RPM's stick at 1800/80 klm

04-silver · January 22, 2006

First off, I think I should of posted this under the gassers but two of my previous posts were here. So if you mods think this should be moved, OK.

The vehicle-2004 Silverado, 6.0, EC, SB, 4x4, 4L80-E, 4.10

I’ve been having a problem with this for awhile now. What I view as a problem.

Nov. 26/05

http://www.gm-trucks.com/forums/index.php?...topic=47226&hl=

Mar. 20/05

http://www.gm-trucks.com/forums/index.php?...topic=39840&hl=

Mar.1/05

http://www.gm-trucks.com/forums/index.php?...topic=39163&hl=

Before I took my truck in for its semi-annual check up this month, I made a few videos of my problem. Out of those videos I cut a section out so I could show every one at this forum what I've been trying to explain for the past year in my 3 previous posts. Its hard in forums

The video itself does not do 100% justice, it's one those things better to be there but having said that, the clip should give you a pretty good idea of what I'm trying explain. Just a reminder, Steven Speilberg I am not.

When your watching the clip take special note at the 7 to 9 seconds and again at 22 to 25 seconds. You might not be able to hear the motor drop at 7 to 9 seconds, in the cab you certainly due. (The cab noise in the background is from the hi-flow cats, magna flow muffler and 3" pipe which were put in after this problem)

click 4 Clip

During the clip my foot was always on the accelerater, untill the end. When I say pushing harder, yes I was pushing on the accelerater pretty firm, to give you an idea probably enough to flatten an orange I guess.

I’m not discrediting the GM fellow but I was told this is due to the converter locking or unlocking? Locking I think he said and this is normal! If this is normal I'm not liking it. He said that GM had raised the klm/h for the converter to lockup to 80klms from a previous lower speed and it is a programmed in by GM and cannot be changed by anyone except GM themselves.

When I’m pulling the 5th wheel in 3rd gear with tow/haul on and the truck spikes like in the vid........... is it normal to be jolted and to have a feeling that the king pin is about to be ripped out? My wife and the kids, we all look back its a good jolt/tug.

I noticed yesterday, now its not just at 80-84 klm/h, but also now at 105 klm/h, seems like when its changing to a higher gear.

I only way I can prevent this to to take my foot off the accelerater for a split second and go, but now I find I'm constantly doing this as the truck drops the RPMs slightly and gets right back into that bad spot. Locked Converter!

I tried to explain this to you people best I could.

What do you fellows think?

Is a problem or just me?

Any suggestions? Ford maybe.......YIKES.

Anyone els have this problem.

John

lrymal · January 22, 2006

What I heard and saw was the motor lugging in "D" which is overdrive. When towing, even in tow/haul, and the motor lugs like that, it really does need to toe in third gear.

When you place it in third gear while going at freeway speed, it will bump up in the rev. Back off the accelerator and place it in third.

But, if you are towing in a way that a load is being placed on the motor, you should have it in third.

04-silver · January 22, 2006

When I took these videos the truck wasn't pulling anything, this rpm spike will also happen when in 3rd whether I'm pulling or not .The 5th wheel was just to emphasis the jolt or spike. Haven't tried 2nd, what for?

as per Irymal "What I heard and saw was the motor lugging in "D" which is overdrive."

Lugging? I agree, this is what I'm trying to say, there is a problem, why is it lugging then?

The truck was empty during this video and it was only doing what its supposed to do, go forward and change gears when speed increases......... .

I always use overdrive for highway speeds when empty? Besides 80klms here is only 20 klms over the city speed limit anyway. ($200.00 there abouts )

thanks Irymal

John

Edit-BTW the GM fellow I talked to did say it was a good thing about the cats-magnaflow, opens it up he said. Whatever, take it for what its worth.

mmmikkke · January 22, 2006

The torque converter is a cool invention. When it's allowed to "convert", it actually converts HP to torque. That slip you feel in the torque converter allows the engine to run at a couple hundred rpm higher than the torque converter output shaft. The engine's power (HP) at 2000 rpm, is converted to a torque converter output rpm of say 1700. Ignoring hydraulic losses, HP in = HP out, and if "out" is running at 1700 rpm, then the torque at that rpm has to be 2000/1700 the input torque. It's roughly equivalent to having a gear reduction of 17:20 in that the torque coming out of the converter is 20/17 times the torque being supplied by the engine. Remember, this conversion (amplification) only occurs when the torque converter is unlocked.

When you lock the converter, you eliminate the hydraulic losses, but you also give up that 20/17 torque amplification. After it locks, your truck's drivetrain sends less torque into the transmission's gearing, and so less torque is delivered to the rear wheels, because the torque converter is no longer converting any torque.

With light throttle, the torque converter will lock at 45 mph, and the 200-300 rpm drop that you show (at 7 or 8 seconds) is the torque converter locking. So if you're above 45 mph, cruising at a steady speed, the TC is usually locked. But as you begin climbing a grade, you press on the throttle, more, more, and finally the trans decides to downshift. As a side effect of its downshifting decision, it also unlocks the torque converter. So you get a blast of torque, partly from the downshift, and partly because the torque converter is converting torque again.

