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Hot start issues / vapour lock / something else? [updated]

ch3tman

Well-known member
Joined
8 Dec 2012
Messages
1,079
Anyone experienced so called 'vapour lock' on a 993?

After a long run >45min, in hot weather conditions ~30degreesC, turning the engine off and then attempting to restart within a few minutes results in a failed start: starter turns per normal but engine doesn't fire. Waiting ~30 sec, going through the immobiliser cycle, and trying a second time results in success with no hesitation. This has only happened 4 times in 4 years - all this summer! Incidentally, a cold start is always fine.

Searches for hot start issues tend to point to the starter motor being on its way out, but it seems to turn over just fine. Trusted indy has suggested vapour lock, so will have this tested for during the next visit.

Would be good to know if others have experienced anything similar?
 
I have a spare DME you can try to rule out this as a possible issue.
 
I would change the earth strap - the route of all evil and cheap to fix ......
 
Happened to me in Spain about eight years ago when it was extremely hot and I had filled the tank to the brim ....... nothing .....couldn't start the car ....... then a memory from the dim and distant past came to mind of when I was running a VW Beetle and had much the same problem and I loosened off the filler cap and the car started first turn of the key ....... did the same on the 993 and likewise the car started immediately ...... perhaps that might of some help for others down the line ...... :)
 
I've had exactly the same recently especially if the car has been out in the sun and I've no rear blower so the engine compartment gets pretty hot.
 
Sutton said:
I have a spare DME you can try to rule out this as a possible issue.
I appreciate kind your offer :thumbs: I also have a spare DME but never really know when this issue is going to occur (its not consistent or frequent but crucially starts just fine on the second attempt). If I could reproduce it I could easily test between DMEs.

ColinC said:
I would change the earth strap - the route of all evil and cheap to fix ......
Thanks! Will do this for piece of mind.

Endoman said:
I've had exactly the same recently especially if the car has been out in the sun and I've no rear blower so the engine compartment gets pretty hot.
Yes, it's only happened in this heatwave the UK is currently experiencing - or the one I experienced on a recent Euro roadtrip. In normal, milder conditions, it's never been an issue. Given you're rather clued up mechanically :wink:, are you generally accepting of this phenomenon or doing anything to investigate/address it? if so, what..? :) If it's considered normal, I'll be content to live with it.
 
I had the same problem during a tour of Scotland during a spell of particularly clement weather a few years ago.

A DME relay change soon sorted that starting issue.
 
All very strange, I blasted up to Tetbury on Friday, parked for a meal . . . two and half hours later, started the car no problem and drove to my son's house about six miles away, parked for twenty minutes and then . . .

No start!

Swapped the DME relay and all was well.

What I need to do now is swap the DME relay back to confirm it was the DME relay not any other 'vapour lock' or whatnot. (Except I hear that dodgy relays can repair themselves, hot or cold solder in the innards or something)

Funnily enough my last words to my son before turning the key were "these engines are bulletproof. . ."


:bandit:
 
HPNer said:
What I need to do now is swap the DME relay back to confirm it was the DME relay not any other 'vapour lock' or whatnot. (Except I hear that dodgy relays can repair themselves, hot or cold solder in the innards or something)
It's got to be related to this recent hot weather! Though since creating the thread I've tried to reproduce the issue several times (with the same/original DME), unsuccessfully. Starts every time, without hesitation... :lol:.
 
Without tempting fate :what: , I think I can update this post with the cause/fix (although time will tell!).

