Correct MAF Voltage??

[rsmithdrift]

Ok, so I went and got another MAF sensor for my car today. I installed it and it idled PERFECT. But when I hit the gas, it starts misfiring and won't rev past 3-4k rpm.

In neutral it seems to run ok unless you floor it. As soon as you go above 1/2 throttle it inveriably starts misfiring and won't gain rpm at all.

So I checked the voltage to the maf.

With the key on but the engine off it reads .25vAt idle, the new one has 1.2v it very slowly increases as you increase rpm, the highest I've ever seen it go was when I got it to 4k rpm and went wide open and it spiked to 2.3v and the engine was missing and not gaining rpm at all.

So I put the old maf in out of curiosity. It reads 10v with the key on.At idle it read 10.6v and at WOT no matter what rpm it read 12.2v(car runs pig rich, won't idle, and plumes black smoke with this maf)

So I tried to find a middle ground by putting a 5v resistor on the old maf. It then read 5.6v at idle and would only go to 6.2v at WOT. The car would missfire and not gain rpm at WOT. (behaving like the new maf but with a crappy idle lol)

So what is correct. I take it both are bad, so what should it read??

[modulation]

MAF Should have 3-4 wires.

1 wire is gnd1 wire is 12v in.1 wire is ~1-5v out.

The possible 4th wire is signal gnd, but sometimes nissan mafs use only 1 gnd for both power/signal.

At idle maf voltage out should be ~1.0-1.5v volts, I can check for you in a bit what exactly it'll be.

Where did you get the other maf sensor from? Is it possible it's broken too?

Remember that to hit signal 5v the 240sx engine would have to be pulling in ~280-300hp worth of air. (I know people say it maxes out at 250hp but that's crap.)

[rsmithdrift]

The new one is out of a 93 Altima with a KA24DE and the old one is out of another 91 240sx. IDK how it can be putting out 10v at idle. YIKES!! Amazing it runs at all.

But the new one only going to 2.3v at WOT at 4k rpm?? Isn't that a bit low??

[pricery]

I've been having the same problem. At 4000rpm the output signal should be at 4V. Mine has only been able to reach 2.3V at 4k rpm. The voltage signal should grow linearly with rpm and peak at 4000rpm around 4V. I bought a new MAFsensor and the problem continued so don't spend the money.

Make sure you have a good ground and check the resistance through the sensor and on the plug.

This is not much but a start....

[Cone Junky]

The new one is out of a 93 Altima with a KA24DE and the old one is out of another 91 240sx. IDK how it can be putting out 10v at idle. YIKES!! Amazing it runs at all.

But the new one only going to 2.3v at WOT at 4k rpm?? Isn't that a bit low??

Are they the same part #? Have you verified that an Altima MAF is even compatable? Same engine is far from being the same sensors and air/fuel statagies...

[rsmithdrift]

Same exact part numbers, same sensor in every way shape and form. And yes I looked it up and made sure it was compatible before I got it.

[Cone Junky]

The only specs I can find are for idle= 1-1.4Vand ign on, engine off= 0.2V

[modulation]

I've been having the same problem. At 4000rpm the output signal should be at 4V.

What makes you think that..If it was putting out 4v that would be..

5volts/290hp = 4volts/Xhp

So 4volts * 290hp = 11601160/5 = 232

You think at 4K rpm's your car puts out 232 hp? Are you turbo'ed?

[rsmithdrift]

On that note is sounds like my MAF is not the problem and that new/used one I got is working properly.

So what could cause these bad maf like symptoms then?? All my other sensors are perfect. The CTS reads .4k fully warmed up 160* (spot on) the O2 sensor reads .2v at idle (spot on) the fuel filter is a new 300zxTT one, plugs are all new NGK, Wires are new NGK, cap and rotor are newish, coil's newish, air filters been cleaned recently, besides I run it without it half the time anyways when I'm working on it, Timing is spot on, I don't know anything else to do or check....

With the new/used maf installed it idles correctly most of the time, but if you try to give it gas it immediately starts cutting out and won't gain rpm. It's actually UNDRIVABLE it gets so bad. It actually stalls sometimes when I give it gas, and the more throttle I give it and the more rpm it gets the worse it is. It just isn't getting enough gas to keep up with the airflow.

That's why I've been driving with the MAF that pulls 10v at idle and runs pig rich becuase it may not idle, but it runs good and more rpm = more power like it should. I just have to deal with NO gas mileage and black smoke POURing out of my exhaust.

[modulation]

Check your Tps values per fsm.

The new maf just plugged into the same plug as the old one?

[rsmithdrift]

Yes, same plug. And something really bad happened to my car while test driving it with the 10v idle MAF last night. There was electrical burning smell, then smoke, all the while my lights dimmed and my voltage dropped to 9v.

Car seemed to have not changed otherwise, smoke went away, but the voltage never came back up, it just stays at 9v. I checked the alternator by pulling the battery cable off while the car was running and it kept running. Later that night it starts getting worse, all electrical barely works, voltage dropped to 7.7v (has to be jump started) and when I hit the gas it shuts the engine off and then BACKFIRES huge when I let back off the gas. The battery has 12.0v when not connected to the car. It doesn't even recognize what an airflow meter is anymore as unplugging it now has no effect on the way it runs.

So now the car gets to sit for a while till I figure out what it's problem is.

[modulation]

Where did the smoke come from?

[rsmithdrift]

I have no idea, by the time I opened the hood it was done smoking and there was just a cloud under thier. Nothing is burn't or damaged looking.

[rsmithdrift]

Where did the smoke come from?

The smoke came from the alternator belt being burnt through and thrown.

Car still runs with bad MAF like symptoms thoguh, with a good MAF. It's very odd. But my voltage is back again. lol.

[modulation]

What makes you think that..If it was putting out 4v that would be..

5volts/290hp = 4volts/Xhp

So 4volts * 290hp = 11601160/5 = 232

You think at 4K rpm's your car puts out 232 hp? Are you turbo'ed?

I have to come clean here and admit that I'm totally wrong here.It's not a linear relation. Maf Voltage is exponential compared to HP.Sucks to admit I was wrong, but we all learn and I didn't want to spread disinformation.

[rsmithdrift]

So I put a new/used fuel rail on the car last week and it REALLY helped this problem. I ALWAYS run with the good MAF now.

It still cuts out a little bit between 2krpm and 4krpm... but then the power comes back after that.

I check the MAF voltage now and it show's 1.0 - 1.1 at idle and at 4k rpm reads about 3.3v.

I have NO CLUE what could be causing the hesitation. I checked all the vacumn lines too and they are all good. I removed the EGR and that wierd valve on the exhaust manifold that injects air INTO the exhaust... I still don't see the point in NISSAN putting that under the hood in the first place... lol.

Anyways. I'm clueless, I think I'm going to remove the intake manifold and replace the PCV valve and the intake manifold gasgets and see what that does....