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September 12, 2010

Replacing a Fuel Pump on a 1984 Fiero

Just for fun, I took photos as I replaced the fuel pump in my 1984 Fiero S.E. Perhaps what I have to say here will assist the next person with a little do-it-yourself spirit who wants to tackle the project.

Here it is before I started. It's the only place I have to change the pump because it's the only available level surface (using jack stands on a sloping driveway just doesn't seem like a good idea).

1984 Fiero Special Edition (SE)

The challenge at this point is to get the front wheels up onto the ramps. Obviously, I can't start the car and drive it up onto them, and 6 inches of pushing room does not give me enough space to build up speed to coast up onto the ramps. So, I lifted one side of the car first with the Fiero's jack as high as it would go...

Fiero up on a jack.

...and then tried to lift just the front wheel by putting a floor jack under...that thing...whatever the heck it's called (best guess: "lower control arm").

Getting the Fiero up in the air.

Of course the car lifted too, but it still worked out well; the Fiero was not lifted off of its own jack. And, of course, I then did the other side the same way.

Next, I put the jack stands in back. Major paranoia here. I kept thinking, "Is that really the frame?" I guess after a while you just grow accustomed to what is where:

Fiero on jack stands.

And finally, for extra safety, I put the Fiero's jack back on the car's right hand side and another car's jack on its left hand side:

Fiero Fuel Pump Replacement

Now, if I really wanted to be safe, I would have strapped those front wheels to the ramps. I didn't have straps and I thought that what I did here was probably overkill anyway. But strapping the wheels to the ramps is definitely the right thing to do.

You can see that the tank is being supported by a floor jack, and you can see the straps which hold the tank in place are now hanging loosely:

Removing the Fiero's gas tank.

No matter how much I wiggled or maneuvered those straps, I could not make them hang out of the way of the tank. In order to get them out of the way so that the tank would drop, I had to bend those straps, which suggests that they had to be bent to fit against the tank at the time the tank was being installed. That seems wrong, but it appears to be how it works, and it all came together fine in the end.

Below is the total of the instructions from the Chilton manual ('84-'88) to replace the fuel pump:

1. Disconnect the negative (-) battery cable.

2. Relieve the fuel system pressure. Remove the fuel pump fuse from the fuse block located in the passenger compartment. Start the engine and run until the engine stops due to the lack of fuel. Crank the engine for 3 seconds to ensure all pressure is relieved.

3. Drain all the fuel from the tank using a suction pump.

4. Raise the vehicle and support with jackstands [sic].

5. Disconnect the wiring from the tank.

6. Remove the ground wire retaining screw from under the body.

7. Disconnect all hoses and filler neck from the tank.

8. Support the tank on a jack and remove the retaining strap nuts.

9. Lower the tank enough to disconnect the fuel sending unit wires.

10. Disconnect the fuel line, vapor line and return line.

11. Remove the tank from the vehicle.

Now those instructions must not actually be for an '84, because they make no sense. Number 3, for example, says to drain the fuel from the tank using a suction pump. Not possible. (I'm not the only one I know of who has reported failure at being able to siphon gas from an '84 Fiero's tank through the filling location (where the gas cap goes).

Number 5 says to disconnect the wiring from the tank, but there's no place to disconnect wires. You can see them running up to the back of the firewall, but to get to where the plugs are would require removing lot of stuff that would have to be moved out of the way in the engine compartment, and that would be a pain even if the car wasn't on jack stands. There certainly isn't a way to remove the wires from any location near the tank. Maybe if I hadn't progressed so far already, I would have dug out this wiring, but I'm glad I didn't. Just leaving it hanging under the car worked fine.

Number 6 says to remove a ground wire retaining screw. There is no such animal. Anywhere. Nada. Zip. Zero. Zilch.

