CIS Control Pressure Plunger & Cold Starts

[echrisconnor]

Let me see if my cleaningof the FD in the car has any results. I also blasted in at the bottom of the control plunger through the airbox for a while when the plunger was fully retracted. I've been having some oil get sucked into the airbox recently from an overfill, which also could have gooked up the bottom of it.

If any of you wouldn't mind checking to see what sort of resistance you get on a cold car, I'd appreciate it.

Thanks all!

Chris

[vash]

chris, i just checked last week on a cold car for someone else. i do have resistance right from the start. and a phwisssh sound. 81SC

[echrisconnor]

Vash -- was the car you tested running (fuel pump running)? Or was it just cold with nothing running? If it was off, what was the "pfwiish" sound? I'm curious about before the fuel pump starts and the system is completely depressurized and at rest.

[vash]

oh, sorry didnt give enough info. the car was completely cold and i had the keys in my pocket. i dont know what the sound was, it actually surprised me, it wasnt loud. but i definately felt pressure. i only lifted the bar once. dont know if the pressure gets less or more after the first lift. you want me to do anything else? (later tonight?now @work)

[Paulporsche]

Chris,
To clean the plunger Haynes recommends using crocus cloth, which is a fine emery cloth like product for use by mechanics. 3M makes it. Maybe others do too.

[echrisconnor]

Crocus cloth... Never heard of it. Well, if I do end up pulling the thing out and cleaning it, I'll try to track some down. We'll see how the great carb-cleaning blast off works. Wouldn't carb cleaner eat any accumulated junk upon contact pretty well?

[stormcrow]

So, the problem now is that after a hot run, the next morning when I turn the ignition on the injectors start spraying as soon as the fuel pump goes on (I have my pump jumpered to run as soon as the ignition is turned on). I can hear them singing away, and they will continue to do so for about a minute as system pressure builds and the control plunger drops down. If I lift up on the metering plate while this is happening, there is no resistance, the plunger has sucked itself up to the top overnight. if I keep my hand on the metering plate I can feel the plunger coming down slowly -- all the while the injectors are squirting away flooding the engine. This didn't happen before.

Chris,

It appears that the plunger is up too high in the fuel distributor. The system should work as follows:

Cold - when you turn the key on, and start the engine, the air flow across the sensor plate will lift the plunger high enough to allow fuel to flow to the injectors. If there is no air flow, there shouldl be no flow to the injectors even though the fuel pump is running.

The fact that there is no resistance when you lift the sensor plate with the engine cold indicates that the pressure regulator is doing its job. This allows for a rich mixture when the engine is cold and the cold start valve adds fuel momentarily during the starting process.

You need to lower the plunger in the fuel distributor until the fuel stops flowing with the fuel pump running. This is your starting point.

Turn the engine over and see if it starts. If it does then the plunger is at the low end of the fuel distributor slits which is where it needs to be.

If it doesn't start, raise the plunger with the 3mm adjusting screw about a 1/4 turn at a time clockwise.
Do this until it starts and stays running. That will be your starting point to adjust your fuel mixture. If it backfires once it starts and runs, turn the adjusting screw clockwise another 1/8 turn to enrichen the mixture and that problem will go away.

Hope this info helps

Steve

"A Porsche does more then just go fast in a straight line"

[echrisconnor]

I think I've fixed it. Still not 100% sure since I need to take it out and get it good and hot again, however, the cleaning seems to have had some results.

Earlier I stated that the control plunger moves freely, and "takes about a minute after the fuel pump is turned on to drop down and stop the injectors spraying". After the cleaning I did, I can push the plunger up to the top, and then when I flick the fuel pump on, by the time I can get to the back of the car and check, the plunger is already back at the bottom. So, my definition of moving freely was off before. It simply moved, and was sluggish. Now it appears to be moving the way it's supposed to. I'm still not sure why it was getting sucked up, but we'll see if the cleaning has fixed things.

I'll post results after a good hot run. I'm looking forward to that drive.

Chris

[TurboBert]

Hi Chris,
Has the problem returned, or did this in fact finally fix it?

[echrisconnor]

To be honest, I'm not sure there ever was a problem now. Cleaning the FD plunger did make a difference though. I ended up examining a couple of friends cars and on all of them, the plunger was lifted up at least to some degree on all these CIS cars when the engine was stone cold. So my mystery floating plunger seems to be fairly normal.

