Hi everyone,

I have a new to me 2012 3500 QC G56 DRW with about 14k miles that I installed an H&S race tuner and removed the DPF & filter. Other than an oil sample, switch to AMSOIL and an AFE PG7 stage 2 intake, the truck us stock - EGR, cooler, etc in place just turned off by the H&S

TM is off, timing is on #2 and I've been running this on the "street" setting mostly.

The truck has always been somewhat difficult to shift smoothly with a pronounced 2-500 RPM flare between each shifts unless I get it just right (I'm an experienced driver so I'd like to think it isn't me). In addition, despite the deletes and extra power the truck feels sluggish - nothing like what I am reading how they should feel. There is good response off idle, the a very pronounced flat spot unless you hang with it long enough. When letting off the pedal after a load there is a short surge of acceleration - this always follows the flat spot described above.

The above symptoms are not always present, but can be replicated on the same roads & hills pretty regularly. When running normally or when out of the "flat spot" the truck pulls pretty hard and runs great.

I tried searching but either can't figure out what to type in the box or no one else has had this problem. Truck pulls my trailers just fine but it just seems sluggish as if the TM is still on & the surge of fuel after letting off the pedal is strange.

Any input is much appreciated.

 

Are you sure the clutch isn't slipping, my sons 2011 3500 G56 clutch didn't last very long after deleting with the mini maxx, he was only using the "MILD' setting with TM off and NO timing because of standard head bolts. He went with the Southbend Double disc clutch and was very pleased with it but destroyed the G56 after that. If you didn't take off the intake manifold at the grid heaters you may find it almost completely plugged with carbon. Pull out the air sensor (can't think what it's called) in the intake horn and see what condition it's in, I was able to clean mine but the G56 truck needed replacing after only 20,000ml.

 

Thanks for the reply. I don't think the clutch is slipping as there isnt any rise in RPM under load...also doesnt explain the little burst of accelleration when letting off the pedal.

I'll check that sensor, but the truck has been deleted since 8k. I wonder if removing the EGR and cooler would help even though it's supposed to be turned off.

This thing isn't anything like my '03 with a built 48re and Smarty. Towed heavy for 250k miles on level 7 and I have no doubt it would smoke this thing. With everything I real about head gaskets and tuning quirks this 6.7 seems fragile in comparison. Bought this '12 so I could delete and make it run like my '03..I have a lot to learn

Thanks for any help

 

Actually a slipping clutch might explain the surge when letting off power, under power the clutch will slip but as the power is let off there is a point where it ceases to slip and drives straight through, the power that was lost in the slippage is now put to the wheels. My 2011 auto was deleted at about 7000km 4500ml and was quite dirty but no carbon blockage my manifold temp/pressure sensor was also dirty but cleanable, the manual trucks seemed to be way worse that the autos, my sons even had a fast idle that the dealer installed but still clogged up until he deleted. The stock clutch and flywheel is definitely the weak link in that truck that's why the engine was de-rated when new.

 

That's actually an interesting thought about the clutch slippage. It may be loosing just enough pressure to make the truck bog but not let the RPM's rise then grab again when the power is eased enough to handle it. Sure doesn't feel like clutch slippage I have felt in a big rig or tractor but this whole truck is different than I am used to.

Think I'll pull the EGR, cooler and TV off just to be sure, but I agree with your thought. I'll turn the H&S power down to stock and see if that changes anything. I'll check and clean everything in the process.

Thanks for the insight