My daughter's 1992 Mk 3 1.05 Genesis (AAU Engine) is driving me nuts!

The intermittent starting issue is weird to say the least. Starts OK for days and then suddenly nothing. Even though battery has good charge and engine turns over OK it just won't fire until jump leads are applied from another car with its engine running. It just seems to need the extra voltage to kick it into life.

So far all the obvious have been checked/changed: plugs, leads, dizzy cap, coil and even the ECU.

On the recommendation of a garage who previously looked at this problem the Fuel Pump relay has also been changed. But again tonight it was reluctant to start (with a well charged battery).

The last AA man who visited reckoned it was ignition related. Certainly I can hear the fuel pump prime OK when the ignition is turned on so maybe he's right but what left to check?. My thoughts are now down to a dodgy earth somewhere or the hall effect sender. Sorry this is a tad long but its been an ongoing saga...

Anyone got any suggestions?

Particularly location of any earthing points that are known to give trouble.

Thanks for reading this...

Does it only do short journeys or is it quick trips to the shops every now and then?

I noticed with my Mk3 that when I used it for work (70mile round trip) it was the most reliable machine on earth but start just doing tiny journeys and you have problems.

I'd definately say earths, they aren't the best stuff in the first place and once they have a few years behind them...

I'd check the main battery one first I think.

Does it only do short journeys or is it quick trips to the shops every now and then?

I noticed with my Mk3 that when I used it for work (70mile round trip) it was the most reliable machine on earth but start just doing tiny journeys and you have problems.

To be honest its pretty random (and highy irritaing!)- after a 100 mile journey it just wouldn't play the next morning and sometimes it plays up after a short journey. However, once started it always starts first time until its been left overnight or parked up for say 6 hours or so - after which time the intermittent fault may (or may not!) occur.

I'd definately say earths, they aren't the best stuff in the first place and once they have a few years behind them...

I'd check the main battery one first I think.

My thoughts too but I suspect the main battery one is OK as there is no issue with headlights or starter motor - worth a good look though. From the Haynes manual its difficult to identify where critical earth locations are - clues like "In Mono motronic wiring loom" aren't exactly helpful.

Does sound like Hall Sender as well... THey seem to have a habit of random starting/running issues.

The car doesn't have a rev counter at all does it?

2nd vote for earths! i had the same prob with my gt when it started getting cold. i used an old amp wiring kit and ran an earth from chassis to the alternator body, one from the block to chassis, another from the inlet manifold to chassis and also replaced the main neg cable for the battery. bit overkill but its made a massive improvement! my stereo even sounds better!! I left the orignal earths on too and cleaned up the contacts on the battery terminals and alternator terminal. make sure you use some copper grease or vas to stop them going gammy again!

Does sound like Hall Sender as well... THey seem to have a habit of random starting/running issues.

The car doesn't have a rev counter at all does it?

if the hall sender were at fault, using the jump leads to get it started wouldnt work ( i know this from experience (it wasnt a very nice experience either cos i was down some random country lane!)

Does sound like Hall Sender as well... THey seem to have a habit of random starting/running issues.

The car doesn't have a rev counter at all does it?

There is a rev counter.

What I find strange is that once started it runs like a dream - I would have expected a hall sender fault to be more permanent in nature. That said it is next on the list after earthing checks...

On the multipoint injection Mk3s one of the earth points uses the mounting bolt for the coil (I think this is the 'in the loom' one mentioned in the Haynes manual). I had problems with my car not starting which was traced to this. The alloy coil body corrodes. Not sure if the SPi is the same but worth a check. Also had an intermittent problem with an Ibiza which was the coil/amp packing in when it was hot. Started and ran fine then wouldn't start again when left for a short while. When fully cooled down would work again. Only fixed that when it eventually stopped working completely.

On the multipoint injection Mk3s one of the earth points uses the mounting bolt for the coil (I think this is the 'in the loom' one mentioned in the Haynes manual). I had problems with my car not starting which was traced to this. The alloy coil body corrodes. Not sure if the SPi is the same but worth a check. Also had an intermittent problem with an Ibiza which was the coil/amp packing in when it was hot. Started and ran fine then wouldn't start again when left for a short while. When fully cooled down would work again. Only fixed that when it eventually stopped working completely.

