Cold Start Valve/Injector Testing

[BOPE]

Is there a way to test the cold start injector, P/N 911 606 107 01, on a 1980 911 SC without removing it?

And if not, can the valve be removed without dropping the engine?

It somethimes takes two (2) starting attempts to get the motor running on my '80 SC. Notably, once started it runs perfrectly. I've tested the thermal-time switch and it appears to be working faultlessly, hence I suspect a faulty cold start valve.

Thanks!

Jason

[Schulisco]

There must be a black red cable connected to the bigger round connector of the thermo time switch. Disconnect it from the thermo time switch and pull it to the engine case/ground while the engine idles. When the cold start valve works, the additional fuel will let the engine either surge or let the engine stall due to uberrich mixture. If not, the valve is bad, or gets no fuel, is clogged or sth else.



Further reading, and teach yourself on reading the circuit plan:

https://cis911primer.com/pages/elec_csv.html
https://classickabelboomcompany.com/wiring-diagram-porsche/ (1982 911SC part 1)

[BOPE]

Excellent suggestion Shulisco; thank you!
Jason

[Schulisco]

If it's bad you can remove the CSV without dropping the engine, but it's a fiddly job, even for people with small hands, because you have to act blind mostly with mirror, lamps etc. It's pretty much the worst reachable part of the CIS. Be aware when replacing it to order the correct rubber seal ring too, it's got a non standard size. As well the grey/red flange holding it as they may break after decades in the engine heat and creating hard to find vacuum leaks...
Consult the Porsche original parts catalogue:
https://www.porsche.com/international/accessoriesandservice/classic/originalpartscatalogue/

[BOPE]

Thank you again. Does removal of the intake "boot" help to access the valve?
Jason

[Schulisco]

Not really. You can remove it to make it a bit easier, but it helps more likely to remove the heater blower motor and other stuff from the left side of the engine as the CSV is more on the left side of the lower airbox. You can partially lowering the engine and secure it with thread studs replacing the rear mounting bolts of the engine:

https://www.pelicanparts.com/techarticles/911_partial_engine_drop/911_partial_engine_drop.htm

[BOPE]

Thank you again. I'll test the CSV per your method today and hopefully the results will be good.

Jason

[BOPE]

If I'm interpreting the wiring diagram correctly, the CSV gets voltage from the starter solenoid. So once the motor starts, there will not be voltage supply to the CSV. Therefore, grounding the black/red wire with the motor idling will not activate the CSV.

Jason

[PeteKz]

Correct analysis. The CSV only operates while cranking. Thus, you have to test it while cranking, or provide 12v to the yellow wire of the TTV (thus to the CSV), and then ground the blk/red wire.

Why do you suspect the CSV? Another component that will cause hard starting, especially when warm, is the fuel accumulator. Many of these have failed at this age. Other possible causes: A leaking check valve at the fuel pump, a leaking SP valve at the fuel distributor, or a leaking WUR.

Do you have a fuel injection pressure tester? If not, buy this from Amazon, as you will need it eventually and it's not expensive:

https://www.amazon.com/BETOOLL-Injection-Pressure-Tester-Gauge/dp/B01L17TPT2/ref=sr_1_1?crid=34XBXCJ3GLXCV&dib=eyJ2IjoiMSJ9.QpE3QCUBfm8y8_zBv8HgxlJJhJJFU-or9zovhSZgHp9QwmfK_dpjELjqkoxSvKAqhplkaFi_1EaHBdEI 2WOMupk7qtlGnTzEV_VgLrkd2rqqqce6XQerr0xGPM-G-n7XJZXsRsRarPXsgqkoW_bVhjGmGrS1tjk1IuINHsqt4ltS09d H4xM533pdMbH2PYnQ_86nBAigudAgxElkZEyHTrQ6JTdvWJXBy wMp_dwG83L2_I5oNWsVQXQj94lSR8pMqrXE4xr9jWoNjvdCvk3 kMGcOXH1sAXlYs20kM4MzHww.VRS4lXVwX5UOClQeVH-fez6ZAKlgJ8x-vT0luwImokw&dib_tag=se&keywords=betooll%2Bfuel%2Bpressure%2Btester&qid=1766390219&sprefix=betool%2Caps%2C280&sr=8-1&th=1

[BOPE]

Originally Posted by PeteKz

Correct analysis. The CSV only operates while cranking. Thus, you have to test it while cranking, or provide 12v to the yellow wire of the TTV (thus to the CSV), and then ground the blk/red wire.

