RPM surge ?

***Power Hungry*** · #1 Thu, March 19th, 2009, 10:10 AM

Quote:

Originally Posted by MercedesTech

Also, converter will NOT stay locked. No matter what speed (took her up to 80 on the way home the other day to be sure) , if I remove my foot from the gas, the converter automatically unlocks.

Converter unlocking during decel (ie. foot off the pedal) or when quicly accelerating (pressing down quickly on the throttle) is normal. However if the converter keeps locking and unlocking while at a steady cruise, there is a problem.

Let me know if this is what's happening.

***Jackpine*** · #2 Thu, March 19th, 2009, 10:42 AM

Quote:

Originally Posted by Power Hungry

Converter unlocking during decel (ie. foot off the pedal) or when quicly accelerating (pressing down quickly on the throttle) is normal. However if the converter keeps locking and unlocking while at a steady cruise, there is a problem.

Let me know if this is what's happening.

Interestingly, at least to me, Bill, is how the converter tends to stay locked with the cruise control on when going downhill. At least it did on our trip to and from California. It's almost as though it's trying to maintain the speed in a coast situation (up to a point of course) instead of just letting the vehicle speed up.

Also, reducing the shift points and torque converter lockup points both for upshifts and downshifts does seem to have helped get rid of the "eagerness" to unlock under mild load that I complained about before.

I know this post is a bit of a hijack, but thought it might add something to the knowledge base.

- Jack

***Power Hungry*** · #3 Thu, March 19th, 2009, 10:58 AM

Oddly, I've never really paid attention as to whether the converter unlocked on decel when in cruise. Since it uses an inferred throttle value, I'd assume it handled shifting in a relatively similar fashion. I do know that the throttle feed rates are much less aggressive than using your foot which may account for less frequent unlocks.

I'll have to throw something in the Expy and go for a ride this evening so I can take a closer look.

Thanks for pointing that out. Might be quite helpful!

MercedesTech · #4 Thu, March 19th, 2009, 03:16 PM

On cruise, the converter stays locked !

Quote:

Converter unlocking during decel (ie. foot off the pedal) or when quicly accelerating (pressing down quickly on the throttle) is normal. However if the converter keeps locking and unlocking while at a steady cruise, there is a problem.

Hmm.... Because no matter what speed, it unlocks immediately. Doesn't feel right, but maybe just me looking for something wrong.

Anyways, yes, the converter will lock and unlock under steady acceleration. The RPMS also bounce around. when it first goes into 4th. I will feel the surge. While under steady pedal, I will feel the RPMs go up, and the truck pull (talking only a second) then drop right back down and feel slugish, then shoot back up and pull, etc. Maybe I should hook up a video camera on my guages so you can see whats happening. Sure is hard driving, and trying to stare at 8+ guages !

Jack&Janet: don't worry about hijack at all. The more the better ! Really.

kokopellimotorsports · #5 Thu, March 19th, 2009, 03:45 PM

Subscribed.

Ty

MercedesTech · #6 Mon, March 23rd, 2009, 12:37 PM

OK, this thing is sporadic at best. Trying to be able to give you details is hard. 3rd gear, everything is fine. 3rd gear, converter locked, rpms bounce around slightly, nothing bad. If its at 1800 rpm in 3rd, when it shifts to 4th it shoots up to 2400-2500 rpm. Then calms down. While in fourth, it will bounce between 1400 rpms, and 2300 RPMs pretty consistantly. During my drive on sunday, it jumped up to over 3k, then back down around 1900. When it jumps up, you can feel the engine pull, and you go faster. So, its not "dry revving" but fully engaged and still revving up.

I dropped timing -2, also tried -1 neither seemed to help at all.

Shudder is still there.

***Jackpine*** · #7 Mon, March 23rd, 2009, 01:46 PM

That's got to be awful! I hope you and Bill can get this figured out soon. It DOES sort of sound like a TC that can't get itself locked up, doesn't it?

You say there's little RPM bounce in third? Is this with the OD locked out? And, is the TC locking properly here? (Sorry, I just went back and saw that you said it seemed "almost fine" in this condition in a previous post). But, that bothers me too. "Almost fine" is not good enough in my book.

So, this really sounds like a transmission problem, doesn't it?

And now I see that Lars has jumped in with a "perfect" question. If it runs fine in stock, the problem's with the tune, not the transmission.

- Jack

***88Racing*** · #8 Mon, March 23rd, 2009, 01:36 PM

Don't want to have to mention this, but have you tried it with the STOCK program?

Just trying to eliminate weather its the tune or the tq converter.

Lars