Interesting...

Last night I changed the coil again back to the spare I had which is from a Golf (I think) and has very slightly different fixing, the bolts go through flanges at the base only rather than through the whole alloy coil body. In so doing this earth strap was moved to under the coil rather than on the top as originally placed. This morning she started OK - but only time will tell if its a real fix or yet another fix fail...

Thanks to all for the advice - looks like a thorough goig over of all earth bonding points is this weekends first task.

Sad to report it was yet another fix fail.

Having been OK for several days this morning it just would not start. Engine turned over fast so battery in good shape but not even a hint of starting.

So following up on previous advice I have now meticulously cleaned up all the earhing points, spade terminals bolts etc and made sure they are all making really good contact. I did the battery -ve connections at the battery and the bodywork. The braided lead between engine and bodywork (near the alternator), the earthing strap from the coil, and also the two brown wires from the loom that bolt to the bracket at the top rear of the engine cambox.

If there are any more earthing points anywhere I couln't find them!

The upshot of this work was a very nicely spinning engine on the starter motor but still a non starter!

Everything in sight was checked yet again but still no obvious issues visible.

Once again as soon as jump leads were applied to the battery from another car (engine running) the Polo burst into life and has been starting first time ever since... It idles steadily (about 90rpm) and drives perfectly with no hesitations or hiccups and a performance that defies it's 113K miles.

Not knowing where to go next chasing this fault I just cleaned the bloody car instead!

It looks good now but I have zero confidence it will start tomorrow.

So I may (will!) have to do the unthinkable and get professional help to get to the bottom of this one.

Unless of course anyone out there has got any more ideas to try first?

faulty ignition switch?

common complaint on Mk3 Golfs & Mk4 Polos

Edited 5 January, 200818 yr by Mister D

faulty ignition switch?

common complaint on Mk3 Golfs & Mk4 Polos

Certainly worth a check - thanks for the suggestion as I had mentally discounted this on the basis that the starter motor turned the engine over fine and all the lights on the dash and the radio come on fine. However, the way things are nothing should be discounted. I guess I need to look at the wiring diagram to see just how many contacts are actually in the ignition switch - maybe it's just one pair that are dodgy.

What I really can't get my head around is why jump starting always brings it to life even when the battery is fine and it should start perfectly OK without needing a jump.

a Mk3 Golf of a friend had the same problem and he left the car with me till it was fixed, it would start fine for days then would just turn over and over without firing. If you turned the ignition off and then tried again it would usually start. A checking a lot of things I replaced the ignition switch and problem solved. Sounds similar to you problem

Edited 5 January, 200818 yr by Mister D

Clutching at straws with this one, but how old is the battery? Although it's providing enough output to turn the engine over, is this then robbing it of the power to provide a healthy spark at the plugs? This could explain why jump leads from another car are helping out and why it seems most likely to occur after the car has been left for over 6 hours.

Failing that, go back to basics and see what missing: spark or fuel and report back.

Clutching at straws with this one, but how old is the battery? Although it's providing enough output to turn the engine over, is this then robbing it of the power to provide a healthy spark at the plugs? This could explain why jump leads from another car are helping out and why it seems most likely to occur after the car has been left for over 6 hours.

Failing that, go back to basics and see what missing: spark or fuel and report back.

Thanks for taking time to offer advice.

The battery is less than 6 months old and has been tested and found sound with low internal impedance.

Not 100% sure if its fuel or spark to be honest but as far as I can tell the spark is OK - Haynes recommend using an inductively coupled timing light to check this and I hope to get access to one these soon to confirm.

Testing the "old fashioned" way by drawing a spark from an HT lead seems to show a spark at least most of the time!

I am pleased to report it looks like this one is finally resolved as my daughter has now taken the car back to University and we have had a week without any more starting issues.

The culprit would seem to have been that dreaded blue temperature sensor.

After checking its resistance value for several mornings it was clear that it was to say the least behaving rather erratically. One morning when it was about 10 degrees it was telling the ecu that the temperature was "minus a hell of a lot"! The end result was it just wouln't start.

What a lot of grief for £10 sensor...

