My dad's Octy has recently developped a starting issue, but it only appears to happen when warm / not stone cold.

 

Battery is fine and starter motor turns without any issue in all cases.

 

When cold / first thing in the morning, it starts absolutely fine.

 

When warm, after a 20 minute + drive, it won't start. Starter motor turns properly, but it doesn't fire up.

 

When it happened first time, RAC came out to look at it and said everything (superficially and visibly) looked OK, and when we went to start it, it fired up straight away. My dad was a little embarassed about it, but as he had to wait a couple of hours for the RAC to turn up, the engine had cooled down.

 

He then took it to a garage and they charged £70 + VAT just to do a scan on it and it did come up apparently with a cam belt / crank case sensor problem. Unfortunately, they cleared it without checking date / mileage when it happened so I don't know if it's a recent fault or a one-off that might have happened 6 months ago and be unrelated. Naturally, he hasn't gone back to get it checked again and I'm not nearby to do a VCDS scan to see for myself.

 

This morning, it's happened again: started fine when cold, went 10 minutes down the road, then it wouldn't start, just turn over fine but not fire up. He's just texted me to say it's started fine now after leaving it for an hour or so.

 

Car has been regularly serviced and remapped. It runs absolutely great.

 

The only thing I can think of is the possibility of some dodgy fuel - I once put some unleaded in my 1.9 Fabia vRS and it started fine cold, but struggled when warm. He's pretty sure he's not accidentally put in unleaded though.

 

So any ideas on what to check?

 

Thanks

I'd say the cam sensor sounds like the likely culprit. It's quite a common failure mode to only stop working when it gets hot and work fine once it has cooled down.

Next time it does it there should be a fault code stored.

In the german forum they say,necessary to raise up the warmstart engine map range.sorry,Don t know if thats the correct technical term

Coolant temp sensor, battery and starter can all cause hot start problems.

When hot the engine needs to turn over at a certain number of revs before fuel is injected, but from cold fuel injection starts immediately. So a poor battery or lazy starter can seem ok but cause problems.

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I'd say the cam sensor sounds like the likely culprit. It's quite a common failure mode to only stop working when it gets hot and work fine once it has cooled down.

Next time it does it there should be a fault code stored.

I'll look out for it when I next see him / the car. What would an apparently failing cam sensor have though as an impact? I mean what would it be doing or not doing that would cause the engine to turn over but not start?

 

In the german forum they say,necessary to raise up the warmstart engine map range.sorry,Don t know if thats the correct technical term

It's been a while since the car was mapped and it's been running fine since, so I doubt it's an ECU tuning requirement.

 

Coolant temp sensor, battery and starter can all cause hot start problems.

When hot the engine needs to turn over at a certain number of revs before fuel is injected, but from cold fuel injection starts immediately. So a poor battery or lazy starter can seem ok but cause problems.

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I haven't heard it myself, but I doubt it's the battery. It apparently cranks absolutely fine. When it first happened and he tried several times, it was only like after 10 minutes that the starter motor was starting to dip in speed due to battery drainage. Plus it started absolutely fine in -5 deg temps which is a normal indication of a dieing battery.

When my car's battery was dying it started fine but beeped and flashed the steering and esp lights when you turned the ignition off.

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I've had my fabia do that. Sometimes power steering won't work properly, light stays on.

 

But none of that on his - it looks and behaves as it should except for the fact it doesn't start.

 

My guess is that it's more likely to be a sensor / mechanical thing that is impacted with temp than an electrical (immobiliser?) or ECU mapping gremlin.

 

I didn't pick up on your coolant sensor problem. How might that manifest itself? Same sensor as that which gives temp on dash? My guess is it doesn't need to be running long from cold for the problem to occur, so engine hasn't fully warmed up and still the problem happens.

 

Could it be a fuelling issue?

I've had my fabia do that. Sometimes power steering won't work properly, light stays on.

But none of that on his - it looks and behaves as it should except for the fact it doesn't start.

My guess is that it's more likely to be a sensor / mechanical thing that is impacted with temp than an electrical (immobiliser?) or ECU mapping gremlin.

