Short shifting at 3000-3500 rpms at wot!
09-18-2007, 10:03 PM
#1
Short shifting at 3000-3500 rpms at wot! Ok, just recently had ms4 cam installed with longtubes and custom 3" duals. I already had 3500 stall converter installed with tranny cooler. Now I'm having a problem with part and wot. it will seem to hesistate, then shift from 2nd-3rd WAY prematurely at about 3000-3500 rpms. I am having an issue with the driver's side pipe banging the tranny cross member and believe that to be the problem, but when I scan it with hptuners i'm not showing any knock retard like i thought would show up. Any ideas? I'm still betting on the pipe banging the cross member as the problem, but wanted some input from some of you guys.
Also....it shifted fine before the install. I increased shift rpm and mph at wot too.
Also....it shifted fine before the install. I increased shift rpm and mph at wot too.
09-18-2007, 10:39 PM
#2
A premature shift thats comanded can have several causes, But I have read of this in several places after a cam change and something to do with MAF calibration and PO121. Beware you can damage the trans by allowing the premature shift.
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12-23-2007, 08:06 AM
#5
Just an update for anyone searching and having the same problem. Ended up being a TPS tuning problem. The KPA at idle was well over the 60 needed to trip the code for a tps error because of running the MS4 cam. Changed the Error to 70 and has been running great since! Thanks for all the help! I think i know who I'll be going to when the stock tranny goes!
12-23-2007, 05:01 PM
#7
This is one of the exact reasons that I am a huge proponent of the Vacuum Modulator in performance applications. I personally have watched more than a few units shred themselves on the chassis dyno because the tune was incorrect after a cam / heads swap. My research proves my position on this.
Line pressure can be modified / manipulated by many different variables not directly related to the transmission. Because I do not like to see the wild fluctuations in pressures at high RPM's, I do not run EPC's in anything I think will see more than a CAI mod. But hey... that's my opinion. Others may vary.
To the OP. I recommend changin the fluid and filter in your transmission since it has been through some odd conditions. It would be a good time to take a look around the pan. If nothing is found to be errant, then you will have peace of mind for some time to come.
Good Luck and have fun with the new cam and pipes!
g
Line pressure can be modified / manipulated by many different variables not directly related to the transmission. Because I do not like to see the wild fluctuations in pressures at high RPM's, I do not run EPC's in anything I think will see more than a CAI mod. But hey... that's my opinion. Others may vary.
To the OP. I recommend changin the fluid and filter in your transmission since it has been through some odd conditions. It would be a good time to take a look around the pan. If nothing is found to be errant, then you will have peace of mind for some time to come.
Good Luck and have fun with the new cam and pipes!
g
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12-23-2007, 09:16 PM
#8
This is one of the exact reasons that I am a huge proponent of the Vacuum Modulator in performance applications. I personally have watched more than a few units shred themselves on the chassis dyno because the tune was incorrect after a cam / heads swap. My research proves my position on this.
Line pressure can be modified / manipulated by many different variables not directly related to the transmission. Because I do not like to see the wild fluctuations in pressures at high RPM's, I do not run EPC's in anything I think will see more than a CAI mod. But hey... that's my opinion. Others may vary.
To the OP. I recommend changin the fluid and filter in your transmission since it has been through some odd conditions. It would be a good time to take a look around the pan. If nothing is found to be errant, then you will have peace of mind for some time to come.
Good Luck and have fun with the new cam and pipes!
g
Line pressure can be modified / manipulated by many different variables not directly related to the transmission. Because I do not like to see the wild fluctuations in pressures at high RPM's, I do not run EPC's in anything I think will see more than a CAI mod. But hey... that's my opinion. Others may vary.
To the OP. I recommend changin the fluid and filter in your transmission since it has been through some odd conditions. It would be a good time to take a look around the pan. If nothing is found to be errant, then you will have peace of mind for some time to come.
Good Luck and have fun with the new cam and pipes!
g
12-24-2007, 12:13 AM
#9
A vaccume modulator would have no effect on shift timing. Even with it you would still have to have made that ajustment to correct the shift timing. Though I have seen times when cars had chronic presure issues where a mod a can be a solution. And the same issue that was causing the shorts shifts could have also caused lower line and damage to the fricitions. But hopefully you will be fine now. And I am glad you posted the solution. As I mentioned have seen several people run into that issue and the solution has been elusive
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12-24-2007, 07:44 AM
#10
Ya, I get tired of searching on here for problems that come up, only to find other people have had the same problem....but the thread died off and they never gave a solution to the problem. Figured if I help one person down the road having the same problem as me, then my 3 min. of extra typing was worth it 
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12-24-2007, 01:30 PM
#11
Of course, I agree the Vac Mod will not have a bearing on the shift timing... however the TPS can and will have an affect on the Line Pressure. And that was the point I was trying to make. Hope it all ends well for you.
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