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Dead pedal in low range

D.Camilleri

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My 02 duramax sometimes gets a dead pedal in low range. It only does it in low range. Sometimes letting off completely on the pedal and it will work normal. Sometimes the transmission won't shift out of 1st gear and then only will rev to about 2000 rpms and dead pedal. Let off the throttle, and reapply and it will shift and go fine. Any of you ever run into this? I think I have read somewhere about cutting a wire that won't tell the tcm that the transfer case is in low range. This is sometimes a pia when you need some wheel speed to get out of a spot and the only way you can do it is to shift to 4 hi. I have tried data logging and when I log it it won't mess up.
 

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FRANKENBURBAN
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Mine does it to with an 02 ECm operating system in it. Cutting the wire to the TCM will put you in a world of limp mode hurt though. I believe it is in teh torque limiting tables in the ECM though. Mine is evry consistent though, and will not go back to normal until I go back to high range and restart it.
 

D.Camilleri

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I don't think the wire that was talked about was for the ecm, I think it was a wire from the transfercase loom that was a signal telling the ecm truck was in low range. I have also heard about people engaging low range and then pulling the plug from the transfer case and making their pull. Would it be possible to rewrite the ecm to a different year operating system? I haven't ever tried tuning the truck back to stock to see if it still does this. I do remember the last time I tried data logging in low range, that one of the torque values came out as being 35xxx, just a little high don't you think? This problem is a pia because sometimes when towing heavy in the mountains, I like to use 4 low and sometimes it works and sometimes it doesn't.
 

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FRANKENBURBAN
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The ECM will multiply the torque values when in low range by the transfer case and gear ratio for the front end. If you have EFILIVE go in and max out the torque limiting tables and see if it still does it. I know on mine my front end can't take the extra power so I have mine turned down to save my tie rods and links.
 

D.Camilleri

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I am not running efi live as of yet. I am runnng a ppe hot + 2 et. Last week I took a little stroll down a 4wd road up in the national forest and used 4 low do to all the rocks around just so I could go slow. Driving along and I noticed the dead pedal, would only rev to 15-1800 rpms and wouldn't shift out of 1st gear. I fully released the pedal and started pushing it down and no dead pedal and the trans shifted like it should. This is kind of frustrating because sometimes it works and sometimes it doesn't. The problem is that I don't even think about it until I use 4 low. It seems this problem is also related to the way the transmission shifts in that when it is acting up, it holds a gear much longer than it should and then shifts very harsh. Never an issue in high range. I have posted questions on this for the last two years on all the forums I visit and one recomendation was to cut the gray wire with a black stripe on the three wire harness that goes to the transfer case. Aparently this is the signal wire that lets the ecm know that the tc is in low range. I just hate cutting wires.
 

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I am not running efi live as of yet. I am runnng a ppe hot + 2 et. Last week I took a little stroll down a 4wd road up in the national forest and used 4 low do to all the rocks around just so I could go slow. Driving along and I noticed the dead pedal, would only rev to 15-1800 rpms and wouldn't shift out of 1st gear. I fully released the pedal and started pushing it down and no dead pedal and the trans shifted like it should. This is kind of frustrating because sometimes it works and sometimes it doesn't. The problem is that I don't even think about it until I use 4 low. It seems this problem is also related to the way the transmission shifts in that when it is acting up, it holds a gear much longer than it should and then shifts very harsh. Never an issue in high range. I have posted questions on this for the last two years on all the forums I visit and one recomendation was to cut the gray wire with a black stripe on the three wire harness that goes to the transfer case. Aparently this is the signal wire that lets the ecm know that the tc is in low range. I just hate cutting wires.

If you cut the wire from the Tcase, it wil lalso cut the signal to the TCM and give you a 2000 RPM limit and limp mode. You could cut the wire at the ECM and it would stop the ECM from knowing, but the TCM MUST know. If you have a floor shift it is pretty easy to do, but if it is a push button shift then I believe the 4X4 signal goes out over teh databus and you cannot stop it.
 

D.Camilleri

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Good reason to not cut the wire I guess. Any guess on why the data log would show 30,000+ on the torque and the number doesn't change, just stays there?
 

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FRANKENBURBAN
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Could be something with your PPE tune, or in how it is datalogging. Teh ECM uses alot of variables when it comes up with a torque value, so who knows what is going on without seeing an actual log of it and what tune you are running. I know you are not alone as it bugs me to with mine. Mine isn't as extreme as yours, but it just bugs me how it has NO power when in 4 low.
 

