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Rev limiter in an 01 8.1? Engine expert help needed.

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17K views 23 replies 15 participants last post by  Ic3man  
I
#1 · (Edited)
Does anyone know the stock rev limiter on the 8.1's? And what is the best way to increase it? And what controls the rev limiter...?

Any help is appreciated,

Thanks
 
#2 ·
Only way I know of is tuning with EFILive. There is a section just for Rev Limiter. Maybe find a local tuning guy with EFILive and see if they would change it as you wish or disable it. Minimum cost this way is just under $100.00 for a ECM/TCM license for tuning through a FlashScan V2. No idea if handheld tuners offer this feature.

Brian
 
#5 ·
x2
Tanc Crusher said:
Only way I know of is tuning with EFILive. There is a section just for Rev Limiter. Maybe find a local tuning guy with EFILive and see if they would change it as you wish or disable it. Minimum cost this way is just under $100.00 for a ECM/TCM license for tuning through a FlashScan V2. No idea if handheld tuners offer this feature.

Brian
Click to expand...
 
I
#4 · (Edited)
Well, a little back story would be I have a 2000 GMC Sierra 1500, we swapped the 5.3L out of there and dropped an 8.1L in. Only problem we have run into is the rev limiter cuts the engine off at 2800 RPM, no matter if it is in park or in gear. I use a Superchip programmer but that only gives a 600 increase maximum while in gear. The mechanics are trying to pin point what could be causing this problem, but are having no luck.

So I was wondering where the other 8.1L users get cut off. In park and in gear, if you know... How high can you get the RPM's up?

And then what actually controls the rev limiter, maybe we can get in there and change settings but I don't know what controls that.

Anyone know what kind of an increase you are looking at from the EFILive tune?

I am in Idaho.
 
#6 ·
Ic3man said:
Well, a little back story would be I have a 2000 GMC Sierra 1500, we swapped the 5.3L out of there and dropped an 8.1L in. Only problem we have run into is the rev limiter cuts the engine off at 2800 RPM, no matter if it is in park or in gear. I use a Superchip programmer but that only gives a 600 increase maximum while in gear. The mechanics are trying to pin point what could be causing this problem, but are having no luck.

So I was wondering where the other 8.1L users get cut off. In park and in gear, if you know... How high can you get the RPM's up?

And then what actually controls the rev limiter, maybe we can get in there and change settings but I don't know what controls that.

Anyone know what kind of an increase you are looking at from the EFILive tune?

I am in Idaho.
Click to expand...

Oh yea! Your goin to need a custom tune for that!!!
What trans did you use? Did you use the 5.3l wiring harness?
In gear cut off is 5200 RPM. Park 3000 RPM
 
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I
#9 ·
This is not an ongoing project, haha. It is done :)

Drives like it's off the lot, shifts flawlessly, everything is beyond perfect, except when you try to take her over 2800 RPM.

We swapped EVERYTHING. NOTHING in that engine bay is the same. Everything was swapped to the 8.1L stuff or custom made, even have the electronic pedal. Only thing that is still 5.3L is the body control module and the radiator. There is no way I am getting the 8.1L radiator in there, size difference is about 2 inches that isn't there so I would have to start cutting into the chassis. But I have not had any problems whatsoever with the engine even getting a tad hot, so it is fine by me.

Custom drive shafts and a rebuilt rear end to top it all off. Oh yeah and we put an Allison tranny in there, no way I was going with anything less.

So with the EFILive tune, does anyone know what kind of increase with the rev limiter I am looking at... 1000? less? more? :)
 
#11 ·
Without good information you can speculate a lot and accomplish nothing. Based on what is most recently disclosed I'll say this. The Allison TCM and the 8.1 Throttle Body Control Module work together. You may be missing a communication circuit. I doubt it's the PCM as much as the TCM that's limiting the revs. If you swapped everything you should have codes to work with, is this the case?

Vernon
 
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I
#13 ·
A shop logged all of the hours in the build, so this wasn't backyard work. I am in no way that good with engines to attempt something like this. And I understand it will be hard to get any help since you guys were not present for the build so you are in the dark for information, but I will try my best to relay what is needed. Is the throttle body control module the same as the body control module? The one inside the cab?
 
D
#14 · (Edited)
I inquired about this at a GM dealership one time. They told that the older GM's were limited at around 2800 to 3000 rpm while in park because of the PTO option that was available 2001 to 200(7?). The newer trucks have had the PTO take off on the transmission removed to save GM money, and I believe will rev higher in neutral. My 2004 will cut off at 2800 rpm while revving in park also.
 
G
#15 ·
If your using the EFI Live software which I hope with that kind of swap I think its somewhere in the B33xx cells. Theres a few of em pertaining to RMP limits and fuel cut offs. I would get EFI Live if you dont already or youll never get it right. What year 8.1 and what year PCM and TCM?
 
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#16 ·
The throttle body controll module is mounted on the exterior fire wall just outside the brake booster unit. The 8.1 unit has a communication circut with the Allison TCM that the 6.0 does not.

Vernon
 
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G
#18 ·
I would get EFI Live so at least you know where your at. Try it thru there and see what happens. Can log it too to see if anything is outta ordinary. Its gonna be the only way to see whats going on and to tune everything over without a Tech II
 
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#19 ·
Sounds like a plan. Will have to save for a bit to snag something for $800, but hopefully it is worth it.

Thanks for all the contributors, really appreciate the help. And feel free to post if you have any breakthroughs on how the problem may be solved, an idea is better than no idea. :)
 
#20 ·
HP Tuners is what I have and it's awesome. It's easy to use and it does everything most guys could ever want. You can easily adjust your spark cut and your fuel cut in every gear, etc. You can customize your torque management tables, trans tables, electronic throttle behavior, etc....
Dont get me wrong, EFI Live is nice, but I like HP tuners better. Just personal preference really. They both do the same things for the most part.

One thing that came to mind was your tach signal. I know that LS1 Trans Ams have a different tach signal than the traditional V8, and the 8.1 borrowed a lot of traits from the LS series engines.... others probably know much more about this than I do.

I hope that helps!
 
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#22 ·
I agree with John. I think your PCM thinks your still in Park for whatever reason. I'd figure out the problem before you start tinkering with EFI Live or any tuner.

Just my 2 cents.
 
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I
#24 ·
Yep the problem is fixed. Just had to tamper with some programs on my Superchip tuner, for whatever reason it wasn't working before but now it does in performance mode. I've hit near 5k on the rpms so far without a cutoff problem so we are good to go.

Thanks to everyone for their input and help!
 
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