its a small dip and the blower just made it bigger exact same rpm

[realcanuk]

Is that a canned edelbrock tune ? Why is the Cylinder volume changed ?

[vsellens]

Is that a canned edelbrock tune ? Why is the Cylinder volume changed ?

yes it is and damed if i know

[vsellens]

it wont let me post the before dyno sheet the files too big or something

[realcanuk]

I never used the canned tune but I dont here much good about it. Apparently they update it often, I would check their site for that. Im going to look at it closer later when I can. I am curious as to what they do.

[vsellens]

its there latest updated tune

[IDRIVEAG8GT]

Hmm, well fuck. And it's that RPM everytime? I'm almost going to say shitty crank trigger sensor that is, since plugs are ruled out. I don't like seeing injectors that high on the Duty Cycle. BAP perhaps if you don't already have one.

Unless we have an issue in the cylinder head. Try doing a simple Write Entire and see what happens. I've seen stranger things go away simply by doing that.

[realcanuk]

There are a lot of things I dont like in the tune, but I suppose it should work fine if thats what so many people use.
I have yet to hear of it being a problem, especially with the car being stock, but I never liked how the fuel rails are fed on the eforce. #8 gets fuel last and could possibly get short changed on delivery. I have changed mine to feed directly to both rails. I suppose it is a possiblity especially if the pressure got a bit low.