newbie 1976 CIS troubleshooting

[SanchoBunce]

My 1976 911S (us spec) run great some years ago.
Because of house renovations and "life that got in the way" I did not drive it for 6 years.

It didn't wanted to start anymore so I replaced the fuel pump. (put an inline filter in front of it cause some dirt came out of the tank)

When I now try to start it, it will give me 2 or 3 strokes and then it stops.
When I remove the air filter and manually open the airflow sensor plate. (just open it a little bit)
I can hear the fuel going into the engine.
When I start like that the engine will run (at idle).

Opening the airflow valve any further will not make it run any faster (even with throttle open/partially open/closed/...)

Only results in backfires (luckily I have a pop off valve).

I googled and search this site and others.

But first thing to do in the test is getting the fuel pump to run.

So since it's a 1976 I removed the relay in the engine compartment, run a metal wire between the 30 and 87a (on the relay) and put the relay back into position .
Put on the ignition switch (not starting, just ignition).
But my fuel pump won't run!
If I start or manually open the air sensor plate, then it does pump!

Sofar I tested fuelflow behind the fuelfilter/accumulator combo.
And that is more then sufficient.

What am I doing wrong here?

Thanks for your help.

Tanguy

The 911 in better times...

[boyt911sc]

Tanguy,

You came to the right place to seek advice. There are a lot of guys in this forum that could help you in troubleshooting this problem. But first, post a picture of your ride. This is a protocol new members are requested to do otherwise help would not be coming fast as you would expect.

Tony

[SanchoBunce]

My Porsche
In much better times

[911SauCy]

Amazing resource:
911 CIS Primer - Troubleshooting

[ossiblue]

Yes, read up on the CIS using the link provided by 911SauCy as well as the thread on this forum, "CIS for Dummies."

Your pump should run when you turn on the ignition after jumping 30/87a. First, be absolutely certain you have jumped the correct pins on the relay. Next, try the same test but this time, remove the relay completely and push the jumper wire ends into socket 30 and 87a of the relay base. Make sure you have good contact in the sockets. Does the pump work now?

The fact your pump runs when you lift the plunger tells you power is getting to the pump (30), via the relay from 87a. It also tells you the relay is switching power from 87 to 87a when the plunger is moved off the air flow sensor switch. Rerun your jumper, as above, and let us know the results.

[timmy2]

On your 76 there is a brown with black markings single wire with connector beside/below/near the 14 pin connector on the rear fuse panel.

Disconnect it and you don't have to jumper the relay to get the fuel pump to run in the ignition run position.

Reconnect it for the air flow safety switch to work properly when done troubleshooting.

[SanchoBunce]

I will test it when home.

Quick question.
Is the fuelpump switched on by the positive side?
Or does it has a constant plus and is it ground triggered?

[boyt911sc]

Originally Posted by SanchoBunce

My 1976 911S (us spec) run great some years ago.
Because of house renovations and "life that got in the way" I did not drive it for 6 years.

It didn't wanted to start anymore so I replaced the fuel pump. (put an inline filter in front of it cause some dirt came out of the tank)

When I now try to start it, it will give me 2 or 3 strokes and then it stops.
When I remove the air filter and manually open the airflow sensor plate. (just open it a little bit)
I can hear the fuel going into the engine.
When I start like that the engine will run (at idle).

Opening the airflow valve any further will not make it run any faster (even with throttle open/partially open/closed/...)

Only results in backfires (luckily I have a pop off valve).

I googled and search this site and others.

But first thing to do in the test is getting the fuel pump to run.

So since it's a 1976 I removed the relay in the engine compartment, run a metal wire between the 30 and 87a (on the relay) and put the relay back into position .
Put on the ignition switch (not starting, just ignition).
But my fuel pump won't run!
If I start or manually open the air sensor plate, then it does pump!

Sofar I tested fuelflow behind the fuelfilter/accumulator combo.
And that is more then sufficient.

What am I doing wrong here?

Thanks for your help.

Tanguy

Tanguy,

You are doing the FP relay test the wrong way. Do yourself a favor and get familiarized how the FP relay works by reading DKLever48's post about FP relay tests. The subject is discussed and covered enough to give you a good understanding of the subject. You need a fuel pressure gauge to do an effective diagnostic test.

