Testing a Cold Start Valve/Removal & Replacement

Sunroof · 12-13-2007, 08:46 AM

After the thermotime switch controversy (not applicable to the 1973.5T CIS model), I was going to look at my cold start valve as a part of my cold start issue.

Does anyone know how to test them? Would this be as simple as removing it and turning the key to measure spray volume or even if a spray is evident?

They are behind the engine and can be tough to get to. Simple enough to remove them (two allen bolts), but can it be accessed by removing the air bellows on the throttle body without lowering the engine? Thats key here......

Thanks
Bob

john walker's workshop · 12-13-2007, 08:52 AM

remove the throttle body and you can see the tip of the CSV. have someone turn the key or use a starter button. it works off the starter circuit. only works when the engine is good and cold.

Sunroof · 12-13-2007, 09:02 AM

John,
Does it matter how much spray comes out? Is the performance of the valve based on any defined volume of fuel? I never removed a throttle body before, so does this require that the engine be lowered to access the rear bolts? I will assume to that the gasket would requiure changing as well .

Appreciate the input.

A John Walker response is something you take to the bank!

Bob

john walker's workshop · 12-13-2007, 09:38 AM

pretty easy. remove the big air boot, then the four allen bolts that hold it to the plastic airbox. the throttle rod pops off and then you should be able to slide it back enough to look down the hole. there's a big o-ring under it, so don't lose it. i suppose you could prop the throttle open and look down there with a mirror and flashlight, but it's kind of hard to see that way. there's a fuel line attached to the control pressure valve on the side which doesn't need to be disconnected. you might want to disable the ignition so it doesn't start or backfire accidently.

Sunroof · 12-13-2007, 10:17 AM

Thanks John,

With the cold start valve, is it just an issue of working or not working? They are fairly expensive items ($175.00 +), so I have to wonder what is going on inside electronically speaking. The current must open up the passage to allow the fuel to be released and then close it back up.

What do I look for in the spray quantity? Do these valves really spew it out or can I expect more of a mist type release.? Have you ever encountered a clogged orifice on these as with a regular fuel injector where they can be cleaned or cleared?

Thanks

Bob

boyt911sc · boyt911sc's Garage

Bob,

Place the CSV in a small container and start the motor. The volume and spray pattern of the fuel will tell you a lot about the injector. If the injector failed to deliver fuel, check for power. The CSV is of the solenoid-operated type. When enegized the electromagnet armature (valve) inside the injector moves and allow pressurized fuel to flow out. This test should be done with a cold motor and a working TTS. Good luck.

Tony

Sunroof · 12-13-2007, 11:32 AM

Thanks Tony.

If I take the CSV off I am limited to how much stretch I have on the electrical and fuel line attachment behind the airbox. Perhaps what John has suggested in opening the throttle body valve and looking down with a mirror and flashlight would be the first approach. I would think if the CSV was working, still attached, the fuel smell would be pretty powerful indicating some degree of function.

As posted on another thread and getting rather controversial, the 1973.5T/CIS does not have a thermotime switch as part of the cold start system.

Any additional recommendations are always welcome.

Bob

Mysterytrain · 12-13-2007, 01:29 PM

Bob,
I blew up the schematic of the cold start valve circuit for the 73 CIS.
Number 2 is the starter, 12 is the cold start valve, 14 is the microswitch. From the drawing you can see that the CSV gets 12 volts from terminal 50 on the starter solenoid. The microswitch [14] provides a switched ground for the CSV. So before you pull the CSV you might want to check that you have 12 volts going to the CSV when cranking. Check this at the CSV connector. If that checks then take a close look a the microswitch. You can test it to see if its working and if the ground connection is good. You can also bypass the microswitch by connecting the red/blk wire to ground while cranking the engine. If the electricals check out I would bet there is some sort of adjustment procedure for the microswitch. Seems that it might operate from the position of the air sensor plate like the later CIS fuel cutoff switch. So whenever the plate is at rest and you crank the engine the CSV squirts. Once the plate raises the microswitch opens. Just my theory..maybe, John can clear this up.

john walker's workshop · 12-13-2007, 01:44 PM

normally you would set your hand throttle, if you have one, so the micro-switch closes and completes the circuit to ground so the valve solenoid activates and it sprays. otherwise just open the throttle a tad as you crank. i forgot that a 73.5 doesn't use a thermo-time switch, so it sprays whenever the starter functions as long as the switch is closed.

