Autoblog Maintenance 101: In-tank fuel pump R&R
If you own enough vehicles with an electric fuel pump, eventually it's likely that your luck will run out and you'll find yourself with a vehicle that refuses to operate properly due to a lack of go-juice. Most modern vehicles place the pump in the tank where it can be kept cool with a constant bath of fuel, but this location isn't so ideal when it comes time to replace that troublesome component. Fortunately, the task usually isn't quite as daunting as it may first appear, and tackling this project yourself can save several hundred dollars.
Fuel pumps can either fail outright, in which case the vehicle will simply refuse to run, or they will lose pressure over time, causing a slow and sometimes not easily noticed drop-off in performance and drivability. Increased fuel pump noise (it's the whine coming from the area of the tank) or longer cranking times are often signs that your fuel pump may not have much longer to go.
Originally, this article was going to be written using our '96 Buick Roadmaster as the subject (its fuel pump is dying a slow death), but then our '91 Chevrolet Caprice wagon decided to stop running. Yep - we have two vehicles down at the same time, with the same problem. Hopefully that emphasizes the frequency of this particular problem. Fortunately, the fix is straightforward, and the wagon died in our own driveway and with a nearly empty tank of fuel.
Since we're working with a highly flammable liquid, hopefully it's clear that extreme caution must be taken to avoid an unintentional fire. Also keep in mind that gasoline is hazardous if it comes in contact with the eyes or skin, so don the appropriate safety gear. The toxicity of gasoline also means that it should not be allowed to soak into the ground, so be prepared to soak up any spills with kitty litter or rags.
After proceeding past the first step in the fuel pump diagnosis (Will the damn thing start/run?), we then moved to energizing the fuel pump by using the test jumper. This connects +12V directly to the pump, and bypasses the relay. If the pump doesn't run at this point - and ours didn't - then it's either the wiring or the pump. And the odds are very good that it's the pump, and not the wiring, so it's time to drop the fuel tank.
If the pump does run, connect a fuel pressure gauge to the test port and compare the results with the recommended operating range in the service manual. In the case of our Roadmaster, the gauge read about 32 PSI at idle, and 18-20 PSI under load (we taped the gauge to the windshield wiper and went for a quick drive; not a recommended technique, but an effective one). The idle fuel pressure wasn't far off from the expected 32-37 PSI, but the WOT fuel pressure should be at least 42 PSI. This likely explains the vehicle's severe hesitation, surging, and spark knock upon tip-in, and continued operation with such low fuel pressure could cause engine damage.
Anyways, back to the wagon project...
We're not always as good as we should be with regards to disconnecting the negative battery cable before starting any work, but gasoline and sparks make for a poor combination, and so it's a step that we don't skip when playing with an electric fuel pump.
Lift the vehicle as high as practical, as you'll need enough room for yourself and the fuel tank. As always, don't depend on a hydraulic jack to keep the vehicle in the air, so drag out a set of appropriately rated jack stands and place them under the vehicle.
With the vehicle in the air, we now see the plastic fuel tank, and the metal straps that hold it in place. The rear two bolts only serve as a pivot for the straps, and do not need to be removed.
Remove any heat shields that may interfere with lowering the tank or accessing the fasteners, fuel lines, or wiring harnesses.
Disconnect the fuel tank filler and vent lines.
Take this opportunity to disconnect the wiring harness, because it's easier to do it now than when the fuel tank is resting on your chest (er, we cheated and moved this photo up two spots to show the way that it should be done, rather than how it was done).
Remove the bolts that hold the straps in place. Be sure to support the fuel tank during this step; we simply braced it up using any appendages that were free at the time.
Gently tug down on the retaining straps and pivot them out of the way, while still holding the tank in place under the car.
At this point, we perform a small dance number under the car, as we attempt to squirm out from under the tank while trying to avoid the retaining straps. The "empty" tank had about seven gallons in it, and when that gets sloshing around, it feels far heavier than its nominal weight of 45 lbs would suggest.
