RPM cut on stock PCM (3bar OS p01 computer) - LS1TECH - Camaro and Firebird Forum Discussion



PCM Diagnostics & Tuning HP Tuners | Diablo | Pantera EFI
Sponsored by:
Sponsored by:

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

Reply
 
Thread Tools Search this Thread
Old 04-19-2017, 08:33 AM   #1
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default 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.





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.
Attached Files
File Type: hpt six liter swap 2.3.2.hpt (237.0 KB, 7 views)
truckdoug is online now   Reply With Quote
Old 04-19-2017, 08:35 AM   #2
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

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


truckdoug is online now   Reply With Quote
Old 04-19-2017, 08:42 AM   #3
TECH Fanatic
iTrader: (11)
 
T/A KID's Avatar
 
Join Date: Jul 2004
Posts: 1,775
Default

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
T/A KID is online now   Reply With Quote
Old 04-19-2017, 11:40 AM   #4
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

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
truckdoug is online now   Reply With Quote
Old 04-19-2017, 06:28 PM   #5
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

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?
Attached Files
File Type: hpl 3.30-1.hpl (1.67 MB, 16 views)

Last edited by truckdoug; 04-19-2017 at 06:29 PM. Reason: added file
truckdoug is online now   Reply With Quote
Old 04-19-2017, 06:42 PM   #6
10 Second Club
iTrader: (24)
 
ddnspider's Avatar
 
Join Date: Aug 2004
Location: FL
Posts: 5,757
Default

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.
ddnspider is offline   Reply With Quote
Old 04-19-2017, 08:45 PM   #7
TECH Addict
iTrader: (1)
 
Join Date: Sep 2004
Location: Stockbridge GA
Posts: 2,458
Default

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.
gametech is offline   Reply With Quote
Old 04-19-2017, 09:58 PM   #8
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

see I think I'm getting two different stories

this dude over in another thread said this

Quote:
Originally Posted by NicD View Post
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
truckdoug is online now   Reply With Quote
Old 04-19-2017, 10:01 PM   #9
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

Quote:
Originally Posted by ddnspider View Post
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
truckdoug is online now   Reply With Quote
Old 04-19-2017, 10:34 PM   #10
TECH Enthusiast
iTrader: (5)
 
subeone's Avatar
 
Join Date: Apr 2013
Posts: 695
Default

problem wasn't the limiter, for sure.
subeone is offline   Reply With Quote
Old 04-20-2017, 08:16 AM   #11
10 Second Club
iTrader: (24)
 
ddnspider's Avatar
 
Join Date: Aug 2004
Location: FL
Posts: 5,757
Default

Quote:
Originally Posted by truckdoug View Post
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.
ddnspider is offline   Reply With Quote
Old 04-20-2017, 08:30 AM   #12
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

Quote:
Originally Posted by subeone View Post
problem wasn't the limiter, for sure.
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.
truckdoug is online now   Reply With Quote
Old 04-20-2017, 10:19 AM   #13
10 Second Club
iTrader: (2)
 
RonSSNova's Avatar
 
Join Date: Aug 2011
Location: Portland, OR
Posts: 2,652
Default

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.
RonSSNova is online now   Reply With Quote
Old 04-20-2017, 10:27 AM   #14
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

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.
truckdoug is online now   Reply With Quote
Old 04-20-2017, 10:35 AM   #15
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

ok lets try again. i couldnt open in from the posted version either.I renamed it without the dash
Attached Files
File Type: hpl bustedringlands.hpl (1.67 MB, 7 views)
truckdoug is online now   Reply With Quote
Old 04-20-2017, 10:36 AM   #16
10 Second Club
iTrader: (2)
 
RonSSNova's Avatar
 
Join Date: Aug 2011
Location: Portland, OR
Posts: 2,652
Default

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?
RonSSNova is online now   Reply With Quote
Old 04-20-2017, 10:37 AM   #17
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

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,
truckdoug is online now   Reply With Quote
Old 04-20-2017, 10:39 AM   #18
TECH Addict
Thread Starter
iTrader: (19)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 2,429
Default

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
truckdoug is online now   Reply With Quote
Old 04-20-2017, 11:33 AM   #19
TECH Enthusiast
iTrader: (5)
 
subeone's Avatar
 
Join Date: Apr 2013
Posts: 695
Default

this caused your damage or all the other boost spikes you have in the log doug
Attached Thumbnails
RPM cut on stock PCM (3bar OS p01 computer)-damage.png  
subeone is offline   Reply With Quote
Old 04-20-2017, 11:34 AM   #20
10 Second Club
iTrader: (2)
 
RonSSNova's Avatar
 
Join Date: Aug 2011
Location: Portland, OR
Posts: 2,652
Default

I've known Jerry, Randy, and the guys for 40 years.
Good folks.
RonSSNova is online now   Reply With Quote
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Meziere ewp 300 55gpm bth2278 Parts Classifieds 8 07-06-2017 03:04 PM
83 GMC shortbed. Twin turbo 5.3, TH350 build moe4541 Forced Induction 0 06-11-2017 05:08 PM
NIB Nitrous Outlet Fuel Nitrous and purge solenoids and -6 line Turbo306Fox Parts Classifieds 8 02-27-2017 11:41 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 09:51 AM.


 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: