So make a long story short my engine has lost a lot of power and no codes are being thrown. When im going slow (20 mph) or fast (65 mph) it is always downshifting and rev-ing out to get more power... I changed the fuel filter, air filter, spark plugs, plug wires, all with no success...

So after that i had to take it into my mechanic because im at a loss for what it can be. I have had my catalytic converters checked and they are ok. My mechanic is looking at changing my distributor assembly tomorrow morning where he said that it has been known to fail. Not sure if this will fix it but i should find out tomorrow morning when it gets installed. does anyone have any other suggestions what it could be?

Any information is appreciated!

Did you check the MAF sensor? That can produce some strange behavior, but it usually throws a code.

k_enn

How many miles are on it?
Have you ever had the fuel system serviced?
How is your fuel mileage?

Injectors get clogged and/or dirty enough to effect the spray pattern and quantity of the fuel. This sometimes results in a CEL, but not always, depending the level of severity

Some good info here:
http://www.aa1car.com/library/2003/ic30336.htm

Just a thought. . .

thanks the MAF was my next guess.

About 140,000 miles.
No fuel system service.
fuel mileage now about 8mpg and was around 14mpg it dropped off very quick within the last week...

fuel injectors would be my next guess.

You have an automatic transmission, right?

Yup

Update: So my mechanic and i have checked the following which is not issue:

Fuel filter
Air filter
Spark plugs
Spark plug wires
Mass airflow sensor
Distributor assembly
Catalytic converter sensors (cats are fine)

Anyone have any other idea's? Maybe i should say screw it and drop in a carborated small block V-8 and get all the power i need... take out the AC to make room

But in all seriousness if someone has any ideas let me know.

I think Bklyn.X may have been eluding to transmission issues?

I've always had manual tranny's, so I wouldn't know where to start with auto tranny issues. . . filter, fluid, valve body . . .

Has your mechanic done compression or leak-down tests?

When was the last time the x-fer case and rear end fluids were changed? If they get gunked up it could make the whole truck feel sluggish.

Hmm i did my transmission fluid and diff fluid i think between 20 and 30k miles ago. I didnt check that yet so might be worth a shot.

When I had distributor problems it would misfire/stall not strain or lose power…same with any fuel or aspiration troubles.

…I’m no mechanic and admit to knowing nutin’ but that has me thinking it might be transmission related. Check the AT fluid.

Not trying to be a wise ass (at least not right now) but did you change the filter when you changed fluid? Did you use the correct AT fluid (I think it is Nissan Matic D)?

I called him and he checked the ATF which is still good. I did use the correct stuff i believe. Next on the list tomorrow morning he will check the fuel injectors. I guess he cant work on it the rest of the day which is fine with me since he wont charge me when he isnt working on it... Either way i expect a big price tag on this one...

Well this might not apply here but my first car has similar issues and there was a sensor in the transmission that needed to be changed, $40 part but a bitch to get to.... just a thought

Ok every idea helps at this point. Ill let you all know what happens tomrrow...

Thanks again everyone for the help

One potentially off the wall item -- check the air intake tube that runs from the air filter box to the engine. Once, when I broke the driver side motor mount, the shifting of the engine overtime put a small break in that intake tube. The result was unpredictable surges and losses of power.

k_enn

So as of now he has checked 3 of the 6 fuel injectors (all on the passenger side) are possibly clogged. Next he will check the ones under the intake manifold which might be clogged as well... this is going to be pricey...