Number 7 would have been nearly impossible with the tank in place. There just isn't enough room to maneuver there. Instead, I had to lower the tank in order to stretch the hoses a bit in that area and make room to get them loose (which still wasn't easy; well, okay, it was easy, but tedious).

I removed the smaller hose - the vent hose - first, since it was higher up on the tank. This was important because the tank was COMPLETELY full. It also is a reason why it was important to lower the other end of the tank. After getting this smaller hose off, I pushed my siphon hose into the tank through this small hole and began siphoning:

Siphoning a Fiero's fuel tank.

Siphoning a Fiero's gas tank.

I read where someone reported having difficulty siphoning gas through one of these holes and mentioned something about "baffles" in the tank being a reason. I am pleased to report that I had absolutely no difficulty whatsoever. I drained the entire tank, in fact. After removing the tank and taking the "lid" off (which holds the fuel pump), I dumped out the remaining fuel - which amounted to, at most, 8 fluid ounces (1 cup), and probably more like 5 or 6. (Of course, while nearing the end of the siphoning process, I had to raise the rear of the tank back up as high as I could get it to go.)

Speaking of that "lid", let's take a look at it:

Fiero fuel tank cap and wiring.

You can see the black ground wire and two other wires. All three of them take off in the same direction and enter a single retaining sleeve which (as was previously mentioned) moves up the other side of the firewall into la-la-land. (There is certainly no "ground wire retaining screw...under the body," as Chilton claimed.)

Which brings us back to Number 5: "Disconnect the wiring from the tank." In an attempt to follow this instruction, I pulled on that little black thing (with the two reddish wires going into it) stuck to the cap (or lid) and it wouldn't budge. Next, I tried to gently pry it with a screwdriver. No luck. But it did lift it a little. I'm thinking that I shouldn't have been trying to do that at all. I'm thinking that Chilton's instruction "Number 5" was a fools errand meant to break a person's '84 Fiero. Fortunately, I don't think I pried hard enough to create a leak, but I wish I hadn't pried on it at all.

Next, the tank as it looks out once removed from the car:

Fiero Fuel Pump Replacement

It's a little rusty around those edges, but not bad, and overall I'd say it looks fairly good. At this point, I debated on whether to paint it or not. I intended to do so, but it's in pretty good shape. Still, it's out - so...I did. It looks very clean inside. (One thing to understand about my Fiero is that I've had it for at least a decade and a half, and it has less than 110,000 miles on it. It's probably in better shape than one would expect of a quarter-century old car. I have two cars and, for at least the last 5 years, I've driven less than 5,000 miles per year between the both of them, and not much more in the 5 years before that.)

Then there's the fuel pump and gas gauge mechanism, just hangin' around:

Fiero fuel pump and fuel level gauge mechanism.

Quite a few people suggested buying an AC Delco pump and gave horror stories about other pumps, so that's the one I bought. Here's a look at what's in the box. It comes with a bit of submersible line which replaces a "pulsator" which originally would have been included. There wasn't a pulsator on mine, so I know that the pump had been changed before. I know I had a pump of some kind changed before - maybe the fuel pump, maybe the water pump - I don't remember. But, in any case, This seems to suggest a 55,000 mile (or less) wear out period for fuel pumps.

Fiero Fuel Pump Replacement

The electrical connectors on the pump aren't exactly the same as the ones which were made in '84. I had to cut the one that was on there off and rewire the new one on using the butt connectors in the above photo. It seems a little strange to have these wires non-insulated and exposed to the gasoline in the tank. But the fuse would burn out before the wires could ever get hot, and, although the conductivity of gasoline is not zero, it's not large enough to interfere with the operation of the fuel pump. (I'll admit that I had to convince myself of this. It gave me some hesitation.)

A view of the new pump, and the old together with it's completely worn out strainer (with holes in it):

Fiero Fuel Pump Replacement

And then, below, is another image of the fuel level sender/resistor assembly.

Fiero Fuel Pump Replacement

If I had it to do over again, I probably wouldn't paint the tank:

Painted Fiero fuel tank.

