96' Fuel Pump Issue

I have read here and there on the forum, and have gathered some pretty good knowledge on my Fuel Pump issue.My 1996 S-10 Blazer, 4x4, Vin W, has started to hard start in the mornings. A fuel psi test found that at engine key on, I get 53-54 psi. Obviuosly allot lower than the expect 60-66 psi. Fuel Pump is crapola with 127K Mile son it.I called the local Chevy Dealer and he gave me a part number of P/N 25163487 and wanted $460 for it. YIKES!!So a quick internet search found that it is an AC Delco part number and it matches with P/N MU13. For some reason the data plate apparently lists both??So other than a completely drained tank. What tips, How to's, can the group offer on changing this thing out? How long should it take? Thanks.

Fuel Pump Replacement

First of all, I would hook up a jumper wire to the fuel pump test wire and double check the fuel pump pressure. (see below for location of test wire) Also, make sure your battery is fully charged. A weak battery will not power the fuel pump 100% and will cause a no start. If you have over 61 psi when using a jumper on the test wire then you pump may be ok?? If so check your wiring as described in this thread (http://www.automotiveforums.com/vbulletin/showthread.php?t=588381&highlight=Fuel+Pump).

Also check this Thread about low voltage (http://www.automotiveforums.com/vbulletin/showthread.php?t=568768&highlight=Fuel+Pump)

Second, the consensus on this board is to use a Bosch or AC Delco replacement pump.

I’ve included a couple photos from when I replaced my pump, but mine is a ’95 4x4, which has a different type pump, but the gas tank, etc. should be the same. Probably take about 4-hours to replace the pump the first time you do it.

On a 4x4 - Remove the spare tire – Remove the skid plate under the gas tank if so equipped. Remove the left rear wheel and make sure you have good support, (jack stands on a solid surface) under the vehicle so it won’t fall on ya. Remove the neg battery cable.

The fuel line nuts that connect to the sending unit and fuel pump at the gas tank freeze up with rust. The line nuts get rusted to the fuel line and when you try to turn the line nut the fuel line will twist. Thus, I suggest getting a good penetrating oil from your auto parts store,- WD-40 won’t do it. Spray the line nuts up real good before trying to disconnect them. If the line starts to twist spray it up real good and let soak for a couple hours, maybe overnight.

Also, spray the 15mm nuts on the front and rear gas tank support straps with penetrating oil. These also get rusted and the ends of the straps have been known to twist off.

There is no drain plug on the gas tank, and the tank will weight well over 100 pounds when full, not fun when lying on your back under your vehicle, even with only a couple of gallons of gas in it. No problem I thought, just stick a small rubber gas hose down the filler neck and pump the gas out, right? Wrong!! Where the filler tube connects to the fuel tank, there is a little plastic ball inside the filler neck, which is only a couple millimeters smaller than the inside of the filler neck. It lets gas go into the tank, but not a small hose. (see photo) The purpose of the little ball is to prevent gas from running out of the tank if the vehicle turns upside down, as the gas will press the ball against a seat and seal off the filler neck. Next I thought I would disconnect the filler tubes and remove them from the vehicle. Wrong again. The filler tubes have a bracket made onto them that is bolted to the frame where they cross over the rear axle, and there is not enough room between the body and the bolt to get a wrench on the bolt.

So, before you drop the tank, try to get all the gas out of it. This can be done two ways:

1) If your fuel pump still works half way; There’s a fuel pump test wire under the hood on the driver’s side next to the fender, under the hood hinge. It’s a red wire that has a gray or black plastic cover on the end of it and it just hangs there next to the electrical junction box, not hooked to anything. Put a live 12 volt jumper wire to it and the fuel pump will run if it's not toast. If the pump runs then disconnect the fuel line at the fuel filter, (which is located on the inside of the frame under the driver’s door) put a hose onto the gas line coming from the tank and into a container. Then connect the battery cable, run the fuel pump to empty the tank and then disconnect the battery cable again. Or, you can connect an auxiliary gas pump to the gas line and pump the gas out of the tank.

