OK....so air enters the mass air flow sensor and sends the computer a voltage which is used to calculate the mass of the incoming air...thats how i understand it, PLEASE correct me if I'm wrong...im just getting a grip on how these computers work... The PCM by this then determines time/length injectors will fire, etc. So could a bad MAF cause a drop in fuel pressure? No, correct? The PCM only receives info from the oxygen sensor, temp. sensors, detonation, throttle position and MAF sensor and has nothing to with pressurizing...only delivery from injectors. Is this correct? --I just want to be sure my MAF sensor is good cuz about 2 months ago I descreened/ported/polished/cleaned it all (I was extremely careful and did not touch any of the 3 resistors). Since then, increasingly, my car has had hesitation/powerloss/stubling/etc... However, it has ALWAYS had hard starts...and stumbling worse after hard start....so im thinking that it was just coincidence because fuel pressure is low (upper 20s) and I know its the pump (I'm changing mid-week).

So I guess what I'm asking is how can I determine if my MAF sensor is bad? (ignore fuel pressure problem listed above) If i unplug it, will it just use speed/density? f so how does it measure intake air temp? preset values? And finally -- does the car have to be running to first unplug it and do this?

If anyone has any idea at all what im trying to say, please help me out... Thanks!

--Fred

 

home porting your stock maf will cause you to run lean...

(it was on granetelli's website... it says after 200 miles home porting will cause the car to run rich...

get a z06 maf for LT1 at ls1speed.com its the cheapest performance tuned maf for LT1s (150 compared to GMS' 350-400)

 

yea, I noticed the Z06 MAFs on ls1speed.com just a week ago when I realized ls1speed.com existed, and is 20 mins from where I live!.....anywayz, I'm not sure i understand 100% how it would cause a car to run lean.... I'd also be a little reluctant to believe this coming from Granatelli Motorsports who is trying to sell MAFs for over $250. Thanks for the input.

_fred

 

Get yourself a stock MAF. JMHO

 

Pretty close. The output of the MAF sensor is a variable frequency, which is roughly proportional to mass flow. The PCM has a calibration table, that converts frequency to mass flow.
Yes... in closed loop it calculates what injector pulse width is required to provide 1 pound of fuel for each 14.7 pounds of air the MAF has measured.
Correct. Fuel pressure is controlled only by the (mechanical) fuel pressure regulator. The PCM can not measure fuel pressure, nor can it change fuel pressure.

Fix the fuel pressure problem first. If the system pressure really is 20psig, it means the injectors are only delivering 67% of the required fuel, and the spray pattern is probably poor. The PCM can not adjust for more than a 25% fuel shortfall.

Attempting to diagnose an MAF problem, when you know you have the fuel pressure problem is pointless.

 

hey - thanks for the clear explanation Injuneer, it really helped me to piece together how everything works and understand it all better - thanks for your time!

_fred