Chevrolet S10 pickup with an in tank fuel pump
Diagnosing a failing fuel pump can be tricky. You can look for the most common symptoms – failure to start, or stumbling/stalling when the accelerator is pressed, but those can be symptomatic of other problems as well. The stumbling (very jerky movement) will be most evident when the vehicle is under load, like pulling weight or going up a hill. This makes sense, since you’d be asking the truck for more fuel, and a failing fuel pump wouldn’t deliver. The same thing happens when your spark plugs are failing (ask me how I know), and probably during many other car-part failure events as well.
A failing fuel pump may make a very loud whining noise, and a failed pump won’t make any noise at all when the key is turned to ‘on’. If the pump has failed completely your truck won’t start. This is a good time to get to know the neighbors down the street who now have your dead truck sitting in front of their house. If you’re trying to diagnose the problem before the pump has failed completely there are a few more tests you can do, such as checking fuel pressure, but these require specialized tools or a trip to the shop to get it diagnosed. In my case the fuel pump enacted a death scene worthy of bad opera with a screeching whine followed by a prolonged demise, with as much drama as mechanically possible. I had no doubts about the problem.
If you, too, are sure it’s the pump, and you want to replace it yourself, it’s not difficult, but it does take some attention to detail. Before you head to the store, check online to find the lowest price around you. Most online auto parts stores let you input your vehicle make/model/year so you can look up the right parts and get an idea of what else you might need to purchase to complete the repair. If you go to a brick-and-mortar store to buy your parts, talk to the guy when you’re buying your new pump and find out about things like replacing the filter, buying a separate wire harness and the difference in quality/longevity of the pump as compared to price. I’ve found that some people behind the counter are more knowledgeable than others so don’t be afraid to ask for someone more experienced. And of course, make sure you have whatever tools you need before you start.
Relieve the pressure in the fuel system by removing the fuel pump fuse and running the engine to consume any fuel left in the lines. There may still be a bit of pressure in the line so be careful when you pull any fuel lines. Since the truck was in my front yard we hosed off the little bit of sprayed gas to avoid starting any accidental fires.
Unhook the battery just in case. No point in getting shocked.
Remove the gas cap from the outside of the truck, it's held in with screws.
Now here’s the cool part: Instead of dropping the tank, just lift the bed of the truck. My truck had eight bolts. We removed the six closest to the cab, and loosened the last two a lot so we could lift the bed up to get to the fuel tank. I think I saw this called “dump position” somewhere. You’ll see in the pictures that we took the tailgate off also, but that’s because it’s a bit damaged and bent. I would strongly recommend using a better support system than garden stakes and firewood. Maybe rig a hoist from tree branches or use some good jacks. We supported the bed with the stakes, then used pieces of wood on the tires as a secondary support system. I also stood next to the bed holding it any time my partner was underneath it. I wasn’t comfortable with the setup, and I would never ever suggest you do something so jerry-rigged if you’re alone.
Remove and replace the pump
Clean all the debris from the top of the tank and disconnect everything visible on the outside of the fuel tank. To get the pump out of my tank, the locking ring required you to push down and turn, otherwise it wouldn’t move at all. You’ll need to gently twist and tilt the pump to get it out of the access hole because, as you see from the photos, the pieces aren’t all in a straight line. Remove the entire pump and take it to your work spot. The tailgate worked nicely for this.
The wires on the pump are connected in a specific order to specific parts. As you replace the pump and harness, make sure you replace each wire and plug it into it’s proper place. Don’t just rip everything apart at once, and keep the instructions open in front of you. Technology has changed over the last 20 years, and the new pump we installed looked a little different from the old pump. Try to identify all the parts on the new pump before you go changing things. We had extra o-ring seals, but the instructions made it clear that the pump would work in a few different vehicles, and the different size seals were provided for that reason. You really shouldn’t have any extra parts left over, unless you know why you didn’t use them.
Now is a good time to inspect the inside of the fuel tank to check for excess dirt or crud. You can only do this if your tank is nearly empty. Consider trying to clean out the tank if it really looks bad.
When you’ve got all the wires hooked back in, you need to carefully put the new pump back into the tank. Put the new o-ring in the groove at the fuel tank opening and insert the new fuel pump without unseating the o-ring. Be gentle and don’t bend the float assembly or mangle the filter. Put the metal retaining ring back on, reconnect the hoses and the battery, and start the truck. Your truck should start and run well without roughness or stalling. If everything works, turn off the truck and recheck all your connections before putting the bed back down.
Put it all back together
Remove whatever jack system you used to keep the bed elevated. Gently put the bed back down and line up the bolt holes. Replace the bolts you removed and remember to tighten the two at the very back. Do a short test drive to make sure it’s all working well. This probably never happens to anyone else, but we somehow popped a vacuum hose off under the hood, which was evident by the complete lack of brakes during the test drive. A simple fix – just put the hose back on. Your test drive is not just to check that you’ve installed the fuel pump correctly, but also to make sure you haven’t knocked anything else loose during your work.