Multimeter Settings

[highspeed]

Hi everyone. This site seems to be more towards computers and home electronics, but I think the same process would apply for what I am trying to do. I am trying to determine if the wiring to my car's fuel pump is good, I would hate to take the tank off to change it if it is an electrical problem. The car runs but only at 20 PSI fuel pressure, where it is supposed to be at 40 PSI.

I have read that it can be an issue of the pump not getting enough power to run as it was intended.

I have attached a picture of what my multimeter is set to for the voltage drop test, please let me know if I have this wrong.

As for the process, I am basically doing what I saw in a youtube video where I run a jumper wire to the ground wire close to the fuel pump, and connect the red lead from the multimeter to it, then connect the black lead from the multimeter to the negative post of the battery. When I do this the display goes from 1. to 0.000, which I think is what is supposed to happen. Then when the key is turned on and the pump is activated, it goes to 0.25. I have read that anything below a half volt is acceptable. Is the 2K option on the meter the correct setting to use for this?

I do have a next part where I am stuck testing the power wire to the pump, but I think I will wait and see what you guys think so far because responses to this may answer my own question.

Thank you for any helpful tips or advice anyone might have on this.

[budm]

Re: Multimeter Settings

"what I saw in a youtube video where I run a jumper wire to the ground wire close to the fuel pump, and connect the red lead from the multimeter to it, then connect the black lead from the multimeter to the negative post of the battery" OK, on this test, it is trying to see you do have high resistance between the Negative terminal of the batterry and the ground return of the fuel pump. '1' on you meter when the probe is not attach mean over range (or infinite resistance), using 2K scale will not give you good resolution when trying to look for low resistance, you should use 200 Ohm scale instead, the ground return reading should be < 1 Ohm, but you have to remember that what you see on the meter you will have to subtract the resistance of your meter probe (touch your meter probes together and see what you read, that will be the resistance of you test leads) to get the resistance of what you are reading. Now, I do not understand what youtube is trying to tell you when it tells you to applied power to the pump, that will cause error reading on you meter sine will be in resistance reading mode, not volt mode.
Second thing is that you are only checking the pump ground return wire, how about the resistance from the batteries + terminal, through relay contact, then the wire all the way to the pump + wire? I would try get access to the + wire right at the pump and see if you do get full batteries voltage right at the pump.

[highspeed]

Re: Multimeter Settings

Hi, thanks for the help. I think my terminology might be wrong when trying to describe what I am doing. The youtube video is here:
http://www.youtube.com/watch?v=boAA6_saiSk

If you have the time to watch it, it will likely explain what I am trying to do better than I can.

I did try this procedure on the power wire but the meter was not looking at all like it did in the video or even like it did for the ground so I figured I would come inside and see if I could figure anything out through a forum. That is where I found this great site. I appreciate you time and thanks again for helping me out.

[budm]

Re: Multimeter Settings

OK, he is showing you how to test the DC Voltage drop on the fuel pump feeding wire (and relay contact) between the positive terminal of the batteries and the fuel pump + terminal and , and the voltage drop on the return wire between the negative terminal of the batteries and the return terminal of the fuel pump. He forgets to tell you to put the DMM in DC Volt mode. You should put your meter in DC V 2V scale.
I hope my diagram will help explain what we are trying to test. You are basically looking for <0.25Vdc Voltage drops on the wires.

[highspeed]

Re: Multimeter Settings

Perfect! Thank you so much. I have spent a lot of time today searching the internet trying to figure out what setting the multimeter should be in, but had no luck. And like you say in the video, he doesn't mention it, he just turns it on and I couldn't see what he put it to.

I will head back out tomorrow with the setting information and your very nice diagram and give it another shot. Hopefully the wiring is all good. I think changing the pump would be easier than chasing a bad wire problem. I have changed the fuses/relays because they were cheap and easy to get to, but no luck there.

Thanks again, this is above and beyond what I was looking for.

[retiredcaps]

Re: Multimeter Settings

And like you say in the video, he doesn't mention it, he just turns it on and I couldn't see what he put it to.

At 3:27 (and 4:54) into the video, you can see he has the Fluke 87V set to DCV.

A good tutorial on multimeter usage from another fellow Canadian.

http://www.youtube.com/watch?v=bF3OyQ3HwfU

[stj]

Re: Multimeter Settings

it would be faster to just hook the pump directly to a good power source and see if the pressure rises.

did you check the fuel filter(s) and check for crushed or kinked pipes?

[highspeed]

Re: Multimeter Settings

I have also changed the fuel filter and pressure regulator. I figured I would change all the cheap quick things first. When you say hook the pump up to a good power source, do you mean while still in place, like directly to a battery?

