power fluctuates throughout the powerband

[7M > V8]

My car's power really picks up at 4000 rpm. I can feel slight power fluctuations throughout the powerband. It doesn't cut out or seem to lose much power, it just doen't feel very consistent. It feels strong but seems like my car acts the opposite of the things i've read here. Could clogged injectors or bad MAFS cause this behavior?

I cleaned up under the hood
- Discarded clutch fan for Efans
- Header with 2 1/2 inch outlet
- 2 1/2 inch mandrel bend exhaust
- Removed spider web of vacuum lines
- Battery moved to trunk
- Re-routed air intake to front passenger side air duct
- New clutch
- Changed fuel filter
- Replaced timing set

[D-Bo]

could be many things
-clogged fuel filter/lines
-mafs like you said

any others?

[lost180]

What engine do you have? I'd start by giving the car a COMPLETE tune-up. New plugs, [wires, distributor, coil (if KA)]. Change all fluids, including tranny and diff. Check/clean all electrical connections. Dump in some injector cleaner. Change Fuel and air filters.

Then let us know if it's still acting up...

[nissanfanatic]

Check plugs and coil. Sounds ignition related to me.

Your power increase is due to the modifications you did.

[D-Bo]

Originally Posted by SR20DETpower

clogged fuel system wouldn't make it work better at higher RPM's..... it would be the opposite

to me, his problem sounded like it accelerates as usual and sounds/feels sightly more intense once you get to higher rpms but then fluctuates.. maybe its more like he really gets a rush at 4k.. more than he's supposed to.. if thats the case then i don't know.. there's definitely something wrong if its driving faster than you want it to..

[monooxide]

I like peoples problems when it comes to engine not putting out power...Automatically they go to saying REPLACE COIL DISTRIBUTOR AND WIRES AND PLUGS...why dont you use a Multimeter and do some tests to see if any of those the problem. I like solutions that resolve in REPLACE it...not jsut the part that is broken but everythign pertaining to it. now NissanFanatic said Check not replace.

[7M > V8]

Originally Posted by lost180

What engine do you have? I'd start by giving the car a COMPLETE tune-up. New plugs, [wires, distributor, coil (if KA)]. Change all fluids, including tranny and diff. Check/clean all electrical connections. Dump in some injector cleaner. Change Fuel and air filters.

Then let us know if it's still acting up...

I did all of that when we cleaned up under the hood. All fluids are synthetic. Wires are fine, distributor is fine. Replaced cap and rotor. I have KA24DE. All electical components check out ok. Set ignition timing after timing set instal. PCM pulled an O2 sensor after minor overhaul/tune up so we replaced it. The TPS was off so we adjusted it correctly.

Maybe i'm suffering a little on low end because of the exhaust mods. I forgot to mention that the diaphram that accuates the swirl control valve is shot, put the vac gauge on it and it will not stay open. Im going to order one soon. But im not exactly clear on what the SCV does.

[nissanfanatic]

Originally Posted by monooxide

I like peoples problems when it comes to engine not putting out power...Automatically they go to saying REPLACE COIL DISTRIBUTOR AND WIRES AND PLUGS...why dont you use a Multimeter and do some tests to see if any of those the problem. I like solutions that resolve in REPLACE it...not jsut the part that is broken but everythign pertaining to it. now NissanFanatic said Check not replace.

Would you believe me if I told you that there really are people out there that don't know how to use a multimeter?

I agree with you. Replacing that stuff can get costly. It is much better to run tests than just replace. Unless its simple stuff that you know is old. If you haven't changed plugs, fuel filter, or other matinence items in a long time, you should take this opportunity to do a tune up and poteintially solve future problems before the become problems.

[7M > V8]

Originally Posted by nissanfanatic

Would you believe me if I told you that there really are people out there that don't know how to use a multimeter?

I agree with you. Replacing that stuff can get costly. It is much better to run tests than just replace. Unless its simple stuff that you know is old. If you haven't changed plugs, fuel filter, or other matinence items in a long time, you should take this opportunity to do a tune up and poteintially solve future problems before the become problems.

Yeah, I've done everything anyone has mentioned. I even replaced the clutch when doing the timing set. Money is not an issue for the small stuff. I would rather it be done while I had the engine out of the car. But i've already taken all of that into consideration.

I hesitated before i posted this thread because i knew it would be tough because its hard to explain the behavior. Has anyone ever had a MAFS that started acting up, if so how did it act?

[nissanfanatic]

I had one MAFS problem. The best way to diagnose them is to unplug it and drive the car. Unplug the MAFS with the car completely off. Then drive it under easy load. It will hit a brick wall under heavy acceleration. If the problem clears up with it unplugged, then you have a MAFS problem.

[Waltz]

humm , dont even have to drive it , if you know how to use a multimeter that is ... TPS and MAFS are both 3 wire sensors * one for BAT+ - one for sensor signal - one for ground *

check the tps resistance or voltage (cant remember wich depends on make and model) while pulling the throttle , should either start with low resistance/voltage then work its way up as you pull the throttle or the other way around *depends on how ecu works* for voltage it should not be less then 0.5 volts and no more then 4.5 volts and should NOT fluctuate up and down while pulling throttle

as for the mafs , same thing as tps check for signal voltage , should stay put at idle and work it way up when rapidly pressing the accelerator pedal (thus creating vacuum) again no less then 0.5v and no more then 4.5v
basic sensor troubleshooting from my mecanics course
Best of luck

[7M > V8]

I forgot to post for closure of this thread. FYI after tracing wires coming from MAFS, we found some minor corrosion. We cleaned it and wrapped it up. I'm not sure if the car was just getting used to the changes, or if that was the fix but it runs fine now.

[wotandsdwys]

I'd say, check O2 sensor, fuel filter, and maybe some random ground points.