This is exactly the same way my truck behaves (it's a 2005 2500HD 6.0L 4L80E). I believe that it is normal and it's not bad for the engine or trans. My '95 K3500 6.0L 4L80E behaved similarly, although the torque converter locked at a lower mph. (I commend GM for the "improvement" they made by raising the lock speed to 45 mph.)

When you let off the gas completely, GM unlocks the torque converter again, partly because if you're off the throttle, you might be about to brake. (This philosophy has been used at GM for many years.) And so that is what you have discovered as a remedy for the blast-of-torque that you show late in your clip. First let off the gas completely (zero the throttle), and then accelerate briskly and the TC will stay unlocked (permitting torque conversion) until the hill is climbed, possibly avoiding the downshift because the added torque due to torque conversion is sufficient without the downshift.

One additional note: You could also try tapping the brake with your left foot instead of zeroing the throttle. I think tapping the brake unlocks the torque converter also, assuming your other foot is still on the gas. Try it, and report back if it helped.

It's too bad GM doesn't seem interested in making their trans (or their power locks) behave the way their skillful driving customers want them to behave. A $2 sensor could give us incremental torque amplification, by unlocking the TC at 40% throttle and downshifting at 70% throttle. If they did that, many of us would immediately use that sweet spot you are so desparately trying to find in your truck that doesn't have one.

04-silver · January 22, 2006

Nothing against anyone who has replied to any of my posts but finally, someone who knows exactly what I am talking about and what the truck is actually doing. Which is a p155 off. Pull a trailer and see what it does......... /

The GM fellow pretty much said the same thing,, not that I did'nt believe him its just better to get more opinions, advice or possibilities.

I kind of got lost in that 20:17, hydraulic lose and less torque no longer converting thing .........okeedokee.......

The moral of the story is all is well with the truck and the king pin is going to get yarded off.

Actually the jolt is more prominent since I did the exhaust, fix one problem(more pep/HP) create another one (that jolt)

Thanks very much mmmikkke, I guess I'll put this issue to bed and ponder over the future of this truck.

I let you know on the brake thing. Edit-just tried it, nothing

Edit-I just re-read my previous posts and noticed the GM-tech here had it in the beginning, duh! had I known what TCC was or actually did back then, then maybe..........oh well, hats off to him too.

John

04-silver · January 22, 2006

ok here's a thought.

If I was to chip it out, with a Predator say, as I hear this one allows for more options/changes (can you see a driveway ornament coming here)

Would this help that torque converter lockup any or aleast that jolt? Mind you I was told by the GM service guy that the converter lockup was a GM factory thing.

John

mmmikkke · January 23, 2006

I had to try the tapping-the-brake thing on my 2005 2500HD today. Didn't work. Torque converter stayed locked.

But I also tried the zero-the-throttle technique, and that *worked*! I zeroed, then put my foot about half way into it, and the TC stayed unlocked until I got up to my target speed, around 60 mph.

That's gotta bum some pencilhead at GM. They'd probably say: "A customer actually achieved desirable operation of their vehicle's automation. We must close this loophole! All thinking customers must be neutralized!"

I'm going to use your zero-the-throttle technique now. Thanks for the tip!

04-silver · January 23, 2006

I did try the brakes and that did nothing. (Did an edit on previous post)

But I also tried the zero-the-throttle technique, and that *worked*! I zeroed, then put my foot about half way into it, and the TC stayed unlocked until I got up to my target speed, around 60 mph.

........and then the truck, well mine anyway will get back into that locked mode again and I'm right back where I started from except now I'm going 20 to 25 klms faster. Lately this has become a lot worse or more noticable, one of the two.

This is not good, you can't be driving with your foot on and off the accellerater all the time. When the truck is cruising in that 7 to 9 second area like in the video and I need to accelerate quickly, like lets say the guy beside you all of a sudden wants in your lane, one of two things will happen if I don't release the accelerater, which is a 1 second delay just to do that.

1-initially nothing, the truck won't increase speed- there went 1 second of nothing

2-you push so hard that the rpms spike to 3500/4000 and that sudden burst makes the tires spin on the ice

OK, maybe a little dramatic but this is a forum and I hope you do get the general idea.

Maybe I'm wrong here but to drive a vehicle properly I don't think you need to be continously releasing the accelerater! Don't get me wrong here (like that would happen on a forum ) I'm not venting or mad I really do like the truck and that, but this little qwerk here has to be looked onto.

I called GM today, lets see what they have to say?

John

mmmikkke · January 29, 2006

So what did GM actually say?

For around $700 you can fix this problem yourself.

Programmable Transmission Controller

I'm actually considering this. It'd be nice to escape from the pinhead dogma that GM has applied, at least in the case of the trans.

But I should also point out that I like the 4L80E's programming much better than the 4L60E's programming on my 2002 Z71. At least there seems to be some deference to the thinking driver in the 4L80E's logic.

04-silver · February 19, 2006

Sorry, I've been out of town for awhile but I did call GM prior.

A nut in an egg shell.........live with it, when/if enough people complain then GM will do something,...........ah.......ok.

That PCS thing is 700.00 + 150.00 for wiring harness, now put that in Canuck dollars, ouch.

I'm still thinking on the predator, but I'm a little leary on either of these as I'm not all that knowledgable with these items and the potential for me creating a lawn ornament are pretty good..........