Am i reading this multi-meter right? (pics)

[kenversusryu]

I've been trying to test my MAF. I backprobed the Maf like the manual states but i've been wondering if I'm on the wrong setting.

My multimeter is a pocket multimeter from power tools
http://www.shopatmidway.com/images/product/large/WIL-W2979C.jpg
http://www.toolking.com/images/Products/BigW2979.jpg

when i check the maf its on the DC V side like this on 10.
http://img120.imagevenue.com/loc111/th_40107_meter.jpg (http://img120.imagevenue.com/img.php?loc=loc111&image=40107_meter.jpg)

I get a reading of .8 at idle and 2.5 at 4k rpm on the ac10v like this. (the red) It's way off i know.
http://img9.imagevenue.com/loc40/th_40112_meter2.jpg (http://img9.imagevenue.com/img.php?loc=loc40&image=40112_meter2.jpg)

When i click it to the AC V on 10(i dont have a picture but i just click it 4 times counterclockwise.. look at the above pictures). I get a little past 2 on the ac10v scale.

So my question is... Is it DC V (10) or AC V (10) that i should be using to test the MAF. And my second question... Am I reading it correctly on the needle? (the red scale where it says AC 10V right)

Much appreciated.

[kenversusryu]

oh yeah one more thing. This is the harness.

http://www.autozone.com/images/cds/gif/medium/0900823d801b61ff.gif

I'm supposed to backprobe the wire thats towards passenger side.. not the driver side right? Meaning if you were to look at the harness from your drivers seat.. it's the far right.. not the far left. Correct?

and on this image
http://img31.imagevenue.com/loc230/th_59664_Untitled_5.jpg (http://img31.imagevenue.com/img.php?loc=loc230&image=59664_Untitled_5.jpg)
the harness is disconnected. Are you backprobing or probing from the other side. I'm getting more confused.

[docrice]

Ok, lets try and address whats going on here. You are going to be measuring the DC voltage coming from the output of the MAF. With the connector still plugged into the MAF, you can measure the output voltage of the maf, which I believe has a 0-5vdc output range. Unless you are maxing out your maf (forced induction with high boost,etc), even at high RPM you're probably not over about 4V. Idle will be probably around 0.5V, don't know the specs but they're in the FSM.
The pictures at the bottom show a way to test continuity of the wires going from the maf to the ECU. With the maf and ecu unplugged, measuring the resistance between the connector at the maf and it's counterpart at the ECU should provide a very low resistance (very few ohms, single digits are preferable but once again i do not know the specs).

Good luck...do not hesitate to ask more questions, I do this shit for a living so its no problem...

[kenversusryu]

wow.

Okay then regarding the 95 maf. Which wire am I backprobing. and testing the continuity of the wire like you said, do i backprobe the harness?... or probe it on the maf side.

I dunno if i'm making sense but i wanna ask you since you do this for a living. thanks!

[dopeassjackson]

you need to get a DVOM (digital volt ohm meter).

[docrice]

wow.

Okay then regarding the 95 maf. Which wire am I backprobing. and testing the continuity of the wire like you said, do i backprobe the harness?... or probe it on the maf side.

I dunno if i'm making sense but i wanna ask you since you do this for a living. thanks!
what is backprobing? I've never heard the term before.

When you test continuity of the wires, disconnect both the maf and ecu and measure between corresponding points on each connector. if the resistance is high or infinite, then you have a broken wire and that's the problem. If the resistance is low, then the wires are ok.

[kenversusryu]

backprobing is where you stick one of the leads into the other side of the harness while the harness is connected. So basically while the harness is connected, you stick the lead in where one of the wires are going into the harness(ground, etc). That make sense?

[Ess14]

So your basically checking the continuity of the harness...?
And OHMS are measured in thousands and tens of thousands, it wouldn't end up in single digits - or am I wrong?


you need to get a DVOM (digital volt ohm meter).

His multimeter has an OHM setting located at 11 oclock of the turn dial.
Thanks for trying to help but someone that didn't know much of what they were doing could have just wasted more money.
Anyways...
I've never heard of backprobing either ;)

[g6civcx]

First off, it's really hard to tell what's going on in the pictures you took. I can't barely make out the multimeter.

With regards to the harness diagrams, I know what you're struggling with. Nissan has a bad habit of making the diagrams very hard to read. Whenever you see a diagram like that, look directly into the plug at the metal terminals. That's the correct orientation.

[kenversusryu]

yeah checking for continuty.

yeah sorry for sorry ass pics. Best i could do.

The thing is, if a test requires a harness to be connected.. theres no way to look directly into the plug and stick the lead into the metal terminals because basically its already plugged in and engine is on. So that's where backprobing comes in. But the Nissan FSM seem to use that harness image for the disconnected and connected harness, so its confusing as to whether to look directly into the plug or probe it from the back where the wires are going into the harness (when testing for ground and engine is off).

Thanks for the reply guys this is really helpful.

[Ess14]

yeah checking for continuty.

yeah sorry for sorry ass pics. Best i could do.

The thing is, if a test requires a harness to be connected.. theres no way to look directly into the plug and stick the lead into the metal terminals because basically its already plugged in and engine is on. So that's where backprobing comes in. But the Nissan FSM seem to use that harness image for the disconnected and connected harness, so its confusing as to whether to look directly into the plug or probe it from the back where the wires are going into the harness (when testing for ground and engine is off).

Thanks for the reply guys this is really helpful.

mmm... Wouldn't splcing the mafs wire before the plug give you the same reading?

[kenversusryu]

eek. I dunno about splicing anything. I suppose it would give the same reading but its just easier to backprobe i suppose.

http://us1.webpublications.com.au/static/images/articles/i21/2190_16lo.jpg
See this is back-probing! I knew I wasn't making it up.

Or do what my friend does. Get a paper clip, straighten it out, backprobe it to the harness wire and touch the paper clip with the lead. It isn't so scary this way because the paper clip is a cm thick while the lead on my multimeter is pretty damn thick. Seems to work for him.

one last annoying question. That last picture i had. "ECM connector" means the ecm harness, correct? So many questions! I want to be proficient in this.

[g6civcx]

I'd be careful with backprobing. You don't want to introduce extra components into the circuit that wasn't intended to be there.

On the 2 small pictures, what you're checking for is broken wiring. You unplug the harnesses they show. Then you set your multimeter to check for resistance and probe the 2 points they show. If you have continuity, you will be able to read a resistance. If you have no resistance, you have a broken wire and you have to track down where the damage is.