I didn't pick up on your coolant sensor problem. How might that manifest itself? Same sensor as that which gives temp on dash? My guess is it doesn't need to be running long from cold for the problem to occur, so engine hasn't fully warmed up and still the problem happens.

Could it be a fuelling issue?

IIRC the Cts is dual circuit, one goes to the ecu and one to the dash. One can go wrong but the other can be fine. So the dash can read the right value but the ecu gets something else.

If the Cts is telling the ecu the coolant temp is higher than it actually is or lower then weirdness can ensue.

Unless the Cts starts reading stupid values you won't necessarily get a fault logged.

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I have just seen another case very similar to this. The car started like a diesel from a gone by era 1 cylinder, 2 cylinders , 3 cylinders and then leapt into life. The starter motor appeared to turn the engine over without problem. However I was still suspicious and as it was a few years old (5+ years) I told him to get it changed as a matter or course. He took it to a friend who runs a battery shop, they tested the battery and found it to be faulty. He replaced the battery and car now start easily when hot or cold. 

 

I like to rule out the simple stuff first. Here is what I would do

 

1. Discount the battery as being the problem by attaching it to another car via jump leads when warm and see if it make any difference to starting. Keep the slave car running.

2. Do a VCDS scan for the faults next time you over that way and do some measuring blocks(Temp sensor).

3. Consider starter motor (could it do with a refurb), what mileage has engine (more specifically the stater motor done - has it been used for a lot of stop / start etc)

 

The symptoms you describe sound like a battery problem and I would definitely focus my attention there, a new battery can be had for around £46 delivered.

 

http://www.ebay.co.uk/itm/VW-PASSAT-1-9-TDI-DIESEL-CAR-BATTERY-096-100-12V-HEAVY-DUTY-SEALED-24HR-DEL-/111829890321?hash=item1a0994b511:m:msGo6HpRBz0wwd2GvD5m6Hw 

I had the cam sensor go on my long sold 2.0PD140 Superb MK2.. Same symptoms, starts perfectly when cold but very difficult when warm.

 

The car will start when warm, but you must crank it for quiet sometime, a LOT longer than usual.

 

VCDS may not log any faults, as the car may think the sensor is working correctly. When the engine is cold, the ECU uses the crankshaft sensor to work out the ignition timing, when warm it uses a combination of the cam and crank sensor. When starting warm, the car will failover to crank sensor only when it realises something is wrong but that takes a lot of juice, on my superb it could be cranking for 30seconds or more before it started when warm.

 

Replaced camshaft sensor, quiet easy job and it was perfect afterwards.

Edited 14 March, 201610 yr by mannyo

I had the cam sensor go on my long sold 2.0PD140 Superb MK2.. Same symptoms, starts perfectly when cold but very difficult when warm.

 

The car will start when warm, but you must crank it for quiet sometime, a LOT longer than usual.

 

VCDS may not log any faults, as the car may think the sensor is working correctly. When the engine is cold, the ECU uses the crankshaft sensor to work out the ignition timing, when warm it uses a combination of the cam and crank sensor. When starting warm, the car will failover to crank sensor only when it realises something is wrong but that takes a lot of juice, on my superb it could be cranking for 30seconds or more before it started when warm.

 

Replaced camshaft sensor, quiet easy job and it was perfect afterwards.

My next step after the obvious ones would be to do the cam sensor. Good advice.

Thanks Trundlenut and Manny

Eliminating the batter as a culprit is a great idea, something I'll suggest and easy to test first. Then it's looking at the cam sensor which, if a fault was logged, sounds very plausible too.

Hello all, I recently purchased a Pd140 Octavia 2 Elegance from available car in castle donnington and it had the warm start issue (started fine when the engine wasn't up to temperature, but when it was, it turned over excessively before eventually firing up).

They've replaced the cam position sensor today under warranty and the problem disappeared straight away. The car was showing this sensor at fault though which was a good starting point!

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Edited 23 March, 201610 yr by AshVrs