How to Diagnose and Replace a Fuel Pump


Hey guys, ChrisFix here. Today i’m gonna show you how to replace a fuel pump in your car or truck. In this case we’ll be working on a 1998 Mustang GT. Project Crowd Control. The “driftstang”. But this process applies to most makes and models on the road that have a fuel pump in the gas tank. So after you watch this video, you’ll be able to change the fuel pump on your vehicle. Now if you remember from the last episode, I had a dead battery. So I replaced the battery with a brand new one. So now we have complete power to the vehicle. Before we go and change out the fuel pump, there’s a few things I wanna’ check. And I wanna’ show you how to check. Just in case it isn’t the fuel pump that’s actually bad and it’s something a lot easier to fix. So the first thing I do is grab the key and you’re gonna’ wanna’ put it in the ignition. and turn it to the run position. When you turn it to the run position listen for a “hum” or a “whine” from the fuel pump in the rear of the car. Just to give you an idea, we’re in my Corvette, ready to listen to the fuel pump prime. So you could hear that fuel pump run for about two to three seconds. And it runs like that so we can build up fuel pressure and start the car. But in the case of the Mustang, when we turn it to the run position… We don’t here that fuel pump prime. But that doesn’t mean the fuel pump is bad. It could be something simple as a fuse that you just need to check and replace. So grab your owners manual and flip through it until you get to the page about fuses. And you can see, right there it says, “Fuel Pump”. On our Mustang the fuse box is located in the engine bay right behind the battery. And according to our diagram the fuse should be right there. So we’ll remove the fuse. And you can see there’s no break in the connection. So our fuse is good. So grab a multi-meter. Then stick one prong into one side of the fuse holder, and another prong into the other side. And you can see we have just about twelve volts going through this circuit. So that means we’re getting power to at least the fuse box. Now let’s check to see if we’re getting power to the back of the car where the fuel pump is. And that’s right down here by the gas tank. And if we’re looking up, there’s a wiring harness right here. And this runs to the fuel pump. So this is where the fuel pump is getting its power. Now disconnect the wires by pressing down the little tab and pulling them apart. Since the pump only gets power with the car in the run position. Turn the key to the run position. Now grab the black lead and ground it. I’m gonna ground it to the exhaust but any bare metal part will act as a ground. Now grab your red lead, and we’re gonna’ each of the prongs in this connector to see if there’s voltage. And right away we have twelve volts. So just check the others real quick. And the others are getting power as well. So it’s safe to say we’re getting power to the fuel pump. Now I’m gonna’ leave these wires disconnected because we’re gonna’ be dropping the fuel tank. But lets just say we weren’t getting any power to these wires. The next thing to check is something called the inertia switch. And its usually located in the trunk. In this case on the Mustang it’s right back here. This right here is the inertia switch, and the red button on the top should be pressed all the way in. To test this, all you do is you get something and you hit it. And this should pop up. And then you should be able to press the button down. It’ll click, and it’ll reset. This switch is designed to cut the power to the fuel pump in case there’s an accident. But sometimes it can get triggered just from hitting a pothole, or maybe you have some junk in the trunk that just hits it. So if you’re not getting any voltage to the pump, real quick, check the inertia switch because that might be the easy solution to your problem. You also might have noticed that the interior pieces of my car are in the trunk. And the reason why is because on the passenger side, right over here in the foot well is the location of the fuel pump relay. So this has to click on when you turn your key to the run position. And if it doesn’t click on you won’t get any power to the fuel pump. And you can here it when I turn the key to the run position… There’s a couple of clicks. And one of those clicks is the fuel pump relay. But if you don’t here the relay click on, then its a good idea to swap out the relay. They’re cheap enough, and it might fix the problem. In this case i’m guessing the previous owner couldn’t figure out the problem. Which is probably why he donated the car to charity. But now I have the car. So Mr. Owner, if you’re watching, at the end of this video, we will get this car running! Now just to be thorough, there’s one more thing we could check, and that’s using a fuel pressure tester gauge. Right down here at the fuel rail you just take off the schrader valve cap, and you screw on the gauge. And with our gauge connected this will give us the exact fuel pressure when we turn the key on. We should see it jump up to at least thirty PSI, maybe higher, and it should stay there. So with the key in the run position, we turn it on, and the fuel pressure doesn’t even budge. So now we know for sure that there’s no fuel pressure at all. The pump isn’t running but it’s getting voltage. And then you might say, “Hey, what if the fuel filter’s clogged?” Well if the fuel filter’s clogged