No Start Problem - In Process Diagnosis

[My442]

Originally Posted By: brianl703
You can connect a jumper cable from the battery positive terminal to the terminal on the starter solenoid where the battery cable is connected. This will bypass the battery cable and allow the engine to start if it's bad.

Or you could try jump-starting it to rule out the Optima battery.

Hey, how about checking the voltage at the battery when you try to start it? How low does it drop?


The battery voltage does not move when you go to start the car. It is like the starter curcuit is not connected to the rest of the car.

I bench tested both starters, and the solenoid kicks when I jump them.

 

[brianl703]

This problem sounds like it's somewhere between the ignition switch and the solenoid. You can use a fused jumper wire to inject 12V at each point along that circuit until you find out where it engages the starter solenoid (or it just blows the fuse, indicating a short circuit).

 

[My442]

Here are the voltage readings with no starter installed:

Battery – 12.47

Positive Cable – 12.46

Horn Relay – 12.46

Ignition Switch (Purple) – 12.27

Neutral Safety – 12.27

Thick purple wire at starter solenoid in Start – 12.27

Thin yellow wire in Run – 12.27

It appears that I have a bad starter - will advise.

 

[My442]

Fixed it.....the culprit was the positive battery cable.

It had a crack where the lug has the 90 degree bend. You could not see the crack unless you specifically looked for it. That crack prevented the starter from getting the 40 amps required to spin it.

I replaced the lug, and threw in a new solenoid to be sure.

Only 12 hours of ball busting, where it should have taken 1 hour..... :rant:

I have to say that the digital volt meter is much better than a test light, as you can read voltages at each step.

 

[brianl703]

Glad you fixed it.

The only issue with a digital voltmeter is that it has a very high impedance so a very poor connection on an unloaded circuit can still read normal voltage.

How poor of a connection, you might ask?

Try this. Connect the negative probe from the digital multimeter to ground or the battery negative.

Wet one of your fingers and touch the positive probe. Wet another finger and touch the battery positive terminal.

I bet the multimeter reads close to full voltage (if not higher due to your finger acting as a battery against the metal terminal).

The multimeter is most useful for testing voltage drop through a circuit with a load. You can use a test light for a load; any poor connection will show reduced voltage with the light hooked up.