Do I have a problem or...?

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NRA223

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So there was a mobile dyno at a local truck pull this weekend and i thought it would be fun to see what my truck put down. My last experience trying to dyno didn't go well because the dyno operator couldn't get the truck to spool. This was only the 2nd time he had tried to dyno a diesel truck so i just figured he didn't know what he was doing. This mobile dyno was from a diesel shop so i figured all would go well.

When they tried to make a pull in 4th, it kept shifting early into 5th. It would wind out about half way thru 4th and then shift into 5th. No matter what they did it kept doing this. They said they have dynoed thousands of trucks and never seen this. I know this isn't a lot to go off of but is this a dyno issue, or is my TCM tuning causing this issue?
 
Awenta

Awenta

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Sep 28, 2014
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Don't have the od lockout upgrade?

Why didn't they correct for 5th ratio and run it?

Sent from my SM-N910V using Tapatalk
 
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NRA223

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No mine won't lock out OD. They said they didn't really want to run it in 5th and didn't know what kind of numbers it would put down. So i figured why pay for something the dyno operator is not sure of, so i just had them pull it back off. My bigger concern is if i run it at the track is it going to short shift into 5th too, or is this just an issue with the truck not liking the dyno for whatever reason.
 
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NRA223

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I don't think I have. I never pay attention to what gear I'm in. Can't remember the last time I had the truck over 80.
 
N

NRA223

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Until I get to the track. Would be a pretty crappy deal to drive 2 hours to find out I have a problem that could have been fixed before.
 
Burn Down

Burn Down

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Sep 14, 2008
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Not sure but I thought/heard you need to build a special "Dyno tune" for the LB7 to keep it in 4th??? I can't recall for sure though. Reece was messing with one for his LB7 when the dyno guy in Anchorage smoked his trans. letting it shift into 5th gear. Dyno chart looked like the Rocky Mts. till 750 then poof trans was done:eek:


You need to find some time to do full throttle runs in "Mexico;)" before you head to the track. Log it and see what it's doing or not doing.
 
THEFERMANATOR

THEFERMANATOR

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For dyno purposes it is best to have a dyno tune for the trans. You want to keep it in 4th to keep the numbers accurate. The TCM if stock is programmed to shift at roughly 3250 RPM's, but the TCM tries it's best to estimate and make the shift occur at that exact RPM. So if it is revving very quickly, the TCM will short shift as it's afraid the engine will over rev and shift after the desired RPM. I've had to raise my WOT shift RPM's up to 3350 to get it to shift at 3250-3300. Stock is 3200 for most, and mine was shifting at 3100-3150 on my bigger tune because the TCM was trying to keep it under 3200 when it shifted. On a dyno where RPM's shoot up quickly, I could easily see it shifting at 3000 or less. As to OD/LO, you have to add in a switch, wiring, indicator light, and make sure you have the updated tune to have it with a switch. Kennedy diesel has the directions on his site. If you're much over stock power, you may want to look into some trans tuning to keep your shifts above 3000-3100.
 
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NRA223

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01s and 02s won't lock out unless tuned to do so from what I've heard. I guess testing on the street is the only way to know for sure. I just don't like running that far over the speed limit anymore.
 
Chevy1925

Chevy1925

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NRA223 said:
01s and 02s won't lock out unless tuned to do so from what I've heard. I guess testing on the street is the only way to know for sure. I just don't like running that far over the speed limit anymore.
Click to expand...

you need the updated stock TCM tune OS 2881. there are other OS's with over drive lock out active as well. then all you need is to wire a momentary switch to the tcm via two pins and you now can lock out 5th gear. i use mine all the time for towing.

for the dyno, i just use the DVT controls and lock it in 4th gear. easier that way unless you are trying to log data.
 
2004LB7

2004LB7

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Chevy1925 said:
for the dyno, i just use the DVT controls and lock it in 4th gear. easier that way unless you are trying to log data.
Click to expand...

2x

just use the EfiLive (if you have it) scan DVT controls to select 4th gear and it will stay put in that gear
 
THEFERMANATOR

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NRA223 said:
01s and 02s won't lock out unless tuned to do so from what I've heard. I guess testing on the street is the only way to know for sure. I just don't like running that far over the speed limit anymore.
Click to expand...

As I said above, it isnt special tuning, it's a factory update and install of a momentary switch and led indicator to obtain od/lo. Kennedy diesel has the directions on his site, and 01 tunes are all over to download.
 
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NRA223

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So it shifts fine on the street. I don't want to re-flash the TCM since i already have TCM tuning. I guess i just have to make sure somebody has a V2 the next time i dyno.
 
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