RPM Limiter

Ok tuning guru's, can someone please tell me exactly what happens when the engine smacks into it's rpm limiter? Fuel cut? Ignition cut? TB closed? Also any supporting information is greatly appreciated. Thanks,

Bump, Ive always wanted to know this also.

Pretty sure it's just a power cut like when you hit the governor. You can still rev and keep the speed but you won't go any faster. Not sure what exactly causes it though. Hmmmm now I'm curious as well lol

Most ECU's cut fuel (The LS1's do). If you think about it if they cut ignition you would have unburned fuel passing thru the motor not good for most emissions eqpt in the exhuast system.

Thanks, I agree the fuel would be cut as there is no backfire or indication anything is rich. I'm hoping the TB continues to operate without closing. I feel it is independent, but was looking for confirmation, Thanks.

The 2 time's i hit the limiter when i first got a tuner and playing with it, the truck just died for a sec. or 2 then came back to life. (1st gear burnout) There was no doubt it had cut fuel. The only way to know for sure if the TB is closing would be to log the correct pid's and run it up and hit the limiter. The log should show what is being effected.

I hit the speed limiter (105) the firts time I raced it on the interstate against a Silverado SS. It just wouldn't go any faster; no bogging, no bucking, nothing. It stayed at that speed and would not go any higher. I attributed this to it being a fly-by-wire all the computer has to do is stop the TB from opeing any more.

Originally Posted by blk05hemi

The 2 time's i hit the limiter when i first got a tuner and playing with it, the truck just died for a sec. or 2 then came back to life. (1st gear burnout) There was no doubt it had cut fuel. The only way to know for sure if the TB is closing would be to log the correct pid's and run it up and hit the limiter. The log should show what is being effected.

That's a good plan. I'll do that using my SC when I return stateside.. Thanks..

Originally Posted by HemiLonestar

I hit the speed limiter (105) the firts time I raced it on the interstate against a Silverado SS. It just wouldn't go any faster; no bogging, no bucking, nothing. It stayed at that speed and would not go any higher. I attributed this to it being a fly-by-wire all the computer has to do is stop the TB from opeing any more.

I can't say that the rpm limiter and speed limiter operate in the same manner. I've never tried as I have adjusted my speed limiter to 140mph but have read that turning the ignition key to the starter position will override the speed limiter. Good luck with that........

Greg, got to think'in after my post, i do know a tuner/friend. It's about time i gave him a call. He may have seen this in a customer's log and may be able to answer that question. He can be a little hard to get ahold of, but i'll see if i get an answer to that question for you. I'll post up if i have any luck.

Originally Posted by blk05hemi

Greg, got to think'in after my post, i do know a tuner/friend. It's about time i gave him a call. He may have seen this in a customer's log and may be able to answer that question. He can be a little hard to get ahold of, but i'll see if i get an answer to that question for you. I'll post up if i have any luck.

That would be great! Much appreciate.

Greg i got ahold of him and he believe's that all 3 are cut, but he's not 100% sure. I asked if he had any customer log's of the rev limiter being hit. He did so i got him to take a look at it. In the log he could see fuel and spark being reduced. The spark was not a lot and might have been from the rpm drop but it was reduced. As far as the TB % it was not a pid he used or use's so there was no data on that. Sorry Bro!!!, Guess were back to the experiment stage. lol

Originally Posted by Redtruck-VA

I can't say that the rpm limiter and speed limiter operate in the same manner. I've never tried as I have adjusted my speed limiter to 140mph but have read that turning the ignition key to the starter position will override the speed limiter. Good luck with that........

You should know Superchips will extend the speed limiter to 140 & the rev limiter to 6500. Without digging into the manual I figured it was a safe assumption that the rev limiter would work similarly to the speed one.

Originally Posted by HemiLonestar

You should know Superchips will extend the speed limiter to 140 & the rev limiter to 6500. Without digging into the manual I figured it was a safe assumption that the rev limiter would work similarly to the speed one.

I'm not disagreeing just stating I don't know. Obviously one is triggered by vehicle speed which I'm guessing is generated in the instrument cluster and the rpm possibly straight from the PCM. I'll chase more wires, but there is only so much that can be done without a schematic of the PCM itself which I don't have.
I'm hoping the FBW operates independent of the rpm/speed limiters so that cruise control can be retained and more of the original configuration is maintained. I want to maintain the basic functions of the OEM PCM only removing fuel, ignition and knock sensors. I'm planning to work first moving ignition to the MS unit. When that's up and running then move fuel control over. That will be when the FBW will let me know if it's going to play nice or not. The knock sensor I don't believe will be a problem.
Very much appreciate everyone's input, this is doable, just need to figure out the simplest approach. Thanks,

Keep us updated.