RPM restriction in 4HI

[Diacom]

Rather than take up any further space on the pcm4less post with my question, i'll repost here.

With the TB in 4-HI and in first gear in the snow, I was unable to see my RPM's go above 2000rpm. I asked about the possibility of the torque management being an issue as it was brought up by Hardtrailz.

He then asked if perhaps Stabilitrac or traction control kicking in. I'll have to see if I have Stabilitrac or not, don't believe I do.

Here are the clips that will show some of what I mean. Again, in 4-hi, first gear, foot to the floor...





and a few additional pics





Guess I'll check on the traction control for starters...

[fishsticks]

I don't spin my tires very fast in 4HI as a general rule, but I'm sure I've been well over 2000RPMs before.

[bgwolfpack]

Heavy truck. Grabby tires. Snow = No horsepower and no low end torque. We run what we brung.

[The Roadie]

No traction control in 2003. Torque management likely isn't involved here. Clogged cat maybe? Did 4LO do anything better for you?

Ahhhhhh, what's your altitude?

[Trail X]

It could be a preventative built into the PCM (do the PCM and TCC talk? I assume so because the speedometer adjusts when in LO.)

I know when in lo 1st, the truck can be very jerky. Drive-train jerks are what break things because they carry high acceleration changes.

Until one of us confirms that 1st lo is unlimited, we're just shooting in the dark anyways.

[fishsticks]

It could be a preventative built into the PCM (do the PCM and TCC talk? I assume so because the speedometer adjusts when in LO.)

VSS is on the output side of the TC (or on the axle)... no speedo correction needed for 4Lo.

[Trail X]

Oh dang, you're right.

[KE7WOX]

I know when in lo 1st, the truck can be very jerky. Drive-train jerks are what break things because they carry high acceleration changes.

Never had issues when in 1st, but the 2nd->1st shift in 4LO is really jerky

[BSalty]

I was in the snow/mud in December between the large storms we had and I had it in 4 hi 1st gear and was able to get way more than 2k to get out of a bowel that was slick as heck, I had to really give it hell to get out. Ice and mud on slick flat rocks and a good size hill.

Mine is also an 03 without traction control or stablitrak. I was at 5200' elevation. However I am still on my stock tires (dang Christmas and family vacation to Disneyland stole my shoe fund) so that may be the difference.

Sorry bout the crappy pictures, I was solo, didn't have my camera, and wasn't planning on that slick of conditions in this area. I figured I better get a picture of it while it was dirty but finding a place dry enough to stop was rough. I frequent it a lot and it is usually not that bad.

[The Roadie]

...to get out of a bowel that was slick as heck, I had to really give it hell to get out....

Indeed. You don't say.....

[bartonmd]

FWIW, I can attest that I have no restriction short of redline in 4HI.

[BSalty]

...to get out of a bowel that was slick as heck, I had to really give it hell to get out....

Indeed. You don't say.....

I even fixed another spelling error when I edited the post. And yeah I gave it hell in that bowel.

[Diacom]

No traction control in 2003. Torque management likely isn't involved here. Clogged cat maybe? Did 4LO do anything better for you?

Ahhhhhh, what's your altitude?

Alititude was right around 8,500'.

Clogged Cat? Perhaps, I did have the rotten egg smell slightly, so perhaps this is a large contributor.

Uh, yeah, about 4-Lo, I um... well I didn't think to use it until after the fact. That's the plain truth, was something I discussed with my buddy once we got back down off the mountain. Seem a similar issue I have with my '09 Silverado 2500HD that I use for work. On a pretty good decline, in 4-hi and reverse I could not back up the hillside, I had to engage 4-Lo to get the truck to move, other wise it would hit the limiter in reverse and no movement. I sort of wondered if this was a common thing with GM trucks. Until I had it happen with the TB though, I guess I never really had thought to ask anyone.

I may be going back up this weekend, and if so I will try 4-Lo and again in 4-Hi to see what if any difference there is. I will guess that if it is in fact the Cat, then there will be no difference. In this case it may be headed in for warranty work, only about 86,000 miles and iirc they are 100,000 warranty.

[BSalty]

Something I thought of last night in relation to the OPs question. Every time I take the TB over 8000-8500' elevation (10-12 times per year) my check engine light turns on and the fan clutch acts like its going out and the power is reduced. It will turn itself off then back on again several times over a week long trip at that altitude. When I come down off the mountain it turns itself off and runs fine. It has done this since I have owned the truck (bought it at 43k miles or so) and I have just gotten used to it figuring its the PCM tuning. I have replaced the fan clutch and it didn't change how it acted at that elevation.

My house is at 4600' so its quite a jump when I do get to those places. I looked into a "High Elevation" tune but I never did get it done figuring I was about to start modifying and would get it done after the lift and tires.

Have you ever noticed anything like this? Kind of curious since your house is probably at a higher elevation than mine if your in Wyoming.

Mod sorry if this needs to be moved or split.

[Diacom]

Sorry for no update with further information.

Was tied up the last two weekends so I have not had an opportunity to head back and test 4-Lo to see if it produces the same results. I may do a compression check once it warms up a bit, that should help determine if the Cat is clogging up.

[Hpimichael02]

its could be a saftey feature getting triggered, i know most envoys and the SAAB's and some trailblazers are equiped with the low rev feature while in Park- this wont allow you to rev higher than 2500rpm(for saftey reasons), if your truck doesnt rev past 2500rpm in park then try it in netural, maybe being in 4Lo or HI is triggereing something to enaguge this. just another idea

[KE7WOX]

its could be a saftey feature getting triggered, i know most envoys and the SAAB's and some trailblazers are equiped with the low rev feature while in Park- this wont allow you to rev higher than 2500rpm(for saftey reasons)

Mine does that, 2004 with the I6