911 1976 cis

[Mike6619]

Hi all

I have a 1976 911 c3.0
It has been running perfectly, rebuilt WUR, rebuilt FD matched and tested to the injectors, new fuel lines pump and filter. A few months ago it would just keep pumping fuel and not shut off and found the FD plunger had gummed up and the person that rebuilt it said to remove the centre fuel line and push air through it. This freed up the plunger and appeared to be working correctly. Ever since then it’s run very poorly. Has this “gum” now blocked somewhere else? It starts fine and idles well it sometimes performs and pulls as it should but then it just completely has no power and then back fires loudly. Do I start with emptying the fuel tank and a new filter? I did place some of the recommended injection cleaner but doesn’t appear to have helped. Thanks for your time in helping me out.
Mike

[Schulisco]

How old is the fuel? Did you added fuel stabilizer last fillup?
If fuel is older than 2yrs without fuel stabilizer it detoriates more and more. Especially when it contains at least 5-10% ehanol which attracts water which forces detoriation too.

I would drain as much as possible of the old fuel.and refill fresh gas, add a good injection cleaner and then drive it as long and as much you can. It should getting better more and more. Then start using fuel stabilizer and drive it regularly. Prevent resting times longer than 4-6 months.

Thomas

[Mike6619]

Thanks @Schulisco , the last fill up(1/4) tank was about 6 months ago and that’s when I placed the injection cleaner. The tank was on reserve before this and the fuel was only a few months old. It was still running rough before then and this is when I found the fuel distributor plunger wasn’t moving freely

I’ll drain the fuel and put some fresh in

[E Sully]

You could consider removing the injectors and putting them in containers. Lift the arm and see if they flow evenly, and if the plate moves smoothly.

[Mike6619]

Originally Posted by E Sully

You could consider removing the injectors and putting them in containers. Lift the arm and see if they flow evenly, and if the plate moves smoothly.

Thanks E sully, I will do this as well.

Thanks

[Mike6619]

I’ve pulled the injectors and they appear to be pushing out the same amount of fuel.

However the FD plunger is still stuck and causes the fuel to keep running without shutting off. but when I undid the centre fuel line that goes into the FD which then goes into the WUR and I placed my thumb over it the pressure caused the plunger to close. My assumption is that there is not enough back pressure on the line that goes to the WUR and allows the plunger not to close correctly?

Is my assumption correct and what issue do I have withe the WUR? It was recently rebuilt and has been working

Thanks again

[boyt911sc]

Mike,

Perform a flow test by just running the FP with all the fuel injectors pulled or removed from the fuel lines. Place the fuel lines in suitable containers and secure them. Test run the FP by lifting the air flow sensor arm and observe the 6 fuel lines. Let go of the lever and allow the arm lever to drop down. All fuel deliveries from the fuel lines SHOULD STOP ABRUPTLY. Repeat the test several times and take note how the fuel deliveries behave during the test. Keep us posted. Thanks.

Tony

[boyt911sc]

Mike,

I noticed something weird and strange with your fuel line adaptor. What is this thing inside the adaptor? Looks like a ferrule or something(?).



Tony

[Schulisco]

The central connection Tony highlighted is the line to the WUR. This is a return line via the WUR to the fuel tank, so there should be no extra adapter there. Maybe a check valve? That shouldn't be there! But someone may have added it "to fix a bad WUR"? Not good.
You need a CIS pressure gauge to check the control and system pressure. Correct fuel pressure is one of the most important things in a CIS, along with (vacuum) tightness.
The WUR applies back pressure to the FD piston, forcing it to move more or less depending on engine temperature to enrich or lean the mixture.

[E Sully]

Could just be the optics. While these are slightly different since they are for an earlier '73-74 TPS, it can look like the Mikes from the right angle.


The main purpose of the WUR is back pressure to push down on the piston. The fact that it stays up until he puts his finger over the port would mean the piston is sticking, or there is not enough of a restriction from the WUR.
Definitely need to get the CIS gauge on it and see what's going on with System and Control pressure.
Along that line, Mike you say the piston went down when you plugged it with your finger. Considering the normal system pressure is close to 70 psi, how hard was it to keep your finger over the port?

[Mike6619]

Thanks all

The pressure that I had to apply to the Central FD line that goes to the WUR was as hard as I could apply and even then it didn’t seal it so the pressure was very high. And it shut the flap/ plunger straight away. Once I turn off the cars fuel pump and press the plate / plunger up the plunger doesn’t come back down.

