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Hey guys I ran into a problem with my 6.0/7875 build and killed a piston.
I think it when lean when I pedaled it off the rev limiter, but some guys are telling me that's impossible since it cuts fuel AND spark so it should just be an air pump.
Well I'm not sure what exactly happened but I want to take some preventative measures for my rev limiter after the motor is back together.
I am looking through the HPT "how-to" section on rpm limits and they show a spark cut box on the same dialog box that fuel cut is on.
My computer doesnt show that.
So I'm wondering where and what I can do to limit rpm safely, even if this was not the root cause of my piston damage.
here is screenshot of the log where I think I hurt the motor
I'm including my tune. Let me know if you need any more info.
That's actually a pic of it after it bounced off the limiter. That white line is injector duty cycle, you can see they closed and then opened for a sec again before hitting the limit a second time.
I'll post the log file tonight.
just want to clarify that I'm cutting spark as well as fuel since I don't see an rpm spark cut table
Your destruction pics made me start thinking of what I can do to mine as well. Personally, I don't buy the fuel cut as the solution. SO, I set my rev limiter sky high (8k) and have it pull a ton of timing above 6400rpms. Something else I'm wondering is what if PE mode table also set the AFR to something rich or lean depending on what you believe is the solution.
The factory computers DO NOT cut spark. If they did, you could potentially send unburned fuel into the exhaust, which would fry and clog catalytic converters.
That's not how it works, it cuts fuel entirely to the cylinder so there is no such thing as a half pulse that causes a lean condition on the limiter... as long as the injector is the only fuel source, ie no meth injection, etc. You had other problems that caused that.
so ok, the injector is closed. no fuel coming from the injectors for however many revs you're on the limiter. but, what about any mixture thats in the intake due to reversion? I'm seeing drive pressures of like 40psi...thats gotta push some unburnt fuel back in. but it's not enough to really run the motor on, just enough to cause a bang at the wrong time.
so color me confused.
if there is no spark cut than what is the spark cut table for? (note, i dont have this table on my PCM/OS but it's listed in parameters for the p59 computers)
I get that the wideband is only reading the results of combustion, but if you really slow down my log...you can see there is quite a lag between what the injector does and what the wideband sees. say it's half a second....at 6200 rpm thats 13 combustion cycles
anyways i'm clear as mud on what the fix is. i'm gonna put a 4.8 in and beat on that for awhile until I get it figured out so I dont croak a decent six liter
Your destruction pics made me start thinking of what I can do to mine as well. Personally, I don't buy the fuel cut as the solution. SO, I set my rev limiter sky high (8k) and have it pull a ton of timing above 6400rpms. Something else I'm wondering is what if PE mode table also set the AFR to something rich or lean depending on what you believe is the solution.
yeah thats my plan currently. i'm not gonna pull too much timing. just enough to nose it over.
depending on your cam, too much timing retard will act like an anti-lag and light the fuse when the exhaust valve is still open...and that's also hard on parts
yeah thats my plan currently. i'm not gonna pull too much timing. just enough to nose it over.
depending on your cam, too much timing retard will act like an anti-lag and light the fuse when the exhaust valve is still open...and that's also hard on parts
that sounds like it would be similar to a 2 step where a ton of timing is pulled, which won't break anything. This is just during a bad event, i.e. hitting the limiter, so it shouldn't break anything.
yeah i'm beginning to think it might have been cracked before i ever got the motor (stock untouched sludge monster) and a couple braps at 18psi rattled it loose.
04-19-2017, 08:33 AM
RPM cut on stock PCM (3bar OS p01 computer) 
