Low power in 4 lo

[DmaxCC6spd]

I thought I remembered some information about the PCM decreasing engine power when in 4 lo. I searched but came up empty. Is this true? If so, is there a fix? I was recently trying to pull a live tree out of the ground. (Live ones put up a good fight) I used 4 lo and low gear. As I fed more throttle and eased off the clutch the rpms kept going down. It wouldn't even spin the tires. ( I was on blacktop). What was GM thinking? I thought the point of 4 lo was to add power through torque multiplication. My old 6.5 dually (bone stock)with 4:10 gears would spin all 6 tires at a dead idle when in low gear(manual tranny) and 4 low. Whats up with this, and is there a fix?

[77TransAm]

I didn't see a bulletin about it, but I do seem to remember that early trucks that had not had any software updates suffered from that problem. Updating to the latest available software for the PCM and TCM fixed that condition.

[CPMac632]

All 6 speed Duramax trucks have a severe power derate when in low range. It is to protect the drivetrain and isn't easy to disable.

[DmaxCC6spd]

Isn't easy to disable? But doable?

I have the manual shift transfer case. There must be a sensor someplace that could be "tricked" or disabled. Anyone have any thoughts?

Duramaxallitech: Help!!!!!!!

[Kennedy]

If you haven't had any reflash stuff done, that's the first place I'd start. Most think that it is sufficient to gut the air box, but there are updates for false codes etc. Not sure if the update will unleash more power in 4x4 low, but likely will.

[CPMac632]

It isn't easy but yes I do know how to do it. Email me if you want to know how. But my main question is what do you need that much power in low for. Most things high 1st is plent low enough and it still has full power.

[mark45678]

get a reflash done it made a big differance with my 01 allison!

[Alli-max]

it is as simple as a reflash. I was doing the EXACT same thing 2 years ago and couldnt spin the tires in dirt. Had the updates and it pulled fine.

[CPMac632]

With the Allison the reflash will work. With the 6 speed it will not help.

[VA_Dmax]

I had the same problem here right after Isabel passed through and was trying to pull stubborn stumps. I ended up using 4hi and using the low 1st gear more often than dropping to 4 lo. Just seemed like it wound up better in 4 hi.

[Ira Chandler]

Before reflash, my 2001 would not pass 1000 RPM in reverse in 4Lo. After new flash, I got a whopping 1500. 4Hi is good enough for most everything I pull, 4Lo is best for controlled descent downhill.

[JRM]

My friend exploded his front axle on his 99' dodge when pulling a car out of a creek- 4low litterly broke the axle and outer cv. so maybe its smart thing to have :( but the entire point of 4low is then eraced :confused:
My old 90' toyota can smoke all 4 in 4low on blacktop and never had any drivetrain problems- but it also never had any power either tongue.gif