D.Camilleri

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I am not sure if it has anything to do with the PPE tuner or not. When I data logged it, I used a OTC Genysis Scan tool. I guess I should scan it again and write down the chart that was off the wall. What I don't like is one time I can get a dead pedal and the next time I can put the 500 hp to the ground. Every once in a while I feel like going to the local fair and hooking to the sled, but when I hook, I want to win and falling flat on my face doesn't thrill me.
 

D.Camilleri

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OK, just did a test. Hooked up the Genysis scan tool and data logged the TCM:

Torque requested: 0

Engine Torque at idle: 48315

Driver requested engine torque: 48315

Requested torque always stayed at 0. As soon as I started leaning on the gas pedal, torque dropped from the 48315 down to 26, then 126 let off the pedal and right back to 48315. This was with transfer case in 2 hi or 4 lo

Shifted to 4 lo 3rd gear, slight power brake and mashed the pedal, took off like a rocked to 4500 rpms. Stopped tried to repeat and defueled and would only rev to 3000 with no power. Stopped again and retried, off like a rocket. So it either works or it doesn't. When I log the throttle position it appears to work correctly. Any Thoughts? I am not sure why the torque requested is always at 0. I might try and hook the scan tool up to the wifes 01 and see what kind of numbers I am getting. There also was a line for torque management, but I only saw 0 for the value.
 

D.Camilleri

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Did another experiment with the scan tool. This time I listed the truck as a 2001 instead of a 02 and the torque readings when logged into the tcm matched the readings from the 01 truck. The 48315 number still came up, but only after quickly releasing the gas pedal. So, I don't think this is the problem. Back to square one. I did a mild launch today in 4 lo and the truck worked perfect. Weird
 

millsroger

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Wiring is different on some and with or without mods, BUT, my sig had some of these problems. Very hard high RPM shift in 4 lo. Never did the dead pedal thing cause I didn't push it. ECM pin was not getting a solid signal, kind of jumping around. If ECM does not see 4 lo signal no tranny re program, but if signal comes and goes ECM goes to limp. Bad xfer case switch.
 

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FRANKENBURBAN
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Wiring is different on some and with or without mods, BUT, my sig had some of these problems. Very hard high RPM shift in 4 lo. Never did the dead pedal thing cause I didn't push it. ECM pin was not getting a solid signal, kind of jumping around. If ECM does not see 4 lo signal no tranny re program, but if signal comes and goes ECM goes to limp. Bad xfer case switch.

Teh DURAMAX is a whole nother ball game from the 6.5. If the low range signal doesn't make it to the TCM(the ALLISON uses it's own TCM seperate from the ECM), it will IMMEDIATELY go into limp mode with a P0700 and most likely a P0500 DTC listed and default to 3rd gear. I just raised up the torque limits in my ECM tune for the transfer case and front components via EFILIVE and it is a friggin ANIMAL now in 4X4. Could only boost to maybe 2 pounds before even in 2WD, now it will spool up and blow the tires off in 2WD and flat out LAUNCH in 4X4. It was a wierd feeling doing a boosted launch in the BURB earlier today.
 

Ratman

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Teh DURAMAX is a whole nother ball game from the 6.5. If the low range signal doesn't make it to the TCM(the ALLISON uses it's own TCM seperate from the ECM), it will IMMEDIATELY go into limp mode with a P0700 and most likely a P0500 DTC listed and default to 3rd gear. I just raised up the torque limits in my ECM tune for the transfer case and front components via EFILIVE and it is a friggin ANIMAL now in 4X4. Could only boost to maybe 2 pounds before even in 2WD, now it will spool up and blow the tires off in 2WD and flat out LAUNCH in 4X4. It was a wierd feeling doing a boosted launch in the BURB earlier today.

What is a ECM??

sorry, I just couldn't resist..........my bad........:hihi:

I'mmmmmm BAAAAACK!!! :thumbsup:
 

D.Camilleri

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I thought I would jump back in and post what I did to fix this issue. I bought a Fleece Performance Tap Shifter, installed it and took it to my local dealer and had them reflash my TCM so that my tap shifter would work. My build date required the reflash. Bingo, dead pedal is fixed!
 
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