How frequently was this happening?
  • In the last 26 months: observed 6, maybe 7 times.
    Most often at a petrol station; the most embarrassing place :lol:.
Under what circumstances was it happening?
  • After the car has been running hot for a while (25min+, oil temp 9 o'clock & above)) in hot temperatures (25c-30c+). Turn off. Come back to it after 10-15min and it will fail to start on the first attempt, instead just stutter.
  • Mild temps did not cause the same behaviour, hence difficult to reproduce in the 'normal' UK climate
  • Note, placing a blanket over the spoiler grill, to force high temps to build, did not appear to allow us to replicate the issue on
  • Note, cold engine starting never an issue, regardless of ambient temperatures
What was investigated?
  • New DME - no luck
  • Fuel pressure test - all good - no luck
  • New Bosch supplied refurbed starter motor - no luck
  • New battery Earth strap - no luck
  • New gearbox Earth strap - no luck
  • New Cylinder Head Temperature Sensor - :)
  • >>> Next up was going to be: new flywheel reference sensor, then looking at the ignition side of things (ignition coil, HT leads, caps and rotors), before a deeper dive on the fuelling (starting with fuel pressure regulator) despite the fuel lines holding as expected.
Interestingly the fault codes did not flag anything during testing across the 2 years either.

The following thread, amongst others, proved to be very helpful, too:
https://rennlist.com/forums/993-forum/1187096-new-to-me-97-rasberry-red-metallic-c2s.html

Testing during the few lockdown heatwaves have been promising. Fingers crossed all remains well.
 
Hi mate can you give me the part number for the sensor have a similar issue with mine thx
 
ch3tman said:
Without tempting fate :what: , I think I can update this post with the cause/fix (although time will tell!).

How frequently was this happening?
  • In the last 26 months: observed 6, maybe 7 times.
    Most often at a petrol station; the most embarrassing place :lol:.
Under what circumstances was it happening?
  • After the car has been running hot for a while (25min+, oil temp 9 o'clock & above)) in hot temperatures (25c-30c+). Turn off. Come back to it after 10-15min and it will fail to start on the first attempt, instead just stutter.
  • Mild temps did not cause the same behaviour, hence difficult to reproduce in the 'normal' UK climate
  • Note, placing a blanket over the spoiler grill, to force high temps to build, did not appear to allow us to replicate the issue on
  • Note, cold engine starting never an issue, regardless of ambient temperatures
What was investigated?
  • New DME - no luck
  • Fuel pressure test - all good - no luck
  • New Bosch supplied refurbed starter motor - no luck
  • New battery Earth strap - no luck
  • New gearbox Earth strap - no luck
  • New Cylinder Head Temperature Sensor - :)
  • >>> Next up was going to be: new flywheel reference sensor, then looking at the ignition side of things (ignition coil, HT leads, caps and rotors), before a deeper dive on the fuelling (starting with fuel pressure regulator) despite the fuel lines holding as expected.
Interestingly the fault codes did not flag anything during testing across the 2 years either.

The following thread, amongst others, proved to be very helpful, too:
https://rennlist.com/forums/993-forum/1187096-new-to-me-97-rasberry-red-metallic-c2s.html

Testing during the few lockdown heatwaves have been promising. Fingers crossed all remains well.

Could it be as simple as a relay sticking with heat? Maybe take fuel injector relay (metal cased one) out and see it's working as expected.

Also (and this is a bit sad) I took all my no 53 relays out the other day and tested their resistance when circuit is closed (applied voltage with 9v battery and crocodile clips) all were acceptable but those that were most 'out' I put in less imported slots like sunroof and fog lights. Perhaps it's minor solder cracking issue made worse by heat.
 
Gwsinc - thanks for remembering and posting :thumb:, however...
The reason for me resurrecting this thread earlier this month, was sharing what appears to be 'the fix'! :thumbs:

Surinder Randhawa said:
Hi mate can you give me the part number for the sensor have a similar issue with mine thx
It's in the Rennlist link.
 
Re: Hot start issues / vapour lock / something else? [update

ch3tman said:
After a long run >45min, in hot weather conditions ~30degreesC, turning the engine off and then attempting to restart within a few minutes results in a failed start: starter turns per normal but engine doesn't fire. Waiting ~30 sec, going through the immobiliser cycle, and trying a second time results in success with no hesitation.
Failing throwout gear on the starter could present like this.
Another possibility is flywheel missing some teeth so it fails to engage correctly with the throwout gear and the starter just spins freely.
 

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