Hey everyone, since I have been struggling with the fuel system these past days because of a leaking fuel hose, I thought I would take some pictures and share it to those who might be interested in understanding how the fuel system works in their car. First I want to thank Kevin at UMW for helping me solve my problem, he probably saved my engine. He also taught me how the system work. You don't get just good parts with him, you get excellent customer service. I will keep sending him some logs from time to time so he can analyse my car and make sure everything is correct.

This is a quick survey of all the parts, if I am wrong somewhere or if something is not well explained, please let me know so I can correct it.

So the fuel pump system is composed of a couple of things. First of all, when you want to change a leaking hose on the fuel system as it often happens, you can not buy only replacement parts from the dealer, you have to buy the whole fuel pump assemble. Only thing that can be purchased separately is the venturi tubes, we'll get to that later.

I have not taken pics of the process on how to remove the fuel pump but it is pretty straight forward and easy. I might take some when I'll install everything back together and add the pictures to this thread.

Now as you can see, with the fuel pump in place, I have a hole in my rubber hose. The outside is looking pretty bad but there is only a tiny hole in the inside layer. My symptoms were slower car and slight hesitation at WOT. With the durametric logs, Kevin was able to diagnose that I was missing fuel pressure. My injectors were showing 100% duty cycle and the AFR would keep raising up. Luckily the ecu pulls timing when this happens, which saved my engine.

Picture of bad hose and fuel pump in place with the fuel sender removed.



To remove the fuel pump assembly, you have to turn it counter-clockwise about 15 deg. Here is a picture of the bracket at the bottom of the fuel pump that holds the assembly in place.



Here are a couple of picture of the fuel pump assembly with the venturi tubes.






Now how does the system work. First you got to know that the fuel pump is in a big plastic tank, called also a surge tank. It is a system that prevents the fuel pump from missing fuel when hard acceleration, braking or long cornering is happening with a lower fuel level in the tank. This prevents fuel starvation and possible blown engine.

The way the fuel tank is made on the 996tt and C4 is a big tank on top of the front differential with two small "pod" going on each side of the differential to add some extra fuel storage. I don't think you have those on the 2wd 911 since there is no diff in the way of the fuel tank.

On this diagram, you can see the pod I am talking about (sorry don't know what other word to use). You can only see one in the picture but there is an other one on the other side we can't see.



Now for the surge tank to get the fuel that is located in the "pods" and the lower part of the fuel tank, the system is using two venturi tubes, one on each side. Since the pump is hanging in the middle of the fuel tank, it has to have a way to get the fuel to the bottom of it. The way the venturi tube is working is pretty simple. Fuel from the fuel pump goes to these tubes and creates a low pressure zone (vacuum) which then sucks fuel and send it in the surge tank. So basically, the fuel pump, on top of sending fuel to the injectors, send fuel to those tubes to create the vacuum to pump the fuel in the surge tank. Pretty weird design and I don't know why they didn't use an other electric pump or something else instead of putting extra stress on the fuel pump but I guess Porsche engineers had good reasons. It seems that one of the fuel pressure failure can be on those venturi tubes, if one fail, all fuel pressure goes to that pipe and back to the fuel tank and you get almost no pressure to the injectors. So it is a good time to inspect them if you remove your fuel pump from the tank.

Here is the end of one of the venturi tube.





To remove the venturi tube from the fuel pump assembly (which you have to do in tank before removing the fuel pump assembly) you just remove the two flexible fuel line on top and unclip the plastic block by the back of the surge tank (took me a while to figure out how to remove those pipes)

Here is a shot of the back of the surge tank where you can see the two holes for the clips of the venturi tubes. (sorry about the workbench mess)



Now here is a picture of the fuel pump assembly with some lines to see where fuel goes.

The big white piece is the surge tank. In the middle (black circle) is the fuel pump itself. The red line is the fuel pressure hose going to the injectors.
The blue line is the fuel return hose from the fuel rail (After the fpr)
The green line seems to come from the fuel filler neck probably to fill the surge tank first when you fill up with gas (not sure on that one)
The yellow line is the fuel coming from the fuel pump and going to the venturi tubes. You can see there are two, fuel splits up in two but can't see it in the pic.
The orange line is the fuel picked up in the "pods" and going back to the surge tank after the venturi did it's thing.



On my car it was the rubber 180 deg hose that failed but it seems like usually it is the flexible nylon hose that fails so if your car has some years and some mileage, it will eventually fail, might has well inspect it or just change it in a preventive manner. It is expensive and I didn't want to try some cheaper replacement part just by buying some in-tank fuel hose but I guess it could be done. If someone had good success with a custom fix, please share you experience as I find it kind of stupid to replace the whole fuel pump assembly only to change some hose that will eventually fail again anyway. If tuners are reading, maybe making a tougher system would be a good thing to sell. I just have to fix my car quick to be able to hit the track in a week, it couldn't have happened in a worst time. At least I found the problem before I hit the track…

If you find anything wrong in my text, please let me know. Hope this will be of some interest to some people. Happy Porsching.

 

That is detailed! Wish I read this before.. I had serious hell with the fuel pump. I replaced mine with a bigger unit and different hoses and I just kept blowing lines. I blew 3 different fuel lines.. each one stronger than the other. In the end, I spoke w/ Kevin as well and just ordered the original stuff w/ the original pump and absolutely no problems. Pain in the ***... oh and dont use plastic gloves, they tend to dissolve in the gas tank then you need to fish them out.

Great write up though, big props. I envy you guys that have the patience to take pics and do great writeups like this.

Bojan

 

You didn't say how you gained access to the fuel pump and I can't really see from the pictures. Where is this located?

 

Awsome write up! Great job! i wish i new this when my pump failed a couple of months ago.

 

Very informative and well done write up. I like what you did with John Madden's eraser board.

Colors r purdy

 

Under the front bonnet, it's that black medal mound on top of the carpet.
BTW, great writeup to the OP! rep added!

 

update, here are pictures of both new and old pump one next to each other. You can see how dry the lines get. Also, the new version of the fuel pump doesn't have the rubber hoses that failed on my car.




here you can see the venturi or tractor pump attached to the pump in the bottom.



To take out the fuel pump, you have to disconnect those 3 lines and the electrical connector. Then you unscrew the big plastic that hold everything in place.



Make sure you mark the position of the fuel sender relatively to the fuel tank, there are 3 marks but i didn't have any on my plastic so make one before you remove. I had problem trying to figure out how to put it back on.



All you have left to do is unplug both fuel lines and the fuel pump connector and the level sender comes out. After just remove the venturi tubes, remove the big black plastic that goes to the filler neck and you can twist the fuel pump counter-clockwise so it can come out.



Hope it helped. Maybe this thread could be usefull for further references.

have a nice day.

 

Awesome and timely for me as mine died too.
What was the pn for your new pump? Thanks much.

 

can't recall but there is just one number so your parts guy will find it quick. I didn't call lot of places but sunset had a really good price compared to the others, too bad i was too much in a hurry.

 

Cool. Just wanted to make sure that I get the new one and not old stock.

 

Great Job!!
My fuel pump just failed last month, required a tow and $$$$$$ .

 

Awesome write up. Kevin said I should check and replace mine, good timming on your write up.

 

Excellent contribution to 6speed. Thanks.

 

very nice work i have no probs as of yet. but gee wizz now i can ad that to my list of worries, really thanks for all the pics. maybe thats why my car seems a little slower or could it be the 100 plus weather we had last week in ca.???

 

VERY good post! Thanks for taking the time to do it.