My 2007 Navi has been a good truck and given me 137,000 miles, but I am having trouble solving a power loss issue between 3000 and 4000 rpm. Engine runs smooth and strong right up to 3000 rpms or so. Then the engine feels like it is struggling to get air(or enough fuel) and the power falls way off. If I let the rpms come back down under 3000, the truck continues to accelerate strongly with no missing. If i hold it in gear to push it into the 4000+ rpm range, power returns. Between 3- 4k, the engine coughs, sputters, hesitates big time and misfires. I can't get the cel to come on so I can get a code. It has all new coils, new fuel filter and new MAF. Any ideas on this issue are appreciated!
Plugs were changed at 97,000, using 87 octane, and at 110,000 the timing sprocket and chain were replaced. I don't drive the truck hard, so I don't really know when this issue started. I've been reading up on problems at 3000 rpm....could it be an intake manifold tuning valve issue?
It only gets above 3000 rpms when I am merging onto the freeway or passing and have to mash the gas. It is not that it can't be driven effectively now, I just want to be able to pass and accelerate quickly if needed.
I decided to go ahead and get a SCT flash programming tuner for the PCM. Looking at it on the dyno, the technician was able to see what was happening between 3-4000 rpms and made tweaks to limit the low value for spark timing in the mid rpms and adjustments in air/fuel mixture. Now the truck runs great and accelerates through the whole powerband effectively. It's like I have a new truck. Nice.... I'll run a few tanks of gas through to see where gas mileage ended up. I was getting 13.7 mpg before the tune.
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