# Mass Air Flow Sensor



## ibosley (Mar 6, 2007)

87' VG30I

I recently tore apart my throttle body to have the injectors rebuilt. Despite the other problem it created I have noticed much better throttle response and more overall power. However, it seems as thought I put something back together wrong. 

If I'm not mistaken the Mass Air Flow sensor is the black plastic case with two diodes sticking out that is held onto the upper throttle body by three screws. I removed this and all other components before soaking the upper throttle body in parts cleaner for 7 days. 

After I cleaned everything up and added new gaskets I noticed that my motor now bucks like a 383 stroker engine at 300 rpm. It also isn't quite what it used to be as far as power goes, much better than with better injectors, but not like it should be. 

Upon checking the ECU it gave a code 12, Mass Air Flow sensor. I know I didn't break it when I took it out, I know they are expensive so I was careful with it. All I can think of is that maybe the wire harness is corroded enough to where its not fully functioning. 

Any ideas? Has anyone else ever had this problem?


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## 88pathoffroad (Jun 6, 2004)

Did you blow out all the air passages in the TB before reassembling? There could be a piece of crud in there somewhere impeding airflow. Also, did you pull the two other switches off the TBI before dunking it?  

300 RPM???


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## OchnofConcrete (Jan 7, 2008)

thaz why i don't dunk stuff... i scrap and spray stuff. it requires more elbow grease but doesn't allow minor seal like electrical seals to degenerate and allow fluids into the electrical compartment of that particular sensor.

seals are vulnerable to highpowered cleaners, as well as hoses... basically anything not stationary metal.

if the TPS was corroded inside... which is possible if it was sitting in cleaner for 7 days... hell, all it takes is one day for cleaner to work if you're soaking it. but i don't know about your Throttle Body unless i saw it, but on mine the TPS is part of it... when the throttle butterfly valve opens it's turning a little needle inside the TPS contacting a few (or more on more sophisticated TPS's) contacts telling the ecu what rpm to set the engine at for the amount of air flow into the intake. basically telling it how much fuel and when and when to fire the spark plugs. but it's real basic at the TPS..
but even still if it got corroded in there, then your ecu doesn't know how much air the engine is getting.. giving it the incorrect amount of fuel, and firing at the wrong time.

someone else elaborate... probably missing something as usual.


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## Kaizen101 (Jun 24, 2008)

*VG30i air flow meter*

I have a problem with my wiring on the mass air flow meter, the pluc connector is missing and i need to know which of the four wires goes where.

I also need to find out the wiring for the throttle possition sensor.

I have a Nissan Hardbody D21 shape 1996 with a VG30 engine.

Please help, I bought the manual and found only the 2.4's diagrams.

Carl


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## ibosley (Mar 6, 2007)

Ochno- I'm not sure what you're talking about. I think you are elaborating on some mechanical/electrical component that adjusts idle based on butterfly position? This component was not dunked, see below. 

88pathoffroad- All passages were clear because I probed them with a pipe cleaner. 

Kaizen- Your VG30 engine has multi port fuel injection and is different than mine, these guys would be able to tell you more though. Use the search function to find out more. 

All components were removed from the upper throttle body before soaking. I took a lot of attention to detail and removed all o-rings and gaskets. It was a combination of bare metal and rust going into the bath. My HB has the nickname Mud Doctor for a reason. I have had it in so many creeks and ponds the throttle body had a nice thick coat of rust where the injectors go. Thats why it took 7 days and 7 nights to clean. Thanks for the suggestions guys.

I cleaned up my contacts for the wire harness last night. It seemed to idle better as I pulled into work this morning but I haven't checked the ECU, I'll take care of it at lunch.


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## ibosley (Mar 6, 2007)

I cleaned all the contacts, shot everything with electrical cleaner, and put it back together. I'm still getting a code 12. The MAF is working to some extent, when I unplug it the engine stops running. It has two filaments, I was thinking that maybe one side is working but not the other? Possibly it has a bad connection? 

If you order a new MAF does it come with a new female harness as well? What is the best method to clean the inside of the female harness? I tried using a really small drill bit to score the surface, but that didn't help much either.


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## OchnofConcrete (Jan 7, 2008)

i don't wanna tell you the wrong thing. on my s-13, the MAF is next to the airbox and the Throttle Position Sensor (a needle gauge that hits a few contacts on the inside of the sensor) is directly connected to the TB's butterfly valve.. just telling the ecu how far open the throttle is.

any chance you knocked a small vacuum hose lose?
but a vacuum leak doesn't really cause it too much harm unless it's a hose connected to a solenoid for the Swirl Control valve or something like that... but not sure.
what 88Path said sounds about right... if a chunk of something got lodged inside that'd cause a problem, but you said you cleaned it real good. that would prevent flow *thinking* 
a clogged Throttle Body though... clogs the Idle... not really the air flow into the engine. at idle it might mess things up, but i've closed an idle screw all the way before and because the TB still allowed a slight bit passed it, it was fine.

