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95 eclipse 420a Lacks power at higher rpms (4500 and up)

09-07-2009, 11:58 PM
I just got done rebuilding the engine (eagle rods, 8.8 wiseco pistons) and other quality parts. i've broke the engine in by loading it down, and then creating lots of vacuum multiple times like your supposed to.

I believe its idleing where it is supposed to, right around 800 rpms. It has great power between 2500 and 3500 rpms but once i hit about 5200 in any gear other than 1st, it pretty much just hangs theres. revs up fine in nuetral of coarse.

now i know the 8.8 pistons are lower compression and will reduce some power, but it shouldn't be that much right?

Also I am pretty sure its not a fuel problem being that i have a 10.1 to 1 afr when accelerating - even when the rpms are hanging. even if only one fuel injector wasn't spraying very well, it would throw the afr way out of range - I would think.

So, are there any other thing you guys can think of? i have new sparkplugs, how important is the gap?

09-08-2009, 12:02 AM
Dammit, forgot to mention that i double checked the timing when i had the engine on the stand and then just to make sure, checked it again after i ran it. so i am 110% positive that the timing is right.

09-08-2009, 12:03 AM
So is this car turbo or not?

09-08-2009, 12:14 AM
i have the turbo setup, but i don't want to run boost for a while. i want to work out all the problems, like this one i'm having now, before i run any boost.

i have the wiring harness setup for my aem F/IC, but i have the bypass connector in it right now just to ensure that it doesn't affect anything.

09-08-2009, 12:23 AM
Im guessing you have a wideband o2 sensor that you got that afr reading from. 10:1 is WAY to rich for a NA car. Hell its to rich for a turbo car. Most people tune NA cars to 12.5-13.0 at WOT. Under boost you want to tune to around 11.2:1. Maybe a tad leaner below 10psi or so.

Also some sensor wont read below 10.1:1 so if you have bottomed out your sensor you are running even richer than that.

So this is your problem, you are bogging the motor down.

09-08-2009, 12:33 AM
yes i have an analog aem wideband. and i competley forgot that the sensor could bottom out. i think i will just mess aroud with the fuel pressure tomorrow.

I know that 10.1 is really rich, but i just figured that rich is safe so i would tune that later.

Thanks man!

09-08-2009, 01:57 AM
lol yea reduce fuel pressure if you have no other way to tune.

09-09-2009, 07:47 AM
yeah i just adjusted the fuel pressure for now, untill i get the fic going.

So whats everybodys opinion on afr's at:


light load crusing?

also is it normal for the afr to jump up to 18+ when downshifting (engine braking)

09-09-2009, 09:22 AM
Idle - 14.7

Cruising - 14.7-16.0
You can lean out the car some when cruising

You go lean when engine breaking because the ECU cuts off the injectors above a certain rpm to save fuel. Your WB must max at 18.0afr so it gets pinned there.

09-09-2009, 10:22 AM
Yeah thats what i had guessed... just double checking to see what you guys thought.


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