Hesitating/slow shifts... bad tune?

[big_news_1]

Scans for tune revision "H":

First of all, I noticed this tune is almost identical to the tune entitled "Bonnie Mod 8-5-08" I posted on page 2. The only differences I could find were a few shift speeds and RPMs. Appropriately, revision "H" acted very similar to that tune.

The speedometer seems to be dead-on, with variances of only .5mph at certain speeds.

The 1-2 and 2-3 shifts both occurred without bouncing the limiter, but they are both still sluggish and slow. There is a noticeable feeling of lag between gears as one disengages and next engages. You can see the data in the scan entitled "WOT".

Cruising performance was pretty good. In 10-15 minutes on the freeway I never lost TCC lockup. Downshift performance could be better, and TCC lockup could be a bit firmer. I did a lengthy scan of cruising/downshift performance on the freeway in the scan entitled "Cruise + Downshifts".


Let me know what you guys think!

[big_news_1]

Russ, I also wanted to specifically ask if you think this is a tuning issue, mechanical issue, or combination of both based on what we've seen so far. Thank you sir!

[Russ K]

On this tune. I lowered the WOT 1-2 & 2-3 upshift speeds. Lowered the WOT 3-2 & 2-1 downshift speeds by the same %. Also raised the part throttle downshift speeds. I maxed the TCC min duty cycle (100%), but on the scans the TCC slip is very minimal. Yet the scanned TCC duty cycle drops from 100% to 9% when the TCC is locked.

Do you have any kind of shift kit installed? Maybe an adjustable vac modulator is available, like on the TH400 trans?

Russ Kemp

[mylittleblackbird]

No shift kit, lest you count the trans-go 4t60-e Jr shift kit. the vac modulator is adjustable and doesn't seem to increase shift firmness when closed.

[big_news_1]

No shift kit, lest you count the trans-go 4t60-e Jr shift kit. the vac modulator is adjustable and doesn't seem to increase shift firmness when closed.

Yes, what he said

I'm still waiting to scan. I came down with a cold and have been inside all day. I might get to it tonight. At the very least I'll get it done by tomorrow night.

[BillBoost37]

Not to hijack Ben, but to answer your question about mechanical or tuning. With my experience, this definately seems to be tuning.

Hopefully you don't smoke the clutches off in the meantime of getting it straightened out.

[Russ K]

No shift kit, lest you count the trans-go 4t60-e Jr shift kit. the vac modulator is adjustable and doesn't seem to increase shift firmness when closed.

An adjustable vacuum modulator won't affect the WOT shifts, only the part throttle shifts. Maybe you could weld a spacer on the end of the modulator valve? Call Transgo for more info.

Has the trans line pressure been checked? Higher line pressure would also increase the TCC apply pressure.

Russ Kemp

[big_news_1]

An adjustable vacuum modulator won't affect the WOT shifts, only the part throttle shifts. Maybe you could weld a spacer on the end of the modulator valve? Call Transgo for more info.

Has the trans line pressure been checked? Higher line pressure would also increase the TCC apply pressure.

Russ Kemp

Still need to check the line pressure with a mechanical gauge. We'll see what happens in the next few scan/tune cycles. I'm heading out now to try the latest tune you posted. I'll report back ASAP.

[big_news_1]

Scans for tune revision "I":

We might be getting closer! First and foremost I tightened down the adjustment screw in the vac modulator to give higher line pressure. This seemed to give more response to part throttle shifts, but I don't know if it affected WOT. Russ, your previous comments seem to indicate it would not affect WOT.

The 1-2 still commanded at 5130 but didn't complete until ~5700. Despite this, I think the scan shows shift completion in less time than previous tunes. I am not sure why this is, but it did feel a bit better.

The 2-3 seemed better, commanding at 5400 and completing by ~5500. This shift has consistently been better on all tune revisions. Not sure why, just throwing it out there.

As usual I attached WOT and cruising scans to this post. Have at 'em!


EDIT: And if it is advisable, I can get the car into the shop that built the tranny and have them check line pressure and get their thoughts on the matter. Let me know if I should do this.

[Russ K]

On this tune, I lowered the WOT 1-2 shift rpm. And lowered the WOT 2-3 shift speed. For some reason, the commanded WOT 2-3 shift mph is higher then the editor table. On the WOT 1-2 shift, the commanded shift mph is also higher then the editor table, but the shift occurs 476 rpm later.

