607motorsports

iTrader: (6)

To make a long story short this is a completely new build. Motor is a forged 6.0 based block from a reputable builder. Since startup and first drive the car has been missing/skipping when trying to drive it around town. I initially thought the issue was plug wires since I had burnt a couple up that contacted the turbo headers so i've replaced them but still no improvement.

New plugs (NGK br8ef), coils were on the car last season before pulling the motor and worked fine, new wires, new FIC 1000's, i've checked all grounds and made sure they were clean and solid but still skipping and I can't figure it out, any advice/help is greatly appreciated!

02 z/28

iTrader: (19)

Is the miss rpm related?

black06g85

iTrader: (6)

is it cutting out as in motor dies and comes back, or just a random miss?

607motorsports

iTrader: (6)

It's really more of a constant skipping than a missfire. At idle it seems decent but as soon as you start driving it the car skips like crazy.

607motorsports

iTrader: (6)

Did a test tonight to check for leaks at the intake and didn't find anything there however It appears at just 10psi im leaking air past the valves, into the headers and out my wastegate...

Heads are brand new and were bench tested by my machine shop, any other reason why this may be happening? I'm using the same pushrods I had on my old setup with 241 heads. The new heads are 317's, would the pushrod length be any different?

stevieturbo

So you removed the rockers before the pressure test ? Otherwise air will of course get past the open valves and potentially out the exhaust.

and if something is also leaking out the wastegate, is it not shut ?

And datalog for any anomalies that might be causing the miss

forcd ind

iTrader: (7)

What is your lifter preload-was it checked
Anytime you swap parts that were diff, you need to ck everything
How do the plugs look, #8 is a cold plug depending on usage
Try running it at night, in the dark, look for spark leakage

607motorsports

iTrader: (6)

I did not pull the rockers but i bumped the motor over a few times to get it off the exhaust stroke and still no change. I was pressurizing the intake trying to find a leak at about 12-15psi and my gate spring in there right now is about a 10psi spring so I thought that was normal?

stevieturbo

Unless you remove the rockers, a leak test as you describe is pointless.

Or you could plug the exhausts instead.


If you're only testing the gate operation by applying pressure to the bottom chamber to open it, then yes it should take roughly same air pressure as spring pressure to start opening it.

607motorsports

iTrader: (6)

Planning on pulling the rockers this weekend to do a leak test. The wires are all secure and no blowout there. If the leak test is good to go gonna throw in a new set of br7ef's and test a buddies coils on it. I'm running out of ideas

Fat Jesus 808

iTrader: (5)

pushrod length?

coltboostin

Have you checked compression? Always go back to the basics. That will also show if a pushrod issue is hanging the valve open.

607motorsports

iTrader: (6)

I have done a compression test a couple of times now and numbers are right around 160-165 across the board. Pushrod length was in my thoughts but this same cam/pushrod combo was in my ls6 motor and 241 heads. The new setup is an LQ4 based 6.0 block and 317 heads that have not been decked. Everything I could find said the length should be the same?