Set the tank on the ground, making sure that none of the fuel lines are being stretched.
Pinch the retaining clips and remove the fuel lines from the tank (high-pressure EFI systems may require an inexpensive disconnect tool, available at most parts stores).
Drag the tank out from under the vehicle while attempting not to spill any fuel from the now-disconnected filler and vent lines.
Remove the ring that retains the pump and sender assembly. While studs and nuts are used here, other vehicles may use a twist-lock retaining ring. A bit of force may be required to remove those rings, but go slowly so that the tank is not damaged (it's better to hurt the retaining ring than it is to deform or crack the tank).
Gently remove the sender/pump assembly, being especially careful of the sending unit's delicate float arm. If this is damaged, a new sending unit may need to be installed, which can greatly add to the expense of the project.
Here we see the reason for the fuel pump failure. The bottom of the tank was filled with crud, and the in-tank filter (commonly called a "sock") was obviously dirty. Since this is a plastic tank, the contamination likely came from an outside source. This much dirt probably wasn't the result of a single "bad tank of gas", but rather the result of repeated refills from a contaminated source. One of the vent lines was also disconnected, the apparent result of prior work by an inattentive mechanic, and this also could have been an easy route for debris to enter the tank.
We procured a new sock, and spent about an hour emptying the tank of the contaminated fuel and cleaning out its internals (both tasks were made somewhat more difficult by the tank's internal baffles).
Installing the new pump on the existing sending unit is as easy as loosening a hose clamp and unplugging the power connector. This is a good time to inspect the wiring harness, as the additional current draw of a failing pump can result in thermal damage. If the wiring or connectors appear to be burned, replace the sending unit.
While it's usually a good idea to simply install a direct replacement for the original pump, it's not necessarily a bad idea to consider a high-flow replacement if engine modifications are likely in the future (there are a large number of different Walbro-style in-tank pumps available). In this case, we replaced the stock low-pressure pump with a high-pressure unit, as eventually we'll be swapping out the low-pressure Throttle Body Injection (TBI) unit for a higher-performance Tuned Port Injection (TPI) unit that requires greater fuel pressure (approximately 45 PSI, compared to the stock 12 PSI). Since we've left the stock regulator intact for now, the fuel pressure will remain at the lower stock level until those future modifications are performed.
If in doubt, just get a stock replacement, and don't be afraid to spend a bit extra for a pump with a longer warranty.
Reinstall the gasket at the top of the tank.
Drop the pump/sending unit assembly into place, once again being careful not to damage the float arm.
Torque the fasteners to specification, or until snug.
We replaced the plastic clips at the end of the fuel lines, since they got a bit chewed up during removal.
Prepare the retaining strap bolts by applying a coat of anti-sieze compound.
Slide the tank back under the car.
Reconnect the fuel lines. They should make an audible click when fully seated, and it's not a bad idea to give them a gentle tug just to make sure.
Lift the now-empty (and much lighter) tank back up into position, and install the retaining strap bolts.
Hook up the filler neck, vent line, and electrical connections, and reinstall any heat shields that were removed. Turn the key to the On position, and listen for the pump. Assuming that it runs (it may operate for only a second or two), fire up the engine and make a careful and thorough examination for leaks.
Reader Comments (Page 1 of 2)
http:carwaterguide.blogspot.com 9:00AM (11/25/2008)
it's has review many sites like gas for free,run your car on water etc.
You can truly get better mileage...... http://carwaterguide.blogspot.com
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Phil L. 3:30PM (8/03/2006)
Another great Autoblog Maintenance article. Keep up the good work!
A few thoughts, having done this myself:
- The procedure doesn't specifically mention emptying the gas tank before starting the job. Yeah, so it's a pain to balance 7 gallons of gas on the tank on your chest. But here's another reason: 7 gallons times $3 means it's worth my while to cleanly siphon the gas for use in another vehicle. Once I drop the tank (now with an open fill hose banging around the dirty underside of the car), I probably won't want to use that gas someplace else.
