Starter Diagnosis - Help needed

[MTWGB]

Hi All - I’m new poster on the forum though I’ve been reading posts for a while.

I have a RIB with a 90’s vintage Mariner 40hp 2 stroke with a starter problem and could use some help in diagnosing the fault. Last season the starter motor worked intermittently and this season, having tried to get the boat into service, it doesn’t seem to work at all. Although the engine started first time on the chord which was pleasing!

I’m getting no response at all from the starter motor or the solenoid, not even a click. I’ve tested the starter by connecting direct to the battery and and it seems to work fine.

It’s a straightforward system with Mariner ignition switch on the console and battery isolator, both look in OK condition as does the wiring. I’ve bought and tested a new 12v battery and tested the circuits using a Voltmeter according to the steps detailed in the Acro Marine solenoid testing instructions (copied below) with the following results:

Test 1 - 10v
Test 
2 - 1v

Test 3 - 0v
Test 
4- 0.7v

(All the results were variable with the Voltmeter fluctuating +/- 1v on most readings)

http://www.arcomarine.com/xhtml/Tech...%20Testing.pdf

STEP 1: Check the voltage on the battery side of the solenoid as shown on the left. The reading should be the same as the battery reading (12.6V = Full Charged Battery).
STEP 2: With the voltmeter still connected, turn the key to the start position and read the voltage. The voltage should not drop below 10.0 volts on this terminal. If the voltage drops below 10.0 volts, The battery cable should be cleaned or replaced. If the reading is 10.0 volts or more move on to step 3.
STEP 3: Keep the negative voltmeter lead on the metal base of the solenoid and move the positive voltmeter lead to the terminal marked “S” on the solenoid. Turn the key to the start position and read the voltage. The Voltage could read a little lower than the previous reading but should never be below 10.0 volts. If the voltage is lower than 10.0 volts, You must troubleshoot the start circuit (ignition switch, voltage supply to the ignition switch, neutral safety switch).
STEP 4: Move the positive voltmeter lead to the battery terminal on the solenoid and the negative voltmeter lead to the terminal that the starter cable is attached. Turn the key to the start position and read the voltage. The voltage should read no more than .3 volts. If the reading is more than .3 volts the contacts have excessive resistance and the solenoid should be replaced.

So my problem is where do I start in terms of rectifying the fault? Should I start with the wiring or the solenoid? Obviously I want to start with the most likely parts for repair / replacement but this has stretched the limits of technical competence.

Can anyone help?

[PeterM]

Step 2 seems to be the place to look - which in my mind means that when you are pulling a high current when trying to start the engine the voltage is dropping to 1 volt - which I think means that something is amiss between battery and solenoid ... I think .

It was on my old engine ! I only had a drop to 5v - but things do corrode over a winter of no use.

[jambo]

I would think along the same lines as Peter. I had a similar problem last year but it turned out to be the starter as I did have a click from the solenoid under test. Fitted new starter and 'bang' away she went.
Hope you find the problem soon and you are back out on the water enjoying yourself in all this bloody rain!

[PeterM]

Oh and your 10v reading seems very low for a fully charged battery at the engine end (if I understand your test correctly) which again points to problems between the battery & engine- either switch or wiring.

[jambo]

Is you battery placed away from your engine for exampl under the steering consol. If so check the leads maybe coroded or have some breaks in them, if in doubt replace as I had that also one year. The leads and connections have to be clean and tight.

[Nightfisher]

The first thing to do is charge then take a battery reading at battery -- 10 volts is NO good and may not be enough power to close the solenoid switch which activates or sends power through to the starter (which explains why the starter cranks on a direct battery connection to it).

You might try a Amperage draw meter. There is a type of meter (low cost) which sits over the positive battery lead (I have one). If the meter jumps 75+ amps when engine start is engaged and the starter fails to crank, it's the solenoid or starter internals that are the problem. If nothing when switch engaged, disconnect battery then disconnect start switch (all wires) and check for continuity between the wires (switch on) using an ohm meter set at 2K resitence.

[MTWGB]

Thanks to everyone for the suggestions, in the end i narrowed it down to the battery isolator switched which i was surpirised by as i thought they were pretty much infalable but it had been mounted with the key hole in a vertical position so i expect over time water had corroded the inside. So all working again now!