Why do you suspect the CSV? Another component that will cause hard starting, especially when warm, is the fuel accumulator. Many of these have failed at this age. Other possible causes: A leaking check valve at the fuel pump, a leaking SP valve at the fuel distributor, or a leaking WUR.

Do you have a fuel injection pressure tester? If not, buy this from Amazon, as you will need it eventually and it's not expensive:

https://www.amazon.com/BETOOLL-Injection-Pressure-Tester-Gauge/dp/B01L17TPT2/ref=sr_1_1?crid=34XBXCJ3GLXCV&dib=eyJ2IjoiMSJ9.QpE3QCUBfm8y8_zBv8HgxlJJhJJFU-or9zovhSZgHp9QwmfK_dpjELjqkoxSvKAqhplkaFi_1EaHBdEI 2WOMupk7qtlGnTzEV_VgLrkd2rqqqce6XQerr0xGPM-G-n7XJZXsRsRarPXsgqkoW_bVhjGmGrS1tjk1IuINHsqt4ltS09d H4xM533pdMbH2PYnQ_86nBAigudAgxElkZEyHTrQ6JTdvWJXBy wMp_dwG83L2_I5oNWsVQXQj94lSR8pMqrXE4xr9jWoNjvdCvk3 kMGcOXH1sAXlYs20kM4MzHww.VRS4lXVwX5UOClQeVH-fez6ZAKlgJ8x-vT0luwImokw&dib_tag=se&keywords=betooll%2Bfuel%2Bpressure%2Btester&qid=1766390219&sprefix=betool%2Caps%2C280&sr=8-1&th=1

Thank you Pete.

I replaced the fuel accumulator, which immediately cured the hot-start problem. However, I now seem to have an intermittent cold-start problem. When I say "problem" I mean that instead of starting on the first attempt, it may take a second activation of the starter to get the motor to run. But once running, it idles and runs up to speed perfectly. So, I’m suspecting some part of the "start" fuel system is not operating properly.

Indeed I should purchase a fuel injection pressure tester. Thank you for the link, but it doesn't seem to work on my end.

Jason

[Schulisco]

BOPE, PeteKz,
You guys are correct - the TTS is powered only when the starter motor is engaged. My fault, apologize, I forgot this. But you already posted the solution - powering the CSV with +12V from another source is key, probably from the fuse holder on the left side of the engine compartment.
If the CSV fails, more likely the TTS is bad, as they used to be a electromechanic switch with a bimetal strip within. The contacts fail over decades which is pretty normal. New TTS are fully electronic. Here's more info on them and how to bench test them:
https://forums.pelicanparts.com/porsche-911-technical-forum/594010-thermo-time-switch-1978-sc-3-0-a-3.html
https://forums.pelicanparts.com/porsche-911-technical-forum/1156114-help-35-degree-temperature-switch-911sc.html

Originally Posted by BOPE

Thank you Pete.

I replaced the fuel accumulator, which immediately cured the hot-start problem. However, I now seem to have an intermittent cold-start problem. When I say "problem" I mean that instead of starting on the first attempt, it may take a second activation of the starter to get the motor to run. But once running, it idles and runs up to speed perfectly. So, I’m suspecting some part of the "start" fuel system is not operating properly.

Indeed I should purchase a fuel injection pressure tester. Thank you for the link, but it doesn't seem to work on my end.

Jason

A CIS fuel pressure tester is key on any troubleshoot on a CIS car!
There are plenty of kits universal available on the net, I purchased this one, designed for Bosch CIS (they deal more on Mercedes, but it fits too on other CIS cars):
https://kurth-classics-autoparts.de/gb/warm-up-regulator-wur/227-k-jetronic-pressure-testing-gauge.html

There are also manuals to build it by yourself, like
https://jetronic-org.translate.goog/de/k-jetronic/179-manometer-kjetronic?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp
https://www.924board.org/viewtopic.php?t=38729
https://www.youtube.com/watch?v=Q7qjmfJHoLI

When you chase an intermittend starting issue, this may caused by several possible reasons and is hard to find.
1. Check for vacuum leaks with a smoke generator, vacuum leaks are the final boss on a CIS for issues
2. Check with the CIS fuel pressure tester the residual pressure, even while you already replaced the fuel accumulator; it works closely together with the check valve at the fuel pump
3. Make a cross check with giving a shot of starting fluid sprayed in the air filter duct to "simulate" a working CSV/TTS before engine start - does it start then right away?
4. Check the ignition, ignition wires, coil for contact problems - a weak spark due to an old / dying ignition coil can also cause such issues.

