Shift points in 4X4 low

[Slowrockr]

Searched for my other post about this but couldn't find it. I thought I had this figured out but apparently I was wrong. It's a '02 car 4l60e in a rock crawler/ rock racer, when in 4x4 low range it shifts like crap, hangs on the rev limiter bad before each shift. It's costing us valuable seconds on the race track and I need to find a cure. I'm wondering if I need to have the 4 low input in the pcm like the trucks have, segment swap? Any ideas/help for a novice tuner? Scan is on the laptop at the shop, I'll post it up tomorrow.

[Mike@ADS]

Are you saying that you do not have the 4x4 selector hooked up to the ecu? You must have this for it to shift correctly, or it does not that there was a gear change (basically a rear end gear for all intensive purposes). With this hooked up, you should have no problem.

Mike

[Slowrockr]

No I have no input for the 4x switch, this was an F body motor, trans, pcm. I guess what I'm wondering is if I can just reflash it with the truck programing, modify the tune as necessary, than add the pin and a switch for 4Low or if it's not that simple if it will require a segment swap.

[Mike@ADS]

I'm not sure if it will work with the F-body tune in it at all, but reflashing it with a write entire of a truck program (4x4 obviously) should work just fine. This should change the necessary segments for the transmission and activate the transfer case options.

[waynehartwig]

SOunds like you are pulling the VSS from the back of the transfer case and not at the tail of the trans? If you put it on the trans, then the engine/trans won't care what the tcase is doing and will shift/operate as it would it 2/4hi. The only bad part is you will not have an accurate speedo then - unless you are using a programmable autometer or etc....

[Slowrockr]

No, VSS is off the tail shaft of trans and that's my biggest problem. With the gears and Tcase ratio on the scanner the VSS goes from 0-180mph+ quick, too quick. It acts like the pcm can't react fast enough, gonna try to set the MPH to 0 than shift off RPM otherwise time to try the truck tune route I guess.

[slow67]

No, VSS is off the tail shaft of trans and that's my biggest problem. With the gears and Tcase ratio on the scanner the VSS goes from 0-180mph+ quick, too quick. It acts like the pcm can't react fast enough, gonna try to set the MPH to 0 than shift off RPM otherwise time to try the truck tune route I guess.

If you try the 4x4 truck tune, be sure and move the VSS to the transfer case.

[Slowrockr]

Can't move the VSS to the rear. It's an Atlas transfer case, yes they offer it with VSS in the tail but it adds length that I don't have room for. Rear driveshaft is already borderline too short. Not to mention the cost of the parts from them to do it is insane. Hopefully there's a way to make this work the way it is. Would hate to have to build a new rig just to move the VSS.

[waynehartwig]

No, VSS is off the tail shaft of trans and that's my biggest problem. With the gears and Tcase ratio on the scanner the VSS goes from 0-180mph+ quick, too quick. It acts like the pcm can't react fast enough, gonna try to set the MPH to 0 than shift off RPM otherwise time to try the truck tune route I guess.

Not sure then, because mine has no issues there. Trans shifts just fine in 4 low, even with my 4:1 tcase, 5.13 gears and 39" tires. Maybe there is something with the tune? Try posting the tune and lets see it. I'm no expert, but I'm self learning pretty dang fast on my own junk! lol

[Slowrockr]

I'll post it up tonight when I get home, didn't mess with much. Your running same gears and tires as I, my Tcase is 3.8 is only difference. Gives me some hope seeing how yours works ok. I'll have to check the laptop for a log too, I can't remember if I saved one. Rig is going through some suspension changes right now so I can't run a new log for a couple weeks. Really want to get this figured out before our next race on memorial day weekend. Thanks for the help guys.

[slow67]

I'll post it up tonight when I get home, didn't mess with much. Your running same gears and tires as I, my Tcase is 3.8 is only difference. Gives me some hope seeing how yours works ok. I'll have to check the laptop for a log too, I can't remember if I saved one. Rig is going through some suspension changes right now so I can't run a new log for a couple weeks. Really want to get this figured out before our next race on memorial day weekend. Thanks for the help guys.