Thanks again
Mike

[Mike6619]

Originally Posted by boyt911sc

Mike,

Perform a flow test by just running the FP with all the fuel injectors pulled or removed from the fuel lines. Place the fuel lines in suitable containers and secure them. Test run the FP by lifting the air flow sensor arm and observe the 6 fuel lines. Let go of the lever and allow the arm lever to drop down. All fuel deliveries from the fuel lines SHOULD STOP ABRUPTLY. Repeat the test several times and take note how the fuel deliveries behave during the test. Keep us posted. Thanks.

Tony

Thanks Tony

I pulled the injectors and they all appeared to pump out the same amount of fuel . However the plunger which normally cuts out After a short period( I think it’s a pre prime?) doesn’t shut them off and it keeps running way longer than it should it then eventually shuts off. So could it be too much pressure coming from the FD to the WUR line and or the WUR not “applying “ enough back pressure?
I don’t have any gauges to test what the pressures should be so I guess I need to get it to a mechanic?

Thanks
Mike

[boyt911sc]

Originally Posted by Mike6619

Thanks Tony

I pulled the injectors and they all appeared to pump out the same amount of fuel . However the plunger which normally cuts out After a short period( I think it’s a pre prime?) doesn’t shut them off and it keeps running way longer than it should it then eventually shuts off. So could it be too much pressure coming from the FD to the WUR line and or the WUR not “applying “ enough back pressure?
I don’t have any gauges to test what the pressures should be so I guess I need to get it to a mechanic?

Thanks
Mike

Mike,

The plunger of your FD is sticking to the barrel. You need to fix this problem for your CIS to run well. Does your car start and idle correctly? With a sticking plunger, you will have high idle speed. Are you having this problem? What are the last 3 digits of your FD? Thanks.

Tony

[Mike6619]

Originally Posted by boyt911sc

Mike,

The plunger of your FD is sticking to the barrel. You need to fix this problem for your CIS to run well. Does your car start and idle correctly? With a sticking plunger, you will have high idle speed. Are you having this problem? What are the last 3 digits of your FD? Thanks.

Tony

Thanks Tony

It was starting and idling ok. The FD was rebuilt around 400km ago the FD ends in

100 010

[PeteKz]

Mike, all the advice given here is good, but I think before you start pulling more things apart, you should put at least 1/2 tank of FRESH fuel in it, add a bottle of TECHRON CONCENTRATE, and go drive the snot out of it. If the fuel in the tank was 6 months old, it could easily be bad, especially if you live in a humid environment. You certainly won't hurt anything, and it could help get the gum out of the CIS parts. If it doesn't improve, then go deeper.

And, it's a lot more fun to drive it hard than sitting in your garage puzzling over it.

[Mike6619]

Originally Posted by PeteKz

Mike, all the advice given here is good, but I think before you start pulling more things apart, you should put at least 1/2 tank of FRESH fuel in it, add a bottle of TECHRON CONCENTRATE, and go drive the snot out of it. If the fuel in the tank was 6 months old, it could easily be bad, especially if you live in a humid environment. You certainly won't hurt anything, and it could help get the gum out of the CIS parts. If it doesn't improve, then go deeper.

And, it's a lot more fun to drive it hard than sitting in your garage puzzling over it.

Thanks @Petekz , I tried this 6 months ago put in the injection cleaner and 1/4-1/2 fresh fuel… it didn’t work and then again last week and tried to drive it via the Italian tuneup but it was scarily bad with the car dying 1/2 way across intersections .. driving back streets to get home so I didn’t have to stop!

[Schulisco]

Try to apply injection cleaner directly via the central line of the FD showed above. Flood the FD to clean the gum out. The FD plunger must be able to move freely without any resistance.

[Mike6619]

Originally Posted by Schulisco

Try to apply injection cleaner directly via the central line of the FD showed above. Flood the FD to clean the gum out. The FD plunger must be able to move freely without any resistance.

Thanks… after watching about 4 hours of YouTube videos and the recommendations on here I can see that the plunger should drop against the flapper arm. I pushed it up and it just doesn’t come down under its own weight Will go and try this tomorrow

Fingers crossed!!

Thanks all

[Mike6619]

I pulled the centre fuel line and sprayed in the carb cleaner. I did this a few times pushing up the plate and the using compressed air to push t down again. The plunger moves freely but doesn’t descend on it own. Not sure what happens when the car is running? I also read as mine is a cast iron FD and there is no spring, that this is normal?

The cars starts up easy and rins .. will need to drive it again. To see if it’s changed anything?

[Schulisco]

Some FD had a spring, some people added them? In general - on a proper working CIS not necessary. The plunger must move freely up and down, no matter if pressurized with fuel or not. When FD dismantled the plunger will fall off the case...