Fuel Pump Replacement tips and tricks
03-05-2007, 09:29 AM
#1
AudiWorld Senior Member
Thread Starter
Fuel Pump Replacement tips and tricks
I helped Heinz, a fellow A8 owner, change his fuel pump assembly on Saturday morning. I don't think it took us more than three hours total, certainly better than my saga of cutting out the old assembly with a home-made foot-long hole saw I welded up. Anyway, a couple of tricks to add to the vague Bentley procedure.
The Audi specified method of confirming that you installed the pump correctly - Put in a gallon of gas and drive around, hoping you won't stall out - is idiotic and more than just a little bit dangerous. Hey, speaking of dangerous, did I mention we replaced the pump with a full tank of gas? No cigars please. I begrudgingly disconnected the battery at Heinz's insistence...wuss...did I mention his unnatural fascination with gladiator movies....not that there is anything wrong with that. I digress.
OK, my tip is: Confirm that the new pump is installed properly by using it to pump out the tank. How? Two steps.
INSTALL TEMPORARY FUEL LINE
The High pressure flow from the pump feeds into the fuel line via a banjo bolt and fitting. I had a banjo fitting of the almost correct size (I drilled it out to fit when I did my pump last Summer) and attached six feet or so of clear plastic fuel line to it...not high pressure stuff just cheapo clear plastic. So, once we got the pump installed and the long bolt snugged down, I attached the banjo fitting and the plastic hose and ran it into a 5 Gallon Gas can.
next...
HOTWIRE THE FUEL PUMP
Heinz already removed the passenger's side front carpet and the cover to the relay box. On his cherry 1997, the fuel pump relay is the last one on the bottom right. I unscrewed the one retaining screw that holds the relay tray into the box and slid out the tray slightly. Then I gently popped the COVER off the fuel pump relay with a small flat screw driver and left the relay in place. Then Heinz reconnected the battery. With him watching the homemade banjo fitting and the gas can, I slid a piece of folded over plastic fuel line (unused) In between the gap between the fuel pump relay and the one to its left. This pushed the fuel pump relay points closed and energized the fuel pump. So now, the newly installed fuel tank pump is pumping out the tank...Its all good....until we get to about 1/3 of a tank (we simply reinserted the fuel gauge sender to monitor the level, but did not put the spring loaded cover back on it BTW) Then the fuel flow starts to aerate and spit...This means the pump assembly is not seated properly. So, I pull out the wedge of hose holding the relay closed and the fuel pump stops; disconnect the negative battery cable again; slide out the fuel gauge sender, loosen the foot long retaining bolt which holds the fuel pump assembly to the internal Cup/Baffle until about half an inch of the bolt shaft is showing then rap the head of the bolt down (plastic screwdriver handle and rubber mallet - NO SPARKS PLEASE) to push the baffle down and separate it from the fuel pump housing. Remove the bolt.
Then we try to position the assembly again. The two essential components on the new fuel pump assembly which must mate up with the baffle are the FOOT which the bolt passes through and the SUCTION PIPE. The thing to keep in mind is that the Baffle/cup assembly in the tank is not actually secured in place. Rather, it has a couple of different hoses clipped into the top and bottom of it, all of which have some slack in them allowing the whole unit to move around a little. So we remove and reinstall the pump assembly and this time it feels a little different when it seats. When I wiggle it slightly, it feels like it is pivoting on the axis of the suction pipe, so I think it is seated correctly (It is BTW). But let's prove it!
My able assistant pours in about a quart of gas to prime the pump When you pour in fuel through the gas cap, it flows through a corrugated plastic pipe inside the tank that dumps into the top of the Baffle/Cup assembly. This hose is just clipped into the top of the baffle assembly, and the fuel pours out of it and spills into the cup. If the top hose becomes unclipped, you won't primer the pump at all. So if the top hose is properly positioned, at least the the pump will run and pump out the fuel that we primered the cup with, and then start to spit and aerate if the pump is still seated wrong. If the pump is installed correctly, it will start with this primer and then suck up fuel through a network of hoses off the bottom of the tank, continually re-filling the cup which the pump pumps out. We continue to pump out the tank until the fuel gauge reads less than empty. Then it spits, aerates and stops, and I remove the wedge from the relay. Pour in the last 5 gallons of fuel and we are good to go knowing with certainty that it is all installed correctly.
