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Lower RPM power question...

Old 08-29-2014, 09:39 AM
altoncustomtech's Avatar
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Default Lower RPM power question...

Hey guys, I've gotten about 2,000 miles accumulated so far on the new Marshall rebuild in the Jimmy. It runs fairly good, gets about the same fuel mileage as the old engine did before the swap and in general is doing great.

My question though, probably isn't specific to the truck itself and could be a general issue that could be found in anything. When I'm driving it, either on take off or at speed it's not got much power/torque when it's below ~2400 RPM. For example, cruising down the highway in a flat area at 55mph the engine is turning about 1600 RPM. If I edge into the throttle it will respond with what I feel is acceptable acceleration. However, if I'm driving at 55mph on the same highway and come to a grade/hill it will have to at the very least unlock the TC and often times shift to 3rd and still generally lose speed as I go up the hill. In the same respect, taking off from a dead stop, once it winds up to ~2400 RPM you can feel it come to life and really start pulling hard, like a 2 stroke motocross bike winding up to the power band and BAM you start to fly.

I'm sure the problem is a simple one, I just can't wrap my head around it. I'm having a hell of a time figuring out why it's not pulling that strong lower in RPM's. It has a K&N CAI on it, the filter was nicely cleaned and re-oiled when I put the new engine in (less than 2,000 miles ago) and I don't have a CIL or any DTC's stored, and it idles smooth and has revved up to about 4k RPM without any hiccups or issues. It's just the fact it comes to life and starts to pull HARD, like shove back in the seat hard, like a 2 stroke engine when it gets to ~2400 RPM.

Thanks for any help guys, it has me stumped.
Old 10-20-2014, 08:33 AM
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Same issue I had. It's the way the PCM is tuned stock. I have HP Tuners and I got it nice now that I removed a lot of the limiters and torque management and adjusted my fuel, spark, and PE. The 4.3 is more of an economy tower from the factory with conservative tuning. Try a custom tune but before you get one from somewhere, do your mods like if you want a new exhaust or bigger cam, etc.

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