you’ll see that pressure rise slowly or rise just a little bit. In this case we have nothing at all. And from all this testing we know, we need a new fuel pump. Which is easy to replace with common hand tools And when you’re replacing a fuel pump you also wanna’ replace the fuel filter so that the new pump can run efficiently. And thanks a lot to AutoZone for providing me with a fuel pump so I could get my car running. Now let’s get started. First grab your safety goggles since we’re working with fuel. Next thing we wanna’ do is remove the negative battery terminals so we don’t have any power to the car. That way if we ground something out by mistake it won’t spark and ignite the fuel. With the negative terminals disconnected, in the back of the car, I have the rear end lifted up safely. And I also have a fire extinguisher on hand since we’re working with gasoline. Do a little bit of research because with your specific car you might be able to go in the trunk and lift up the carpeting and get access to the top of the fuel tank. In this case there’s nothing under here except the spare and there’s no access. But in many cars there’s access here or in the rear seats. So just check that before you go and drop the fuel tank. Even if you have to drop the fuel tank don’t be intimidated because it’s very easy to do. The first thing you need to do is go to the fuel filler door. You saw me do this in the last episode but be sure to remove as much gas from the tank as you can. To make the tank as light as possible. Next remove the three screws holding in the filler neck. So when the tank drops down this’ll drop down with it. Basically we wanna remove anything that might get hung up as we drop the tank. Now that this is loose, lets slide under the car, and disconnect the fuel lines over by the fuel filter so we can drop the tank. So right here we have two fuel lines going into the tank that are not gonna move when we drop the tank. So we need to make sure to disconnect them and right up here is our fuel filter which we’re gonna disconnect as well. So now we wanna remove our fuel filter and there’s a connector there and a connector there. But first we need to pop this off. Now this right here is a quick disconnect. So we need these special tools that slide over the fuel line. And then you push it in towards the quick disconnect, and that’ll pop the hose off. Also be sure to have some paper towels ready and I like to use the cap that came with the new fuel filter so that I don’t get gas leaking all over me as I disconnect the other side. and the other side is the exact same process. Good with the fuel filter removed we have this fuel line right here that we’re gonna disconnect in a couple of seconds as we drop the tank down. Now with our fuel lines disconnected and our old fuel filter removed and the filler neck unscrewed we can go and drop the tank. So grab your jack, place it in the middle of the gas tank to try to evenly balance it and lightly press up against the gas tank so when we remove the straps holding the tank in, the tank wont just fall. And with our tank supported this is really easy to undo. There’s a strap right here and a strap right there. At the end of each strap is a bolt. We’ll remove em’ one at a time. And that’s one Now that we have this removed we have to go to the other side. And then the bolt is actually on the other side underneath the car. I love how nothing is rusty under this car. It makes everything so easy to remove. And now we can use the jack to slowly lower the tank. With the gas tank half way down I wanna block it off so we can remove that last fuel line. At the top of the tank we have two fuel lines and we only need to remove the one that we didn’t remove before. Now with all our hoses disconnected right over here our filler tube is getting hung up a little bit. There’s a rubber boot right up there which is holding it I don’ t wanna rip the boot So instead of dropping this straight down we’re gonna drop it down at an angle. And then make sure as the tank drops it isn’t hanging by anything. Good! And that gives us plenty of room to get to our fuel pump which is located right down in here. Now er’re gonna have to remove all six bolts holding this cap on the gas tank. But before we do that we have to remove this wire from the sensor back there And you just pull the pigtail right off the sensor. So now our entire wiring harness is loose. And now we can remove these six bolts holding the fuel pump assembly in. Alright our last bolt is out now we can pop the lid off and just be careful because you don’t wanna break any of these hoses. Now if we look into the fuel tank you can see the fuel pump assembly. There is a clip on either side that you need to push in with your fingers. You can see there’s one there and one there. Push those inwards and pull the assembly out. So now we can wiggle it the rest of the way out. Be careful with the float because you don’t want to bend it and then your gas gauge won’t be accurate. Now this whole thing here is the fuel pump assembly It has the float on it so that you know how much gas is in your tank. It has the fuel sock and all the wires attached to it. Now there’s two options, you can get rid of this old fuel pump assembly and replace it with a nice new fuel pump assembly and this just drops in the tank and you’re good to go Or you can get a new fuel pump, Since this is the only thing that’s bad in this assembly, and replace it