Replacing 1999 Fuel Pump Assembly
grandlaker
10-29-2003, 02:33 PM
Stopped at convenience store and shut off vehicle. Came back out to start Tahoe (129K miles on it) and it would only crank. I am not a true mechanic but money is tight so I decided to fix the problem myself. Although I searched the web and learned some things, I also had a few experience lessons. Decided to post what I learned in case others have the same problem. Originally thought it was the control module but was told that they do not usually fail and the more likely culprit was the fuel pump.
Diagnosis: Make sure you have gas in your tank. Turn switch on (don't crank) and listen for the start up whir of the pump located inside the tank. The tank is plastic and located on the driver's side of the vehicle under the rear seat area of the car in front of the rear axle. You can see the top of the fuel pump assembly by looking into the the left rear wheelwell in front of the tire. Turning on the switch causes the pump to prime the injectors or something. Some people suggest that you kick or hit the middle area of the tank with a board to see if that movement solves the problem. In my case, it didn't. Surprisingly, the tank sounded hollow but I knew it was more than half full of gas. Anyway it you hear it running, then you have another problem like a clogged fuel filer. If you don't hear it, then check the fuse (ECM-B I think). Fuse box located on driver's side under hood. Look in your manual for more info. If the fuse is blown, then you may want to try replacing it once to see if it blows again and if so, chances are you have a short in the fuel pump. If fuse is good, then listen for the click of the relay switch (also in the same fuse box) when you turn the switch. If you hear the click, then the relay is good and you are probably in for a new pump. Someone also suggested to pour a little fuel in the carb (be sure and replace the air filer hose before starting). If it starts, then you know it is the pump. I did that and it tried to start but the O2 mix etc wouldn't let it run right. That was also before I knew what to listen for on the whir of the pump. By the ay, if another Tahoe is not handy, you can hear the same noise on just about any newer GM truck.
Buying the Pump: If you are doing this on a weekend and the dealer is closed, you have a problem. GM used two pumps that I was told look alike. Both pumps do not work on the same vehicle and the only way to know is to use your VIN. The parts stores said they could not check it by the VIN. As I was trying to find the part before I had pulled the tank, I don't know if the parts store could have matched the old pump with a new one just by looking at it. Also know that the part is expensive and not stocked by smaller parts stores so getting the part on the weekend may be difficult anyway. While you are at he parts store, you may want to buy a "tool" (one I had was actually plastic) that release the keepers on the connection between the female fuel line connection going to the tank and the tank assembly. I ended up breaking the old assmbly connection and being forced to tear the metal keepers out of the connection. The replacement keeper part is plastic and is stocked by most stores. This leads to a discussion of confusion in the instructions which tells you to squeeze the plastic ends to release the assembly. I didn't know what they were talking about until I went back to the parts store and bought the plastic keepers. They must have swtitched from the metal keeper to the plastic keeper but didn't bother to tell anyone that the original part may be metal. Also if you don't have a siphon or several feet of larger diameter plastic hose, buy some to siphon the gas.
Removing the tank: Disconnect negative battery terminal. Raise vehicle on lift or place on jackstands. You can't get to the connections or remove the tank from under the vehicle without raising it higher than just ramps will allow. At the back of the tank near the axle, you will find two rubber hoses. Loosen the clamps and pull the hoses off the tank connections. Then take your siphon and drain gas from the tank. I tried to use a small plastic hose and it was taking forever. Some people try to replace it without draining the tank but it makes the job harder and more dangerous. If you pour the gas into the tank of another car, be sure and save enough to restart the Tahoe when you are finished. If you are working in a dusty environment, put rags in the tank holes or tape them over to keep out dirt.
Unloosen the two metal bands the hold the tank in place to the frame (metric bolts). The tank will drop a little but the front edge of the tank has an edge formed in the plastic extruding process. The edge will catch on the frame. If you can, reach up and disconect the two wiring harness connections at the front and back. I don't know what these are actually for but they disconnect easily. If you can't reach them yet, tha'ts OK also. You can lower the tank a little more and then disconnect. The fit of the tank in the frame is a little tight and that's why the fron of the tank catches on the frame. I tride to pull it sideways and that didn't work so I took a large scredriver (thin pry bar would also work) and bent the front of the tank (remember it is plastic) a little to bring the extrusion below the frame edge. The tank will then drop far enough to disconnect the front and rear harnesses. Although the tank is not heavy, I used a hydraulic jack just to hold it up while I tried to get to it. Using the jack prevented stress on the wiring harnesses.
