Well my new motor has approx. 10k miles on it and ever since I installed it, it has been just a little less powerful than the original and it has a stumble when excellerating hard.

I don't have any codes and no lights and EVERYTHING is connected the exact correct way it was on the original motor. The only sensors I used from the old motors were the Cam Sensors, the only things I transferred from the old motor was the intake and accessories like the Altenator, starter, A/C etc...

The only change I did to the motor is the Underdrive Harmonic Balancer.

I thought it might take some time for the ECU to get used to adjust or something but nothing has changed and I hate the loss of power.

I am thinking I lost 25hp or so. It's a difference I can definatlty feel.

What do you think it could be?

Here is the motor swap thread from MArch.
https://g35driver.com/forums/g35-cou...ain-broke.html

 

No one has any ideas?

 

I didn't get to read the build thread because it was too long but i would guess maybe
1. you used earlier year engine component ?
2. your timing is off and you are running rich ?
3. have you test compressions?

 

Motor just now has 10k miles on it and had approx. 3k-5k on it originally.

 

lol that did not answer none of his questions.... low mileage motor can still cause problem.

check your compression like that guy said. if you do have good compression im guessing its just all in your head.

 

...

 

I can do that, but I know something is slightly off. Especially with the stuble. It's an abrupt stumble under hard accelleration.

The motor was in a 05' , my car is an 05' so they are they exact same motor.
I can check the compression, BUT the motor looked absolutely new on the inside of the intake valves and the exhaust valves had VERY LITTLE carbon on them. It was hardly run.
The variable timing is working but may not be working correctly, but I don't know how to check it or test it. When the Timing changes, it almost feels like it's not changing fast enough.

 

That will be the next purchase but I want to fix what ever is wrong first.
I have that on my list for sure. Good call though

 

i am guessing your current timing is retarded. good luck

 

I think you are right cause I can hear it pinging when i get on it a little. How do I adjust the timing?

 

I am replacing the passenger side Cam sensor this week. Hopefully it will fix my lack of power below 5k rpms and the studder around 4krpms.

 

I replaced the Passenger side yesterday and then drove the car. It felt the same but then gave me a Check Engine Light with a code of P0011. Driverside Cam Position Sensor, so I ordered that one and should have it in a day or 2.
We will see, what happens.

 

Woa. This has been going on for a while.

 

30k miles worth.

 

3/24/10 was when I replaced the motor
https://g35driver.com/forums/g35-cou...ain-broke.html

Yea, it's been a while. I have had a lot going on.
I swapped the motor, then was trying to pack and move, had a egg size and shape brain tumor, had it removed and then moved and still getting used to all of it.
Been a little busy to fix it. Trying to figure it all out now. LOL!