Quicker starts for CIS - hot or cold

[prebordao]

A couple of months ago i installed an electric shutoff valve on the return line to the tank.
The purpose was to fix an old warm start problem that i traced to an unability of the Wur to retain warm residual pressure after shutdown.
Replacing a Wur is expensive but the shutoff valve is cheap - 20 bucks - so despite some naysayers here on the forum i decided to give it a go and install it at the "beginning" of the return line thus shutting all return exits from the engine.

Here's what i found:
Warm starts have been a non issue, since. Admittedly i will reserve a final judgement for the really hot days in a few months.
But cold starts have improved too and are now usually a quarter turn affair. It's not a huge improvement, as previously, with the right cold pressure set, starting was not a problem but it still took a few turns. Now it's instant.

I guess it makes sense. With the new valve, with the engine off, fuel is trapped and pressurized permanently between the FP check valve and the shutoff valve. When you crank it, no matter how many days it last run, fuel is already there where it's needed. No need to travel...

Sorry for the long post, but i believe this may be useful to others.

[Targalid]

Can you post photos of valve, manufacturer and location of the install? This sounds like a valuable modification to the fuel system. Did you wire it directly to the ignition switch?

[Joe Bob]

Have you checked the check valve in the neck of the fuel pump?

[prebordao]

Believe me Joe, before going this way, i did all the usual steps...

check valve, accumulator, pressures, etc....

Originally Posted by Joe Bob

Have you checked the check valve in the neck of the fuel pump?

[prebordao]

Originally Posted by Targalid

Can you post photos of valve, manufacturer and location of the install? This sounds like a valuable modification to the fuel system. Did you wire it directly to the ignition switch?

I installed the valve in the engine bulkhead. Took power from fuse #2 on the rear fuse block. It only gets power with the engine running. Valve opens with power on.

Valve is model SKY from OMB. See link:

OMB-SALERI

[soren.911]

Hi Pjr

I am glad to hear it seems to work out and i am going to install the same valve on my car this winter.

[T77911S]

i dont want anything else electrical that will leave me stranded. right now it is just a fuel pump. i carry an extra CD and coil.

did you try cleaning the WUR? mainly the meatal diaphragm that makes up the seat valve.

another option is to change to the later FD that has the shutoff vlave for the return line in the primary pressure reg.

[prebordao]

I've been on this argument before...

- Yes, I cleaned the Wur, but the problem is on the bimetal spring.
- The shutoff valve in the FD (is there one ?) only shuts down the return from the FD, probably not the return from Wur.
- How much for an FD ?

Anyway, the valve has a manual override.

PS - T77911S, must of your other vehicles have plenty more electronics than our 911s

[manbridge 74]

So I'm trying to understand.

If return is completely shut off, and pressures are higher, isn't the mixture a little leaner?

Wasn't your original issue a lack of residual holding pressure?

Not trying to detract. You are in a rather warm part of the world compared to my locale.
If it works for you, more power to you. Maybe I'll try it with a manual line clamp and see what happens.

[prebordao]

Shutoff only happens when engine stops. No effect at all with engine running.

[steves31]

what a great idea can you share with us where u can get the valve and what type did you use thanks,steve

[steves31]

srry just saw the link thanks again

[prebordao]

I found it on ebay

[Reiver]

Nice to think thru and fix an issue....simple. Man, that is greeeen.

[boyt911sc]

Originally Posted by prebordao

I've been on this argument before...

- Yes, I cleaned the Wur, but the problem is on the bimetal spring.
- The shutoff valve in the FD (is there one ?) only shuts down the return from the FD, probably not the return from Wur.
- How much for an FD ?

Anyway, the valve has a manual override.

PS - T77911S, must of your other vehicles have plenty more electronics than our 911s

PJR,

You have done something that I really like and won't disagree with your innovation. This is a good fix if you don't want to replace a some what defective WUR. And in your case, you have a WUR that is expensive and not rebuildable. And you have given me something to research and determine the problem in your particular case. The main problem about your WUR, it is not maintaining residual pressure long enough and installing a check valve to prevent the loss of fuel pressure is a pretty good approach.

You were some what correct in saying that the Bosch WUR for CIS was a 'check valve' and I strongly disagreed with you (old posts). So, I went back to work to determine if your statement was correct or not. What I found out after the tests and experimenting numerous CIS WUR's including one for 73.5 CIS, was that a good WUR will hold pressure between 8 - 12 psi of fuel after shutdown.

The '76-'83 FD have additional relieve valve to maintain the residual fuel pressure at an acceptable level. I have not done any test with the '73.5 - '75 FD's because I don't have any at hand. The FD ('76-'83) have built-in relief valves for both the primary and return (control) fuel pressures. While the FP's of the '76-'83 don't run until the engine starts, residual fuel pressure is more critical for these engines than those of the early CIS engines ('73.5-'75) with FP running as you turn the ignition switch to ON/RUN position (not start) and begin to develop fuel pressure in the system.

Having this shut-off valve would surely help in the cold/hot start process for maintaining a residual fuel pressure. Good job!!!!!

Tony

[manbridge 74]

Okay, I see your approach and will give your method another plus.

I have a 74 that has no FA and it starts and runs normally. But it is quite cold here and I'm sure it would not hot start easy in the summer. Possibly your valve idea could save people having to buy an increasingly expensive part(FA)?

Are you concerned it might leak after, say, ethanol gas and many miles?

[soren.911]

Here you go eBay: Neue und gebrauchte Elektronikartikel, Autos, Kleidung, Sammlerst

[prebordao]

Are you concerned it might leak after, say, ethanol gas and many miles?

For ethanol i can't speak, but this is a valve specifically made for petrol engines. It is commonly used in LPG conversion setups, so i'm assuming it's reliable but only time will tell... At least there's a manual override.

[prebordao]

Originally Posted by boyt911sc

You were some what correct in saying that the Bosch WUR for CIS was a 'check valve' and I strongly disagreed with you (old posts). So, I went back to work to determine if your statement was correct or not. What I found out after the tests and experimenting numerous CIS WUR's including one for 73.5 CIS, was that a good WUR will hold pressure between 8 - 12 psi of fuel after shutdown.

The '76-'83 FD have additional relieve valve to maintain the residual fuel pressure at an acceptable level. I have not done any test with the '73.5 - '75 FD's because I don't have any at hand. The FD ('76-'83) have built-in relief valves for both the primary and return (control) fuel pressures. While the FP's of the '76-'83 don't run until the engine starts, residual fuel pressure is more critical for these engines than those of the early CIS engines ('73.5-'75) with FP running as you turn the ignition switch to ON/RUN position (not start) and begin to develop fuel pressure in the system.

Having this shut-off valve would surely help in the cold/hot start process for maintaining a residual fuel pressure. Good job!!!!!

Tony

Tony,
I've found that the problem with my WUR is the bimetal spring. Due to old age it doesn't flex as much as it should. So if I adjust it for enough low pressure to have good cold starts I can't get enough residual pressure at the other end, and vice versa. So I decided to adjust it for a good cold start, and installed the shutoff valve to take care of the rest.

Now, I think this approach doesn't work for everyone with CIS, as starting in 77 (?) the WUR return line goes through a push valve in the FD before reaching the tank. This push valve does approximately the same job as my shutoff valve, so here my solution probably wouldn't solve anything...

[josborn10]

My 74 suffers from cold start issues. I would like to try the fuel shut off valve. 3 questions. Is this the link to the right item (below)? Where is the best place to put the valve? Lastly, would this be a good place to perhaps run an anti-theft fuel cut-off?

New AFC Model 152 Solenoid Shut Off Valve fuel filter | eBay