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Replacing Fuel pumps on a W126

Old Jul 31, 2009 | 09:47 AM
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Default Replacing Fuel pumps on a W126

I wish I had pics but I dont even have a camera. Dont worry I just did this and thi s job is pretty easy.

Tools you will need is a screwdriver and a wrench. I used an adjustable wrench for the small nuts and the larger ones. Also you might want a drip pan or other large container. And small metallic replacement washers.

Problem: Fuel pump leaking gas like a stuck pig. Loss of expensive 91 octane gas.

First thing to do is to drain the tank. I opened the gas cap to relieve any built up pressure from this hot el paso weather and didnt have to worry bout draining the tank as the gass leaked into the large drip pan by the time the fuel pump arrived in the mail. Actually it took 3 hours for a half tank. Another way is to clamp off the hose that run from the gas tank to the fuel pumps, but I found draining the tank pretty easy as one way or another, you will need a drip pan to catch some of the fuel that is still in the lines anyways.

Once the fuel tank is drain or clamped. Disconnect the wires that are on the fuel pumps. Two per fuel pump and pay attention as one is for positive and one for negative. The small wrench is good for this job.The further fuel pump (closer to the front of vehicle) wires are a tad bit tight to reach. If you cant get the further wire off. Then wait till further steps. At this point it's good to have a drip pan ready and the screw driver. There is a long screw securing each of the fuel pumps. I did the closest pump first so use the screwdriver to remove the bracket screw. and the connecter on the rubber hose that leads to the fuel pump. Now, make sure your drain pan is aim right and your eyes are not in the way. Also this is not a good time to smoke for obvious reasons. Once you have that connecter loose, slowly pull the hose away from the pump. There should be some resistance as it go over the flange and at this point any left over gas in the tank and hose will come flowing out rapidly. Mine was already dry do I had a small splash. Now you can take off the other connector but you will need a larger sized wrench of in my case, I just adjusted my wrench. The connecter should come off, uhmm, if ya lucky which I wasnt as it didnt want to budge. No problem. I then decided to take off that whole metal line assembly that connect to two pumps off. The end that leads into the second pump (the further pump) is much easier to remove. If you remove the assembly, you can proceed to spray down the connector with liquid wrench and can set it aside. Or if you had trouble getting a wire off, you can actually rotate the whole pump and metal pipe link to better reach, but be careful at those wires dont have too much slack. Now at this point you can move on to the second pump. disconnect any wires you havent already disconnected and use the large wrench to get the line off the pump. Shouldnt be too much gas spill here. This pump came off pretty easy but might have to use liquid wrench on this one too but unless ya replacing the fuel filter too, then it's best leave the assembly attached to the car.
Now back to that trouble pump and metal connector. After the liquid wrench did it's magic, the pump seemingly came off easy but to my amazement, the check valve was still attached to the metal line connecter instead of the fuel pump as intended. The new fuel pump came with a new check valve. So after wresling with that thing for a while, it finally came out. By this time the second pump and connecter might be ready to come off too. Remove the fuel pump in the same manner as the first one and dont forget to make sure you take the check valve with it. And dont forget to loosen up the bracket to slide the pump out.
Now I found it easier tor re-install to the back pump first if you are replacing that one too. Slide the new pump in line it up, and I found out after the fact, that two brass washers is very useful here or you will have a leak when the car is running. I'm not sure what happened to my original washers but new ones worked just fine. I put one washer on before the check valve and one where the check valve connects to the fuel pump. Leak free now. So connect the fuel pump check valve side first, the screw on side and wrench it down so you'll have no leaks. Also make sure it's level and straight as deviation creates leak point. Took me twice to get it just straight but you'll be glad you did it right instead of spraying gas. You can connect to the wires now too. positive wire to positve terminal and negattive wire to negative terminal. Dont worry, the fuel pump have markings on it that show you which terminal is which. Now once you have that fuel pump nice and secure into it's bracket you can move on to the other pump.
Connect the fuel pump check valve side into the metal line connecter assembly. Slide the pump back into it's bracket and then connect the other end of the metal line connecter assembly to the other end of the further pump. The easiest way is to slide the first pump with the metal assembly forward to get the rubber hose over the further pump connecter and slide the pump into first pump into proper position while guilding the hose onto the further pump's connector. Make sure it's tight, flushed and all the way on. You can ue the screwdriver to tighting thw hose fitting now. At this point you can connect the gas tank rubber hose to the first pump and just like the other pump make sure it's on as far it can go. Then tighten up that connector. Place the wires on in the proper place and secure the pump bracket. Now make sure everything is nice tight and the connectors are on tight. If all looks well, add some gas to the tank, Prefer not a full tank just in case you have to redo a part or two, and start it up to make sure everything works. Check for leaks. You will smel and usually see leaks at the connectors if they are not tight. If you find a leak, turn the car off and tighten it. SOmetimes you might have to realign the hose and connectors so hopefully you did not put a full tan in. If all is well then all is well. Dont worry you'll know if something is wrong. If the pumps dont work the wires are probably crossed or time ot send those pumps back. If you got a leak, there is something loose or you forgot a washer. Or the rubber hoses are bad if it is the source of the leak. If the fuel pump itself is leaking, hopefully you did not reinstall the old pump.
Cranking the car for the first time after this procedure might take a little bit longer than usual so it's ok. After that, it should start up normally. I didnt replace my fuel filter for this time as it was a recent replacement but if it been a while it is a good time to replace that too as it's real easy to get too with the fuel pumps out the way and only thing extra is two connecters and a bracket.

Hopefully this can help someone who was going to take on this endeavor or havea bs dealership mechanic complaining it is a complicated procedure and require special tools and blah blah blah $900. It took me about an hour and that included the lemonade break. I skipped the smoke break.
 
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