X5 3.0d won't start

[omodos]

Originally Posted by andrewwynn

You will see almost no voltage until you start to crank. If you see voltage like 0.1v wait until it drops, turn off any power draw like fan. You might see a negative value which will happen when power is coming up the right side cable.

70mm SQ is about 9mm diameter

hmmm i reading your notes above must have done something wrong,says I should see no voltage until i start to crank? I never read this instead when the probe was dead center in the lighter socket indeed got no reading and thought this is wrong, so then as mentioned touched inside barrel of ligher socket that gave me reading of 13.01 v that i thought was the battery voltage, I then cranked and watched the meter reading drop, thinking that this was voltage drop you were referring to...please note my meter is one of these exxactly

[wpoll]

Originally Posted by omodos

hmmm i reading your notes above must have done something wrong,says I should see no voltage until i start to crank? I never read this instead when the probe was dead center in the lighter socket indeed got no reading and thought this is wrong, so then as mentioned touched inside barrel of ligher socket that gave me reading of 13.01 v that i thought was the battery voltage, I then cranked and watched the meter reading drop, thinking that this was voltage drop you were referring to...please note my meter is one of these exxactly

I think you've misunderstood what you are testing here... you are trying to measure the voltage drop in the main cable due to the starter current. Once you know this voltage drop, you can calculate the starter current draw (using ohms law).

This voltage should be less than 1v but may be a bit more in your case. It also very hard to measure this voltage if you meter doesn't have a peak hold function....

To measure this voltage drop, put the black lead from the DVM on the B+ terminal in the engine bay.

Put the red lead from the DVM on the centre contact in the cigarette lighter socket in the dash.

You should see a voltage very close to zero.

Now start the car and note the voltage that appears during cranking. It could be between 0.5 and 1.5v so set your meter to a low voltage range before testing.

[omodos]

Thanks..made a pigs ear of it....will try again as you described tomorrow , you maybe right that my DMM isnt up to task but i was able to see reading by recording it and playing it back frame by frame...thanks once again

[wpoll]

Originally Posted by omodos

Thanks..made a pigs ear of it....will try again as you described tomorrow , you maybe right that my DMM isnt up to task but i was able to see reading by recording it and playing it back frame by frame...thanks once again

Not at all (love that phrase, btw!) - it is a little confusing.

And your trick of recording the meter is a great idea - I must try that. Don't know why I didn't think of it myself - I work with high-speed imaging!!

Here's an image that might help you understand this a bit better...



From this web site...

You are trying to determine the voltage drop across the positive cable (the red one) and normally you would place the meter as shown. On a X5 this is hard to do due to the cable length. Using the cigarette lighter socket gives a "near enough" value, as the cable feeding the cigarette lighter socket runs back to the battery (+) and as long as it isn't carrying any current, there will be negligible voltage drop on it.