Fuelpump running but no fuel supply ???
 

Hi guys,

I recently restored the tank support brackets and replacing all fuel lines in the process.
So when tring to restart the car (after a long time with an empty tank and fuel lines) it did not work.
Fuel tank is filled with about 4 gallons fuel.

I jump started the fuel pump (via pin 30 & 87 at fuel relay) . fuel pump is working but no fuel is coming out ????
As if it is running dry...since pump becomes also warm and you can hear it pumping air ??

Could it be a problem with little curved hose from tank to pump , since I had to replace this one with an extra adaptor. Adaptor was needed since diameter of pipe fueltank is smaller than diameter pipe fuelpump ??
(When disconnecting this curved hose, fuel is coming out of the tank)

make sure your not running the pump backwards :) I did that once.

Yep, that is a possibility , although I marked - and +.
- (brown wire) and + (red/green wire)

I'm completely lost now...and then I'm beginning to doubt everything

Got gas in it?

No fuel coming put where? Can you post a picture of your installation?

Hi, I replaced my fuel lines on my '79 once and the fuel hose was slightly too long and with the pump and cover in place the same thing happened. Fuel pump ran but no fuel to the engine. I just unbolted the cover and this took the kink out of the hose. Fired right up. Just had to shorted the hose.

Aryan,

here is a picture :
http://www.cleo-instituut.be/fuelpump.jpg

Indeed, the hose is a little bit longer than the original, due to the fact that I also had to add the adaptor piece (black plastic piece needed to enlarge from small diameter to larger diameter in order to fit on my fuelpump)

How is it possible that I could not reuse my original hose. It was too narrow on diameter at the end that fits on my fuelpump.
Although it had fit ????

Paul , could this be my problem ?
Is it that sensitive when changing the length ?
What kind of hose did you use to solve the problem ?

Gerrit,

Your hose appears to be flattened on the curved section and may be restricting or cutting off the flow.

In addition did you renew your filter, as it may be blocked from debris?

Do you have a set of electrical drawing for your car to check that the electrical connections are correct. For some to check for you, if you don't have electrical drawings, we require to know what model car you have?

Tails 1990 928S4 Auto.

I did notice this when installing but thought it should not be a problem...
I did renew my filter. Is there also a filter in the tank that I should check ?
Wiring is correct according to the electr scheme.

So the only issue can be the hose...

If you pull the input line off the pump (power off), do you get fuel there? There is an in-tank pump and fuel strainer that can plug. Also, the strainer to the input pump has to be completely covered in fuel and that requires more than you would guess. You might consider geting the correct line that goes between the two pumps and put that in to avoid kinking at some point in the future. I seem the recall that that hose is pretty inexpensive.
Next step would be to pull the output line off the pump (power on) and see if you get fuel there.

First thing is to get the correct hose this has a car fire written all over it,
dont add any connectors to the hose fit the correct part.
The wires will only fit on the pump one way as the power wire end is smaller ID than the ground connector fitting and the studs on the pump are also different sizes. Also the hose you used may be disintagrating from the fuel .

Gerrit,
I agree with Tails, that hose looks flat in the bend. It has been about 10 years since it happened on my car but I remember being surprised how sensitive the hose was to lenght to keep it from kinking.

Gerrit,

From the photo you have an intake pump and not a strainer (wires running to the pump). The in tank pumps have a rubber tube that connects the pump to the outlet and these are a weak point. When they deteriorate the intank pump simple recirculates fuel into the tank. With the fuel relay jumped and the main pump electrically disconnected you should hear the internal pump spinning but if the rubber connector is ruptured you are still just recirculating gas. Need to pull it to visually inspect. I have read that you can pull the intank pump by just loosening the tank strap to give enough access.

The intank pump or strainer is threaded into a metal insert which is pressed into the plastic tank. I believe it requires a 36MM (memory) socket to get the intank pump out. Be very careful as the inserts are known to start spinning in the plastic tank (pump / strainer frozen to metal insert) and if that happens you will need to replace the tank or use JB Weld to repair the insert (ask me how I know). If the intank pump is bad you can replace it with a less costly strainer and the car should run fine (intank pump is suppose to be for hot /high environments so I am told). Once the insert spun I ended up dropping the tank.

I used sharksin's tank drop write up (link below) and had the tank out by myself in less than 2 hours.

http://members.rennlist.com/sharkski...0-FuelTank.htm

BTW the OEM hose used to connect an in tank pump to the external pump is different from the one used to attach a in tank strainer to the external pump so get the right hose depending on what you end up with in the tank.

Good luck!!

Another possibility: a reversed check valve.

Anyway, the only way to find the cause is to work you way back from the fuel pump. Take off one component at a time and check if fuel flows.

