Lady Redhawk

iTrader: (6)

Have friend with a 2001 C5.....while cruising, a little throttle, will down shift, then upshifts, down shifts, upshifts. Any ideas?

jimmyblue

iTrader: (11)

Are you sure this is not the converter locking and
unlocking (misfires from cam & light-mass converter)?
If it's truly shifting, check that your upshift and
downshift points, by TPS, are separated by at least
1 MPH in 1st, more in 2nd and third (up > down).

Lady Redhawk

iTrader: (6)

We have the converter set to not lock during shift and misfire detect to 32367 in low rpms. I am looking now at a EFI scan he just did, he was crusing at 37.9 mph, TP 16.6% 1655 rpms Throttle possition stayed steady at the 16.5 to 16.6 and it just down shifted to 3rd for no reason, stayed in 3rd 2.2 seconds and then upshifted back to 4th. The whole time the throttle stayed the same.

kp

iTrader: (34)

May want to look at your shift tables and make sure a wrong value didnt get added somewhere if someone had been editing the PCM. Upshifts and downshifts are TPS/mph based so you want to look around that mph and make sure something wasnt changed and its not right at the edge at that mph, same with the TCC table.

Lightly tap the brake at the same speed and make sure it isnt the converter unlocking (if its locked tapping the brakes will unlock it), if its the converter make sure you have all 3, low rpm, idle by cyl and lowropm by cyl set to 32367.

Also make sure if the gear was changed the PCM was flashed for the new gear, even though the speedo will be correct some other things will act wierd if the gear isnt rescaled.

Lady Redhawk

iTrader: (6)

All 3 misfire tables are set at 32367, and have double checked all shifting tables. I have tuned quite a few f-bodies with no such trouble, and someone said to the owner they had heard there was something different with the corvettes that needed to be tuned for.?.? After 3 years of reading, studing and tuning, I have never come across anything like this has anyone else?

jimmyblue

iTrader: (11)

Still wondering whether the 2-3 upshift and 3-2
downshift MPH are too close together (like identical)
at ~16% TPS and any little VSS or TPS "flutter" could kick it
forward & back?

With the way the scanners "decimate" the data (you see
about 1/8 of what the PCM sees, 100mS logger frame vs
12.5mS internal data period) any such "hiccups" could
have a high probability of never being shown.

Lady Redhawk

iTrader: (6)

No, none of the tables are to close. I double and tripble checked all that when he first started with the trouble.
He has the TC1 3500 torque converter, I don't know if that has anything to do with it. There is no problem with the yank converters I have tuned for or an TCI 3500 in an F-body.

jimmyblue

iTrader: (11)

What about the possibility of a dumb ol' electrical
intermittent in the tranny control harness? Is this
problem something you can replicate at will? If so
log the stuff that pertains to slected gear and note
whether the stutter-step is commanded, or freestyle?

Lady Redhawk

iTrader: (6)

I have it logged where it just downshifted on it's own and then it can be also done at will with just a slight throttle at almost any mph.

Not sure how you would know if the problem was in the control harness, any ideas?

Thanks

jimmyblue

iTrader: (11)

Well, I was thinking along the lines of, if it happens but
the scanner doesn't show anything like "last commanded
shift" etc. that would point to something outside the PCM.
I vaguely remember a bunch of odd PIDs like that though
I haven't had any use for them. But if you can instrument
up for the PIDs that pertain to shift commands that should
at least separate the commanded / spurious.

Don't forget the known "get squirrely with low fluid" angle,
neither.

Lady Redhawk

iTrader: (6)

Oh, ok, I will see if we can log some of those pids. He checked the Trans fluid about 100 mph after the torque converter install and it was ok then, he has had maybe 1,000 miles on it now, will have him check that again. Be nice if it turns out to be that simple.