Volkswagen Polo III - VW Polo occasionally wont start when warm

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Wed 29 Oct 2014 17:50
Volkswagen Polo III - VW Polo occasionally wont start when warm - ozzii

Hi,

I've got an intermittent problem with my VW polo

It always starts fine first thing in the morning when it is cold but occasionally if i've gone out in the car and left it some where for anything from 5 minutes it wont start. If I leave it until it cools down it will start no problem.

I first noticed something was wrong when I took the car for a spin and as I was slowing down near a junction the engine simply died leaving me stuck in the middle of the road. I left the car for about 10-15 mins to cool and then it started up fine again. This was dangerous - the engine cutting off whilst driving.

The above happended twice - engine dying whilst driving. Since then the problem with the engine struggling to start when its warm has been intermittent. I've since had the car serviced and the distributor cap replaced but the problem is no where resolved.

I've read a few forums which state it could be a faulty distributor hall sensor or temp seonsor. I took it to the garage and he tested the temp sensor using some diagnostic and he says it fine showing at 75 when hot. Are these diagnostic test accurate? Usually the temp gauge should settle around 90 but mine only ever reaches 75. He says it is fine as diagnostic reading is same as what is showing on temp gauge.

He thinks it could be a faulty relay or crank sensor.

Any one have any ideas or comments on this please?

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Wed 29 Oct 2014 17:58
Volkswagen Polo III - VW Polo occasionally wont start when warm - madf

Failed crankshaft or camshaft sensor...

Miniscule break in wiring. OK when cold, when warm, wire expands and a gap forms..

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Wed 29 Oct 2014 18:13
Volkswagen Polo III - VW Polo occasionally wont start when warm - elekie&a/c doctor
Depending on which engine you have,if there is a distributor cap,then it may not have a crank or cam sensor.the Hall effect pick up device in the dizzy could be a problem.
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Wed 29 Oct 2014 18:38
Volkswagen Polo III - VW Polo occasionally wont start when warm - ozzii
Depending on which engine you have,if there is a distributor cap,then it may not have a crank or cam sensor.the Hall effect pick up device in the dizzy could be a problem.

The dizzy does have a cap.

What about the temp sensor. Is this mechanic correct when he says the reading is fine?

What about the fuel pump relay?

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Wed 29 Oct 2014 18:53
Volkswagen Polo III - VW Polo occasionally wont start when warm - elekie&a/c doctor
Temp sensor looks fine.anything else is just a guess,without more in depth investigation.
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Wed 29 Oct 2014 20:21
Volkswagen Polo III - VW Polo occasionally wont start when warm - Railroad.
Hall sensors don't tend to suffer intermittent faults. They either work or they don't. If the hall sensor had failed then you would have no HT spark, no fuel pump and no fuel injector switching. Next time you have the problem check to see if any of these are missing. If the problem is with the hall chip they'll all be missing.
Check the fuse box for signs of a poor connection. That's a common fault on these cars. So are ignition switch failures. Does the fuel pump ever fail to run? If not the relay won't be the cause of the fault. The easiest way to check injector switching is with a noid lamp. They're cheap to buy and have many uses.
The problem could also be flooding. This isn't uncommon on a partially warm engine. Does the exhaust smell of neat fuel, and does the engine crank like it lacks compression? All things to check when the fault next occurs.
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