Do you have the vacuum modulator set for max part throttle shift firmness?

Russ Kemp

[big_news_1]

Do you have the vacuum modulator set for max part throttle shift firmness?

Russ Kemp

Yes, I have the adjustment screw tightened as far as it will go. It is my understanding that with the Transgo Shiftkit Jr. I shouldn't need to max out my modulator, so it baffles me why the shifts aren't breaking my neck. They should be.

[big_news_1]

Scans for revision "J":


The 1-2 shift was noticeably more immediate than previous tunes. You can see how quickly the RPM changes when the shift is performed compared to other scans.

The 2-3 shift actually seemed more sluggish/slow than previous tunes. I am not sure why, but the 1-2 was a better shift this time around.

Seems like we're making some sort of progress! I have posted the usual scans.



ADDITIONALLY - I spoke with the transmission builder, and they seem happy to check line pressure and electrical connections. This should happen tomorrow or Thursday. He also suggested that the torque converter could be stalling too high and is somehow eating up energy in the shifts. I'm not exactly sure how this works, but I believe mylittleblackbird has some thoughts on the matter. I'll let him comment on this himself if need be.


Please, if anyone has thoughts I would like to hear them! What do you think Russ?

[Russ K]

On this tune, I lowered the 1-2, 2-3 & 3-4 WOT shift RPM. Also lowered the WOT 2-3 & 3-2 shift speed.

For what ever reason, the WOT commanded & actual shift speeds don't match. Yet the speedo is correct, and the trans revs match the trans/revs per mile in the editor, and the trans calculated gear ratio is also correct.

The Transgo Jr kit is a correction kit, not a performance shift kit.

Russ Kemp

[big_news_1]

For what ever reason, the WOT commanded & actual shift speeds don't match.

This is what has been baffling me the entire time. Have you ever seen this before?

I feel like we're missing something. What could cause such a large discrepancy?

[bigbrian442]

Has the trans builder been rebuilding the same trans or replacing it with a different one each time? If he has been rebuilding the same trans, I would begin to suspect a week pressure regulator spring.

[big_news_1]

Has the trans builder been rebuilding the same trans or replacing it with a different one each time? If he has been rebuilding the same trans, I would begin to suspect a week pressure regulator spring.

Of the three transmissions I've had, the first was rebuilt from one core and the next two were built from an entirely different core. There were no common parts between the first trans and the next two rebuilds.

Although I'm starting to believe my luck could just be that bad....

[big_news_1]

Results for revision "K":

Russ, we're almost there! This one was most definitely better in all aspects! I'm totally pumped right now!

The 1-2 was relatively quick this time. It could still use some tweaking, but it was far better than before.

The 2-3 was also better, but ought to be quicker.

Cruise performance seems great. Check out how nicely the TCC snapped in during my cruise scan. Downshifting also felt pretty solid. I posted the normal scans for you all to review.


Ultimately I would like the 1-2 and 2-3 shifts to complete between 5900-6000rpm. They are a bit lower than that right now, but I also realize we're figuring out how to make this PCM do what we want it to do.

Russ, I can't thank you enough for all the help so far! After almost 2 years of struggle I can finally start to taste victory!

[Russ K]

Do you really want to shift at ~ 6000 rpm? On a 2000 GTP that I tuned, the WOT shifts are at 5700. And SLP headers, Intense 3.2 pulley, 1.9 Yella Terra rockers, LS6 springs, and the fenderwell air intake were installed at my shop.

What mods are done to your engine? Keep in mind that the stock fuel shut off is at 5950 rpm.

Russ Kemp

[big_news_1]

Mods currently installed:

Cam (roughly equivalent to a ZZP GT1, with a bit less lift)
Ported and milled (.040) heads
LS6 springs
Ported exhaust manifolds
2.5" straight pipe exhaust
Slightly-less-than-engine-bay-temperature air intake

Here's the dyno chart before the transmission and exhaust were done. This is also prior to making a slight retardation to the cam timing. The car currently has a stronger top end than indicated by this dyno run:



Let me know what you think! I'm always open to suggestions.

[Russ K]

Raising the WOT shift points will put you back to tune J. Try manually shifting at the higher RPM to see yourself. I don't think the WOT shifts should be over ~5500 RPM.

You have to increase the trans line pressure at WOT. You will need to install a stiffer pressure regulator spring.

Russ Kemp