[stj]

Re: Multimeter Settings

exactly.
because then you know the battery & wires are good - it's only the pump & related plumbing letf.

this isnt a honda is it?

[highspeed]

Re: Multimeter Settings

Ok, that makes sense. It is a 1997 Chevrolet Lumina. Are Honda's prone to these issues?

[stj]

Re: Multimeter Settings

honda has a soldering problem on a relay that controls the fuel pump & starter motor.

[desert-rat]

Re: Multimeter Settings

If this were my car I would look for 12 volts at the plug first . I have replaced a few electric full pumps . The tank is usly half full of gas . A tranny jack works good an a gas tank .

[highspeed]

Re: Multimeter Settings

Yeah, I think my girlfriend actually filled the car up just a day or two before this happened, so I will likely be extracting some gas to make the removal a little more manageable. I am going to be heading back out soon to re-run this test using the proper multimeter setting and hopefully there is good results removing any doubt that it is the fuel pump.

[highspeed]

Re: Multimeter Settings

Alright, so I have just re-done the test as shown in the youtube video using the DV Volt 2V scale setting and got the following results:

Negative shows 0.056
Positive ranged from about 0.3 to 0.6

How does the 0.056 reading relate to voltage under the 2V setting. I guess I am just not too sure what the various settings mean. I am told that a loss of 0.5 volts or less is good, so is this actually 0.056 volts or does that decimal need to be moved?

I am also not sure that the test is working right on the positive side. The reading worked the same on both sides in the video, but for me there is a 1. on the meter until the key is turned, then it goes somewhere between the 0.3 to 0.6. Shouldn't it work like the negative where it reads 0.00 until the key is turned?

Thanks everyone.

[budm]

Re: Multimeter Settings

"How does the 0.056 reading relate to voltage under the 2V setting." That means the resistance on the return wire is very low which you would expect since the car chassis is connected to the negative terminal of the batteries.
You will see the '1' on the meter because when the relay is not close, the meter will see 12V and the meter is set to Volt so it shows over range ('1'), when the relay is closed then you are reading the voltage drop on the wire and the relay contact resistance, the amount of voltage drops on this wire is determined by the wire gauge being used and the relay contact resistance. @ 0.3~0.6 will give the pump 12V- 0.6V about 11.4V which is more than enough to run the pump, the pump should easily be able to run at 10VDC. I would say your wiring is OK.

[highspeed]

Re: Multimeter Settings

Awesome information. That is exactly what I was trying to figure out. Next weekend I will get the car back up in the air and get the pump changed. Thanks to everyone for your helpful explanations and links/tutorials. I am still very much a rookie with this stuff, but I have done more and learned more about electrical testing that I ever have before this weekend. Color blindness also makes electrical work difficult, but I can work around that.

Anyway, thanks again for everyone's help, much appreciated.

[desert-rat]

Re: Multimeter Settings

I re-read your first post . You get 20 psi , the pump must be running . I would look more at the filters or regulator . There should be an in line filter and one in the tank at the bottom of the pump . Get a repair manual for that car . One with wiring dir. also .

[stj]

Re: Multimeter Settings

i just thought of something.

maybe your tank has crap in it and needs to be flushed.
it's not that old, but i dont know what they sell you in canada - a lot of fuel these days is blended with all kinds of crap!

it's also possible that if the bastards are blending ethanol then your pump may be partly corroded/melted!

[highspeed]

Re: Multimeter Settings

Thats what I thought too, I was really hoping that it was a plugged filter. I changed that and the regulator and the pressure did not change at all. Changed all the fuses/relays associated with it too, but nothing worked. That at least narrowed it down through process of elimination to the fuel pump. Then I read somewhere that a voltage problem at the pump can cause it to run poorly and I may have an electrical problem.

Through everyone's help here, I think it is safe to say that there is sufficient power at the pump, so hopefully it is just a matter of changing the pump out now. I have never had a pump slowly die, usually just stops working all at once, that's why I was skeptical about changing it right away. But I have read that these late 90's early 2000's GM cars have this sort of thing happen.

Basically if you fight a bit with it, it will start and run poorly, but once it is up to operating temp, if you shut it off to run in a store or something, it won't easily, or at all start again until it has cooled off. It seems to get a little worse each time it is started too, and the fuel level sensor has never worked right since we had the car.

I wouldn't rule out the thought about the tank needing to be flushed, but both jobs require pulling the tank off so I will do that and see what it looks like inside.

Thanks everyone for their helpful tips and suggestions.

[DJ_MIX]

Re: Multimeter Settings

I recondmend you find a lumia forum..
they will help you and you can search on fuel pump and see how others solve their problem.