Sunroof · 12-13-2007, 02:03 PM

Thanks.
The microswitch can be adjusted, but I do not believe thats my issue on the cold start. I will check out the CSV this weekend by Johns recommendation to go thru the throttle body. My system is not holding fuel pressure over night. I have always blamed that internal check valve in the fuel pump only specific to the 1973.5T. All other fuel pumps have an external check valve that can be replaced. So, with hand throttle up I can hear the fuel filling up the lines. Turn the key and she labors a bit to get rolling. But, once the injectors are doing their thing she rides great thru warm-up. I thought the laboring might be the CVS or the fuel distributor. Its time to pressure test the system as well.

These are times that the DME would be a welcome relief. My 1985.5 944 ran like a top for years with never an issue with the DME.

Bob

john walker's workshop · 12-13-2007, 03:37 PM

none of the systems are designed to hold residual pressure overnight. there actually was a check valve available for that early pump. bosch # 1 587 010 001. don't know if it's still around. for an early 924 if i remember right. there's also a larger inline check valve, threaded on each end, that you might be able to attach at the fuel filter. bosch # 1 587 010 004. those can be used to replace the fuel inlet fitting on the fuel distributor '75 and later, but not on 73/74 due to the nylon lines attaching directly to the FD, no fitting used.

Jim Sims · 12-13-2007, 05:03 PM

The 1973.5 911 CIS CSV system/circuit if in OEM configuration is not temperature dependent; the CSV valve will operate whenever the hand throttle is fully pulled up and the starter is turning (engine hot or cold). There is not a TTS in the CSV circuit for the 1973.5 911 CIS.

See the below link for information on the 1974 911 fuel pump output banjo fitting which contains an integral check valve. It can be retrofitted to a 1973.5 fuel pump.

Fuel Distributor - Check Valve 73.5T?

Jim Williams · 12-13-2007, 05:48 PM

You can get almost as good a view of the CSV spray by removing the air boot, and wedging a piece of wood down inside the throttle venturi with the butterfly held open, so that the wood piece holds the butterfly open. The wood piece (or whatever else you have handy that will fit) should be on the rear (toward the rear of the car) side of the venturi so that you can sight down into the side of the throttle closest to the CSV. Using a small mirror with a flashlight so you can sight into the throttle without having your eye over the throttle opening will work well. You should be able to see the spray without having to remove the throttle body.

Disabling the ignition might be a good idea to prevent to possibility of the engine starting and spitting back through the open throttle.

Mysterytrain · 12-13-2007, 06:02 PM

I'm curious as to where the microswitch is located and what is triggering it off and on. It clearly seems to be the controller for the CSV.
Dug thru the schematic again and it appears that the 73.5 doesn't have a fuel pump relay or a fuel cutoff switch. I'm guessing the system primes with the first turn of the key. Is this correct?

Mysterytrain · 12-13-2007, 06:32 PM

aahh,ok. I checked the PET and see that the microswitch is located on the throttle body. So lets see if I've got this right. Movement of the throttle plate via the throttle linkage [the hand throttle] closes the switch and provides a ground for the CSV. 12 volts is applied to the CSV only while cranking the starter. The fact that the microswitch is in closed and providing a ground is of no concern once the ignition is in the run position because there is no power going to the CSV. On a warmed up engine one would not normally lift the hand throttle so the linkage at rest would keep the microswitch open..thus no ground and the CSV will not spray. Rocket Scientists!

theiceman · 07-09-2018, 01:33 PM

might be tough to see if CSV is spraying with the plenum in the new style boxes though huh ?