G50: Looking for MAF Spec Chart. Poor performance over 1500 RPM.

[sdkhalsa]

Does anyone have voltage/rpm chart on the MAF? I saw a couple of values in the service manaual, but looking for more complete info. Have a problem of very poor acceleration, like a large flat spot, at over 1/3 throttle opening. Fuel pressure is fine. Vacuum is fine, 18.5, and completely steady. New TPS with good Consult readings. Injectors are relatively new with very smooth firing. Ign. timing is correct. It appears that engine is providing very little additional power once vacuum drops below about 12 on acceleration.

[goody90q45]

Sounds suspicously like it could be a bad fuel pump control unit (FPCU). I know you say fuel pressure is fine but was it measured at idle only?

You can check it by grounding out the FPCU so the fuel pump only runs at high speed. Real simple to do once you remove the carpeted panel in the trunk. If you get your acceleration back with the FPCU grounded you know this is the problem.

Go to the tech help section at Q45.org or search for a post by Tangalora on NICO for DIY instructions. Good luck.

[elwesso]

You could always just try gounding the fuel pump to force it on high speed to see if that takes care of it..

Dont you have a consult?

[Q45tech]

There really cannot be a voltage vs rpm chart because that depends on temperature, humidity, and barometric pressure [altitude].

However 1.1 volts idle to under 2.0 volts [below 2200 rpm] would be the range.

Since the equation is exponential small numeric increases represent large changes at the top end.

Nissan uses Bosch MAF to gain fine resolution at low rpms whereas Toyota Karman Vortex sensors are iffy at low flows but get better at high flows.

http://www.ecutek.com/tuning/i...2.png

The RED graph in above might be pretty close!Idle might be 6-8 grams per second flow. and 2.0 volts might be 40 grams

[sdkhalsa]

Yes, it does sound like a fuel pump problem, but I ran the vehicle with a t-fitted gauge and the numbers looked good, going all the way up to 44 lbs on acceleration(while experiencing the lean condition). Prior to getting my hands on a pressure gauge, I had jumped the FPCU, but without any difference. The consult shows a leaning out on the Air/Fuel mixture where the problem is experienced, even though the consult is also showing a duty cycle of up to about 20(I think that is m-sec) on mostly wide open throttle. Is it possible that the ECU is making the proper calculation, but not delivering the full power pulse to the injectors? The engine runs very smootly over the whole range.

[sdkhalsa]

Let me throw in one other item. The consult is showing 1.27V on the MAF at idle with about 3.00V at about 3K RPM. This sounds to me like a decent reading.

[Q45tech]

showing 1.27V on the MAF at idle

YOU MUST BE SPECIFIC: what is coolant temperature, what is air temperature, what is barometric pressure and rpm, just the term idle doesn't cut it 650, 675, 700,725, 750 rpm as 750 is 20% more air flow [and fuel] than 625. [per unit of time].

[Q45tech]

Important to learn how to translate a volume of air per unit of time into a WEIGHT/MASS of air in a different time..

Old school USA CFM vs moderm metric grams per second.

1 cubic foot of air at standard temperature and pressure assuming average composition weighs approximately 0.0807 lbs. or 36.6 grams

50 CFM is 0.82585 CFsec or 30 grams per second so one needs 2 grams per second of gasoline to make 14.7 AF IF VE was 100%but remember the IDLE VE is low due to restriction of closed throttle and very slow air speed into cylinder 15-20-25% VE is reality.

It is nice that an engine won't drown at 9 A/F and will work at 16A/FBlack smoke to lean misfire, so the injectors can be off by a few tenths of a millisecond at idle either way.