I made out on the deal because the first 5 gallons went into my other car - a 90 Miata - not that there is anything wrong with driving one of those either. If, like us, you do this job without first siphoning out the tank, have a lot of towels on hand, fire extinguisher (we didn't have one of those) and TWO people present. Oh yeah, neoprene gloves will not dissolve when submerged in a tank full of gas for ...hmmm...about 30 seconds. When your hand starts to feel cold, the glove is breeched. The gloved hand is useful just to confirm that none of the hoses is loose.
The only hose that MIGHT get displaced is the top corrugated feeder hose that clips in to the top. You can feel it by reaching in to the hole back and to the left. It is not far down, rather, just inside the hole to the left at the top of the cup. The CUP is not a complete description of the piece inside the tank. There is a cup (about the size of a Boy Scout issue tin soup bowl) at the bottom and then on the side of it, imagine a vertical silo which, when viewed from above has a curved rectangular cross section. The feed hose from the gas cap pours into the top of this silo. The reason that you loosen the securing bolt a little then rap the top of the bolt head is to separate the fuel pump assembly from the CUP, thus ensuring that you won't pull any of the bottom hoses off the CUP. Also, when testing, you don't have to put the BIG O ring and big plastic nut back on to secure the pump unit in place. All you HAVE TO do is secure the pump assembly to the internal cup/baffle assembly using the foot long securing bolt. This will speed the testing, removing and reinstalling process a bit. Sorry we didn't take photos, but I know there are some in the archives.
So, If you are going to do the job and want to know that it is done right, my advice is to take the fuel line banjo bolt, go to a speed shop and get the correct sized banjo fitting to fab up a cheap hose to pump out the tank. Even if you do empty the tank before beginning, this hose will allow you to test that everything is working correctly. When I did mine, it was bone dry, I poured in 2 gallons of gas, and was able to pump out about 1 2/3 gallons. Keep track of what you pour in and you should get all but.. say.. a half gallon back out of the tank.
Good luck,
Brian C.
The Audi specified method of confirming that you installed the pump correctly - Put in a gallon of gas and drive around, hoping you won't stall out - is idiotic and more than just a little bit dangerous. Hey, speaking of dangerous, did I mention we replaced the pump with a full tank of gas? No cigars please. I begrudgingly disconnected the battery at Heinz's insistence...wuss...did I mention his unnatural fascination with gladiator movies....not that there is anything wrong with that. I digress.
OK, my tip is: Confirm that the new pump is installed properly by using it to pump out the tank. How? Two steps.
INSTALL TEMPORARY FUEL LINE
The High pressure flow from the pump feeds into the fuel line via a banjo bolt and fitting. I had a banjo fitting of the almost correct size (I drilled it out to fit when I did my pump last Summer) and attached six feet or so of clear plastic fuel line to it...not high pressure stuff just cheapo clear plastic. So, once we got the pump installed and the long bolt snugged down, I attached the banjo fitting and the plastic hose and ran it into a 5 Gallon Gas can.
next...
HOTWIRE THE FUEL PUMP
Heinz already removed the passenger's side front carpet and the cover to the relay box. On his cherry 1997, the fuel pump relay is the last one on the bottom right. I unscrewed the one retaining screw that holds the relay tray into the box and slid out the tray slightly. Then I gently popped the COVER off the fuel pump relay with a small flat screw driver and left the relay in place. Then Heinz reconnected the battery. With him watching the homemade banjo fitting and the gas can, I slid a piece of folded over plastic fuel line (unused) In between the gap between the fuel pump relay and the one to its left. This pushed the fuel pump relay points closed and energized the fuel pump. So now, the newly installed fuel tank pump is pumping out the tank...Its all good....until we get to about 1/3 of a tank (we simply reinserted the fuel gauge sender to monitor the level, but did not put the spring loaded cover back on it BTW) Then the fuel flow starts to aerate and spit...This means the pump assembly is not seated properly. So, I pull out the wedge of hose holding the relay closed and the fuel pump stops; disconnect the negative battery cable again; slide out the fuel gauge sender, loosen the foot long retaining bolt which holds the fuel pump assembly to the internal Cup/Baffle until about half an inch of the bolt shaft is showing then rap the head of the bolt down (plastic screwdriver handle and rubber mallet - NO SPARKS PLEASE) to push the baffle down and separate it from the fuel pump housing. Remove the bolt.
