Cold Start Valve

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13 Jan 2021 14:09 #21697 by mike@lemons.com
Cold Start Valve was created by mike@lemons.com
1980 928S (ROW)
Trying to locate the cold start valve. I think I found it under the passenger side spider but it looks like it has more than one fuel line. Does someone have a picture of where it is located? Thanks

Mike

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13 Jan 2021 20:46 #21698 by joejabq
Replied by joejabq on topic Cold Start Valve
Hi Mike. I think that 1980 928S ROW are 16V 4.7L K-Jetronic systems.
Is that right?
If I got that right, the cold start value is on the front of the Intake Distributor (the body of the spider).
It's #21 in this diagram. It will have a fuel line and an electrical connector going to it.



www.autoatlanta.com/porsche-parts/hardpa...78-82§ion=107-10

I hope that I got it right

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15 Jan 2021 11:59 #21701 by mike@lemons.com
Replied by mike@lemons.com on topic Cold Start Valve
Thanks for the response.
I've looked at that diagram also but if it's there it is buried so deep I can't find it and I don't see a steel line that would attach to it. What I do have is this on the passenger rear side of the spider. It looks like it has one or two metal fuel lines going to it and two lines coming out of it. So this may be a shut off valve doing another function or ???

I'll keep looking

Mike

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15 Jan 2021 15:46 #21702 by joejabq
Replied by joejabq on topic Cold Start Valve
Mike,
I don't see your parts on my car.
Here are pictures from my '79 928 US. It is a vanilla K-Jet system (CIS).

Top View of the Cold Start Value (Injector)



Front View (See the turquoise electrical connector):

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16 Jan 2021 07:47 #21704 by mike@lemons.com
Replied by mike@lemons.com on topic Cold Start Valve
Thanks. I found it right where it is supposed to be. My oil filler cap is a little different than yours. From your picture it looks like I have another hose that goes to the oil filler cap which covers most of the cold start valve. Do you happen to know if the electrical connector just pulls off or does it have a locking tab?

The problem I'm having is that the car starts right up and for a couple of seconds seems to run ok (might be an indication that the cold start valve is still working since what I read indicates it is only on while the starter is turning) and then I lose all throttle response and it sounds like it is only hitting on a few cylinders. As it warms up, more cylinders seem to start firing and after probably a couple of minutes it runs like it is supposed to. At that point I have good power. If I shut it off, I can restart within at least an hour or so and everything starts and runs as it should.

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16 Jan 2021 13:58 #21705 by joejabq
Replied by joejabq on topic Cold Start Valve

Thanks. I found it right where it is supposed to be. My oil filler cap is a little different than yours. From your picture it looks like I have another hose that goes to the oil filler cap which covers most of the cold start valve. Do you happen to know if the electrical connector just pulls off or does it have a locking tab?

The problem I'm having is that the car starts right up and for a couple of seconds seems to run ok (might be an indication that the cold start valve is still working since what I read indicates it is only on while the starter is turning) and then I lose all throttle response and it sounds like it is only hitting on a few cylinders. As it warms up, more cylinders seem to start firing and after probably a couple of minutes it runs like it is supposed to. At that point I have good power. If I shut it off, I can restart within at least an hour or so and everything starts and runs as it should.


I have been messing around with my '79's CIS system for a little while now. I'm NOT an expert! I keep learning about how it all works together. It's pretty amazing, actually... when it works. I have done a lot of research and reading as I got mine working. Maybe some of this will help you. I'll try to find some references for you too.

I think that you are right that the cold start valve (and the thermo timing switch) are working. It probably wouldn't start at all if it were not getting the squirt of gas that is coming from the cold start valve. Assuming that you don't have ignition system issues, e.g., weak coil or bad green wire, which seems unlikely since it will eventually run when cold and runs when hot, it comes back to a CIS problem.

Here's the check list from my files (unfortunately, the site that I got this from no longer exists) :

"Difficulty starting engine only when cold"
BTW, it starts with, " This is one the most common problems with the K-Jet system".

1. Control pressure too high. The control pressure is governed by the Warm Up Unit (WUR). Normally, the control pressure starts low, which leads to a rich A/F mixture for cold starts and then slowly increases to a warm engine condition with a higher control pressure and a leaner A/F mixture. This is all done in the WUR, part #1 in the diagram that I shared earlier. If the WUR is stuck in the hot condition, you are getting a lean A/F mix, which does not have enough gas to keep the engine running and is consistent with why your engine starts and runs well when it is hot. You will need to get a CIS fuel pressure tester to know what your control pressure is doing.
Here's a good reference for measuring both the system pressure and the control pressure:

drive.google.com/file/d/1uuj9bm0UfVWtrbxPVGRfaoASQRbQftl3/view

It's a good reference. If you decide to go this route, be sure to record the system pressure too. It's possible that the system pressure is out of whack as well, but it's unlikely since it runs well hot.

If I were to bet, your WUR is not working correctly.
You can send your WUR off to get tested and rebuilt. I have had a very good experience with CISFlowTech, but I'm sure there are others. You can rebuild the WUR yourself too. Personally, I chose not to do that. I wanted assurance that it was fixed and set correctly!

2. Auxiliary air valve is not working or sticking. This seems to be very uncommon. You can check this yourself too.

3. Cold start injector/thermal time switch. You can test the cold start injector by removing it, crank the engine and capture the what gets sprayed. It should spray, of course. You can test the thermal time switch/circuit by measuring the voltage in plug that goes to the cold start switch when a friend cranks the engine. It should measure close to 12 Volts. You asked about the electrical connector on the cold start injector. It has a wire clip on it that holds it in place. To remove the connector, you need to push down on the back side of the clip wire with your finger or a screw driver as you pull the connector off.


I hope that this helps.

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16 Jan 2021 16:16 #21707 by mike@lemons.com
Replied by mike@lemons.com on topic Cold Start Valve
Thanks a lot. This gives me a place to start. I've had this 928 since 1985 and it has really given me few problems. Just replaced the shift linkage front ball socket as well as the rear shift rod joint. Bushings were shot in both. I did it without taking down the exhaust although I did take down the exhaust heat shields. It was quite a chore but I really didn't want to take down the exhaust since it hasn't been off in 40 years.

Mike

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