I finally found the problem but how can it be solved ?? :

apparently the metal fueline between the external master fuel pump
and the filter contains a valve just behind the fuel pump.

So normally with sufficient pressure this valve will open and fuel will flow
through the filter towards the engine.

DOES THIS MEAN THAT I HAVE TO FILL THE TANK COMPLETELY IN ORDER TO BUILD SUFFICIENT PRESSURE BELOW SO THAT THE VALVE BEHIND THE FUEL PUMP OPENS ???

That's what I meant by check valve in my previous post. The valve just blocks fuel running back through the fuel pump, and insures there is fuel pressure at the injectors. Not sure how much pressure is needed to open it but I imagine not much. Did you maybe put the valve back in reverse?

Aryan,

I did not touch it when replacing my fuel lines....strange

I now have for about 4 gallons (15l) in my tank. Fuel gauge reads minimum.

I did not find any threads regarding this issue....what if you are running out of gas....could this reproduce the same thing...

I know that some cars need a full tank to startup again after running empty.

No, you should not need a full tank. The check valve may be stuck. But still do not overlook that kinked fuel line. It may be closed completely - hard to tell due to the braided sheath covering it. Get the proper line. it may not be allowing sufficient flow regardless of the valve.

Also, even if the in-tank pump has a broken hose (most do) or is not working, fuel will flow by gravity. The car will run but may not have good high-speed performance. George Suennen's 91 had a bad in-tank pump. The car ran well until he tried to go over 120 MPH. Anyway, although the in-tank pump should be examined, it's probably not the main issue with starting the car.

How old is the fuel pump? It's likely still the fuel hose, it does look kinked. Is you want to measure the fuel output should be appr. 1150 cc /30 seconds.

I replaced the kinky fuel hose by an original one and still have the same problem. Both pumps are working fine but no fuel coming out of the external fuel pump.

How much pressure is needed to open this check valve..

I'll try to get some more fuel in the tank, you never know.
Logically the check valve needs some retaining force, otherwise fuel would not stay in the hoses towards the injectors.
So the force by the fuel in the tank and pumps needs to be a little bit more than the fuel in the fuel lines in order to open this valve...

I can find little information on the internet regarding this valve.....

However I checked the original manuals and apparently I have a fuel pump of the 1981 model with a separate check valve. Perhaps indeed, this valve got stuck.

I've never seen one of these check valves not open. Even pumping air should open it. Their usual failure mode is to not close. Loosen it a bit and see if fuel drips or squirts out. At this point you don't know where the block is. When you removed the hose fuel should have run freely out of the tank. Did it?

Bill,

it is nothing more than a pin with a spring into a plunger. Blowing air through it doesn't work, so it is really tight. Removing the hose, fuel flows freely out of my tank...
Perhaps due to the fact that my fuelpump was disconnected from the hoses and tank for a couple of months due to restoration of the car, could perhaps have locked the valve since fuel pump went dry.

Here is a picture :

http://www.cleo-instituut.be/Untitled.gif

Like I said, loosen it just a bit and see if fuel flows/drips/squirts from behind it, in which case somehow it got jammed shut. But first I would loosen the line on the downstream side to see if fuel is or is not going through the valve. From what I've read you haven't established whether fuel is really pumping or not.

checked, loosen the banjo bolt and check valve and fuel is flowing out of the fuel pump. ..damn something that little can cause such big problems :jumper:

luckily no major costs ...worst case I will need to replace the check valve if it doesn't come loose.

Hopefully this thread now can help other 928 enthusiasts to solve similar problems :thumbsup:

it's probably a ball or pintle spring loaded check valve
they seldom fail
check it by using a pick to push it open (from the pump side)
the pump may not be making sufficient pressure to open it...
as others ahve said the suction restriction (kinked/constricted) hose may be starving/cavitating the pump
it has very little suction head and needs the static head from the tank to work properly

That fuel pump looks really old, they are a known failure points, it just might be time to replace it.

And as said already, get the proper hose for that car and toss that mess in the trash.

Sean,

perhaps you are right, I can't tell since the car has switched from several owners and no history know (but engine has run only 100000 miles).
I'll just give it try after loosening the check valve and if pressure is not sufficient, I'll definitely buy a new pump.

Any idea how much a new fuel pump costs ?

The correct pump for your car is about US$300...maybe a bit more.

These cars require new parts and maintenance. You can do the very minimum and hopefully have a trouble free ride for many years and kilometers or you can do a lot and hopefully have a trouble free ride for many years and kilometers :) Bottom line is, these cars do require a budget. Personally I set aside about 2000-3000 EUR a year. Sometimes it is more, sometimes it is less.