when i did my intake, when i first cranked the engine (the same time i was first turning it over, so i had to Trial/Error like mad) the revs were automatically hitting 4g's... the throttle was adjusted wrong, was letting air in during idle....making the engine think i was pressing on the gas pedal.
sounds like yours is a problem of NOT getting air or a bad sensor. if it's a bad sensor then the wrong voltage will be going back to the ecu, telling the system to give it so much gas and fire, but not really getting the right amount of air. as the combustion chamber gets the mixture and fires, *thinking again* lol, i don't have any info with me right now.
ok... a MAF... tells your ecu, via the temperature of the air flow passing by from friction, that there's air coming in and the engine won't be flooded, so it's okay to spray fuel and light it... if the MAF is switching on and off due to either A FILIMENT not being good like you said, or too much resistance in a CORRODED WIRE (if there was that much rust, there's a good chance that your harness has corrosion)... then your ecu will think that the flow of air is blocked, telling the other sensors (like Injectors, or a Relay ~i think~, or the Spark Enhancer)to stop doing what they do.. 

if it's your TPS... there's a needle that sends out 0.5-4.5volts depending on the position... 0.5 at idle - 4.5 at full throttle and if there's corrosion on that subharness or in the sensor then, the comp will be getting voltage readings that aren't steady or steadily increasing... it'll be sending a voltage reading through the harness and all of a sudden the reading will go up and down due to that resistance.

truth is, if you really had that much rust under the hood, there's no telling where the Resistance is coming from. it could be anywhere. i'd check the entire harness... under relays... everywhere there's a wire. one important wire goes from the sensor to the ecu (eventually) and no matter what point of the wire you're talking about... it's still part of that individual circuit. too much resistance.... (too many stereo speakers) in this case, rust ...and things don't work from the lack of power. but if it's trying to work that must mean that it's not fully corroded... there's still electrons making the circuit. it's probably one trouble point, that you can fix by soldering in new wire. but you need to check everywhere for it..
doesn't take much to rust out thin wires. a cut in the insulation and bam!, it's corroded... not to mention fraying and grounding out in some cases.
sometimes just over time a part of a harness will rub on a sharp piece of sheet metal that some jerk before you took off the metal's protective rubber piece... and the metal will cut to the wire.. grounding it out.


for the most part i don't think your MAF will come with the female connection. maybe... but not sure... might be able to ask for it.
or you may have to hardwire it, being careful which wire is which... just use some wire disconnects so you can take it off later. ...hell, but that's not easy one the MAF side..the connectors are a part of the sensor, so you'd have to solder wires onto the pins... and it's easy for something like that to fall off during transit unless you doubly make sure with extra elec. tape
;]
had to do it to an A/C comp cuz the connector was ruined.


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## OchnofConcrete (Jan 7, 2008)

another thing, and i know you don't want to hear this, but the sooner the better you check it out, the sooner you know for sure..
if your car's bucking like that... there's a chance a sensor's not working at all.. and if it's really a corrosion problem, you may have to get another harness....
unless you're lucky enough that it's only in one spot.
then you can just solder new wire into place. nothing better for electron movement.

just don't want to freak you out by saying that and it be something simple, i just can't think of something else... another sensor that would cause the engine to do that.
but don't take my word for it before you ask around more...
before you poke around in your engine bay more...
anywhere you believe that same corrosion you saw on the Intake, would cause problems in the electrical systems.
corrosion on an engine part can be worked around...
corrosion on a harness stops things from working.

some main sensors that make your car run..
CPS(crank position sensor, usually on the Distributor)
TPS(throttle " ", usually on the Throttle)
MAF(mass air flow, on mine=by airfilter, but can also be anywhere before the TPS)
sides that, the other sensors are really just warnings (like your knock sensor) or self tuning adjustment sensors (like your IACV ~idle air control valve~, CAV ~cold air valve...this is what causes cars to idle high for a few minutes til the engine is warmed up and pumping oil freely~)
ooh... can't forget the tranny sensors.. but that's for just starting the car... like the sensor that tells your ecu you're in park (or your clutch position sensor)


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## OchnofConcrete (Jan 7, 2008)

this has a longer version of what the TPS does...
http://www.nissanforums.com/ga16de-1-6l-engine/145675-few-94-sentra-problems-help.html


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## ibosley (Mar 6, 2007)

Thanks for your correspondence. I checked the circuits for the MAF sensor. It is getting power on the Black wire with a white stripe. This is also true for the ECU signal, therefore the circuits match. There is a green/yellow, green/black, and black that do not have any fire out of the computer. 

However, in doing this, I seemed to have completely ruined the sensor. I remember doing a trial where I ran the truck with the MAF unplugged to see which effect it would have. The effect is the same as what it is doing now, refusing to idle. 

So it was working for a little bit, and now its not working at all. 

But from what I'm thinking, the black/white and black wires going into the maf should both be hot, because there are two hot wires inside the maf. Just logic I guess, I may be wrong. The manual doesn't say anything about which wires should be hot and which should not. 

If it were another sensor, wouldn't it pop up on the ecu? 

Another problem developed as I poked around on the computer, the coolant temperature sensor flipped as well. Its a code 13, not sure how it happened but it did. 

This thing is quickly becoming a mess! :lame:


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## OchnofConcrete (Jan 7, 2008)

there's a chance a lot of your sensors are real weak from all the corrosion, and now that your fixing stuff on the car it's putting added stress onto them.
...better voltage hitting old sensors.

but that doesn't really make sense if you haven't changed fuses/ relays/ or wires.

your intake have coolant hoses running through it like mine does?

in my cases, i try to go over the whole engine bay, replacing and repairing everything.

then when you do the ecu codes, your search is a lot more limited.


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