Now you ar ready to tackle the connections of the fuel tank assembly and the fuel line. Look at the new assembly. Note the male plastic connections have a flat section. This is the part that is held by the keepers of the metal female fuel line connection. Sliding the keeper relase tool into the female connection pushes the four keepers towards the side of the female connection far enough that the flat section of the assembly male connection is released and can be pulled out. Try spraying WD40 or other lubricant into the connection area to loosen and clear the area of the keepers. If you try like I did for almost an hour and still can't get them off, you may just want to break them and replace the metal keeper with the plastic ones I mentioned above. The tank is now free and you can pull it out from under the vehicle.
Replacing the new assembly: Note and mark the orientation of the old assembly AND the metal locking ring on the tank before removing them. Clean away all dirt from the area of the assemply before removing it from the tank. Take a flatscrewdriver and drive the holding ring off of the top. The assembly will pop up and can be removed. Some more mechanical than I might try to fix the pump at this point but I didn't spend time with it and continued to replace it with a new one. Check the tank to see if it has a lot of dirt and debris. Wipe out with a clear rag if necessary. Put a few drops of fresh oil on the male plastic connection tubes of the assembly.
Dealer assembly came with a new gasket. Push the new assembly down into the tank and turn the locking ring enough to hold it in place while you get your hammer and screwdriver to complete the locking process.
Replacing the tank: Make sure the metal straps are in place in the frame and oriented in the right direction. Pry the tank back into position and reconnect the harnesses. The fuel line connections should go on easily. Push the tank up into position and reinsert the bolts but do not tighten. Replace the negative battery terminal and turn the key to the on position to see if you now have noise in the tank. Check fuel guage for movement.
Although the pump activated, I went to the additional trouble of pushing the large rubber hose onto the back of the tank, lowering the vehicle, and pouring 5 gallons of gas back into the tank and starting it before I reconneted everything.
Tighten the metal tank straps. Reinsert the other rubber hose in the back of the tank and tighten the clamps. You may also want to replace the fuel filter located along the frame rail under the driver's seat area.
Although it took me almost all day because I didn't really know what I was doing and I kept having to make trips to buy one thing or another, I was proud of my job at the end of the day and save a lot of money. Good luck if you attempt it. Hopefully, my trial and error experience will save you time in the long run.
Diagnosis: Make sure you have gas in your tank. Turn switch on (don't crank) and listen for the start up whir of the pump located inside the tank. The tank is plastic and located on the driver's side of the vehicle under the rear seat area of the car in front of the rear axle. You can see the top of the fuel pump assembly by looking into the the left rear wheelwell in front of the tire. Turning on the switch causes the pump to prime the injectors or something. Some people suggest that you kick or hit the middle area of the tank with a board to see if that movement solves the problem. In my case, it didn't. Surprisingly, the tank sounded hollow but I knew it was more than half full of gas. Anyway it you hear it running, then you have another problem like a clogged fuel filer. If you don't hear it, then check the fuse (ECM-B I think). Fuse box located on driver's side under hood. Look in your manual for more info. If the fuse is blown, then you may want to try replacing it once to see if it blows again and if so, chances are you have a short in the fuel pump. If fuse is good, then listen for the click of the relay switch (also in the same fuse box) when you turn the switch. If you hear the click, then the relay is good and you are probably in for a new pump. Someone also suggested to pour a little fuel in the carb (be sure and replace the air filer hose before starting). If it starts, then you know it is the pump. I did that and it tried to start but the O2 mix etc wouldn't let it run right. That was also before I knew what to listen for on the whir of the pump. By the ay, if another Tahoe is not handy, you can hear the same noise on just about any newer GM truck.
Buying the Pump: If you are doing this on a weekend and the dealer is closed, you have a problem. GM used two pumps that I was told look alike. Both pumps do not work on the same vehicle and the only way to know is to use your VIN. The parts stores said they could not check it by the VIN. As I was trying to find the part before I had pulled the tank, I don't know if the parts store could have matched the old pump with a new one just by looking at it. Also know that the part is expensive and not stocked by smaller parts stores so getting the part on the weekend may be difficult anyway. While you are at he parts store, you may want to buy a "tool" (one I had was actually plastic) that release the keepers on the connection between the female fuel line connection going to the tank and the tank assembly. I ended up breaking the old assmbly connection and being forced to tear the metal keepers out of the connection. The replacement keeper part is plastic and is stocked by most stores. This leads to a discussion of confusion in the instructions which tells you to squeeze the plastic ends to release the assembly. I didn't know what they were talking about until I went back to the parts store and bought the plastic keepers. They must have swtitched from the metal keeper to the plastic keeper but didn't bother to tell anyone that the original part may be metal. Also if you don't have a siphon or several feet of larger diameter plastic hose, buy some to siphon the gas.
