RPM surge ?

MercedesTech · #1 Fri, March 13th, 2009, 11:11 AM

I haven't look into it too much to be honest. Anyways, the trans has begun acting "funny". Never did this before. At certain speeds, holding the throttle steady, the rpms will begin to surge. You can feel the truck pull, and then calm down. Pull, then calm down. Needle is jumping around on the tach, probably a good 300-400 RPM's or more.

Also, the converter wont stay locked. No matter what speed, its only locked while I give it gas. I left off, it unlocks. Its doing this more often then it used to. And at some points, it doesn't know whether to lock or unlock, so its starts jumping back and forth.

This started a couple days ago. It's just acting different, and I am unsure what it is. I am fairly certain, its something to do with OD, Since its only acting up in 4th gear. Any ideas ???

If I were to hook up the proper scan tools, will there be any codes stored for trans ? And yes, I have access to dealership style scan tools.

JWBFX4 · #2 Fri, March 13th, 2009, 12:35 PM

Well the rpm surge is from the torque converter which I am sure you know...so I am no help

But its definitely strange that it will not stay locked/and keeps jumping back and forth. Not that I think it has anything to do with it, but have you adjusted the custom options on the TC unlock/lock?

Just wondering...I know you said in OD only, but have you turned it off and seen if it will do it in just 3rd gear?

Maybe someone that knows a lot more than me will punch in...Good Luck man

MercedesTech · #3 Fri, March 13th, 2009, 01:41 PM

hey no worries ! i appreciate all the help I can get.

Yes, the "surge" if from the converter, its just acting strange. If we weren't so busy, I'd be working on it now. When I turn OD off, 3rd acts fine. Converter locks when its suppose to, and stays locked. OD off, and its fine.

And no, I haven't touched the custom options. These are custom tunes from Bill. It was running great for many miles. Went to vegas, LA all multiple times. No issues. So, I do not think this has anything to do with the tune, but its just my trans on its last legs or something. Really not sure right now....

MercedesTech · #4 Wed, March 18th, 2009, 03:01 PM

Still acting funny, and I am no closer to figuring it out !!

could it be from running lean ? Its acting all kinds of "odd". I plan to bring it to the shop friday to tinker some more. SHould be slow enough to have some time.

Another thing to add, right before this started happening, I did the "gotts mod" type deal on my intake, to open it up some. Also dropped in a K&N air filter.

I also was feeling some "shudder". If you get up to speed, about 60 mph or so, then let off the gas and let it slow to roughly 40 mph, then slightly get back on the gas to get back up to speed, there is this violent shudder. Entire truck shakes, and does so very HARD and rapid. It feel like washboard road at 70 MPH. Knock some kidneys around ! Let off the gas, or turn off OD and it stops immediately.

Any help is hugely appreciated !!! This one has me scratching my head some.

***Power Hungry*** · #5 Wed, March 18th, 2009, 04:34 PM

The shudder is not new and is generally related to the converter locking up too quickly after tip-in. That is easily remedied.

I suppose the unstable idle could be related to a lean condition, although it is quite uncommon to see lean conditions at idle. It may also come from too much timing at idle. Try adjusting the custom option for timing back about 2 degrees (-2 degrees) and see if that resolves the unstable idle. If so, we can fix that and the shudder at the same time.

Thanks.

MercedesTech · #6 Wed, March 18th, 2009, 05:25 PM

Cool. Can't thank ya enough Bill. Like I said, friday i should have time to tinker with it some. I will post back what I find.

And it seems fine at idle, while standing still. Its while in 4th gear that things start to seem really "off". Cruising at 52 MPH I found the rpms "hunt" some. They will shoot way up, then calm down, and bounce around a little. The converter will start locking and unlocking at slightly higher speeds. 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.

If I turn OD off, truck drives almost completely fine. The issues are not any where near as pronounced.

04FX4 · #7 Thu, March 19th, 2009, 07:53 AM

Mine has done this a few times as well. The difference is mine does it at low speeds, and in second gear. I notice mine when going through school zones. I have talked to Bill , but my problem is that I can not make it happen when I want, so it is hard for Bill to fix the problem. My RPMs jump about 200-400 and the TQ is not locked and it does not seem to be jumping in and out of gears.

***Power Hungry*** · #8 Thu, March 19th, 2009, 09:10 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*** · #9 Thu, March 19th, 2009, 09:42 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*** · #10 Thu, March 19th, 2009, 09:58 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!