OHM meter

[locoluna825]

ANYONE? know how to properly use a ohm meter? i went to use ours today not sure if i used it right. i set it to OHM's 1k wich is the only (ohm) setting on it the other stuff is dc,ac blah blah funny symbols. i was trying to use it to test the resistance on my injectors, and the numbers i got off all ofr of them were virtually all the same 1.6..k? dont know if i should use the K or not when i write that anyways.. thanks let me know

[AZ89two4Tsx]

Haha. I never know what the hell I'm doing with one of those.

[locoluna825]

aww im not alone

[Tuvara]

A question I'm remotely qualified to answer, this happens very rarely indeed. With an Ohm meter you never check anything with power across it. Boyond that you always check parallel and on the lowest setting that represents a higher value than what you intend to check the resistance of. So that being said, Ohms are not AC or DC in any true fashion, with no power a DC setting woll get you a resistance mesurment across your injector, AC and DC only differ if you want composite measures of multiple components.

In simpler terms if your one injector is supposed to produce 15 Ohms of resistance and your Ohmmeter sets at either 10 or 20, use the twenty, otherwise the meter gives you the wrong measure, unless it is a decently high quality digital meter.

[OutToWinPAHC]

Yeah that sounds like a cheapo meter, selecting range is old school.

But yeah common practice is to never check resistance with power applied (which is because checking ohms is a low impedance function of the meter and can short stuff out, but newer quality meters can do it)

So power off

Set the meter to read ohms (scale is usually 10-100-1K-20K-1M) So if yoiur scale allows that select the 100 scale. (I'm shocked it doesn't auto range, does it have a range button?)

Unplug the injector, connect the leads to the two point on the injector where the wires connect, and take your reading.

[Second Shadow]

you can't get reliable readings with power applied yes, this is because the meter puts a very small current through what ever it's checking and measures the voltage drop. Voltage drop is how everything works.

Now, even if there is no power you also get false readings if whatever your checking is still in circuit, because(and bare with me here) current does NOT actually take the path of least resistance. It portions itself out evenly among the resistance of all other paths. Which means if the injector is still plugged in, absolutely anything that could also complete the circuit but has resistance will screw up the readings.

In short, unplug what your checking when doing resistance.

There's actually a much better way to check resistance, but there's some math and electronic theory involved. I will explain it if asked but it'd be kind of a long post.

[OutToWinPAHC]

you can't get reliable readings with power applied yes, this is because the meter puts a very small current through what ever it's checking and measures the voltage drop. Voltage drop is how everything works.

Now, even if there is no power you also get false readings if whatever your checking is still in circuit, because(and bare with me here) current does NOT actually take the path of least resistance. It portions itself out evenly among the resistance of all other paths. Which means if the injector is still plugged in, absolutely anything that could also complete the circuit but has resistance will screw up the readings.

In short, unplug what your checking when doing resistance.

There's actually a much better way to check resistance, but there's some math and electronic theory involved. I will explain it if asked but it'd be kind of a long post.

...

Current does take the path of least resistance..... Simple ohms laws, also applies to linear and non linear circuits.

[locoluna825]

the ohms meter i have has only one setting, cheap pile of crap. so i guess im gonna go pick up a new one, and i was testing the them "unplugged" ill get one this morning

[locoluna825]

k i went and bought a 50 dolla meter and it came with 5 settings 200 2000 20k 200k 20m settings i set it to 200 the lowest i believe and got a 14.6- 14.8 reading on all the injectors

i did however notice that it was very hard to get a reading off these injectors prongs because of the heavy green buildup. the harness plugs are just like that too. im going to find a tiny wire brush and some contact cleaner. maybe its not getting a solid enough connection??

[OutToWinPAHC]

could be corrosion causes massive issues.

[SirSilvia]

could be corrosion causes massive issues.

find any of it, wire brush it off

[locoluna825]

i did and it did not help. im going to try one more thing before i give up and take it in to a diagnostic guy

[zenkistic]

In short, unplug what your checking when doing resistance.

Unless directed otherwise, you should remove a component to measure its resistance. If you don't. you will measure the parallel combination of the resistance of that component and the rest of the circuit that is connected to that.

edit: I am not an automotive electrician, but I googled for the typical resistance of fuel injectors and I see it is around 12 Ohms. So 14 Ohms, for the impedance of the coil of the injector, is not a crazy value. Of course if you have debris in your measurement contact points, you will have added resistance.

BTW: 1 kOhm = 1 kilo Ohm = 1000 Ohm = 10^3 Ohm 1 MOhm = 1 mega Ohm = 1000000 Ohm = 10^6 OhmThe symbol of Ohm is omega (Ω).

When you put your ohm-meter in kΩ, you are measuring in kiloohms. 14 ohms would read out as 0.014. If you put it in MΩ, you will probably get a zero reading.
Modified by zenkistic at 7:29 PM 8/23/2009

[locoluna825]

when you say that do you mean unplugging the fuel injector, tacking it off the fuel rail then testing it? because all i did was unplug it

[OutToWinPAHC]

no not off the fuel rail, just unplugged from the ECU 13-15 ohms is good

[zenkistic]

remove the component = isolate it from the rest of the circuitry = unplug any wires that connect it to anything else

[locoluna825]

and that's what im getting this things makin me mad car runs good though besides the idle and the annoying engine light

[locoluna825]

does anyone know how to test the fuel pump?