No real problem will appear unless the plunger can't come down quickly enough. If the cold start valve is working properly, this will get the car started and by the time the plunger drops down due to the increase in fuel pressure, you should be running fine. It still takes me a couple cranks to get going with a cold engine, but otherwise all is well.

Thanks for checking back.

Chris

[keoniahlo]

Hi everyone! I know that this is an old post, but I’m sure others with similar symptoms are reading this. I’ve done a lot of work trying to figure out why my plunger was pulling up overnight as well. I mean, I’ve done hours and hours of diagnostics on the vapor vent system, fuel return line, etc, and none of the normal tests showed anything wrong. But after staring at the fuel flow diagram for a couple hours, I had a hunch...

What I believe is causing this slow overnight rise of the center piston in the fuel distributor is the inner check valve of the pressure regulator in the fuel distributor. It’s the one that is controlled by the smaller spring and is non-serviceable. This component does not get discussed much because it is inside and not many understand, the function of that component. I understand that later years, Incorporated a shut off solenoid valve to better control this issue.

I have a new fuel pressure regulator component coming in and I will report my findings. Like most, I have changed the outer O-rings, but my system pressure has never been a problem— but since I personally rebuilt my fuel distributor, I changed those O-rings as part of the process.

Just want to give everyone a heads up that there is a valve inside that regulator that serves a purpose and is often overlooked.

Aloha, Keoni

[boyt911sc]

Originally Posted by keoniahlo

Hi everyone! I know that this is an old post, but I’m sure others with similar symptoms are reading this. I’ve done a lot of work trying to figure out why my plunger was pulling up overnight as well. I mean, I’ve done hours and hours of diagnostics on the vapor vent system, fuel return line, etc, and none of the normal tests showed anything wrong. But after staring at the fuel flow diagram for a couple hours, I had a hunch...

What I believe is causing this slow overnight rise of the center piston in the fuel distributor is the inner check valve of the pressure regulator in the fuel distributor. It’s the one that is controlled by the smaller spring and is non-serviceable. This component does not get discussed much because it is inside and not many understand, the function of that component. I understand that later years, Incorporated a shut off solenoid valve to better control this issue.

I have a new fuel pressure regulator component coming in and I will report my findings. Like most, I have changed the outer O-rings, but my system pressure has never been a problem— but since I personally rebuilt my fuel distributor, I changed those O-rings as part of the process.

Just want to give everyone a heads up that there is a valve inside that regulator that serves a purpose and is often overlooked.

Aloha, Keoni

Keoni,

The valve you are referring is called the “push valve” introduced in later SC fuel distributors. Both the inner and outer o-rings for the primary pressure valve are SERVICEABLE. Replace the o-rings (inner & outer) as needed. And you won’t need to install a solenoid valve to correct the residual pressure loss.

Installing a solenoid valve is a good idea but more expensive way than installing a 10-cents Viton o-ring. Just my two-cents.

Tony

[keoniahlo]

Hey Tony! Thanks for the response!

How do I get to the inner o-ring? Looks like the end of that "pintle rod" with the small spring looks crimped on at the end. Do I just remove the inner section using an Allen wrench and the o-ring is right there?! Man, I was told it wasn't serviceable, so I never tried!

Any chance that o-ring comes in the rebuild kit? I bought one from Germany, comes with o-rings, washers, etc. If not, can I get a couple from you? I also have a some light scuffing and minor marks on the pressure control piston--if you have a spare, I'd love to buy one from you!

Thanks again, bro.

Aloha,
Keoni

[keoniahlo]

Tony, I ended up finding a new regulator w/out the piston. That didn't fix the problem. But before I replaced the piston and regulator, I took a few photos with my endoscope. There appears to be some corrosion where the pressure regulator o-ring sits. My pressure drop-off falls within the manual's specs (and holds pretty long after an hour, btw). Thought I'd share that info, hopefully someone can respond with more experience with a possible slow leak at this o-ring. Thanks, Keoni

[keoniahlo]

Hi everyone! Any updates? I replaced my fuel distributor with a rebuilt one and the phenomenon still exist— plunger pulls up overnight.