MAF Voltage

[ninety1two40]

I'm running a mostly stock RB25DET, stock MAF, and Power FC. When the car is on and the engine off I get a MAF voltage of around 800mV on the Power FC. Is this normal? I'm having a loss of power above 5000rpm when the engine warms up. No boost leaks, walbro 255. I had this problem come and go last year but I just cleaned the MAF (covered in oil), this time I have a catch can installed and the MAF is clean.

Thanks in advance.

[s13point5]

do you have an adjustable fuel pressure regulator?

[ninety1two40]

Nismo Fuel reg (set at 44psi, vac line off)

Also, last year I had a stock intake. This year I just added a FMIC, Greddy Intake Manifold and Q45 TB.

[mello88]

fsm says you should see around 1v from the MAF at idle. So your 800mv sounds a little high... I would think with the key on engine off it would be much lower like < 500mv but I haven't tested for that. What voltage do you see at idle and 2500rpm?

[ninety1two40]

edit:You mean 1mV? - nevermind, miss read your post.

At idle - ~1.1V2500rpm under load - ~2.0V

Here's a shot with a 1-3gear pull.
Modified by ninety1two40 at 2:22 PM 6/10/2008

[mello88]

Yeah 1v/1000mv at idle. Your #s sound very close to the #s they specify in the FSM. Was MAF not plotted on that chart? And out of curiosity, what voltage does it max out at?

I don't think it's your MAF this time. How is your base timing?

[S14-NEO]

Yeah 1v/1000mv at idle. Your #s sound very close to the #s they specify in the FSM. Was MAF not plotted on that chart? And out of curiosity, what voltage does it max out at?

I don't think it's your MAF this time. How is your base timing?

i disagree, the voltage coming out of the maf can be fine, however if the MAF is not reading the airflow volume correctly the power loss will be signifigant.. ive had numerous nissans at the dealership with nearly the exact same issue( no power past 4500k and up.MAF voltage is only one area the ECU looks at coming from the MAF..if the Mass Air Flow measured in cubic feet per minute is not correct this problem he is having is also possible...in fact very possible
Modified by S14-NEO at 10:19 AM 6/12/2008

[ninety1two40]

Yeah 1v/1000mv at idle. Your #s sound very close to the #s they specify in the FSM. Was MAF not plotted on that chart? And out of curiosity, what voltage does it max out at?

I don't think it's your MAF this time. How is your base timing?

Yeah MAF voltage is plotted on that chart. I'll try and get a better chart later. The highest I've seen that MAF is around low 4V.

My timing is set at 15deg +/-1deg, the Power FC also shows the same, sometimes when idling the PFC will drop to 10deg. this is all at 650-700rpm.

[ninety1two40]

i disagree, the voltage coming out of the maf can be fine, however if the MAF is not reading the airflow volume correctly the power loss will be signifigant.. ive had numerous nissans at the dealership with nearly the exact same issue( no power past 4500k and up.MAF voltage is only one area the ECU looks at coming from the MAF..if the Mass Air Flow measured in cubic centimeters per minute is not correct this problem he is having is also possible...in fact very possible

So your saying, replace the MAF. What does the ECU also read? Current?

[S14-NEO]

honestly i would test with a known good part,i see you have a power FC so why not try bumping up to N62 MAF and give that a go....its worth checking for sure.

[ninety1two40]

honestly i would test with a known good part,i see you have a power FC so why not try bumping up to N62 MAF and give that a go....its worth checking for sure.

Will do, thanks alot.

[S14-NEO]

the MAF reads air flow along with voltage...the way it reads air flow is measured in cubic feet per minute..if you had the ability to monitod it with Nissan's Consult you would be able to see it pretty quickly..each time you hit the gas the values should change. if in your case with a MAF not reading properly the values will change slower than normal and could change hardly at all.
Modified by S14-NEO at 10:18 AM 6/12/2008

[Darius]

The way most Nissan MAF sensors work is with a hot-wire. The wire is kept at a constant temp. The voltage required to maintain that temperature is how the computer interprets the mass flow of air passing through the housing. So as air flow through the MAF increases, it takes more current to keep the wire temperature up, which translates into a higher voltage reading to the ECU. ECU sees higher voltage = more mass. The mass is calculated based on the MAF scale for the particular wire and housing size. That is where the unit conversion comes into play. I highly doubt the maf reads in cc/min since that would probably be in the millions. I think you mean cfm.

Found this article that explains hot-wire MAF sensors pretty clearly:http://www.wellsmfgcorp.com/pd...2.pdf

[mello88]

Yeah by all means try a different MAF if you have one just to rule it out... Should be easy with your PFC.

ps the voltage from the MAF eventually represents a MASS (grams) of air per time period, not a volume (cc/min or cfm) hehe..

[S14-NEO]

The way most Nissan MAF sensors work is with a hot-wire. The wire is kept at a constant temp. The voltage required to maintain that temperature is how the computer interprets the mass flow of air passing through the housing. So as air flow through the MAF increases, it takes more current to keep the wire temperature up, which translates into a higher voltage reading to the ECU. ECU sees higher voltage = more mass. The mass is calculated based on the MAF scale for the particular wire and housing size. That is where the unit conversion comes into play. I highly doubt the maf reads in cc/min since that would probably be in the millions. I think you mean cfm.

Found this article that explains hot-wire MAF sensors pretty clearly:http://www.wellsmfgcorp.com/pd...2.pdf

lmao!!!!...it is cfm...couldnt tell ya why i said ccm...wow...this day must be wearing on me...hehe

[Darius]

Must be from my busted fuel injector thread. Still got your brain on cc/min LOL

[S14-NEO]

Must be from my busted fuel injector thread. Still got your brain on cc/min LOL

LMAO ya never know

[ninety1two40]

I think my engine is running wicked lean...

Took it for a quick rip up and down the road for about 4-5minutes and noticed it sputtering under boost and a loss of power and my water temp was up to about 220F. Got it back in the garage and the exhaust manifold and exhaust housing of the turbo were RED hot! The center bearing section on the turbo was fine. So I did some research and found out that it can happen when running really lean. The next day I had to move the car and it seemed to spool fine, hope I didn't do too much damage to the turbo. Anyway I'm going to leave it parked until I get my timing straight. Should I bump up the fuel pressure to be safe?? I think next paycheck I'll pick up a wide-band O2 sensor too.

Edit: I also have a z32 MAF on the way.

[Darius]

Your timing could also be VERY retarded. That will cause the fuel to burn in the manifold and turbo instead of finish in the cylinders.

[ninety1two40]

I don't understand what would make the timing change so much? Last year I didn't have a red manifold/turbo... All I did this year was time it with a timing light by turning the CAS a little. Do you think it's possible that the timing belt might have jumped a tooth? I still have to check the base timing once again, I've been too busy building a paint booth and prepping the car for paint.

[mello88]

I think it's more likely the CAS bolts loosened and the CAS moved than the timing belt jumping a tooth. Do you have adjustable cam gears? Unplug the TPS and recheck the base timing.. GL

[ninety1two40]

I just have the stock cam gears. I'll check it all over tonight. Thanks