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Starter Motor Intermittent failure
mojoTrev - 2/8/10 at 11:18 PM

I am having a very frustrating issue with my starter motor on my Mojo.


This all starter when I replaced the gearbox, which required me taking the
engine out too.


Intermittently, when I turn the ignition key I get nothing from the starter
whatsoever. No clicks, nothing.


I replaced the starter motor, and have exactly the same issue.


I have replaced the 12V trigger wire from under the dash all the way to the
starter motor, including the connector.


When I turn the key whilst its failing, the ignition lights dim slightly as
if there is a voltage pull somewhere.


If I didn't know better its as if I've got a DOA starter motor, but the
chances of two having the same fault is remote.


Any help greatly appreciated!


Trevor.

snapper - 3/8/10 at 03:59 AM

Check your earth straps
Run one from the starter motor attachment bolt straight to the battery
Now check +VE feed
Use a volt meter and check for any voltage drop/ resistance battery stud the battery cable clamp, stud to other end of battery cable, battery cable only, cable to starter +VE stud

[Edited on 3/8/10 by snapper]

big_wasa - 3/8/10 at 05:54 AM

If you havnt used a relay for the solenoide you could have burnt the contacts in the ignition switch.

adithorp - 3/8/10 at 06:50 AM

quote:
Originally posted by big_wasa
If you havnt used a relay for the solenoide you could have burnt the contacts in the ignition switch.


To check that ^^^ try trigering it with a wire from the battery to the starter solenoid trigger.

The 2 suggestions above are the most likely causes.

adrian

khm - 3/8/10 at 07:43 AM

had a similar problem with my old lambo, i got a voltage drop with the length of the cable going battery to switch to starter, i fitted a relay next to the starter, used the starter ( from key ) wire to trigger the relay, then had a live feed from battery to power the relay - hope that makes sense !!

norfolkluego - 3/8/10 at 11:10 AM

I'd go with a dodgy earth first, it caused our starter motor probs and it's easy to fix!

mojoTrev - 3/8/10 at 01:32 PM

Thanks everyone for help so far.

When measuring across from the battery negative to the chassis or engine with the engine off I was getting 0.01 Ohms. With the engine running I was getting 1.8Mega Ohms - almost open circuit! It looks like it was earthing through something small and thin(accelerator cable?) but that would not allow a good starter motor current pull. ( intermittently )

I have removed and cleaned up the earth strap and now I'm getting 40 Ohms with the engine running.

As the problem is intermittent Ive no idea if its fixed.


Could that poor earth have caused the issue given that it was not starting intermittently ?

And should I get a new earth strap to bring the resistance down to 0 Ohms, or is 40 Ohms to engine OK?

Trev.

norfolkluego - 4/8/10 at 11:34 PM

We run two earths, one from battery to chassis, one from battery to engine block, without them we always seem to have earthing probs. No idea why engine doesn't earth without it, but it's a quick easy fix and it works so we go with it.