Removing the tank: Disconnect negative battery terminal. Raise vehicle on lift or place on jackstands. You can't get to the connections or remove the tank from under the vehicle without raising it higher than just ramps will allow. At the back of the tank near the axle, you will find two rubber hoses. Loosen the clamps and pull the hoses off the tank connections. Then take your siphon and drain gas from the tank. I tried to use a small plastic hose and it was taking forever. Some people try to replace it without draining the tank but it makes the job harder and more dangerous. If you pour the gas into the tank of another car, be sure and save enough to restart the Tahoe when you are finished. If you are working in a dusty environment, put rags in the tank holes or tape them over to keep out dirt.
Unloosen the two metal bands the hold the tank in place to the frame (metric bolts). The tank will drop a little but the front edge of the tank has an edge formed in the plastic extruding process. The edge will catch on the frame. If you can, reach up and disconect the two wiring harness connections at the front and back. I don't know what these are actually for but they disconnect easily. If you can't reach them yet, tha'ts OK also. You can lower the tank a little more and then disconnect. The fit of the tank in the frame is a little tight and that's why the fron of the tank catches on the frame. I tride to pull it sideways and that didn't work so I took a large scredriver (thin pry bar would also work) and bent the front of the tank (remember it is plastic) a little to bring the extrusion below the frame edge. The tank will then drop far enough to disconnect the front and rear harnesses. Although the tank is not heavy, I used a hydraulic jack just to hold it up while I tried to get to it. Using the jack prevented stress on the wiring harnesses.
Now you ar ready to tackle the connections of the fuel tank assembly and the fuel line. Look at the new assembly. Note the male plastic connections have a flat section. This is the part that is held by the keepers of the metal female fuel line connection. Sliding the keeper relase tool into the female connection pushes the four keepers towards the side of the female connection far enough that the flat section of the assembly male connection is released and can be pulled out. Try spraying WD40 or other lubricant into the connection area to loosen and clear the area of the keepers. If you try like I did for almost an hour and still can't get them off, you may just want to break them and replace the metal keeper with the plastic ones I mentioned above. The tank is now free and you can pull it out from under the vehicle.
Replacing the new assembly: Note and mark the orientation of the old assembly AND the metal locking ring on the tank before removing them. Clean away all dirt from the area of the assemply before removing it from the tank. Take a flatscrewdriver and drive the holding ring off of the top. The assembly will pop up and can be removed. Some more mechanical than I might try to fix the pump at this point but I didn't spend time with it and continued to replace it with a new one. Check the tank to see if it has a lot of dirt and debris. Wipe out with a clear rag if necessary. Put a few drops of fresh oil on the male plastic connection tubes of the assembly.
Dealer assembly came with a new gasket. Push the new assembly down into the tank and turn the locking ring enough to hold it in place while you get your hammer and screwdriver to complete the locking process.
Replacing the tank: Make sure the metal straps are in place in the frame and oriented in the right direction. Pry the tank back into position and reconnect the harnesses. The fuel line connections should go on easily. Push the tank up into position and reinsert the bolts but do not tighten. Replace the negative battery terminal and turn the key to the on position to see if you now have noise in the tank. Check fuel guage for movement.
Although the pump activated, I went to the additional trouble of pushing the large rubber hose onto the back of the tank, lowering the vehicle, and pouring 5 gallons of gas back into the tank and starting it before I reconneted everything.
Tighten the metal tank straps. Reinsert the other rubber hose in the back of the tank and tighten the clamps. You may also want to replace the fuel filter located along the frame rail under the driver's seat area.
Although it took me almost all day because I didn't really know what I was doing and I kept having to make trips to buy one thing or another, I was proud of my job at the end of the day and save a lot of money. Good luck if you attempt it. Hopefully, my trial and error experience will save you time in the long run.
grandlaker
10-30-2003, 10:34 AM
I forgot to mention about trying to check the electrical circuit at the tank by pulling the harness, hooking up a test light, and then turning the ignition switch on. When I started the project, I didn't know which of the three harnesses was the correct one. My biggest problem, however, was trying to unhook the harnesses before I had dropped the tank. I couldn't see on top of the tank and determine how the release clips operated. I didn't want to tear up the connection causing more problems so I went ahead and dropped the tank. Once the tank dropped, however, I forget to run the test. It didn't matter though because the pump was history. While the diagnosis procedure I posted worked for me, you may want to try and test the circuit at the tank to confirm that you have no electical problem before proceeding to replace the pump.
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