I was advised to do a voltage test on my lines, with a headlamp in place of the fuel pump, but the more I thought about it, the more silly the premise for the test sounded. First consider that a fuel pump is an electric motor, and there's no such thing as an electric motor that can be damaged by being "underpowered"; if it is "underpowered" it will just turn slower. The question then becomes: is a fuel pump more than just an electric motor? Since I don't know what is in a fuel pump, this is a test for my imagination, and I can't imagine anything else which would be in that fuel pump besides the electric motor, at least nothing electricity related (obviously there are non-electricity related components, such as a turbine to pump the gas, for example). Would there be some sort of voltage regulator in there to make sure that the thing always spun at the same angular speed (to provide a specified fuel pressure)? That would be silly - fuel pressure is regulated elsewhere.

Of course it's important that the line have the proper voltage, and if a fuel pressure test comes up low, this could be the source of the problem, but the idea of a failing fuel pump? I mean...what???

I searched the Internet looking for reasons why people might believe that low voltage might harm a fuel pump, and all I've found is occasional claims that low voltage will harm a fuel pump. No reason for believing this to be the case is ever given - just someone claiming that's it's true.

Now suppose, hypothetically, that these people are authorities. If so, at best, the argument supporting the idea that low voltage harms fuel pumps is an appeal to authority - a very weak argument. If an authority really is an authority, he should be able to give valid reasons for believing his claim to be the case, and not just make the claim.

Sometimes, though, people believe claims not because they've heard them from an authority, but because they've heard the claims from numerous people. One person says something, another person believes him and starts saying it himself, so now there's two people saying it. It gets passed around and eventually lots of people are saying it, and saying it to one another, and it becomes common knowledge. Much of what people believe comes from this kind of "sheep" behavior (have you ever heard someone preface a statement with, "They say that...."? It happens often). The result could be widespread belief that fuel pumps die due to low voltage, that carbohydrate content matters more than calorie content in diets, or that "Saquatch lives in them thar hills...everyone knows that!"

Now I'm not saying that underpowering a fuel pump won't shorten its lifespan, I'm just saying that I've given quite a bit of due diligence to finding out whether or not it does, and I can't find any reason to believe it does.

I still did some testing, and the method I used was to employ some (very good) speaker wire to run a line out from under the car so that I could operate the on switch from within the cab:

Fiero Fuel Pump Replacement Fiero fuel pump wiring voltage test.

Now that's one cheap multi-meter. It wasn't going to show me much detail, but I planned on doing the test again with a better borrowed multi-meter in a few days.

Anyway, I've got the multi-meter's leads piercing and penetrating each wire, and the ends of the wires are exposed so that I could hook them up to a headlamp. But, first, I decided to check the voltage without a load. It came back at 7 volts.

That's right: 7.

What the heck?

That's when I realized that my battery had discharged, and that's when I further realized that any test, to be valid, would have to be done with the car running. Under load isn't good enough. What matters is the voltage when the line is kept consistent by the alternator. Even if you have a fully charged battery, "fully charged" has quite a range, and whatever voltage your battery happens to be when you do the test isn't necessarily the voltage that is going to be maintained in your line by the alternator when the car is running.

But, I still moved on for more experimentation. I hooked up my hand-dandy jump start station (whatever it's called, those things are awesome):

Jump start station

Then I did the test, without a load, and came up with around 11 volts (hard to tell on that cheap analogue multi-meter).

I removed a headlamp from my Mercury Topaz and moved on to the "under load" condition.:

Fiero wiring voltage test with a headlamp

I held the leads from the speaker wire to the prongs on the headlamp. I did it once...roughly 11 volts...twice...roughly 11 volts...three times...four times...five times...all roughly 11 volts...sixth time...0 volts.


Try again: seventh time...0 volts.

It blew the fuse.