out. And that’s exactly what I’m gonna do. And i’m gonna show you how to do that right now. So lets get the old fuel pump out of our assembly and you can see the old fuel pump is right here. So disconnect the wiring harness to the old fuel pump And then on the top of our assembly here there’s a couple of bolts. They’re five milometer. First remove these two. Which will hold the pump in. Now once the two screws are removed this should come right off. Like so. And now in order to get the fuel pump removed we need to remove these three bolts out here. Now with the three screws removed we can remove the lid. And now our fuel pump should come right out. Just like that. Next very simple, make our new fuel pump look like our old fuel pump. So put the rubber piece on top. Like that. As well as the rubber piece on the bottom. Get our fuel sock. And what this is, its like a pre-filter. So any larger particles won’t get sucked up through the fuel pump and cause damage. And that is our fuel pump all ready to go. The other fuel sock goes on the actual bucket. So just pull off the old fuel sock, and i’m gonna put in a nice new one. And these things just push right on and click right in. Beautiful! Now drop the pump in the bucket, put the lid on, and screw it down. These screws weren’t tight so tighten them by hand only! Now we have our tube that connects to the fuel pump. Just goes right over. Push it down. And we’ll tighten that down by hand. With the new fuel pump it does come with a new wiring harness There’s a large connector which only fits on this large connector. And then there’s a small connector which only fits on the small connector. Give em’ a little pull make sure they’re good on there. And then this connects into the stock harness. Good! And thats it. Thats all it takes to replace the fuel pump. Installation is the reverse procedure. Put the assembly in the tank, make sure it clicks in, like that, Plug our wire back into the sensor And then we need to tighten all six of these screws down in a criss-cross pattern. This has to be sealed good or you’re gonna get a check engine light. Now we need to reconnect the fuel line, and it just clicks into place. And snap the lock into place as well. Now we can jack the tank up all the way. And with our gas tank jacked up, lets get our two bolts and tighten down the straps to hold the gas tank in. And the strategy here is to press upwards as you screw the bolt in. And this gets tightened to thirty-eight foot pounds of torque. And now we repeat the same exact process for the other tank strap. With the fuel tank strapped in and torqued down lets remove the jack. Now we can slide back under the car and install our fuel filter. I always right the mileage on the filter and pay attention to the arrow on the filter which indicates the flow of fuel. Each fuel line is gonna make a click when it’s all the way in. Now all we need to do is push the locking tabs in All right now everything is attached, we can test out our fuel pump. Normally you want to test things out as you go so you don’t have to take it all apart if it doesn’t work. That being said lets just get this fuel nozzle tightened down to complete the job. This is getting exciting! Tighten these screws down so they’re snug All right fuel pump replacement complete Will the Mustang now start? That is the question we’ve all been waiting for. Was the fuel pump the culprit? Was it whats causing the problem with this car? Is that why the guy donated the car? And is that why I won it for eleven-hundred dollars on an auction site? Let’s connect the negative terminal and find out! Man oh man, am I excited!!! I can not wait to see if this baby starts up! Pretty confident on our diagnosis. Pretty sure it’s the fuel pump. We’re about to find out! So when you change out a fuel pump what you’re gonna want to do is you wanna turn it to the run position, shut it off, turn it to the run position, shut it off, one more time. And what that does, that pressurizes the fuel. And it’s just filling the fuel lines with gas because you emptied them when you replaced the fuel pump. So… Clutch down… In neutral… Here it goes! Moment of truth! Will project crowd control start up? the drift stang Alright!! She’s alive!! This is great!! Awe man!! That’s exciting!!! Ok… No warning lights. We got fuel pressure, good battery, good, good, good!! And does that engine sound good or what?! So we’re at 30 P.S.I. fuel pressure, which is perfect! This engine’s just purring! That is exciting!! So we got the car started, the fuel pump was the culprit, And that is how you diagnose and replace a fuel pump in your car or truck. Project crowd control is now alive. We are going to do some awesome stuff to this car. Hopefully this video was helpful. If it was, remember to give it a thumbs up. If you’re not subscribed, consider subscribing. (engine revving) Now how did that sound? That sounded awesome! But you hear this… (knocking noise) That doesn’t sound good. Luckily looking under the car, it’s just this heat shield making noise. That got me a little bit nervous, I thought it was the engine, but we are good!! Another thing you wanna do right away is make sure there are no fuel leaks anywhere, since we did disconnect those quick-disconnects. So you don’t want to see any dripping fuel, and also check this when you go fill up the tank. But this all looks good!

About the Author: Michael Flood

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