Lotus Elan

New starter solenoid - starter still struggles

PostPost by: mn1 » Sun Jul 24, 2022 10:02 am

Original Lucas solenoid was having intermittent failures so replaced with new one from Paul Matty. The intermittent failure has not re-appeared however the very sluggish starter issue is still the same.
Fully charged battery at 12.62 volts measured at the battery and the input solenoid post. Voltmeter earth at solenoid was the solenoid body.
Disconnected the starter from the output solenoid terminal, connected volt meter and turned ignition key.
Solenoid output voltage 9.5 volts, so that explains the sluggish starter and given the consistent starter behaviour with 2 different solenoids suggests it is not a faulty solenoid. This test also takes a problem between starter and solenoid out of the list of possibilities. Any suggestions??
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PostPost by: Elanman99 » Sun Jul 24, 2022 10:42 am

I think it unlikely that a sluggish starter motor would be caused by the solenoid. Its basically a heavy current relay and when the contacts are closed it will have very low resistance and any voltage dropped across it will be too small to worry about.

During cranking the voltage the starter motor sees is what matters, ie actually what is across the motor itself. Motor current will cause voltage drop in the cables, chassis, and all the terminations and joints. As an exercise its worth measuring across the battery posts when cranking and compare to its off load voltage.

By extending the meter probe wire length you could measure (whilst cranking) the drop in the positive and negative runs separately.

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PostPost by: Craven » Sun Jul 24, 2022 11:19 am

With nothing connected to the out terminal of the solenoid and a measured 9.5 volts would suggest a spurious test method. Ensure you negative probe has a good connection. You could check the voltage across the 2 solenoid terminals in the start position. A fully charged battery would read 12.8 volts.
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PostPost by: alanr » Sun Jul 24, 2022 1:17 pm

Just because you have a surface 12.6v at the battery without any load doesn't mean a lot.
You need a High Rate Discharge Tester held across the battery terminals and see what it shows. If the voltage drops rapidly you have a duff battery cell. It should hold a constant and steady 9volts under heavy load.
Your local Car Electrical/Battery company will have a tester.

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PostPost by: ianthomson72 » Tue Jul 26, 2022 10:04 am

It’s worth physically checking the cable from the battery to the solenoid . I had a similar problem and found that the cable had a cut in the outer cover allowing water to corrode the copper core to the extent that it couldn’t carry the starter current. A replacement cable cured the issue.
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PostPost by: RichardS » Tue Jul 26, 2022 2:45 pm

Presuming the battery is ok I would also suggest checking you have a good earth connection to the battery as a poor earth could cause this symptom
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PostPost by: mn1 » Wed Jul 27, 2022 2:56 am

Tks all,
Going to start with some thorough earth checking and move on from there.
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