98 tuning question
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98 tuning question I have a problem with hitting the rev limiter between 1st and 2nd gear under WOT. I know the 98s are tuff to tune and you have to trick the CPU into submission,but this is getting old. I have been told by several people that after 98 they upgraded the CPUs and 2001s on up don't have this problem. Has anybody got a fix for this? I have considered rewiring the harness and putting in a later year CPU in it, buying the GM aftermarket tranny controller and trying to splice it in or even trying to convert the 4L60E to vacum control. and suggestion would be appreciated. I guess I should have put a 400 or 350 in it last time instead of trying to retain the OD. Its a Bitch to run a 12.01 knowing if didn't hit the rev limiter 3 times you could have had a 11 sec run.
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From: Conway, AR
How hard are your shifts? It sounds like there is a shitload of line pressure building up there and its taking a second for you to shift. Or there is not enough. If there is too much it can slow the shifts down dramatically. What are your shift times set at?
What is/are your Up/down shift pts set at mph/rpm. What is your Rev Limiter set at. The Instrument cluster Tach/Speedos lag. You have to go by what you log in your scanner. These tables are the same for the 98 and up. (Normally, baring tranny problems) You have to meet both conditions in order for the shift to happen. It sounds like you are hitting the RPM /MPH window and having an overshoot that bangs the limiter. You have two choices, raise the Rev limiter or decrease your MPH point-that is if you are happy with the RPM point. I bet you didn't have this problem with the stock settings. Post more info on your setup- Stall, rear end, tire size.
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98 tuning problem
Originally Posted by dedge
I have a problem with hitting the rev limiter between 1st and 2nd gear under WOT. I know the 98s are tuff to tune and you have to trick the CPU into submission,but this is getting old. I have been told by several people that after 98 they upgraded the CPUs and 2001s on up don't have this problem. Has anybody got a fix for this? I have considered rewiring the harness and putting in a later year CPU in it, buying the GM aftermarket tranny controller and trying to splice it in or even trying to convert the 4L60E to vacum control. and suggestion would be appreciated. I guess I should have put a 400 or 350 in it last time instead of trying to retain the OD. Its a Bitch to run a 12.01 knowing if didn't hit the rev limiter 3 times you could have had a 11 sec run.
Last edited by dedge; Nov 29, 2006 at 09:17 AM. Reason: addition
What tuning software suite are you (or your tuner) using? The proper operation of the 4l60e is heavily dependant on having the correct information provided in the pcm. If all the information, Tire/Wheel diameter, rear end ratio, are not up to date the car will "miss" a shift like this. Short of that, as I said before, you are hitting the RPM Rev limiter before you hit your target shift RPM at the given MPH target. Raise the Rev Limiter (Rem 98 rod bolts stretch!)(then again you did say the motor was rebuilt) or lower the MPH shift point(s). I take it you are happy with the RPMs-just don't want the Rev bang.
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Originally Posted by Doc
What tuning software suite are you (or your tuner) using? The proper operation of the 4l60e is heavily dependant on having the correct information provided in the pcm. If all the information, Tire/Wheel diameter, rear end ratio, are not up to date the car will "miss" a shift like this. Short of that, as I said before, you are hitting the RPM Rev limiter before you hit your target shift RPM at the given MPH target. Raise the Rev Limiter (Rem 98 rod bolts stretch!)(then again you did say the motor was rebuilt) or lower the MPH shift point(s). I take it you are happy with the RPMs-just don't want the Rev bang.
I got a brand new 2001 Corvette crate motor in there with 1700 miles on it now so maybe the rod bolts will hold out.If not it still has a 12 month, 12,000 warranty from the GM factory. I really like the way its running at the track exccept for the 1st to 2nd problem. How hard was it to convert over to a later model CPU?
Last edited by dedge; Nov 29, 2006 at 10:50 AM. Reason: addition
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Much harder than straightening out the tables in your tune. Rewire 160 pin PCM connector, Next do you want your fuel gage to work? Remove and replace (R + R) sending unit/fuel pump-might as well change to plastic tank. R + R instrument cluster (IC). Rewire IC. Reroute alt on sig wire to pcm from IC. If you are otherwise happy with the setup and don't plan on F.I. , Turbo, higher MAP, then fix the 98 cal/OS and be done with it. Otherwise, it is only time, experience and money- Not hard.
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