C.S.I Fuel Problem

[Bassethound]

My car for 12years 1977 2.7 911

Hi all,heres a good one for all you brainboxes out there.

1. Turn Key Pump runs, no pressure build up.No start.

2. Connect test gauge setup in line from FD to WUR
turn key,Pump runs,pressure builds up after 10 secs.
Engine starts

3. Remove gauge .Engine starts

4. leave overnight.

5. Same problem ,same procedure.engine starts.

If it helps there is zero residual pressure as soon as the pump stops.

I am starting to wear a groove in my head through scratching it so much
any ideas. Anybody ??
PS It has a new pump and check valve.

[boyt911sc]

Originally Posted by Bassethound

My car for 12years 1977 2.7 911

Hi all,heres a good one for all you brainboxes out there.

1. Turn Key Pump runs, no pressure build up.No start.

2. Connect test gauge setup in line from FD to WUR
turn key,Pump runs,pressure builds up after 10 secs.
Engine starts

3. Remove gauge .Engine starts

4. leave overnight.

5. Same problem ,same procedure.engine starts.

If it helps there is zero residual pressure as soon as the pump stops.

I am starting to wear a groove in my head through scratching it so much
any ideas. Anybody ??
PS It has a new pump and check valve.

Check your cold control fuel pressure.

Tony

[Bassethound]

Hi Tony,
Cold fuel pressures are to spec when pressure is there, but there is no pressure until the valve from the gauge to the wur is closed -and then it shoots up to 70psi-then when the valve is opened it goes down to the control pressure and it will start straight away.
Joe

[pmax]

CIS

Someone has to say it.

[Bassethound]

Yes my mistake CIS I must have worn my brain out trying to sort the problem.

[boyt911sc]

Originally Posted by Bassethound

Hi Tony,

Cold fuel pressures are to spec when pressure is there, but there is no pressure until the valve from the gauge to the wur is closed -and then it shoots up to 70psi-then when the valve is opened it goes down to the control pressure and it will start straight away.
Joe

Joe,

So what is your cold control fuel pressure? What did you mean by “to spec when pressure is there”? The 70 psi. is the system fuel pressure (FP running with valve closed). What pressure gauge kit are you using? Hope you are not using a HF one. Your above explanation is not logical and does not make sense to me.

For your motor to start you need control fuel pressure. Use number (psi./bar) instead of adjective. Control fuel pressure is temperature dependent so you have to consider the ambient temp. when troubleshooting. Keep us posted.

Tony

[coomo]

Start at: Pump check valve.Then check fuel accumulator.The CIS is not just the WUR/metering head.Your losing pressure.Once youve replaced pump check valve & Accumulator, move foward and check EVERY fuel line & replace/check banjos & washers.

[tirwin]

Tony, it sounds like he’s having trouble building fuel pressure to even do the test. Fuel pressure is only there when the gauges are hooked up and then it sounds like pressure is building very slowly.

First thought was bad fuel pump. But then I read it’s a new fuel pump. Possible that it is bad? They don’t make ‘em like they used to...

Next thought is restriction/gummed up (old fuel?). If your fuel gauges are replacing a segment of the lines, maybe that is where the restriction is?

[Bassethound]

Thanks for the replies guys.

Tony, the pressures are as follows;

The system pressure is 72 psi.

The working pressure is about 20 psi when cold
going up to about 45 psi when it has been running awhile.


I have a pipe connected to the male connector on the FD.
That is connected to a tee joint which has a pipe going to the male connector
on the WUR via the on/off valve and the gauge goes to the other leg of the tee
joint.The gauge is just an ordinary pressure gauge intended for fuel.

The car is used at least once a week and the fuel is fresh.

I get the impression that the fuel is being pumped back to the tank
without doing anything but by connecting the piping it gives a few seconds
for the fuel to run quickly while it is filling the test rig up and that is enough
to trigger something to cause the pressure to build up- but what that is I don't
know.

Hope that all makes sense.

[boyt911sc]

Joe,

System fuel pressure is within spec. but the cold and warm control pressures are out of spec. Adjust them higher. Could you post a picture of the fuel connection you have to the FD? Thanks.

