Flat spot in power.
 

let me start off by saying the power curve stock was smooth. ever since i did the injectors, header, exhaust, spacer and intake. my jeep seems to "power up" when just taking off. ill be in first just slowly getting on it then it just comes alive and starts pulling. also on the highway at about 1700rpm's to 2000rpms 55-60mph. its seem like no matter how much i push the pedal down9before down shifting) it wont pull. almost like it needs more fuel. I just changed the fuel filters. and when i run premium or octane booster it helps. any ideas??
-sorry for the long post.

oh and fuel mileage is good. 17-18 mpg 50-50 driving.

basically you gained all high end power... the flat spot is from lack of low end torque.

find out what RPMS it is "catching at" because you need to see where you are starting your "real" power curve...


and i dont know what to do, to be honest, as far as regaining low end torque... because that is what you are missing. if i am reading your post correctly...

also welcome to the site!


btw my jeep does this to at a certain RPM range but it is not that big..... I have ALOT of torque then i hit a transition point and go to horse power...(hard to explain)

Yea im good up to about 1600rpm then the flat spot till 2k. it pulls hard after 2100 all the way to the top.

Sounds like TPS needs to be replaced, as per the "flat spot" in accel. But when you open the exhaust enough you can/do lose some low end power.

You don't need to run premium fuel or add octane booster, you're just wasting money on that stuff. The 4.0 only has 8.7:1 compression, higher octane will only make it harder to ignite the air/fuel mixture.

The 4.0 has 8.8 to 1 compression stock, yes, which means 87 octane is perfect. My 96 has this same problem, though its maby more noticeable, cause its a 5 speed. I originally thought TPS, but the TPS is new, although NAPA new. I have a feeling its the MAP, not working properly, not telling the injectors the right time to be open at that RPM.

The MAP sensor does not tell the injectors when to open, the MAP tells the PCM how much load is on the engine by measuring the amount of vacuum in the intake manifold. The PGM looks at data from the coolant temp sensor, MAP sensor, TPS, vehicle speed sensor, the crank sensor, cam sensor, and O2 sensors to determine and adjust the fuel trim and timing. This is where it is handy to have a scan tool and an understanding of how things work with one another in order to diagnose a problem correctly and not just start replacing parts. Using Dart Board Diagnostics will always cost you way more money and you will never really know if you fixed the problem.

I know not having O2 sensors will mess with the computer, but how much? The new header only came with one O2 sensor bung. I just capped it off because mine has four O2 sensors.
If premium does not do anything for it, why does it run better when I use it?

When I used to have my smallblock S10 and bought high performance/aftermarket parts you have to do some research cause some parts only work in a certain rpm range. Also if you have 4 0/2 sensors you need all 4. You can have a exhaust shop weld in an 0/2 bung in the same spot as the stock manifold.

have your ecm flashed too. it helped me out and got me back to useable power!

were did you get it flashed??

dealership can do it!

How does it run better? It's all in your head:w00t: