1999 Fuel Pump
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Joined: Apr 2006
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From: Las Vegas NV
1999 Fuel Pump
Hi everyone. I'm helping a friend replace the fp in his 99 C5. I'm seeing pumps saying they are left side and right side. Do these have two pumps? What's the deal with left side and right side?
Any help would be appreciated. Thanks in advance.
Constantine
Any help would be appreciated. Thanks in advance.
Constantine
Thread Starter
Pro
Joined: Apr 2006
Posts: 731
Likes: 11
From: Las Vegas NV
Only one electric pump and that is in the DRIVERS side tank. There is a jet syphon pump in the passenger tank. It uses a small stream of fuel from the electric pump to set up a syphon action that transfers fuel from the PASSENGER tank into the drivers side tank so that effectively the drivers side tank remains filled until the passenger tank is empty. Here is more on how the system works:
OK, a little info may help you here .....
* There are two tanks .... each tank has a fuel sender that reports the fuel level to the PCM. The PCM calculates the fuel level based on the info from the two senders and reports that calculated "single tank" level to the IPC which displays it on the fuel gauge.
* The right tank has a "jet siphon" pump in it, the left tank has an electric pump. When the engine is running, the fuel rail is fed by the left tank electric pump. Just after the left pump pressurizes the fuel, there is a line that feeds some of that pressurized fuel into the right siphon pump. The siphon pump has a line that carries the siphoned fuel to the left tank. Both tanks are connected, at the tops of the tanks, by a large diameter "fuel crossover" line which is how the right tank gets fueled ... once the left tank is full during fueling the fuel then crosses over to the right tank, filling it.
* With the engine running more fuel is fed from the right tank than is being taken out of the left tank, so the excess fuel flows back to the right tank via the crossover pipe.
* The "normal" behaviour the PCM expects to see after the tanks are filled is as follows .... the right tank should drain while the left tank remains full. Once the right tank is empty then the left tank should drain. The PCM also knows that the fuel level in either tank should drop as the car is driven a certain distance ..... say 150 miles.
* If the PCM does not see "normal" behaviour (such as the car driving 150 miles and neither sender has moved) then it will set DTC for things like a stuck sender (no movement in 150 miles) or a bad siphon jet pump (the left tank is draining before the right tank) .... or whatever. A P1431 is an example of the codes than can be set.
OK, a little info may help you here .....
* There are two tanks .... each tank has a fuel sender that reports the fuel level to the PCM. The PCM calculates the fuel level based on the info from the two senders and reports that calculated "single tank" level to the IPC which displays it on the fuel gauge.
* The right tank has a "jet siphon" pump in it, the left tank has an electric pump. When the engine is running, the fuel rail is fed by the left tank electric pump. Just after the left pump pressurizes the fuel, there is a line that feeds some of that pressurized fuel into the right siphon pump. The siphon pump has a line that carries the siphoned fuel to the left tank. Both tanks are connected, at the tops of the tanks, by a large diameter "fuel crossover" line which is how the right tank gets fueled ... once the left tank is full during fueling the fuel then crosses over to the right tank, filling it.
* With the engine running more fuel is fed from the right tank than is being taken out of the left tank, so the excess fuel flows back to the right tank via the crossover pipe.
* The "normal" behaviour the PCM expects to see after the tanks are filled is as follows .... the right tank should drain while the left tank remains full. Once the right tank is empty then the left tank should drain. The PCM also knows that the fuel level in either tank should drop as the car is driven a certain distance ..... say 150 miles.
* If the PCM does not see "normal" behaviour (such as the car driving 150 miles and neither sender has moved) then it will set DTC for things like a stuck sender (no movement in 150 miles) or a bad siphon jet pump (the left tank is draining before the right tank) .... or whatever. A P1431 is an example of the codes than can be set.
Also, with key on, I suspect the fp should briefly pressurize the system. What fuel pressure should I be seeing with key on? What pressure should I see with the engine running?
Thanks again.
Thread Starter
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Joined: Apr 2006
Posts: 731
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From: Las Vegas NV
Correct fuel pressure should be around 58lbs. Pump should pressurize the system when the key is turned to the ON position and pressure should hold at that level for at least a few minutes after the key is turned OFF. Engine running should see that same 58lbs... Pressure on the 99 - early 2003 C5's is controlled by the fuel filter. I would definitely replace that when replacing the pump. It's located just forward of the drivers side rear wheel on the inside face of the frame. Because it also controls pressure it is around a $40 part.
If you have no symptoms from the jet syphon pump (codes or gauge dropping to empty while driving the car) I would not replace something that is working. Jet syphon pump assembly is relatively expensive (available on Amazon for around $240 or from a dealer for around $400) so why spend money on replacing a working part.......
If you have no symptoms from the jet syphon pump (codes or gauge dropping to empty while driving the car) I would not replace something that is working. Jet syphon pump assembly is relatively expensive (available on Amazon for around $240 or from a dealer for around $400) so why spend money on replacing a working part.......
Thanks for the advice and information.
