RPM cut on stock PCM (3bar OS p01 computer)
 

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.


https://cimg0.ibsrv.net/gimg/ls1tech...47984b7af8.jpg


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


https://cimg8.ibsrv.net/gimg/ls1tech...edcd0c6888.jpg


I'm including my tune. Let me know if you need any more info.

sorry, I'm running out the door to work i'll add the actual log file.

here is a picture of a dead piston in the mean time :)


https://cimg4.ibsrv.net/gimg/ls1tech...5808332b4e.jpg

Looks like it was lean before you ever got into the rev limiter on the scanner... low 15s for sure do that moving 188kpa and 13 degrees

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

ok here's the log file from the pulls that hurt the motor. does it look like spark is being cut as well as fuel?

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.

see I think I'm getting two different stories

this dude over in another thread said this

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)



https://cimg4.ibsrv.net/gimg/ls1tech...592a84beae.jpg


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

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 :cry:

problem wasn't the limiter, for sure.

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.

Your log file says invalid for me.
Odd.

Why is your rev limit so low? Your tune shows 6200?

Always hard to do a definitive post mortem.
Maybe find another 6.0 piston/rod and throw it in and continue?

I have stock 5.3 unassembled with the rings gapped for boost cheap if you don't have a 4.8 ready to slap in there.

hi ron thanks for taking a peek.

whoa thats weird lemme try and reload the log file...are you on v3.24?


yes I had it set fairly low. 29" tires and a 3.5 gear I didnt think I'd need a whole bunch of rpm.

just got the six liter back from the shop. all checked out ok. talked myself into bearings and rings while it was apart.

I have a "gen 4" 4.8 on the stand that I'm gonna slap in while I take my time with the six liter assembly.

ok lets try again. i couldnt open in from the posted version either.I renamed it without the dash

I'm on 3.4X
Tried to hide 3.2X on the laptop but hpt still blasted it out when I updated to 3.4.
Should be compatible though?

Prob best for me to save the iron 5.3 block just in case......:-)

What machine shop here are you using?

ok that appears to work. i think it was the pull at the ~6 minute mark that did the deed.

Ron, hopefully I'll have this thing wrapped up in the next week or two so i can come see you and work it out on the dyno,

yeah you better hold on to it for a spare....i sold my spare motor just days before I hurt the six liter :(


I used central cylinder head on 12th and powell. two blocks in a row they didnt screw anything up! probably jinxed myself being happy about that lol

this caused your damage or all the other boost spikes you have in the log doug :(

I've known Jerry, Randy, and the guys for 40 years.
Good folks.