Symptoms of a bad / flakey solenoid? - Vintage Mustang Forums
 
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post #1 of 8 (permalink) Old 01-08-2019, 06:24 PM Thread Starter
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Symptoms of a bad / flakey solenoid?

I've been having a heck of a time trying to get my car running right. So I've been cranking my engine a lot. My starter solenoid smokes. I know that sometimes this in and of itself is not indicative of a bad starter solenoid. Seems like I can get my engine to fire and run but it dies and then I cannot get it started again. It still cranks but the solenoid smokes and the car won't start. Is it possible that the starter solenoid can function to engage the starter motor but no longer passes current to the coil during cranking? I know usually a bad solenoid means the engine won't crank, end of story. But can it fail in other ways?

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post #2 of 8 (permalink) Old 01-08-2019, 09:19 PM
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If your starter solenoid is smoking, it should be replaced.

I’d also pull the starter and have it tested. Or just replace it completely.

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post #3 of 8 (permalink) Old 01-08-2019, 09:21 PM
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When you have a bad connection that creates a lot of resistance in the circuit, often the solenoid is the first point of failure. Kind of like a fuse. Therefore people keep replacing solenoids over and over and unfairly blaming them.

So the first thing I would do is perform a voltage drop test. That would show up a bad connection issue, which I suspect is your actual problem but you can prove it. If you saw smoke from the solenoid I would no longer have faith in it being in good condition but you want the cause, not the symptom.
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post #4 of 8 (permalink) Old 01-10-2019, 03:15 AM Thread Starter
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How do I do a voltage drop test? Just measure across the battery while cranking?

I should note that all cables / wires were re-connected during my project. Could be the wires / cables, could be the starter motor, but the connections are clean and tight. I don't think it's the connections themselves.

My engine has 10.75:1 compression. A new starter has been on my list. I've been contemplating which route to go: 1) stock style, 2) high torque aftermarket or 3) late model OEM. I have a 157 tooth flexplate and C4 automatic. I want a starter that will also work with a 157 tooth flywheel and toploader (already have all the other parts for this swap). My understanding is that any 157 tooth starter will work, it's the 164 tooth where the length matters between auto and manual.

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Last edited by jdub; 01-10-2019 at 03:17 AM.
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post #5 of 8 (permalink) Old 01-10-2019, 06:33 AM
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My solenoid was acting flaky last summer when I was in Louisville for the Street Rod Nationals. Had a spare and went to replace it, pulled one of the wires off the front of the solenoid and it had a burn mark on the post, crimped the wire a bit to make a tighter connection. Problem solved.

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post #6 of 8 (permalink) Old 01-10-2019, 10:46 AM
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As much as I like to expound upon how things work, there are actually some good Youtube videos on voltage drop testing that show and explain what it's about better than anything I could type up. You only need a multimeter. Harbor Freight often has a coupon to give you one free with any purchase. Can't get much cheaper than that. I have one of those (it was free!) and it actually works and would do what you need. So would any other low dollar one too.
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post #7 of 8 (permalink) Old 01-10-2019, 11:42 AM
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Is it the solenoid itself that is smoking or the wire connection to it is smoking?


At any rate, they are relatively cheap and easy to replace but I would also consider the starter going out or not having a good engine ground which the starter has to have and it draws a relatively large current. I have a battery cable with eyelets on each end to ground my engine block to the frame rail.


I have had a string of problems with starters and the stock or remanufactured stock starters are not strong enough any more to fire over a 10 + compression engine for very long. It will smoke them sooner or later. I had to get a high torque mini starter for even my old Ford truck because I modified the engine quite a bit and I went through 3 starters in 2 years. I took it off the hot rod which has around 10 1/2 to 1 compression so now I have to address a starter for the hot rod.


Last thought, if the starter is having trouble kicking over the engine it can smoke the solenoid.


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Last edited by macstang; 01-10-2019 at 11:44 AM.
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post #8 of 8 (permalink) Old 01-10-2019, 11:59 AM
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In a series circuit, what ever has the most resistance, drops the most voltage, meaning youíll measure voltage. Obviously on the solenoid you want good contact. Put the VOM leads on the battery side and starter side. With the solenoid not engaged the resistance across the contacts is ifinate this means youíll be reading full battery voltage. When the solenoid is energized and closes the contact to energize the starter you should not read any voltage at all. If you do read voltage, thatís a indicator of resistance. If you read 3 volts for example, subtract that from the voltage across the battery during cranking. The sun will be what the starter is getting. So if battery voltage is 11 volts during cranking and you have a 3 volt drop or loss on the solenoid, the starter is getting 8 volts. This is not taking into account for any voltage loss on the wire or connections and assuming thereís nothing wrong in this example. Now even 1 volt loss means the starter is seeing 7 volts. You can see how quickly thinks can go south.

Tom

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