[928uk] Slow cranking on hot restart issue

[jonathanrackowe at gmail.com]

Hi Simon,

 

I’ve started a new thread for your ‘Slow cranking on hot restart issue’, as I can’t see why Temp Sensor 2 should affect cranking speed.

 

The speed of the starter motor (unloaded) is affected by battery voltage and condition, but if anything the battery should be in a better state at hot restart. The load on the starter motor is of course the engine and ancillaries, but I don’t really see why a hot engine should be harder to turn over – if anything it should be easier because the oil is hot, although perhaps some clearances could tighten up when hot… ?

 

Temp sensor 2 affects fuel mixture enrichment and ignition timing through warm-up from cold. I can’t see fuel mixture affecting engine load on cranking. And ignition timing also seems doubtful to me unless so far out it was firing way before TDC.

 

Smiffy, Paul, anyone, have you got any ideas on this?

Best regards,
Jonathan

1991 928 GT Amethyst Metallic

 

 

 

 

From: Simon Painter <simonpainter101 at gmail.com> 
Sent: 02 June 2024 08:40
To: jonathan at rackowe.net
Cc: Paul <ukkid35 at gmail.com>; 928 List <928uk at lists.928.org.uk>
Subject: Re: [928uk] Cheap LH-Jetronic temp sensor II NTC2

 

The FAE Temp2 sensor reads:

 

20C - 5.3k

32C - 4k

46C - 2.4k

60C - 1.5k

70C - 0.93k

 

I was quite surprised how the Temp2 sensor affects starting. I have an ongoing issue with re-starting when hot, eg re-starting after filling fuel. It will turn over quite slowly compared to a cold start. One day after a fuel stop, I unplugged the Temp2 connector and just plugged in a new FAE sensor and left it hanging loose. The engine turned over really quickly! It didn’t want to start as it was probably running with a super rich mixture as the Temp2 sensor was cold and engine hot.

 

I’m pretty sure my original Bosch Temp2 sensor is causing my hot re-start issue but I have yet to find a good replacement that is in spec.

 

Thanks

 

Simon.

Check me out on Instagram and Facebook @oldcarfixer





On 1 Jun 2024, at 23:41, Jonathan Rackowe <jonathanrackowe at gmail.com <mailto:jonathanrackowe at gmail.com> > wrote:



What does your FAE one measure Simon?

 

Best regards 

Jonathan 

 

1991 928 GT Amethyst Metallic 

 

On Sat, 1 Jun 2024, 3:55 pm Simon Painter, <simonpainter101 at gmail.com <mailto:simonpainter101 at gmail.com> > wrote:

I’ve now bought two (one an FAE) and both measure way off what they are supposed to be. I’m trying to get gold of an original Bosch one.

Thanks

Simon.