Of course it blew the fuse...there's no way that a fuel pump is going to use as much power as a headlamp. I don't know what the internal resistance of a fuel pump is, nor the internal resistance of a headlamp, but my cheap multi-meter definitely shows that the headlamp has significantly less resistance than the fuel pump (and hence allows much greater amperage).

On the one hand, I'm tempted to say that this test is meaningless, but that's not the case. What is meaningless are small variations in voltage. What would matter, by contrast, is if I'd put that headlamp against the wires and it had not blown the fuse. Well, maybe that wouldn't have mattered, but the fact that it did blow the fuse is pretty good indication that the resistance in the line to the fuel pump is not too high. And that's what it really boils down to: the resistance in the line to the fuel pump. If the battery and lines are capable of supplying enough power to blow the fuse, then they're capable of supplying enough power to the pump.

Instead of testing under load, it seems to me to be sufficient to simply connect the positive and negative leads to the fuel pump together, then trip the switch and see if the fuse gets blown. If it doesn't, and your battery is fully charged, it means that the resistance in the lines leading to the fuel pump is high enough that the fuel pump is likely to be underpowered. But if it is able to supply 10 amps (that's the rating of the fuel pump fuse), that's more than enough for the fuel pump.

(That's just my analysis. I welcome contrary arguments.)

I put the thing back together and it works fine, and I haven't found any leaks (via passive visual inspection). No more pictures, as there was nothing interesting of which to snap a photo.

I would like to give some further advice to anyone reading this. I wish someone had given me this advice - it would have knocked an hour, I'll bet, off of my re-install. The advice is do to work in the following order when re-installing the tank:

1) The filler hose and vent hose should (still) be attached to the car. There is no reason for them to have been removed from the car at any time during this process. If they're not in place, put them in place.

2) After replacing the fuel pump, and after putting the cap (or lid) back on the tank, the next step is to attach those three little fuel lines to the tank. Fasten them tightly using hose clamps now, there will be no opportunity to tighten them later.

3) Lift the tank and have it held loosely in place by the strap nearest the front of the car. (Alternatively, you can put a floor jack underneath it and lift this part of the tank into place.)

4) Slather petroleum jelly liberally around the outside of where the filler and vent hoses attach to the tank, and also inside of the filler hose and vent hose. Make sure the hoses have (loose) hose clamps around them, then - both at the same time - work them into place on the tank. Thoroughly lock the hoses into place with the hose clamps. (If it seems like you can only get the hoses half-way on, pull them off and repeat this step. It gets easier with every repeat, and eventually you'll get the hoses on all of the way.)

5) Now, remembering to have a loose hose clamps over each fuel line, work the fuel lines into place on the car, then lock into place with the hose clamps.

Putting hoses on in the wrong order cost me a lot of time. First I put just the filler hose on, then discovered that with it in place, I couldn't get the vent hose on. Then I put them both on at the same time (as in step 4), and discovered that I couldn't get the fuel lines attached to the tank. I took it off again, attached the fuel lines to the tank first, then lifted the tank and put the filler and vent hoses on, but I hadn't fully tightened the hose clamps on the fuel lines because I thought I might need them to twist and turn when attempting to connect them at the other end. What I discovered is that I couldn't get a screwdriver up there to tighten the hose clamps, so off it all came once again. Finally, at this point, I managed to do it all in the right order. (And, as a bonus, learned that getting the filler and vent hoses on all of the way is easy if you put them on as far as possible, take them off, then put them on again as far as possible, then take them off again, then put them on again...etc. This works a lot better than getting one on half way and then continuing to struggle to get it on further.)

Taking off a gas tank seems like such a big deal, but it really isn't.

Posted by Jeff at September 12, 2010 12:28 PM


voltage drop on a device ,motor,fuel pump,ect.
trys to still operate.the amperage will increase
heating will occure thus ,shortining life of the device

Posted by: jay black at September 10, 2012 11:43 AM

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