Testing Mass Airflow Sensor

M

Mr. Mark VIII

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I’ve been trying to hunt down a problem that arose when I first installed a chip. With the chip, my car would bog through the entire RPM range. I went through everything and it all looked great. A friend of mine was certain it was fuel issue. I tested the pressure at high loads and rpm and it check out great. I wasn’t sure at first but after using SCTs tuning software and running different fuel tables, I was convinced. I was about to purchase a new pump when XLRVIII and I had the idea of just unplugging the Mass Air Flow. Bam, the car rocks!! So I cleaned the sensor with tuner cleaner without lubrication. After that, it seems to run a lot better but still not all there. When cleaning it, I did see two coil filaments the appareled not to be broke.

I guess right there pretty much shows the MAF is messed? From the fuel tables, it has been clearly making the car lean all this time. I see a good replacement MAF are pretty $$$ sooo the question is…..can I assume mine is bad and is there away to test mine before I drop some bux?

I’d like to say thanks to XLRVIII for helping me so much and I didn’t even buy anything from him.
 
No problem Kenton.. call me anytime sir.

Testing the maf is possible, but I dont know "which wire" would be the "one" to hit with the voltmeter to see the maf voltage being sent to the PCM.

I used a snap-on MT2500 scan tool {that I borrowed) to datalog MAF voltage to make sure I wasn't pegging the stock Maf... it told me at WOT at 6500RPMs I was getting 4.8 volts from the maf.
The C&L LMS maf only showed 2.50 volts at WOT..which is why I "ditched" the C&L and put the stock maf back on the car.

...need to find out what color wire sends the return signal to the PCM.
Then hit that wire with a Digital Volt meter and see what kind of voltages it's sending to the PCM.

hope it helps... glad to hear your getting "onto the right track".
A little patience and perseverance..goes along ways.. huh?

PRP FTW!!!
 
93 Lincoln BTW

I took some voltages at the MAF plug when car was hot and idling.

Looks like there is a Red positive, it read about 13-14 volts

Black read nothing so ground

Orange with blue (tan with blue) was .13 volts….I think this is the MAF RTN / Mass Air Flow Return Believe its pin 9 in PCM.

Blue with red was .95 and fluctuating a few hundredths. I think this is MAF SIG (MAF output signal) I believe this is pin 50 on the PCM. When I rev a little, it will go to about 2 volts.

How do these numbers look? I did some more driven with the MAF disconnected and it seems to still run a little better then plugged in.
 
I don't know if those measurements will tell you much... you need to test the Voltage at wide open throttle. But if your car runs better with it unplugged you can be 99% sure the MAF is not working properly.
 
Ok after giving it a second really really good clean. I took some tests at WOT. Had to make a pretty crazy setup but I got it some numbers. This time however, as the negative, I just used a ground, not the battery terminal. It seems there was a .03 volt decrease at idle, between the battery terminal and the ground. Anyway, I got a 3.60-3.80 volts at WOT. I never could get to 4 volts.

How does this look? Thanks
 
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Mr. Mark VIII said:
Anyway, I got a 3.60-3.80 volts at WOT. I never could get to 4 volts.

How does this look? Thanks
Click to expand...

that is about 1 volt shy of what my car shows at WOT.

Granted 1 volt doesnt sound like much, but when your MAF voltage scale is .80ish-4.80ish you dont have much room to "give up" and entire volt.

From what it looks like, your missing the "top 25%" of your MAF, which is where the car will make "all it's power at".
 
My stock 98 Mass Air was doing 4.1-4.3 at WOT and it was causing a lean condition with the Sniper Tune (it was fine for stock tune), I swapped to the mass air from my 96 Mark VIII and now it sees 4.5-4.6 at WOT.
 
Yes thank you, those specs look right in line with XLRVIII and what I have been seeing from the mustang guys. Looks like ill have to find a new MAF. Man they looks kinda $$$, now I'm thinking a bad fuel pump would not have been so bad..
 
Mr. Mark VIII said:
now I'm thinking a bad fuel pump would not have been so bad..
Click to expand...

yea and you will still have "that bridge to cross" at some point as well....

the issue with your car doesnt appear to be the fuel pump, but that is not saying your fuel pump wont need to be replaced at some point.

If I were you, I'd get a pump for it.. and install it...and rule that scenario out of the equation... better to "plan to change the pump, rather than being FORCED into changing the pump".

I can assure you that IF you keep this car for any amount of time, you will need to do the fuel pump at some point.
 
Well I’m still trying to troubleshoot the problems with my car. The symptoms suggest I might be running lean. I’m still suspicious about the MAF voltage. I ordered one from Jami hoping it would fix my problem My original one read about 3.8 volts at WOT this one is better 4.38 volts at WOT. But I still think this is low. Now I don’t know what to think. Could my altitude (4600) be affecting the voltage? I’m testing this by running leads from the maf into the car and using a digital volt meter. Is my method of testing wrong? When I unplug the maf the car seems to run a little better. Any suggestions on this?
 
Mr. Mark VIII said:
...My original one read about 3.8 volts at WOT this one is better 4.38 volts at WOT. But I still think this is low. Now I don’t know what to think. Could my altitude (4600) be affecting the voltage?
Click to expand...

I've never checked mine, but 4.38 doesn't sound bad for 4600 feet altitude. After all, the mass of air per volume at higher elevations will be lower.
 
I decided to test the ground of the maf. I found that the black negative and the signal wire are about .85 volts. But when I use a other ground or the battery terminal and the signal wire, the signal is a bit over one volt (1.05). Does this sound right? I still think the problem with my car is the maf because when I unplug it, my car runs more smoothly and stronger. Any comments on this?
 
Clean and tighten the grounds in the engine compartment as well as the ground to the block.
 
Mr. Mark VIII said:
I’ve been trying to hunt down a problem that arose when I first installed a chip. With the chip, my car would bog through the entire RPM range.
Click to expand...

take off your mafs? thats bad advice... your problem started when you put your chip on. Hunting a problem that arose when you first installed the chip.... take off the chip! Sounds to me like your knock sensor is retarding your timing.

remove the chip, everything works fine - its your chip/tune. its probably advancing your timing to the point where your knocking.

or better yet make fun of me some more and take off your o2 sensors as well. :rolleyes:
 
AbrahamLincoln said:
or better yet make fun of me some more and take off your o2 sensors as well. :rolleyes:
Click to expand...

Not making fun, but technically he could take his O2's off because the ECM will just use a base reading after it doesn't receive a signal. :D The MAF....thats a hole different story!
 
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