Without a pressure gauge you leave critical information for a meaningful diagnosis. Air leak is another thing you need to investigate. Remove the fuel filter you installed after the fuel pump. There is already one installed in the engine bay unless someone removed it. Drain and clean the fuel tank. Check and clean the fuel tank filter. Then test run the FP.

Tony

[SanchoBunce]

Originally Posted by boyt911sc

Tanguy,
Remove the fuel filter you installed after the fuel pump. There is already one installed in the engine bay unless someone removed it. Drain and clean the fuel tank. Check and clean the fuel tank filter. Then test run the FP.

Tony

FYI

I installed the filter in front of the pump.
To protect it from any dirt...

[SanchoBunce]

I do have a fuel pressure gauge.
But the 20+ connections that come with it are worthless!!!

I just ordered a new testkit specific to kdfi...

[SanchoBunce]

Ok I found that the yellow thick wire of this connector was loose...
Don't ask me why.
But the cap of the connector was of...
I removed the connector and offcourse 6 other wires came loose...
Which goes where? ??

Oops

[SanchoBunce]

Ok forget the last post...

Google saved that for me ☺

[SanchoBunce]

Originally Posted by timmy2

On your 76 there is a brown with black markings single wire with connector beside/below/near the 14 pin connector on the rear fuse panel.

Disconnect it and you don't have to jumper the relay to get the fuel pump to run in the ignition run position.

Reconnect it for the air flow safety switch to work properly when done troubleshooting.

Perfect this works!

[SanchoBunce]

Ok since vacuum is also very important.

The low small hose from this tank.
The other side was loose in my engine bay..
I found it driver side against the firewall.
But where does it connects to?

[SanchoBunce]

Also found these 2 hoses blocked off...
Won't be THE problem.
Since engine worked ok years ago...

[SanchoBunce]

Update.
Got my new gaugeset.
Pressure went over 10 bar...
Measured between WUR and fuel distributor...

After diagnose I found the return line is open.
But the return in the tank is blocked.

So next tank goes out...

Question: the return into the tank.
Should that just be a straight tube?

Or is it a special bent tube?

[ossiblue]

Originally Posted by SanchoBunce

Update.
Got my new gaugeset.
Pressure went over 10 bar...
Measured between WUR and fuel distributor...

After diagnose I found the return line is open.
But the return in the tank is blocked.

So next tank goes out...

Question: the return into the tank.
Should that just be a straight tube?

Or is it a special bent tube?

From your post, I assume all the hoses and lines, from the engine to connection to the tank are open, is that correct? You found that the return port(where the return line connects) that is attached to the tank is blocked, is that correct?

If I am correct, then the answer to your question is the return line inside the tank is not a straight tube, it is a metal line connected to a swirl pot that causes the return fuel to circulate.

Take a look at the pictures in this thread

Fuel Tank Restoration !! Many Pictures

The return line has a double bend that channels the fuel to the swirl pot. You probably have some gunk in the line or swirl pot. You may be able to clear it by pushing some soft wire, like building wire, through the tube. Maybe even a very small diameter spring-type drain opener will work.

[SanchoBunce]

Hmmm my 76 looks a bit different.
To the engine is on the driverside corner.
Return is on the passengerside corner.
Tried to clear it with a bicycle spoke.
Didn't work. But when al is removed I will try again

[porwolf]

Originally Posted by ossiblue

From your post, I assume all the hoses and lines, from the engine to connection to the tank are open, is that correct? You found that the return port(where the return line connects) that is attached to the tank is blocked, is that correct?

If I am correct, then the answer to your question is the return line inside the tank is not a straight tube, it is a metal line connected to a swirl pot that causes the return fuel to circulate.

Take a look at the pictures in this thread

Fuel Tank Restoration !! Many Pictures

The return line has a double bend that channels the fuel to the swirl pot. You probably have some gunk in the line or swirl pot. You may be able to clear it by pushing some soft wire, like building wire, through the tube. Maybe even a very small diameter spring-type drain opener will work.

I cleared my 1979SC tank return pipe successfully after a 16 year garage hibernation with this tool:


Search drain cleaner tool | osh Site



I did modify the tool by clipping off the tip and bent the end of the wire 90 degrees so it scrapes at the obstruction. I did that repeatably for about one hour because the obstruction was quite hard. Eventually I broke through and the return path was clear. I did it with the tank in place. Since then, 2011 my car runs fine, no complaints

[SanchoBunce]

To be clear.
Yes it is the return port that is blocked!