V5 Bora hot starting problem

[pdhamblin]

Hi,
Firstly, many thanks for all the wealth of info on the forum, it’s been really helpful.
I have a V5 Bora registered in 2000 and up to the last few weeks it’s been a really good, reliable car although having 102K on the clock. Recently, I’ve had a hot start problem that I’d like to pin-point without spending a load of money on changing a number of possible “suspects”. Currently:-

The car always starts when cold
After switching the engine off when hot, it will immediately start again on ignition
When switching the engine off and returning after 30-60 mins, it turns over but no ignition
After leaving it for 30 mins it starts OKI booked it into the garage during the week and the diagnostics didn’t throw up any errors although the guy said that it may be an engine speed sensor problem. They kept it running at the garage to see if they could replicate the fault and at one point it cut out, after which there was no spark at the plugs. After it cooled, it started OK.
I had the car back yesterday, but it stalled at a junction and wouldn’t start again. After leaving it for 30 mins it started OK. A couple of observations that I noticed that hadn’t happened before were:-

When first started, although idling was fine, pulling away was erratic and jumpy for the first minute, after that it was fine. That was repeated this morning.
When warm, I noticed that the temperature gauge went down to zero and then slowly back to 90 deg. It did this a few times.My nephew attached his set of diagnostics this morning and the only error that came up was “Commanded Secondary Air Status”. The Coolant Temperature Sensor reading was fine.
From the forum, I see that the possible problems could be a coolant temperature sensor, battery, alternator, fuel relay, crank position sensor or engine speed sensor and I’d really appreciate any pointers.
Today, I looked at buying the Haynes manual for the 2000 Bora but it didn’t include the V5 engine. Is there a manual available that covers the V5?
Where is the Coolant Temperature Sensor on the V5?
Other observations that may help are:-

Engine type is AGZ
I noticed that the vacuum tube from the top of the engine, when hot, seems too pliable and looks like it was collapsing.
Charging voltage is 13.95V
Battery voltage is 12.25V
Many thanks

Paul

[kenney]

Hi I think the temp sensor would be a good place to start,it is on the thermostat housing at the flywheel end of the engine

[pdhamblin]

Hi I think the temp sensor would be a good place to start,it is on the thermostat housing at the flywheel end of the engine

Thanks kenney, I'll replace the sensor and the collapsed vacuum tube and take it from there.

Cheers

Paul

[pdhamblin]

Hi,

Here's an update on my V5 Bora hot starting problem:


Fitted a new coolant temperature sensor on Monday (special thanks to the forum tip of tying a piece of cotton to the circlip so you can pull it out after you drop it!)
Car started up OK, drove for 15 mins and everything seemed fine
Turned off ignition, tried starting immediately, again after 5 mins and again after 15 mins and all seemed OK
Needed to use the car around an hour later and it wouldn't start.
After leaving it for 30 mins started OK
Picked up the new vacuum tube last night and replaced the collapsed one
Again, all OK on start up, and also after 5, 10 and 30 mins
Start OK this morning, and not as erratic as it had been
Drove for 10 mins had to stop to drop something off, returned to car after 3 mins and it wouldn't start again (suppose I should have left it runnung - ain't hindsight a wonderful thing!)
Sat in car trying to start it every now and then and after 25 mins it started.I know that these intermittent faults can be a pain to diagnose, but if anyone has any idea where to look next it would be much appreciated.

Thanks

Paul

[kenney]

Hi there are so many possibilitys here,you can start with one that wont cost you.Remove the multistick contact on the ECU (plenium chamber) and check the pins for corrosion.Trusting that a faulty engine speed sensor would show up on a diagnose,we can forget about it for the time being. Next time the engine wont start measure the voltage on fuses 10 and 29 while trying to start the engine to see if maybe you have a faulty ignition switch.

[pdhamblin]

Thanks kenney for a few more things to check out on the Bora

Further update on the hot start problem is:-

ECU connector pins seems fine, no corrosion
Engine did stall on tick over, and wouldn't start again - measured voltages on fuses 10 & 29 and voltages were present
On tick over yesterday, did notice that engine stalled a few seconds after cooling fan kicked in and then wouldn't start again for at least 45 mins
Did this again this morningAlthough the engine speed sensor didn't show up as a problem when put through the diagnostics, could this possibly be breaking down under temperature? Have been quoted £86 for a new one. Perhaps it would be best to get it back into the garage for more diagnostic checks before changing any more bits.

Would welcome any further ideas

Thanks

Paul

[buju]

I was searching for something else , but I couldn't resist regestering and posting my experience ....as i also have a Jetta V5 20v ( 180k kms) and have been a VW nut for years ....

