Hard to start the engine when hot. (BKD engine)

49 posts in this topic

If the engine temperature reach 90 degrees is difficult to start it again. This is happening just at 90 degrees. If the coolant has less then 90, the engine starts fine. Also the "magic eye" on the car battery is black. Is it possible to fix this problem by changing the battery?

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Quite a few threads on this, try a search.

A lot of members (finally) traced it back to a worn/faulty starter motor.

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If the starter motor is the problem, why the engine starts fine when is cold?

Address 01: Engine Labels: 03G-906-016-BKD.lbl

Part No SW: 03G 906 016 HF HW: 028 101 139 1

Component: R4 2,0L EDC G000SG 8658

Revision: 12345678 Serial number: SKZ7Z0E2851075

Coding: 0000072

Shop #: WSC 24059 576 91804

VCID: 6EFD19010007

No fault code found.

Readiness: 0 0 0 0 0

I will change the coolant temp sensor and the battery and I'll be back to tell you the results! :)

Edited by Octavia MK1

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Hello mate,

I had the same problem earlier in the year. The car would start fine when cold, however after a run when the engine was up to full temperature, it would fail to start.

This manifested itself in the engine making a hell of a rumbling sound and almost a thump when attempting to turn it over. I changed my battery & everything has been fine since.

Hope this helps.

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If the starter motor is the problem, why the engine starts fine when is cold?

This is the exact same question raised on the many other 'hot starting' related threads.

It's one of the last places you'd look but more often than not it appears to be the main cause of fault.

A tired battery again has also been responsible for lots of weird and wonderful problems on the Octavia, some that you would never link back to the battery.

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If the starter motor is the problem, why the engine starts fine when is cold?

I believe when the engine is hot, it has to attain a certain RPM (200 rpm or so) when cranking before the ECU starts injecting fuel. When cold this logic is not applied by the ECU.

Hence worn starters and old batterys causing hot start problems.

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Interesting post.

I have noticed with my newly acquired Octavia the same thing. It starts when hot, but always needs a three second spin and starts with a clunk. When cold it starts immediately.

I believe when the engine is hot, it has to attain a certain RPM (200 rpm or so) when cranking before the ECU starts injecting fuel. When cold this logic is not applied by the ECU.

Hence worn starters and old batterys causing hot start problems.

This sounds logical.

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mine starts when hot with the same "clunk" noise. Is there any problem if I buy a battery with 74 Ah instead of 64 Ah which is the indicated one? I hope the fuses will be fine! :D

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In looking at this problem I decided to take advantage of KwiK Fits free battery and alternator test.

The system came back with: battery in good condition, 90% start capacity, 540 A, regulation 14.2 volts, alternator ripple too high. Not sure what the latter may indicate, possibly that the rectifier pack is on its way out??

However, I don't think its the battery at fault for the hot start problem.

Further research has indicated it might be the temperature sender out of spec - so may change it. They can be had for about £10 off ebay. If the temp sensor is giving a slightly out of spec signal to the ECU, it could effect the hot start process.

I noticed that during a hot start, there is no discernible sluggish crank speed. The started motor seems to spin well enough. So temp sensor may be worth trying.

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yes, we can try with the sensor. Two days ago I've disconected this sensor and the engine started just fine but the radiator fan was spining all the time and the glow plugs lights up in the dashbord for 2-3 seconds. ( G62 just below the Tandem Pump. You have to take off the air filter cover to see this sensor). How can a sensor do this problems without an error code on the ECU? Excuse my bad english! :-P

Edited by Octavia MK1

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Hi Octavia 1, I don't know the answer to the question you pose. Perhaps the error code is set due to failure.

However if above a certain temperature, the ECU looks for a crank speed proportional to temperature sensed, and the temp sensor is reading high, then this might be a reason, as pointed out by Brooke23. However changing the sensor might be a low cost "try it and see" experiment. So it is located below the air filter box, thanks for that.

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I find if you turn the ignition on and depress the acelerator pedal briefly, then start the car works for me

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Hi

I have a copy of VCDS light which only allows very basic use - but allows monitoring of the engine controller. I just started her up and let it run untill normal temperature acheived. I then recorded the following results:

Fuel temp G81 61.2 deg C

Intake Air temp G72 30.6 deg C

Coolant Temp G62 81.2 deg C

Not sure what these readings should be, but I would have thought G62 possibly a bit low - but then again it is a diesel and they do tend to run cool.

Now does the ECU use the coolant temperature, or the fuel temperature when doing a hot start??

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I've found something interesting about the cooland temp. sensor:

ECT - Engine Coolant Temperature (sensor)

What is it? This is small electrical device for measuring the coolant temperature in the engine

Where is it located? It is usually located on the engine near to the thermostat housing. The ECT is sited on the 'hot' side of the thermostat so that it senses the coolant/engine temperature before the thermostat opens and allows coolant to flow through the radiator.

How does it work? Modern temperature sensors consist of a thermistor in a sealed unit. As the temperature rises the electrical resistance varies proportionately; some thermistors increase their resistance with temperature (PTC - positive temperature correlation) whilst others decrease their resistance (NTC - negative temperature correlation). When the engine is cold at start up the coolant sensor sends an appropriate signal to the ECU. The ECU responds by increasing the length of the injection cycles to enrich the combustion mix. This is an electronic equivalent of pulling the 'choke' out on a carburetor. As the engine warms up the signals from the coolant sensor cause the ECU to shorten the injection cycles making the fuel mix progressively leaner. The process of coolant sensor and ECU interaction explains why engines have a slightly faster idle when starting cold than when running hot.