2) Or, loosen the nut on the rear gas tank strap to lower the rear of the tank just enough to disengage the rubber hose on the filler neck at the rear of the gas tank, then put a small hose into the tank and either use an auxiliary gas pump to pump the gas out of the tank or you can use a siphon. (Whatever you use, it must be designed to pump gas – otherwise you might have a big, big fire) Fire is a great danger when removing a gas tank. I’ve seen repair shops burn down when gas is spilled and a shop light falls into it.

After the gas is out of the tank, if not already lowered, lower the rear of the tank 2-3 inches. On the top rear of the tank towards the left rear wheel, disconnect the rubber hose from the plastic fuel vapor relief valve – see photo for location. Also disconnect the wire connector that goes to the fuel pump. Use a set of flare nut wrenches and a secondary wrench on the fuel lines to loosen them at the fuel pump.

Loosen, but do not completely remove the front gas tank strap, just drop the front of the tank down 2-3 inches and reach around the front of the tank under or through the plastic shield on the front of the tank and remove the hose from another plastic vapor purge valve located on the front left of the tank.- (see photo for location) Usually this plastic connection on the front valve, from people not knowing its there, gets broken off when the tank is lowered. A new one at the dealer is 20 bucks.

The plastic shield on the front of the tank won't come off until the tank is out of the vehicle.

When you are ready to drop the tank, use a floor jack to support it and remove the straps.

Once you get it removed be sure to clean all the dirt and gravel from around the sending unit and locking ring, as you don’t want this dirt to fall in the tank when you remove the pump.

Unless the pump has been replaced before, you will probably find the flange and locking ring on top of the sending unit having a thick coating of some kind of epoxy on it. I had to take a hammer and screw driver to chip all this crap away and then still had a hard time getting the lock ring to turn. After you knock down the 3 tabs, it turns clock wise – See photos. Use a brass punch to prevent sparks when hammering on these rings. After replacing the pump I sealed mine back up again with epoxy glue to keep water out of the tank.

Remove the retaining ring/locking ring from around the sending unit pipes and wire harness. Once free, the sending unit/fuel pump simply comes up and out of the tank. As you withdraw it from the tank it may require a 180 degree twist to get the pump out of the tank. Make note of how the pump sets in the tank and which way the float is pointing before you remove the pump. The new one needs to go back in the same way, with the float facing the same direction.

Make sure the new o-ring gasket that comes with the new pump is the right size, same size as the old one – if not, pick up one at the dealer. They are about 10 bucks. Lubricate the new gasket with oil when installing it.

Follow the directions that come with your new pump and install in reverse order of above. Use the floor jack to hold the tank up while connecting everything. Don’t forget to connect the front hose on the purge valve. While under there replace the fuel filter also.

Once everything is connected and the tank re-installed, put at least 8-10 gallon of gas in it and reconnect the battery cable. You will have a lot of air in the fuel line, so I would again put a jumper on the fuel pump test wire and check the fuel pump pressure again. Once you get over 61 psi remove the jumper wire and it should start up.

Someone else please jump in here with what I missed,

Good Luck

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I recently changed my fuel pump in my 99' LS Blazer. It was a PITA to change. You definitely need a jack to support the tank if you have any fuel left in it.

I took my tank completely down, drained all the gas out, and wiped the inside of the tank. There was noticable amounts of sand inside there. No you can't see it, but you can feel it with your hands and fingers. So my advice is to to clean it out the best you can.

Good Job DelCoch. Copied to the technical forum.

I recently changed my fuel pump in my 99' LS Blazer. It was a PITA to change. You definitely need a jack to support the tank if you have any fuel left in it.

I haven't tried it but I saw another post that suggested using bungie cords to allow the tank to drop enough for the repair.

I haven't tried it but I saw another post that suggested using bungie cords to allow the tank to drop enough for the repair.
That is a good thought, if you don't have a floor jack and have an empty tank, bungie cords would work great to hold it up when you re-install it. However, if you have the straps off with the tank sitting on bungie cords, you just as well pull the tank out to work on it, as everything will have to be disconnected to lower it enough to get the fuel pump out, and it will be a lot easier to replace the pump out in the open. The small style floor jack with a block of wood works just fine.

Bungee cords will give you some slack to get the fittings off and back on the pump module if you don't have a floor jack. I agree the fuel tank still has to be lowered and out from under the car to change out the pump module.
Good thread!!!