Fuel pump install...tech details.

[k9handler]

This is the basic details of trouble shooting and step by step procedures used to install and purge/prime the fuel pump and fuel system. This is for a 911 with the rear mounted pump.

Make sure to clear the area of spark producing devices/materials.

Use small needle nose vice-grips to clamp the fuel line at the fuel tank side of the pump.

Disconnect the fuel pumps electric connection. Inspect the fuse/relay as well to make sure you will have power to the pump. You can also use a voltage meter/test light to test the connection at the pump.

Gather a collection container...you will spill a small amount of fuel.

Disconect the feed line (pull side) from the pump.

Disconnect the rear line (push side) from the pump.

Remove the two nuts that secure the pump mounting bracket to the vehicle, and loosen the clamp that secures the pump to the bracket.

Remove the pump...do not lose the small washers and the crush washer for the rear line (push side)...you will need these for the new pump if it does not have them.

Before you install the new pump, make sure to oil the feed line side with a small amount of oil...this came in the pumps instructions so I did it.

Now it's time to reverse everything and install the new pump, make sure to tighten all the connections and after everything is connected check the fuse/relay once again.

Here is the tricky part...prime the pump!

Use compressed air! Remove the gas tank cap and use the air to pressureize the tank...this will push fuel to the pump.

Now disconnect the fuel line from the accumulator...this will allow you to run the pump and push fuel through and pass the check valve. Only do this for a quick 5-10 sec bursts, once the pump starts to pull fuel through the lines pressure will build and spray from the loose connection at the accumulator.

Now connect the line at the accumulator and make sure there is no leaks on all the connections.

The final step is to simply attempt to start the car...it may take a few attempts to buld pressure in the system...but if the pump was your problem this will work.

DISCLAIMER!!! I am no expert...far from it! I simply needed to get my car working and I accepted the risks of working with the fuel system. Work in a well ventilated area and be safe. This is simply a way to provide a little info to assist others as I have benefited from this BBS.

Good luck.

[HarryD]

I have not needed to do this yet but got a question.

Why not leave the inlet line to the pump unconnected and lower than the fuel tank. Gravity will force the liquid to flow. Once it is flowing, you attach it to the pump. Then start the pump. This aviods this whole pressurization thing with it's attendant risk of popping a vent hose off somewhere.

BTW-The idea is to flood the suction. One thing to consider is that most fuel pumps (never looked at the guts of a Porsche fuel pump) are positive displacement pumps. That means that they can prime themselves by first pumping the air out of the line, creating a vaccum and then pull the liquid to the pump suction. This is how a diaphragm pump works.

[k9handler]

Harry,
All that you describe was attempted...the fuel line from the tank runs through the tub and then up the rear wall before coming back down to the pump. I had the fuel line off and down lower than the car...no fuel.
And yes the pump should be able to prime itself...but after many attempts the pump just could not do it until pressure off the engine side of the pump was released. This may not be the best way...but after 4 hours of hair pulling it worked, and had I done the entire procedure step by step as I discussed the entire project would have only been 1 hour.

[HarryD]

Well, at least you will save me hours of hair pulling when it is my turn!

After reading your procedure, probably the first thing I will do is use my MityVac to pull the fuel to the pump before I hook up. But again, thanks for sharing.

Given the small diameter of the lines, I can see where it may be a problem to get flow started. When I am starting up an industrial piping system, one of the major pains is to get the air out of the pipes so you do not get a vapor lock in the line. We often need high point vents to properly purge a system. We will also disconnect the discharge of a pump to reduce the system back pressure to get flow going. One other thing to be careful is to get all the air out, otherwise you will see fuel stravation at higher speeds due to restricted flow.

But still, thanks for the post. We all struggle with details like this at one time or another.

[Eric Mckenna]

Smitty,
That is a nice read.. you will help some guys out for sure with it.
I had to do this last year, the thing is still pumping fuel so I guess it did it all right..
I wish I would have had this to read before I started though as I was kinda treading new waters at the time.
Thanks bro for posting it up.. I am glad that guys take the time to help others out by writing the step by steps..
Great job!

Eric

[k9handler]

Thanks Harry and Eric,
I know my method may not be the "text book" version, and somebody may be able to post up a much easier way (I hope they do) and we will all be a lille better off. All I can say is it seems the fuel needs to reach specific points of the system before you can advance to the next step...so it was a basic follow the path and ensure fuel was present and then move to the next connection and repeat until you reach the fuel filter. Thanks again for the comments and have a great weekend!

[HarryD]

k9,

We in the land of liquid sun hope for the other kind on a daily basis. I'll be hitting the AutoX course this weekend rain or shine.

[k9handler]

Harry,
The rains have been here as well...but this weekend is nice since I am working! The autox here is next weekend at Bitburg and I will be there...first event since the 3.6 was installed, should be fun!
Enjoy your event, post pics/results if possible.

[Paul Thomas]

I like the part where you say "you will spill a small amount of fuel".

HAHAHAHAHAHa!

I took a gas bath the first time i did it. Good write up.

Cheers,
Paul