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-   -   Cold start question (https://rennlist.com/forums/928-forum/1113094-cold-start-question.html)

yoni_d 11-19-2018 11:40 AM

Cold start question
 
Hi guys,

When the car starts, the RPM goes up and after some time go back down to idle RPM - as expected.
Can you please tell me which component (time switch + cold start valve or the WUR) is responsible for this RPM increase after cold start?
Just curious...
Thanks!

p.s: The car is 1980 4.7 manual.

checkmate1996 11-19-2018 11:42 AM

none of the above. Auxilary Air Bypass valve has a bi-metallic plate that heats up that shuts off the extra air thus lowering the RPMS...

yoni_d 11-19-2018 11:58 AM

Aha! great, thanks a lot :)

jpitman2 11-19-2018 05:16 PM

The time-temp switch controls how long the cold start injector fires. Aux air controls how much opening allows extra air in as it warms - gets heat from 12V and from heat conduction from the block. My cold idle went low a few years ago and was prone to stalling, so I opened it up - drilled out rivets. Bent the spring attachment until it was fully open in the fridge, close to closed when warm. Bolted up with M6 (?) bolts& nuts. Adjusted idle speed very cold ~1100rpm.
jp 83 Euro S AT 57k CIS

yoni_d 11-22-2018 11:26 AM


Originally Posted by jpitman2 (Post 15441924)
The time-temp switch controls how long the cold start injector fires. Aux air controls how much opening allows extra air in as it warms - gets heat from 12V and from heat conduction from the block. My cold idle went low a few years ago and was prone to stalling, so I opened it up - drilled out rivets. Bent the spring attachment until it was fully open in the fridge, close to closed when warm. Bolted up with M6 (?) bolts& nuts. Adjusted idle speed very cold ~1100rpm.
jp 83 Euro S AT 57k CIS

Thanks for the explanation!
My problem is that the cold start valve sometimes doesnt fire and the car wont start. So I am checking whether it is the time-temp switch or the voltage that is getting to the cold start valve is not 12V so it doesnt fully opens.

Mrmerlin 11-22-2018 02:15 PM

check the temp sensor that screws into the FRONT side of the water bridge,
NOTE make sure you see some voltage when you start the car from cold.
this send power to the cold start .
NOTE ref WSM for specific test protocol
also inspect the cold start injector connector for power ,
you need to rig a test pin,

to do this get some thin strand copper wire then add some solder to a peice,
then with a hammer tap the soldered wire onto a flat surface,
this will make a flat pin to insert into your AMP connector,
then it can be attached to your test light .

jpitman2 11-22-2018 05:20 PM

The cold start 'valve' is an injector (front of spider) - check that its seeing fuel pressure - carefully. And that it sprays when powered - you might be able to feel it open if you hold it.
jp 83 Euro S AT 57k

yoni_d 01-15-2019 03:49 PM


Originally Posted by Mrmerlin (Post 15448645)
check the temp sensor that screws into the FRONT side of the water bridge,
NOTE make sure you see some voltage when you start the car from cold.
this send power to the cold start .
NOTE ref WSM for specific test protocol
also inspect the cold start injector connector for power ,
you need to rig a test pin,

to do this get some thin strand copper wire then add some solder to a peice,
then with a hammer tap the soldered wire onto a flat surface,
this will make a flat pin to insert into your AMP connector,
then it can be attached to your test light .

I had no idea I forgot to reply on that. Thanks for the tip! I will perform the test during this weekend and hopefully find the problem. By the way, the temp switch you mentioned is the time switch right? Because the temp switch is only for showing the engine temperature...am I wrong here?

yoni_d 01-15-2019 03:52 PM


Originally Posted by jpitman2 (Post 15448943)
The cold start 'valve' is an injector (front of spider) - check that its seeing fuel pressure - carefully. And that it sprays when powered - you might be able to feel it open if you hold it.
jp 83 Euro S AT 57k

I removed, cleaned and checked the cold start valve and it works fine. Perhaps it doesn't get the proper voltage when I try to start the car... Planning to do some tests this weekend and finally find the problem. Thanks for the advice and so sorry for the late reply.


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