Thomas

[BOPE]

Originally Posted by Schulisco

BOPE, Pete.

You guys are correct - the TTS is powered only when the starter motor is engaged. My fault, apologize, I forgot this. But you already posted the solution - powering the CSV with +12V from another source is key, probably from the fuse holder on the left side of the engine compartment.
If the CSV fails, more likely the TTS is bad, as they used to be a electromechanic switch with a bimetal strip within. The contacts fail over decades which is pretty normal. New TTS are fully electronic. Here's more info on them and how to bench test them:
https://forums.pelicanparts.com/porsche-911-technical-forum/594010-thermo-time-switch-1978-sc-3-0-a-3.html
https://forums.pelicanparts.com/porsche-911-technical-forum/1156114-help-35-degree-temperature-switch-911sc.html

Thomas

I tested my Thermal Time Switch with a test ligth and it works perfectly. I'll see if I can test the Cold Start Valve by supplying an independent power source and report my findings.

I don't think my '80 SC has a TTV that Pete mentioned; please correct me if I have assumed incorrectly.

Also, what is an SP valve?

Thanks!

Jason

[Schulisco]

Originally Posted by BOPE

I tested my Thermal Time Switch with a test ligth and it works perfectly. I'll see if I can test the Cold Start Valve by supplying an independent power source and report my findings.

I don't think my '80 SC has a TTV that Pete mentioned; please correct me if I have assumed incorrectly.

Also, what is an SP valve?

Thanks!

Jason

The '80 SC is the first year of ECU lambda controlled SC engines with catalyst etc. See this for more details:
https://cis911primer.com/pages/descr_lambda.html

SP valve: System pressure valve, sits in the fuel distributor housing and manages the fuel system pressure overall.

Good to know that the TTS works fine. Next is to check the CSV itself as described.

Looks like this as shown here: https://forums.pelicanparts.com/porsche-911-technical-forum/914737-cis-primary-fuel-pressure-regulator-assembly.html

[BOPE]

I tested the Cold Start Valve this AM by providing it with supply voltage from the battery instead of the starter solenoid. I disconnected the red/black wire from the thermal time switch and started the motor. While idling, I touched the black/red wire to ground, which energized the Cold Start Valve. The motor immediately died, suggesting that the Cold Start Valve is functioning properly.

My next step is to purchase a fuel pressure gauge and test the various fuel circuits.

Thanks to all of you I'm much further along in the troubleshooting process than I was a day or so ago.

Jason

[Schulisco]

Originally Posted by BOPE

I tested the Cold Start Valve this AM by providing it with supply voltage from the battery instead of the starter solenoid. I disconnected the red/black wire from the thermal time switch and started the motor. While idling, I touched the black/red wire to ground, which energized the Cold Start Valve. The motor immediately died, suggesting that the Cold Start Valve is functioning properly.

My next step is to purchase a fuel pressure gauge and test the various fuel circuits.

Thanks to all of you I'm much further along in the troubleshooting process than I was a day or so ago.

Jason

Good progress!

Fun fact - yesterday I took the 911 out of the garage here in winterly Germany (sunny, dry, no salt on the roads as the winter time just was very mild with no frost) for 2hrs drive after sitting for 6 weeks...engine started very quick after 1sec cranking without any issue, ambient temp was 9°C/ 48°F. Stable idling of 1300rpms without any surging. But after a 10mins break after one hour of driving, it required 3 start attempts (first failed while I didn't engaged the starter not long enough - my fault, 2nd probably the engine swallowed, 3rd was finally sucessful). No push on the throttle. Residual pressure with hot engine almost 3bar, control pressure 3.3bar. Maybe caused by the sloped parking...don't know.

What I want to say - don't chase non-existing problems.
The CIS is a quite good and efficient injection system, and it works pretty well when it is in shape. But this won't prevent tiny "hickups" like this. There's no central ECU managing everything. Every component of the CIS works on its own without any external control. If there's a spring hanging, a valve is clogged, or sth. else - such hickups happen. More often driving may cures many of these ...

Thomas