It could be the fuel pump , i know it sounds unrelated to the electrical ideas , but try this:

when you unlock your car and open the drivers door you should hear the pump initialize (buzzing sound) , IE come on for a few seconds then stop , this primes / pressurizes the fuel system.

Now next time your car wont start , get out , close the door , activate the remote lock , then unlock , open the drivers door and listen if the pump comes on for a few seconds. If it doesn't then that is probably your problem.

hint: put your head / ear near the ground , as close to under the car as possible and then reach up and open the drivers door, or get someone to help you with this.

Ive seen this before ..... when the fuel pump gets "old" they tend to "stick" when warm or hot , this would explain why your car cut out when it was in the shop ( a warmer ambient temperature)

[kenney]

Hi Bujus post is a good idea,but you maintain when the problem occurs you have no spark.This is one of the worst jobs a mechanic can get,you are working in the dark,so to speak and only guessing.Anyway i have 3 things i can help you with that wont cost you anything.Checking engine speed sensor, and hall sender and the one i fancy is the culprit checking coils with final output stage, You need to send your e-mail address as it is fair bit of info.

[pdhamblin]

Hi buju,

Thanks for the post on checking the fuel pump. Hopefully, I can get it to fail tonight and check it out.

I normally hear the pump come on for a few seconds anyway, but when it's been failing it hasn't been something I've checked.

Hi kenney,

Thanks for your post re engine speed sensor, hall sensor and coils and I'm happy to give anything a try at the moment. I'll send across my email information under separate cover.

Thanks

Paul

[paulthomas75]

I have the same issue with my 2000 Polo and it's really beginning to upset me!

Looking to sell the car but can't pass on in good faith with this issue hanging over it.

My fuel pump comes on but like you I've not checked it when I have a starting issue. I usually wait for the sound to end anyway.

Please let me know if you had any joy.

Cheers,
Paul

[pdhamblin]

Hi Paul,

After spending a lot of time and money on the V5 Bora I did decide to part-ex it with the knowledge of it's condition.

Although I initially enjoyed trying to track down the fault with help from the guys in the forum, unfortunately,the frustration and unreliability, coupled with the lack of V5 manual and equipment meant that I reluctantly had to come to this decision.

Have since found out that the problem was the crank sensor and it wasn't a job for the faint-hearted as it took about 3 hours to remove and replace.

Hope this helps and best of luck with tracking down the problem.

Regards

Paul Hamblin

[ralgex]

just thought i would let you know that my bora has EXACTLY the same prob....v.frustrating

[pdhamblin]

Hi ralgex,

Sorry to hear that your Bora has the same problem and sympathise with your frustration.

Obviously, there seems to be quite a few different type of faults that can cause the intermittent hot start problem.

Have you had any diagnostics run?, as this may eliminate some of the faults.

Afraid I can't be of much help now although with my little experience, a faulty crank sensor has got to be a possibility.

Best of luck with sorting it out.

Regards

Paul Hamblin

[bomicha9]

Hi buju,

Thanks for the post on checking the fuel pump. Hopefully, I can get it to fail tonight and check it out.

I normally hear the pump come on for a few seconds anyway, but when it's been failing it hasn't been something I've checked.

Hi kenney,

Thanks for your post re engine speed sensor, hall sensor and coils and I'm happy to give anything a try at the moment. I'll send across my email information under separate cover.

Thanks

Paul
Hi. i seem to have the same problem. i have a 2000 vw Bora tdi. it struggles to start when the car is warm!!
have you replaced your fuel pump yet?
Regards
Michael

[Bobjuana]

Not sure whether related, but I searched these forums before having my Hot Start problems resolved so thought i'd respond in case it's of use to anyone in future.

I have an '08 Leon FR TDI 170, and for a few weeks have had a problem with the engine not firing up when warm/hot. Started fine when cold i.e. first thing in the morning, but if returning to the car after recently driven, the starter motor would attempt to fire the engine up, but it wouldn't catch and the engine would begin to judder etc (was waiting for 40 mins in Asda carpark before I could get it started the other day!).

Anyway, took into my local Seat dealer today, who have fitted a new Hall Sender/Cam Position Sensor (apparently took them around 3 hours) - and seems to have resolved the problem.

Hope this helps....

[vwlt35]

hi, have you changed you coils? my previous car had a simmilar car and would only start when cold. once warm and switched off it would not start again until its cold again. I changed the coil pack and solved the problme

[riverwhy]

relay 109 would seem to cause this kind of problem on the diesel boras. it's underneath the fuse box