Starter motor won't engage... help with steps to diagnose

Erm... Let's start with: what is a "battery isolator"? Not familiar with that term.

 

Maybe a cut off switch?

 

Try using jumper cables to another battery. Also try putting a thick cable directly to the starter if you have one and check the earth straps at battery/frame and frame to engine. Sounds like a bad battery or bad connection.

 

Solenoid? Relay?

 

Not sure. You’ll need to go down the line one at a time. Do you have a lift?
Starter is not hard to remove if u do. Maybe it’s time for a starter rebuild and new solenoid anyways. It’s your cars way of saying it wants to play

 

You said it's making a rattling sound; different than the normal tired wrrr wrrr cranking sound of the engine?

If YES, (different noise), then have a look at the starter drive components and where it's connecting. The problem may be mechanical.

 

The starter motor relay is mounted on or in the starter motor itself. It's not in the fuse board.

TBH it sounds like a weak battery; I'd change that before messing around with the starter motor, especially as it's relatively newly rebuilt.

 

The solenoid is closing, then the voltage drops and the solenoid opens, then the voltage picks up so the solenoid closes,… click, click, click. You have a bad battery or bad connections. As I said, try another battery and check all of your connections including straps.

If you can hear something turning (but not the engine) perhaps with a grinding noise then it is your starter clutch/Bendix

 

Not necessarily. The battery may report a decent voltage when not loaded, but when loaded with a starter motor, the voltage may drop too low due to a too high battery "internal impedance". In such a case, the battery just don't deliver enough current to the starter. The relay clicking is a perfect example of a bad battery or a bad connection somewhere.

 

Check voltage drops when you attempt to start the engine. I just went through a single click only problem with my 328. The contributors here helped a lot. Here is the link. My starter has now worked properly 22 times in a row so I can assume the problem is solved.

https://www.ferrarichat.com/forum/threads/wires-on-starter.583379/

 

I'd opine that it's a battery or cable/connection issue. If the solenoid is chattering, it indicates insufficient current available to engage the starter. IF there is sufficient current, the solenoid would engage and spin the starter. If the starter was locked up, the solenoid would engage correctly but the starter would not spin. You would hear a single "CLACK" as the solenoid engaged and then (usually) a noticeable hum from the starter motor coils. If that occurs, release the key immediately to avoid damaging the coils/wiring though the related start switch/solenoid fuse should blow pretty quickly and also eliminate any possible damage..

 

There is a large cable that goes directly to the starter motor. Check this for a tight connection. It may be a good idea to clean the connection. Good luck

 

Hi Andy,

how much is the battery voltage while you turn the key? A defective battery can show healthy voltage without load, but collapses when you turn the key.
The noises you describe are exactly the same like on my car each time the battery was tired. The 308 seems not to make the classical noises we know from every other car. Even a dying batterie produces drama music


Best from Germany
Martin

 

it's quite possible that a fully charged battery is incapable of pushing through the amount of current needed by the starter system. With the proper equipment this only takes a few seconds to diagnose.

 

No. But a charger with an amp meter would help monitoring the charging process. If the amps go close to zero it has approximately reached its capacity.
I once had a battery on a daily driver, which failed after 14 months. Due to german warranty law they had to replace it for free. I just wonder, whether this isn't EU-law. Since your Brexit isn't completed yet it may be, that the same warranty (24 months) applies to the Uk as well.

Best from Germany
Martin

 

I've found that batteries that are allowed to discharge don't seem to last very long these days and I've had a few that have failed 'prematurely'. Anyway Bosch is just a label; things are all made for various labels these days and there are plenty of fakes about.

 

It is also possible that the battery was OK but the process of switching them cleaned/corrected a poor connection at the batt terminals.

FWIW, when you check batt voltage, check it in two spots - with the meter probes on the battery posts themselves, and then again with the meter probes on the cable terminals. This will often show up a faulty connection since there should be absolutely no voltage difference in the two measurements. But, as noted, you can have proper voltage but no hi-amperage capability with a faulty battery, cable, or connection. IOW, everything in the car will work. normally..except the starter.