Fuel Pump education

[ekstroemtj]

I know i know its already discussed many times the subject arround fuel pumps. I just would like to learn how exactly these parts are working.

As i know they just work TOGETHER under full load.

Can anybody tell me please if they are starting at a specific RPM or Speed or whatever. What means full load in this way?

Thank you very much

[hahnmgh63]

I can't take credit for this, someone on here posted this a couple of months ago and I just copied it and pasted it to a Pig repair file. Not exactly what you were asking for but some useful info.

With the activation of drivers outer door handle - left pump primes fuel rail.starting procedure: left and right pumps onFuel tank qty >60 Lright pump onfull load: left and right pumps on.Fuel tank qty < 60 Lleft pump on.full load: left and right pumps on.

Here is the info on the elbow:

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955 620 911 00 angled pipe

see technical information service group 2 KD-NR.2066 13/10

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Here are the fuel test specifications:

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Switch on both fuel pumps using the adapter P 9479 and read the pressure on the pressure gauge. The fuel pressure should be approx. 4.0 bar. Then switch off both fuel pumps and check the steady-state pressure. The fuel pressure must not drop below 3.0 bar after 10 minutes.

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You don't need adapter P-9479. You can power on the pumps by starting the engine. To power on a specific pump, pull the fuse for the other pump from the under hood fuse box. The pump that still has power will automatically be switched to. Obviously your P!G failed the pressure-drop test.

[ekstroemtj]

Thank you very much. I was asking because i got new pumps some weeks before. In the beginning car was running like a rocket. After some hundred km now i had a strange behaviour again. Driving in the city or cruising outside without problems. Highway driving and hard acceleration makes me feel the truck sometimes get no fuel or to much fuel. A kind of very short interruption during accelaration. I guess i have to bring it back to porsche for a checking. Even fuel consumtion changed. Before the car tool arround 20-22 liters per 100 km. Now i even hit 24 - 25.

Thank you again

[bigbuzuki]

This is from the publication Porsche Service Technik.

Regulation of Fuel Quantity.

As a result of the on-demand regulation of fuel flow capacity, fuel heating in the tank is reduced.

This is achieved by the DME control module switching on fuel pump 2 only as required, while fuel pump 1 is always activated.

With the following switching criteria, fuel pump 2 is additionally switched on to increase flow capacity.

At engine start and then 2 seconds run-on (with a hot start 5 seconds run-on).

With a calculated fuel consumption of > 50 liters/hour the pump is switched on, and at < 45 liters/hour switched off again.

With a fill level of < 10 liters in the tank, it is switched on and with > 15 liters it is switched off again.

Edited March 25, 2013 by bigbuzuki

[ekstroemtj]

Wow! Great info. This i was looking for. Thank you very much !

[mbagge01]

After fixing one of my fuel filter connections, I will get the line pressure to hold around 1 bar for around 10 minutes when off. I have not changed out the updated angled connecter yet and my filter is about 6 months old as I have been told there is a check valve in it. The car pulling timing has improved with my evom tune but is my holding pressure ok or should I be looking for another source of pressure problems given the data above states it should hold around 3 bar when off. I did check both fuel pumps which run above 4 bar each when running.

[VIPNiSS]

Is there a way to tell if a particular pump is going bad?

[ekstroemtj]

Is there a way to tell if a particular pump is going bad?

To find out if its bad or if its going bad?

[VIPNiSS]

Is there a way to tell if a particular pump is going bad?

To find out if its bad or if its going bad?

to find out if its bad.. sorry

[ekstroemtj]

You should feel it. When starting the car or when driving very hard. Why , because just in this situations BOTH fuel pumps are running

[VIPNiSS]

I noticed when I get on it sometimes it surges like not enough fuel. I know it's not coilpack or plugs cause I just changed them. I also notice when I come to a complete stop the RPM drops like the car is going to die. Someone told me possible fuel pump as well. So today I started the car and pulled the 13 fuse and car idle just fine. Then I inserted 13 fuse in and pulled the 14 fuse and the car wanted to die and struggled to stay on after a few seconds. What does this tell me?

Edited March 28, 2013 by VIPNiSS

[VIPNiSS]

Also it should be normal at cold start for car to idle high at 1krpm then dropped down correct after about 30-40 seconds?

[hahnmgh63]

Yea, when you do a cold start the Secondary Air Injection pumps/compressors are running and the ECU tells the car to idle a little high when cold to work in conjunction with the SAI system to more efficiently burn the slightly richer starting/cold run mixture. When the SAI pumps shut down your idle also will drop, within a couple of seconds.