Thanks to everyone who offered help (and encouragement)

On the multipoint injection Mk3s one of the earth points uses the mounting bolt for the coil (I think this is the 'in the loom' one mentioned in the Haynes manual). I had problems with my car not starting which was traced to this. The alloy coil body corrodes. Not sure if the SPi is the same but worth a check. Also had an intermittent problem with an Ibiza which was the coil/amp packing in when it was hot. Started and ran fine then wouldn't start again when left for a short while. When fully cooled down would work again. Only fixed that when it eventually stopped working completely.

Interesting...

Last night I changed the coil again back to the spare I had which is from a Golf (I think) and has very slightly different fixing, the bolts go through flanges at the base only rather than through the whole alloy coil body. In so doing this earth strap was moved to under the coil rather than on the top as originally placed. This morning she started OK - but only time will tell if its a real fix or yet another fix fail...

Thanks to all for the advice - looks like a thorough goig over of all earth bonding points is this weekends first task.

i had the coil pack replaced the one u described u fitted is the wrong un the one needed is listed as coil without module and the module is listed separately they are then fitted together and bolt through the body imo

the intermotor part numbers are 12621 dry coil and 15865 module i paid 21.31 and 29.46 respectively + vat

Thanks for letting us know

Normally these temp senders just die or give consistently duff readings. Mine died within 24 hours....went from running sweet as a nut to just plain dead, couldn't get it started. Turns out it had gone open circuit, thus telling the ECU it was -40C.

Thanks for letting us know

Normally these temp senders just die or give consistently duff readings. Mine died within 24 hours....went from running sweet as a nut to just plain dead, couldn't get it started. Turns out it had gone open circuit, thus telling the ECU it was -40C.

Hello everyone. I'm new to this site as I'm new to Polo's, but seem to be having the same starting problems with my 1991 Polo I recently bought. Could anyone explain this thing about 'blue temperature sensor'. Where do I find it in my car and where do I best look for replacement? Thanks alot.

Thanks for letting us know

Normally these temp senders just die or give consistently duff readings. Mine died within 24 hours....went from running sweet as a nut to just plain dead, couldn't get it started. Turns out it had gone open circuit, thus telling the ECU it was -40C.

Hello everyone. I'm new to this site as I'm new to Polo's, but seem to be having the same starting problems with my 1991 Polo I recently bought. Could anyone explain this thing about 'blue temperature sensor'. Where do I find it in my car and where do I best look for replacement? Thanks alot.

its at the front of the engine bay to the right of the head and lower than the head itself itl have a rad hose connected to it the bottom rad hose i think itl have wires and a 2 pin plug to it

In case others are suffering:

Damp wreaks havok with mine. (AAU engine) ... Leave it a day or 2 in the winter (sometimes over night) and it'll churn over for ages on the starter with no sign of life... A good dose of WD40 in all the electrical connectors shifts the damp out, and it'll start on the key again...

Just to say that about 1 week after my daughter went back to University the original fault reappeared yet again!!!

She took the car to a local VW specialist garage (not a VW main dealership!) who diagnosed a faulty Lambda probe.

These guys were extremely confident that given everything else that had been done this would sort the problem.

As luck would have it my daughter couldn't pick the car up on the Friday so it stayed with them until Monday.

She called them on the Monday morning to check all was OK and they said "Yes it's ready to collect".

Ten minutes later they called back to say "It won't start!"

The upshot was it was finally fixed by replacing the distributor as the Hall sender was only producing 6 volt pulses rather than 12.

Several weeks later I think I can safely pronounce it fixed at last. Mind you there's not much left to change...

That vw garage must be full of muppets, no way a faulty lambda probe would casue it to not start, the signal is ignored when the engine is cold!!

Plus all you have to do to diagnose a lambda fault is unplug it, if it gets better then you know lambda is faulty. Blue sensor is notorious for causing problems like this, similar thing happened on my MK2 GTI (exactloy the same sensor part) When cold no matter how long you held it on the starter it would never fire, then it would always start without fail the next time you try. New sender fixed it, best £13 you can spend :)

If it was the hall sender I'd expect the rev counter to behave erratically, though it sounds like it was only breaking up when cold?