Then we try to position the assembly again. The two essential components on the new fuel pump assembly which must mate up with the baffle are the FOOT which the bolt passes through and the SUCTION PIPE. The thing to keep in mind is that the Baffle/cup assembly in the tank is not actually secured in place. Rather, it has a couple of different hoses clipped into the top and bottom of it, all of which have some slack in them allowing the whole unit to move around a little. So we remove and reinstall the pump assembly and this time it feels a little different when it seats. When I wiggle it slightly, it feels like it is pivoting on the axis of the suction pipe, so I think it is seated correctly (It is BTW). But let's prove it!
My able assistant pours in about a quart of gas to prime the pump When you pour in fuel through the gas cap, it flows through a corrugated plastic pipe inside the tank that dumps into the top of the Baffle/Cup assembly. This hose is just clipped into the top of the baffle assembly, and the fuel pours out of it and spills into the cup. If the top hose becomes unclipped, you won't primer the pump at all. So if the top hose is properly positioned, at least the the pump will run and pump out the fuel that we primered the cup with, and then start to spit and aerate if the pump is still seated wrong. If the pump is installed correctly, it will start with this primer and then suck up fuel through a network of hoses off the bottom of the tank, continually re-filling the cup which the pump pumps out. We continue to pump out the tank until the fuel gauge reads less than empty. Then it spits, aerates and stops, and I remove the wedge from the relay. Pour in the last 5 gallons of fuel and we are good to go knowing with certainty that it is all installed correctly.
I made out on the deal because the first 5 gallons went into my other car - a 90 Miata - not that there is anything wrong with driving one of those either. If, like us, you do this job without first siphoning out the tank, have a lot of towels on hand, fire extinguisher (we didn't have one of those) and TWO people present. Oh yeah, neoprene gloves will not dissolve when submerged in a tank full of gas for ...hmmm...about 30 seconds. When your hand starts to feel cold, the glove is breeched. The gloved hand is useful just to confirm that none of the hoses is loose.
The only hose that MIGHT get displaced is the top corrugated feeder hose that clips in to the top. You can feel it by reaching in to the hole back and to the left. It is not far down, rather, just inside the hole to the left at the top of the cup. The CUP is not a complete description of the piece inside the tank. There is a cup (about the size of a Boy Scout issue tin soup bowl) at the bottom and then on the side of it, imagine a vertical silo which, when viewed from above has a curved rectangular cross section. The feed hose from the gas cap pours into the top of this silo. The reason that you loosen the securing bolt a little then rap the top of the bolt head is to separate the fuel pump assembly from the CUP, thus ensuring that you won't pull any of the bottom hoses off the CUP. Also, when testing, you don't have to put the BIG O ring and big plastic nut back on to secure the pump unit in place. All you HAVE TO do is secure the pump assembly to the internal cup/baffle assembly using the foot long securing bolt. This will speed the testing, removing and reinstalling process a bit. Sorry we didn't take photos, but I know there are some in the archives.
So, If you are going to do the job and want to know that it is done right, my advice is to take the fuel line banjo bolt, go to a speed shop and get the correct sized banjo fitting to fab up a cheap hose to pump out the tank. Even if you do empty the tank before beginning, this hose will allow you to test that everything is working correctly. When I did mine, it was bone dry, I poured in 2 gallons of gas, and was able to pump out about 1 2/3 gallons. Keep track of what you pour in and you should get all but.. say.. a half gallon back out of the tank.
Good luck,
Brian C.
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