What might cause a flat spot at mid RPM's

#1

When I downshift my new motor I have shit for hp. It doesn’t start pulling until about 5krpm and then seems to pull ok. It doesn’t miss or hiccup, it just has no power in that rpm range. What might be causing this?

Possibilities that come to mind.

  1. My O2 sensor was not hooked up because the new harness didn’t fit it. I’ve a new sensor en route. There has already been a suggestion that this is the culprit because if your O2 sensor isn’t there your mixture gets screwed up. But I’ve also heard that the O2 sensor doesn’t matter when you are WOT.

  2. My spark plugs had unknown mileage. I’ve relatively new plugs ready to go in.

  3. My spark plug wires had unknown mileage. I’ve got newer ones that I can put in.

Your thoughts?

#2

bad spot in the travel of the afm?
weak or failing fuel pressure reg?

#3

Could your buring oil have something to do with the lack of power on downshift?

It may be that when you downshift, there is a flood of oil entering the chamber and that may be blocking the proper combustion. The power will only come back on after the initial oil has been burned off.

One way to test it would be to run up from 2K rpm in just one gear (maybe third) slowly and see if that flat spot is still there.

Just a WAG.

#4

Patton gave you the best advice in the last thread. Put it on the dyno and swap out parts with known good ones until you find the best combo.

Anything that affects spark, air, or fuel is a possibly culprit.

JP

#5

We had a flat spot early last year that we could definitely feel on track and see on the dyno chart… our fix was a new AFM. Swapping out a variety of used ones that we at the shop didn’t do it for us, only a new part seemed to fix it… YMMV
Good luck!