Tony

[Bassethound]

Thanks Tony,
I will do that when I get the chance.

Thinking about things more:
I know it is unlikely in an open system but could air be getting trapped in between
the pump and the FD somewhere and in connecting the test piping it allows the
fuel to run and take the air with it because a few seconds after the pump runs
I can hear it slow down as the pressure builds up and the car will instantly start
and idle perfectly so I don't think there are any leaks in washers or fittings etc.

[T77911S]

I would look at the check valve and fuel accumulator. it definitely sounds like one or both of those are bad. fix them first.

your pressures are bad but it will run.

[Bassethound]

I will check the accumulator .I thought that was just a simple fuel-in,fuel-out
device with a spring loaded diaphragm to provide positive pressure when the
engine isn't running but mine has an additional port at the bottom so what is
the purpose of that ?

I don't think it will be the check valve because there wouldn't be any pressure
build-up.

[T77911S]

the port on the bottom is for fuel that leaks past the diaphragm. in fact if you remove that connection and fuel comes out the diaphragm has a leak in it.

the check valve is cheap, just replace it especially since your residual drops straight to zero.
it helps hold fuel pressure in the system and it actually works with the accumulator to do that.

[boyt911sc]

Originally Posted by T77911S

the port on the bottom is for fuel that leaks past the diaphragm. in fact if you remove that connection and fuel comes out the diaphragm has a leak in it.

the check valve is cheap, just replace it especially since your residual drops straight to zero.
it helps hold fuel pressure in the system and it actually works with the accumulator to do that.

Ty,

There will be always fuel at the bottom of the fuel accumulator whether it is good or bad. This subject had been argued and discussed over the years. It is a misconception or a myth. Why? The three-port FA has a bottom port connected to the main return line to the gas tank. The excess fuel from the fuel distributor goes back to the tank and fills the line to the bottom of the FA with fuel.

In the case of the two-port FA with no drain line, the bottom chamber of the FA should be always dry except when the diaphragm is defective.

Tony

[930cabman]

Originally Posted by Bassethound

Yes my mistake CIS I must have worn my brain out trying to sort the problem.

Does this happen often? there may be a pill for this condition!

[T77911S]

Originally Posted by boyt911sc

Ty,

There will be always fuel at the bottom of the fuel accumulator whether it is good or bad. This subject had been argued and discussed over the years. It is a misconception or a myth. Why? The three-port FA has a bottom port connected to the main return line to the gas tank. The excess fuel from the fuel distributor goes back to the tank and fills the line to the bottom of the FA with fuel.

In the case of the two-port FA with no drain line, the bottom chamber of the FA should be always dry except when the diaphragm is defective.

Tony

i always thought you were one that said that.
mine never had fuel there coming out the bottom.

one way too look at it is if you have a line that is capped at the end (the FA) and it has a "T" that leads to basically and open in (the fuel tank) the fuel cant flow down the line that is capped because of air in the line and it should flow to the tank not towards the FA.

I just did some plumbing in my house.
there were "water hammer" pipes "Teed" on that had caps on the top. there was no water in the pipes because of the air that was trapped.

I know you have done more testing on this than I have. I only ever looked at the FA on my 77 and my engine is out on the 930 so I cant look at it.

[boyt911sc]

Originally Posted by T77911S

i always thought you were one that said that.
mine never had fuel there coming out the bottom.
..................(edit).....

Ty,

I had a show and tell post regarding this subject. Do this test: Disconnect the fuel line connected to the bottom of the fuel accumulator (fuel would be dripping out) and test run the FP. What do you think will happen? Fuel will be gushing out from this fuel line. BTW, do not run the FP too long to avoid flooding your garage floor with raw fuel.

Tony

[Bassethound]

Tony,I took pics but I can't get them to upload

Joe

[boyt911sc]

Originally Posted by Bassethound

Tony,I took pics but I can't get them to upload

Joe

Joe,

Could you send the picture to ATD911@hotmail.com? Thanks.

Tony