VQ25 Feeling "Breathless" on High RPM

[ctk22]

I discovered that my VQ25 feeling some pullback / not smooth whenever the engine in between 3800rpm to 4200rpm. It felt like as if there's a torque dip in that range, and the engine is as if trying to catch some breath. What could the problem be?

1. Is it due to electrical? I suspect maybe the electricity supplied to engine maybe insufficient (alternator issue?), cos I also found dimmed headlight when press brake hard

2. Is it due to spark plug? But if it is, the effect will be in full range RPM right?

3. Is it due to fuel pump? My fuel pump has been serving for more than 400k km.

Anyone has any idea? Pls comment. Thanx!!

 

[weikee]

01) Check your plugs, is it filled with carbon? did you change it recently? it need to be change every 100kkm, I'll do it at 80kkm.
- If all 6 are even color, then is ok.
02) Your AFM working right? get one spare one in chop shop and try. Is handy to keep one, cause is also a common problem.
03) Fuel pump, hmm maybe change fuel filter first. This one you need to check the plug color. if is white, then maybe fueling got problem.
04) electrical grounding, try measure your key voltage vs the battery voltage. I'll do some grounding work from -ve to body, and -ve to engine.
- If voltage drop is significant in the key +ve vs the battery +ve, maybe good time to pull direct +ve into key (please add fuse)

 

[ctk22]

thanx weikee, will try ur suggestions

 

[doraemon98]

What is AFM? got any photos?

 

[ctk22]

This is Air Flow Meter (AFM) taken on my VQ25

 

[doraemon98]

Air flow sensor that sense the speed of air being sucked into the manifold? A33 one looks so different.