Starter Help

[stravalata]

Just replaced my starter, but i have some problems: i have to jump the battery ever time i try to start my truck. I can't get it to turn over, i check the starter and it is good. Could the problem be my relay or the battery

 

[Opera House]

My car doesn't start, must be the starter. Sounds like a costly mistake when you fail to do diagnostics before you replace parts. You can do a lot of testing with something as simple as a 12V lamp. Hook it up to the starter relay on the fender so it lights (block to post). If it goes out when you turn the key, you know you have lost voltage before that point. Sounds like you have a bad battery or really corroded terminals.

 

[lonestar]

i have to jump the battery ever time

Sounds like a battery to me!

Or an alternator, but if it stays running after you disconnect the jumpers it's working.

 

[JDraper]

You could also have corrosion in your battery to starter cable. I had the same problem with my '92, and the cable ended up being bad. Wouldn't start, so I put a new starter in. Still started randomly. Good battery, good alternator. Finally put a multi meter on the cable, and the resistance was way up. Put a new cable in and all was good

 

[FIRE and ICE]

Hate to hijack your thread but I'm curious as to how to test the resistance with a multimeter!

I have a good one but am not familiar with its use. My X is starting to exibit starting glitches :thumbdwn:

JDraper, could you explain how to hook up a multimeter to test the resistance of the starter wire? what should it read if its "normal"

Thanks

 

[Opera House]

Hate to say it, but you can't really make resistance measurments in high current circuits. Most meters only have a resolution of only 0.1 ohms. At just 100 amps, that gives a loss of 10 volts. Just contact resistance of test leads gives a variability of 0.3 ohms. The best way to check for resistance is with a high current passing through the circuit and measuring the voltage. In electronics this is known as a Kelvin circuit. Turn on a high load like headlights. Then measure voltage from the battery post (not terminal) to the starter solenoid or block. Also block to body. A voltage og over 0.1 volts indicates a problem. Measuring voltage drop in a loaded circuit is a prefered method.

 

[JDraper]

Not trying to be a PITA, buy yes, you can use a multimeter to measure the resistance in the cable. If you disconnect the cable from the battery, attach 1 lead to the connector on the cable that goes to the battery, and the other to the end that is attached to the starter, you will get the resistance of the cable. If you cable is good, your reading will be a couple of ohms at most.(Most likely milliohms) If it's shot, it will be well over 20 ohms (Mine was in the neighborhood of 80-100 ohms.). You're not measuring the resistance of the circuit, just the resistance of the cable.

 

[Opera House]

Like I said, you can't make usefull resistance measurements with an ohm meter. Sure, you can measure resistance if the wire has just about fallen off. A 1/4 ohm resistance for all practical purposes in a vehicle is an open circuit. If you can't measure milliohms, it isn't very useful. Resistance X current = voltage. Any combination of resistance and current that produces over a volt causes problems in a circuit that only has 12V to start with. Reading less than one ohm on a meter can often give a false illusion that everything is OK when it isn't.

 

[NOTAJP]

Not trying to be a PITA, buy yes, you can use a multimeter to measure the resistance in the cable. If you disconnect the cable from the battery, attach 1 lead to the connector on the cable that goes to the battery, and the other to the end that is attached to the starter, you will get the resistance of the cable. If you cable is good, your reading will be a couple of ohms at most.(Most likely milliohms) If it's shot, it will be well over 20 ohms (Mine was in the neighborhood of 80-100 ohms.). You're not measuring the resistance of the circuit, just the resistance of the cable.

I agree with JDraper. Opera House, you are thinking way to far into the circuit. You are very correct in your thinking (you must work electronics like I do) but with a simple 12VDC system and large wires your calculations are irrevelant. Large copper core wires can have a ohm or two loss and not affect the starting system.

stravalata,
Have your battery and alternator checked at any parts store (usually for free). That'll give you a good start (no pun intended ) on your troubleshooting quide.

 

[Opera House]

"Large copper core wires can have a ohm or two loss and not affect the starting system."
LOL....... No, I definitely don't work in electronics like you do! What part of Ohms Law don't you like? Perhaps you meant to say volt. It is true that a couple volt loss to the starter can be quite normal if it is distributed. If it occurs in a hot spot, that condition is subject to rapidly change. A volt loss from the engine block to the car body has greater consequences.

Take a worst case example of 25 feet of fairly small #12 copper wire (suitable for brake lights). This would have a resistance of 0.04 ohm. A good multimeter can measure to 0.1 ohm with an accuracy of 0.5%. But, hidden in that spec is an additional two digits. 0.1 ohm could read 0.3 ohm. In actual practice, a resistance of 0.7 can often be measured. Repeated resistance readings of the same resistance can often give several different values because the point contact includes oxidation layer resistance. If I am looking for something more than general continuity, I have to use more sophisticated methods. A starter cable that had 0.1 ohm resistance would not be able to crank a vehicle. And a meter that can only measure 0.1 ohm could not detect this problem.

 

[JDraper]

Editing my response...not worth getting into a pissing match over something simple...I too work in electronics,...have for 12+ years and have degrees in engineering & physics so I'm not just blowing smoke..

It won't hurt to try and measure the resistance..worst thing that will happen is you get an inconclusive result..however, if you measure several ohms the culprit is fairly obvious.