Intermittent Electrical Starting Fault

[Goldstar]

Evening all,

I am plagued by an intermittent starting fault that I need to try and fix tomorrow. Occasionally the car will fail to start and exhibit signs of a flattening battery i.e. it cranks slowly for a very short time and then stops cranking as if the battery is flat. It did it today and I checked the battery volts 12.9 - tried again engine cranked and started. It has happened twice before each time a jump start has sorted it first turn of the key.
I'm thinking
1. Battery earth connection
2. Starter earth
3. Dodgy solenoid wiring/connection
4. Dodgy or dirty Ignition switch

Is there any multimeter magic I can use to trace this or is it a case of clean replace everything as above? I have cleaned inertia switch contacts.

Thanks

Paul

[mallardstag]

Hi Paul,
I had a similar problem some time ago - check that the earth strap from the battery to the engine block is good and that the connections aren't too corroded, if this fails the starter current will be returning though the (high resistance) throttle and choke cables.

Also check that the high current wire from the battery to the starter solenoid is sound.

Simon

[V Mad]

If you put a multimeter on the starter motor main terminal when its cranking and see what you get. If it is a healthy voltage (12v or more) then motor may be faulty. Much lower than 12 volts may indicate a bad connection or solenoid. A good test to eliminate solenoid is to bridge across the the two big terminal with a screwdrive.

[Goldstar]

Thanks guys I'll give it a whirl this afternoon (assuming I can get Mrs S off her sun lounger to crank the engine (presumably with the king lead off?)

Paul

[Goldstar]

So I checked the starter and one of the wires was badly crimped so I fixed that first. Multimeter on the starter main lead gives 12v uncranked and 7 when being cranked so i now need to eliminate the solenoid as that or a dodgy wire appear to be my problem? Chris could you explain your solenoid test a bit further please?

Thanks

Paul

[V Mad]

Yes, there are two big screw terminals on the starter motor solenoid. One (live at 12 volts) comes from the battery and one goes to the motor. Just connect them together momentarily with a screwdriver and the starter should spin. CAREFUL THOUGH: WATCH YOUR EYES in case of a big spark and dont short to chassis!

[Goldstar]

Ok thanks Chris I'll give that a go

[Goldstar]

Yes, there are two big screw terminals on the starter motor solenoid. One (live at 12 volts) comes from the battery and one goes to the motor. Just connect them together momentarily with a screwdriver and the starter should spin. CAREFUL THOUGH: WATCH YOUR EYES in case of a big spark and dont short to chassis!

Spins really well so from your earlier comments am I right in thinking that now points to a connection/wire? Hopefully it was the badly crimped lucar connector that fits to the top of the starter motor-it just pulled off with no force at all when I unplugged it.

Simon, the earth looks good but I am going to take it off tomorrow and do a visual check on its condition and clean it up anyhow-time well spent I think

[V Mad]

By using the screwdriver you have bypassed the solenoid, so if it now spins OK then solenoid is prob bad.

[Goldstar]

Ah, I see. I have a spare so it looks like I should have a go at swapping it out next weekend. Looks a bit fiddly in the ROM and HM but not impossible.

Thanks Chris

Pal

[PhilG]

Paul,
I chased a similar problem and after much frustration it turned out to be a dodgy ignition switch. A squirt of contact cleaner sorted it temporarily but I've now installed a relay to reduce the current going through the igniton.

Phil

[Guest]

Things like this are a nightmare as the cause can be one or more of so many components. The MM is currently not playing ball with me on something broadly similar so that, in combination with the little incident of losing the ATF, I have barely driven it in all the glorious weather this year.

[Goldstar]

Hi guys, yes my knowledge of auto electrickery is quite limited but with my new multimeter, help from others on here and the recent PC guide to diagnosing faults I'm hoping to learn and fix a few bits and pieces at the same time. The worse thing about it is the intermittent nature of the fault.....

Paul

[Richard Saunders]

Paul - without wanting to cast any doubts on your technical abilities let me know if you need the details of that automotive electrician chap.

[Goldstar]

Paul - without wanting to cast any doubts on your technical abilities let me know if you need the details of that automotive electrician chap.

Thanks Richard I told you it would probably need it before long....I'll persevere a bit longer before admitting defeat though

cheers Paul