car won't start sometimes when hot. damaged tooth?

GeX

GeX

GeX

Soldato
Joined
17 Dec 2002
Posts
7,014
Location
Manchester
howdy. car in question is a fiat cinquencento with a fiat stilo engine in it. i'm no stranger to the oily bits and did this swap myself - but it's developed an annoying fault.

Very occasionally, it won't restart from warm / hot. It acts like the battery is flat, with sounds like the starter doesnt even turn the engine over one revolution. The battery is not flat, nor is it old / struggling / needs replacing. It is an oversized deep cycle battery with plenty of life in it.

It's not the coolant temperature sensor, as with the laptop plugged in that all reads fine. It's not the TDC sensor, as again - that is working fine.

I've removed, cleaned and greased all the high power cabling (earths, +ve cables, starter connections etc) and they're all fine.

To get the car to start, a little push will do it. it seems it just needs enough to turn the engine over once, then the starter will kick in. i think the missus is getting fed up of pushing, so want to get this sorted.

I'm leaning towards a damaged tooth on the flywheel that's locking starter up. Or the starter is dying. I think i have spare one in the garage, but it's off a stilo so the wiring needs adapting - but will try it at some point.

So yeah.. any ideas, i've never had it do it from cold but the fault is so intermittent i'm struggling to diagnose it. What would a damaged tooth do re starting?

Cheers
 
no, it's not clicking - that's why i've not suspected the solenoid. turn the key and it just go "hrnn" and stops. It'll be getting 12v, and the cabling is overspecced for what it needs.
 
Sounds like the solenoid isnt throwing the starter gear out. Should be intermittent all the time though if that was the case not just when hot. If a tooth was missing from the flywheel(which is pretty unlikely) the the starter would either spin very fast without the engine turning or would start to engage then lock as it wouldn't be able to mesh with the flywheel gear. Does the solenoid still sound like its clicking when the starter refuses to turn over?
 
GeX said:
no, it's not clicking - that's why i've not suspected the solenoid. turn the key and it just go "hrnn" and stops. It'll be getting 12v, and the cabling is overspecced for what it needs.
Click to expand...

Solenoid on the way out. Pretty sure its new starter time.
 
if the solenoid wasn't working, then the stater should just spin shouldn't it, as it's not locked onto the flywheel?

you've convinced me enough to go dig out the spare starter motor.. now if the rain will hold off.. :D
 
My solenoid used to play up, I used to start it by getting someone to hold the key in the start position, then short out the 2 big bolts on the solenoid with a screwdriver.

There were a lot of sparks and a few black marks on the screwdriver but it started fine. It may be worth trying this to see if your starter motor is ok...

I fixed it in the end by adding a relay in front of the solenoid...
 
GeX said:
if the solenoid wasn't working, then the stater should just spin shouldn't it, as it's not locked onto the flywheel?

you've convinced me enough to go dig out the spare starter motor.. now if the rain will hold off.. :D
Click to expand...

The solenoid throws the starter gear out which also engages power to the main coil to turn it over. If the solenoid is weak then it doesnt throw it out hard enough it may not mesh with the flywheel properly if at all.
 
BigglesPiP said:
IIRC the starter solenoid also makes the connection that powers the starter?
Click to expand...

The soleniod activates from the ignition switch and puts power onto the motor like a relay, the torque of the starter motor turning pushes the starter gear out to engage the flywheel(its on a spring and when the starter isnt working sits pulled away from the flywheel gear). If the solenoid doesnt act fast enough the torque can build up to slow to engage the starter gear same as if the main supply to the starter isnt good or the earth to the chassis from the engine is bad.
 
Dandle said:
The solenoid throws the starter gear out which also engages power to the main coil to turn it over. If the solenoid is weak then it doesnt throw it out hard enough it may not mesh with the flywheel properly if at all.
Click to expand...

THIS

As the starter motor warms up things could expand just enough to make the solenoid lazy / a bit tight for it to not throw out properly, or votage isn't getting tot he starter motor properly, eg a bad earth

Try clamping a jump lead between the back of the starter and the battery.. does it work faultlessly then?

Make sure its out of gear first :D
I've heard quite a few stories of people running themselves over :o
 
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as i said, the wiring is all fine and overkill for the job. i ran ~200A cable through the car when i rebuilt it and changed the ECU etc.

thinking back, the solenoid was jamming out when i first started using that starter again, so it probably is past its best. i just need some time and weather to put the spare on!
 
GeX said:
as i said, the wiring is all fine and overkill for the job. i ran ~200A cable through the car when i rebuilt it and changed the ECU etc.

thinking back, the solenoid was jamming out when i first started using that starter again, so it probably is past its best. i just need some time and weather to put the spare on!
Click to expand...
If you're wiring is good then it's most likely the solenoid. Have you checked the wiring to the solenoid also? Try running an earth straight from the battery... I've found a solenoid will draw enough current to blow 5A fuses so it's worth using thickish wire if you can. :)

If you have a spare, even better, just switch it out and see what happens.
 
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