Yeah, you might need to lower your WOT shift MPH and RPM to give it enough time to shift. In theory it should work fine, just remember that it takes X amount of time to shift the tranny, and in low range you are revving the engine much faster.

[waynehartwig]

I'll post it up tonight when I get home, didn't mess with much. Your running same gears and tires as I, my Tcase is 3.8 is only difference. Gives me some hope seeing how yours works ok. I'll have to check the laptop for a log too, I can't remember if I saved one. Rig is going through some suspension changes right now so I can't run a new log for a couple weeks. Really want to get this figured out before our next race on memorial day weekend. Thanks for the help guys.

I'll help anywhere I can... My rig on the trail, if I'm doing say 5 mph, I'm already in 4th (computer thinks I'm doing 20 - 5x4). But I can take that up to about 30mph before hitting my rev limiter, but I do hit my speed limiter. And from 5 to 30 mph is break neck speed.

[Slowrockr]

Here's the file, I'm still new to this tuning stuff so hopefully I'm just overlooking something. Thanks again for the help.

[waynehartwig]

Here's the file, I'm still new to this tuning stuff so hopefully I'm just overlooking something. Thanks again for the help.

I dont' see anything that jumps out at me...

Can you control the shift in VCM Scanner under the controls? IE switch through the gears, even if you aren't moving?

What exactly is it doing? Just not shifting or?

[Slowrockr]

Yea it hits the rev limiter between shifts and hangs there before it'll shift. Seems worse 2-3 and 3-4 but it'll hit the rev between all shifts. I did a harness and pcm for a fellow racer with a 5.3 and 4l60, we didn't add any input for a 4low switch but his will shift fine in low range. Looking at the 2 tunes I don't really see much different other than the box for the tcase ratio. Doesn't that only come into play when the pcm sees the low range input?

I haven't tried to shift it through the scanner, will try it tomorrow. I know a log would be helpful, just gonna be a couple weeks before we get the new suspension setup done.

[waynehartwig]

You might try lowering the WOT 2-3 shift speed from 74 to 66. And set all of your shift RPM's to 6000. The shift speed might be too high and the RPM's might be too low.

Does the speedo show accurate in VCM Scanner? You might check that as well, as that is off your VSS and used to control the trans.

Not sure if it will help you, but here is mine... 08 Sierra 5.3/4l60e

[Slowrockr]

Spedo is far from accurate when in low range, winding it out in OD I'm doing 55mph or so, scanner shows like 180mph. I think that's my problem, it thinks it's still a 2wd car than I'm puttin it through the reduction of the Tcase that it doesn't know is there.

[slow67]

Spedo is far from accurate when in low range, winding it out in OD I'm doing 55mph or so, scanner shows like 180mph. I think that's my problem, it thinks it's still a 2wd car than I'm puttin it through the reduction of the Tcase that it doesn't know is there.

That's ok, it really doesn't matter. Can you post a log of a run?

Also your rear gear ratio and tire diameter.

[waynehartwig]

Spedo is far from accurate when in low range, winding it out in OD I'm doing 55mph or so, scanner shows like 180mph. I think that's my problem, it thinks it's still a 2wd car than I'm puttin it through the reduction of the Tcase that it doesn't know is there.

That's not an issue... Trans doesn't care that you are doing 55, it cares about the 180 - because that's what it needs to shift off of.

So when I asked if it was accurate, I meant in 2/4hi, where there is no reduction. If so then we have something else going on. If not, then that could be the reason for it shifting so late.

[waynehartwig]

That's ok, it really doesn't matter. Can you post a log of a run?

Also your rear gear ratio and tire diameter.

I think he said earlier 39" tires and 5.13 gears.

If you don't know what he's doing with his rig, take a look at this website.
http://www.xrra.com/
They combine flat out dirt track racing, with rockcrawling. Very intense!!

If that sparks your interest to try something new, check this out too...
http://www.kingofthehammers.com/
They combine desert racing with rockcrawling. Even more intense!! lol