Symptoms of faulty coolant sensor

Associated OBD2 error codes DTCs: P0115 - P119; P0125, P0126, P0128

  • Poor starting - If the coolant sensor reports in error that the engine is warm the ECU will not enrich the fuel mix at ignition. The engine will falter at idle if it is not given additional help by the driver by pressing on the accelerator pedal to maintain speed. Once the engine has warmed up the engine will behave correctly.
  • Fast/erratic idle, Poor fuel economy - conversely if the coolant sensor reports in error that the engine is permanently 'cold' the ECU will keep the fuel mix rich. This is OK at start up but will become more noticeable when the engine is hot; idle will be fast and lumpy. Fuel consumption will be high due the permanently rich fuel mix set by the ECU.
  • Excessive emissions - the enriched fuel mix delivered in response to ECT signal error causes the exhaust to be heavy in un-burnt hydrocarbons. This often results in 'emission test' failure.

How to check? Most often the coolant sensor is quite separate to thetemperature sender, so a correct read-out on the dash board does not necessarily indicate correct sensor function. Using a voltmeter the resistance across the electrical terminals on the sensor can be measured. By removing the device from the car and putting the end of the sensor in a pan of hot water it should be possible to see an immediate change in resistance, it does not matter so much that the resistance goes up or down but that there is a discernable change with change in temperature. Generally high resistance equates to cold temperatures and vice versa. If there is no resistance change commensurate with temperature change then the sensor is at fault. If there is simply no resistance measurable (open circuit) then the sensor is at fault. If the sensor is working correctly check the connector, the wiring and the wiring insulation for faults and possible shorting.

How to fix? Replace if found faulty

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yes, we can try with the sensor. Two days ago I've disconected this sensor and the engine started just fine but the radiator fan was spining all the time and the glow plugs lights up in the dashbord for 2-3 seconds. ( G62 just below the Tandem Pump. You have to take off the air filter cover to see this sensor). How can a sensor do this problems without an error code on the ECU? Excuse my bad english! :-P

That's normal. Unplugging the temp sensor will cause the ECU to default to its cold start setting, and thus ignore the engine cranking speed and start fine. It doesn't mean the temp sensor is faulty, unplugging it is just hiding the symptoms of a (probably) slightly worn starter motor and/or bad battery.

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My superb MK2 PD140 suffered from a hot start problem, it would often take a long time turning over before it fired. After putting up with it for a long time, a sensor which was giving off duff reading finally decided enough was enough and the Check Engine light came on. After replacing the camshaft position sensor, which had finally given up the ghost all was well, the car started first time quickly both cold and hot. The camshaft position sensor is dead easy to change, and cheap to buy on ebay, I am no mechanic and managed it in 10 mins.

A faulty sensor can still give the wrong signals within range so the ECU thinks they are correct, and its only when it fails completely or gives signals out of range does a fault light come on.

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The plot thickens !

My superb MK2 PD140 suffered from a hot start problem, it would often take a long time turning over before it fired. After putting up with it for a long time, a sensor which was giving off duff reading finally decided enough was enough and the Check Engine light came on. After replacing the camshaft position sensor, which had finally given up the ghost all was well, the car started first time quickly both cold and hot. The camshaft position sensor is dead easy to change, and cheap to buy on ebay, I am no mechanic and managed it in 10 mins.

A faulty sensor can still give the wrong signals within range so the ECU thinks they are correct, and its only when it fails completely or gives signals out of range does a fault light come on.

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So, Mannyo where is this camshaft position sensor on a BKD engine? I know it should be near the cambelt but can you give us some more details please? This is interesting! :D:) Thanks!

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Hi Flyerphil!

I have good news! :) The "hard to start when hot" issue just disappear! I've got a brand new Varta battery for 90 pounds and now the engine starts fine. I will also change the starter motor because it has 110.000 miles now and a new one cost less then 200 pounds and easy to fit on the car!

I hope this will help to solve your problems too!

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Well that's good news.

It seems that a new battery that's giving 100% starting efficiency fixes the problem. Other people have reported this too.

Can I ask Octavia mk1:

1) do you know when the battery was last replaced on your car?

2) does it seem to spin the starter motor faster now with the new battery when hot starting

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Hi!

I think the battery on my car has never been replaced.It was 7 years old :)) Skoda recommend for my car a 61Ah-330A battery but to be honest I think this is not enough. Now I've got a 74Ah Varta and I think is brilliant.

In the boot, on the left hand side of the spare wheel you will see a sticker. You can find the same sticker on the first page of the Skoda Owner Manual as well. Go to http://vag-codes.inf...ption-codes.pdf and check the codes to see what options do you have on your car. You can find in there the type of the battery as well.

Yes, the starter motor is spinning faster now and the engine starts like a normal diesel engine. I'm happy now and I love my car! :))

All I need now is a new A/C Compressor. :) Very expensive...

Edited by Octavia MK1

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I think mine may be original also - its an AKUMA CZ UM5 part no 1JO 915 105 AD - but I cant find any date code. The 'magic eye' is almost black with a feint green just discernible. The Kwik Fit check reckoned it was OK though, so it may have already been replaced.

Still you are right, the recent batteries are more powerful and may give much better performance and are not that expensive.

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:) Yes, Flyerphil! That's the original one! This is the one I had on my car and I couldn't start the engine anymore yesterday morning! Just got rid of it! :)

post-75422-0-86865600-1344287836_thumb.jpg

Edited by Octavia MK1

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:) Yes, Flyerphil! That's the original one! This is the one I had on my car and I couldn't start the engine anymore yesterday morning! Just got rid of it! :)

Yup, same as mine. I replaced it at almost 8 years. It was still starting (usually) but I had one or two moments where it was a little worrying. Time to replace. £62 from ECP with the forum discount delivered to my (neighbours) door.

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do anyone know where can I find an alarm horn H12 at a reasonable price?

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