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4.8, torque management and nv3500 manual

6K views 5 replies 3 participants last post by  GriffBowTieOrDie 
#1 ·
I recently picked up a 2005 1500 RCLB 4x4 with the 4.8 and the nv3500 5-speed. I'm used to the 1996-1998 vortec motors without the drive by wire throttle body. I noticed that the throttle response isn't that great on my '05 and suspect it's because the computer is getting in the way. It doesn't feel or sound like the engine is laboring, it sounds and feels more like it's just not opening the throttle body up as much as I'm telling it to.

For example, in 4th gear, which is a direct drive, it has much better response and pulls pretty good even at only 2000 rpm. From the way it pulls in that gear you can tell it's got some power. So drop it down to 3rd and it should pull a little harder. Nope. Pulls just the same and loses some response and some of the howl in the exhaust like the TB isn't opened up as much. Drop it to 2nd and it's even less responsive and still cannot out pull what it can im 4th.

I've done a lot of searching and reading on this site about different tunes. There's a ton of useful information on here but most people are running automatic transmissions. It wasn't clear how much these 4.8's with a manual will gain from doing a PCM tune, whether the ones with a manual have torque management, and whether the tuner will allow you to turn it off. I see the place to turn it off when using an inTune is in the transmission part of the tune. It seems clear to me from driving my truck that the 4.8's with a manual must have TM from the factory. I could be wrong, but I'm a long time hot rodder, you can tell if the TB is open. A motor that's laboring feels and sounds different than one that's not being given any throttle. I'm going to order an inTune this week and dig around in the settings to see if the option to disable TM will be available. Has anyone else with the manual transmission tried this?

I am going to clean the MAF and throttle body as per the how to articles on this site as well. I'm sure it's due for a cleaning.
 
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#3 ·
It's got 93,000 miles on it. It has stock exhaust right now. It's getting a flowmaster super 44 put on it today. I'll see if the shop that's doing that can check the cats in some way while they are at it.
I haven't checked the fuel pressure.
Perhaps I'll change the plugs and wires this weekend when I clean the MAF and TB. I'm going to bet it has the original plugs and wires. It even still has the original shocks so I don't think the previous owner did much beyond oil changes. The oil looks great in it so I think he kept up on that at least. I'll also check the air filter. I'm going to do all of that before I put in the Diablo 87 octane tune. I may log some data on the factory tune before and after I do this stuff just to see how it all affects sensor readings.
 
#4 ·
The muffler and tailpipes are in. I don't really trust the seat of the pants dyno, but it seems to have picked up a little throttle response. I wouldn't go as far as to say that it makes more peak HP.

Since the super 44 allows me to hear the engine now, it's apparent that its not revving down very quickly most of the time. It will hold at 1500-2000 RPM for a little before it revs down. Sometimes it revs down reasonably well, but when it does that, it will fall below 500rpm for a moment before coming up to a more sane idle speed. This leads me to believe that I have a sticking IAC solenoid, sometimes sticking a bit open, sometimes sticking closed. I checked out the TB last night but didn't have time to remove it. It's quite dirty behind the butterfly. What I believe is the passage to the IAC looks pretty dirty too. I'll have to remove that tonight and try to get that clean.

I'm ordering the Diablo inTune today. I'm assuming that my MAF sensor is quite dirty as well. I think I'm going to log some data with the inTune before and after cleaning the MAF. It would be interesting to see if there is a noticeable difference in both seat of the pants, and numerically in the MAF sensor readings.
 
#5 ·
My Diablosport inTune arrived. It did give me the option to disable TCM on my '05 1500 with the 4.8 and the nv3500 transmission. This made a huge difference in throttle response.

1985zx900 is correct also. It does need a hefty tune up. From reviewing data logs I've created, it can see that at least one cat is not working very well, may have some lazy o2 sensors, there may be a vacuum leak/stuck iac valve, and there's quite a few misfires being logged under engine braking.
 
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