RPM's When in park or neutral

HendyPhoto · March 19, 2003

when my truck is in park or neutral, I cant rev up the engine past 3,000 RPM's, is this normal? I was trying to show my friend what it sounds like when its reved really high, but couldnt. Thanks!

BlackSilver · March 19, 2003

No offense, but it seems like the truck is trying to protect itself from abuse. Revving an unloaded engine is begging for things to come apart in an unpleasant manner.

CMNTMXR81 · March 19, 2003

It is a self protect rev limiter. GM has been using it for years on FWD cars. Albeit they're set at 3,500rpm

In park or nuetral is when you'll notice it.

HendyPhoto · March 19, 2003

I didnt exactly want to hold it red-lined for a while! If my GMC blew up at 3500-5500 rpm's I would replace it with a Ford.

Gracias once again CMNT, I was just curious!

Shaners · March 19, 2003

My 6.0L will free rev, so it must be a bigblock feature...

CMNTMXR81 · March 19, 2003

Mine free revs too. Just that it's not uncommon for GM to do this.

Just one of those quirks of assembly. Hendy may have a slightly different PCM, slightly different programming, different re-flashes, etc, etc.

GM does it for good reason though, I have a story on that one, but don't have enough time to tell it right now. It involves a 2000 LS1 powered Camaro that the owner complained of cold knock and proceed to blow his motor to get a new one....Guess how he blew it?

Larry · March 19, 2003

Here is something for you guys with Allison’s to try….Nail the hammer to the floor and yank the shift lever into drive then come back and tell us all what happened.

BlackSilver · March 19, 2003

Here is something for you guys with Allison’s to try….Nail the hammer to the floor and yank the shift lever into drive then come back and tell us all what happened.

Left two black grooves in my concrete driveway!

HendyPhoto · March 19, 2003

I can spin my 36x14.50's just as well as my stock tires. But sorry, I wont rev it in neutral and drop it in gear. I will leave that for you to experiment with!

CMNTMXR81 · March 20, 2003

Here is something for you guys with Allison’s to try….Nail the hammer to the floor and yank the shift lever into drive then come back and tell us all what happened.

I know that Allison would last a lot longer than any other currently available transmission in GM's lineup! And I'd leave two monster blackies in the process!!!

Larry · March 20, 2003

Com’on, don’t be scared go try it. Nothing bad will happen…honest.

Ok, since you guys won’t try it I’ll tell you what happens. One thing that doesn’t happen is leaving two black grooves on your concrete driveway their Blacksilver.

Actually, the Allison LCT1000 transmission control module is programmed to power down the engine RPM’s by interrupting the throttle actuator control module’s signal to the PCM at any engine speed higher than somewhere around 1300 RPM and return it to base idle. So if you nail the throttle to the floor and pull the lever out of park the engine automatically goes to idle until the throttle actuator sees zero input again then shifts the transmission into gear. (have to return throttle to idle position) Pretty cool huh?

I was pretty apprehensive to try shifting a Workhorse 20,000lb motorhome with an 8.1L and Allison 1000 into drive at full throttle when I was at Allison training last fall when the instructor asked me to. I though for sure I would see a driveshaft get launched from underneath that big thing. It is really neat and almost spooky, as someone mentioned it, how smart the Allison programming technology is.

I am not sure if this trick works on the smaller hydromatics or not so I wouldn’t try it with a 4L85E or anything smaller or you might just grenade a driveshaft or u-joint.

BlackSilver · March 21, 2003

Two BLACK grooves.

That's my story and I'm stickin' to it!

Larry · March 21, 2003

Two BLACK grooves.

That's my story and I'm stickin' to it!

Rigghht!

HendyPhoto · March 21, 2003

L O L

CMNTMXR81 · March 21, 2003

Com’on, don’t be scared go try it. Nothing bad will happen…honest.

Ok, since you guys won’t try it I’ll tell you what happens. One thing that doesn’t happen is leaving two black grooves on your concrete driveway their Blacksilver.

Actually, the Allison LCT1000 transmission control module is programmed to power down the engine RPM’s by interrupting the throttle actuator control module’s signal to the PCM at any engine speed higher than somewhere around 1300 RPM and return it to base idle. So if you nail the throttle to the floor and pull the lever out of park the engine automatically goes to idle until the throttle actuator sees zero input again then shifts the transmission into gear. (have to return throttle to idle position) Pretty cool huh?

I was pretty apprehensive to try shifting a Workhorse 20,000lb motorhome with an 8.1L and Allison 1000 into drive at full throttle when I was at Allison training last fall when the instructor asked me to. I though for sure I would see a driveshaft get launched from underneath that big thing. It is really neat and almost spooky, as someone mentioned it, how smart the Allison programming technology is.

I am not sure if this trick works on the smaller hydromatics or not so I wouldn’t try it with a 4L85E or anything smaller or you might just grenade a driveshaft or u-joint.

Yea, that's called Torque Management!