- The directions that came with my last fuel pump specifically stated to fill the gas tank enough to completely cover the top of the fuel pump BEFORE POWERING THE PUMP FOR THE FIRST TIME. Why? Take a close look at a Walbro-style electric fuel pump. Note that pressurized gasoline traves inside the motor mechanism - including where the motor brushes. That's right, the motor brushes run in liquid gasoline all the time (this is also why you need to change your fuel filter reguarly - the worn brush material get in the gas as a normal part of its operation). Liquid gasoline by itself won't burn in the presence of a spark - unless there's also an air supply. The first time the pump is powered up, there could still be air inside of the pump mechanism (the check valve built into the pump keeps it full of gas for the rest of the pump's life). If you look closely at the pump, you'll also notice an extra check valve at the top of the pump (well, mine had one) - whose sole purpose is to allow gasoline inside the motor mechanism before it's first powered. But that can't happen unless the pump is completely submerged in gasoline first.
I suspect the risk from initially running the pump with a minimal gasoline supply is very small - there's not much air inside of the motor - but it still exists (at least enough to prompt a warning on my pump). Of course, many people don't want to go to the trouble to put so much gasoline in a newly-installed tank. It's a hassle to manually move the gas, and it's a further hassle to empty it if initial testing reveals a problem that requires dropping the tank again (you guessed it: It happened to me). But this is still an important item to consider.
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Phil L. 3:45PM (8/03/2006)
Looking more closely at the pictures...
Eric, please tell me you didn't really lift the back of the car using the center of the differential as a jack point...
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Josh Wardell 4:31PM (8/03/2006)
Nice write-up.
Semi-related, but be on the lookout for failing fuel pumps due to states switching over to E10 gas. Dealers around here are scrambling to keep up with the niumber of pumps being corroded by the water absorbed by the ethanol. I was left stranded myself. Read this if you like:
http://www.jwardell.com/mini/2006/06/27/ethanol-gas-problems/
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Mal Fuller 4:34PM (8/03/2006)
As a garage owner and mechanic, I can't think of a job that is any less suited to a backyard mechanic than this one. It's dangerous and fraught with logistical problems when not done on a lift and by an experienced mechanic. Especially in areas where road salt is used for snow and ice removal, rusty hangers/straps, senders, fuel lines, retaining bolts and steel tanks may not survive the ordeal. (Neither, perhaps will the hapless car owner!)
In contrast, a skilled and experienced mechanic with the further benefit of the right tools and a helping hand when needed, can bang this job out in short order.
I appreciate that many car owners enjoy working on their cars, do good work and save money in the process. I would just suggest that this isn't a job that will provide to them the expected pleasure, benefit or savings.
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J ron 4:35PM (8/03/2006)
oh my, it does look like he jacked it up from the diff.......
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Eric Bryant 6:55PM (8/03/2006)
"please tell me you didn't really lift the back of the car using the center of the differential as a jack point..."
I know I'm going to regret asking this, but why is this a problem? I've raised solid-axle cars this way for, well, my entire wrenching life. I'd rather lift via some other means, but there's really no other way to raise the back of this car.
Mal,
Trust me, I'd rather not do this job (there's probably several hundred other service tasks that are more fun), but all of the factors you mentioned are potential issues with just about any work underneath a vehicle.
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Phil L. 9:21PM (8/03/2006)
Eric -
Hmmm - I've always been taught that a vehicle should not be lifted using the differential. The reasoning, as I understood it, was that the differential was more than strong enough to support the vehicle on its wheels - because the wheel is close to the spring mount, resulting in a small twisting moment around the differential itself. Lifting the vehicle with the differential, however, results in a large twisting force on each side of the differential, due to the much larger distance from the center of the axle to each spring mount (which is what will support the weight of the car when lifting this way).
That said, quick Googling didn't reveal horror stories about broken differentials - and a least a few other procedures that lift vehicles using the differential. So it appears it isn't a hard and fast rule.
My method? Put the floor jack under the spring mount on each side of the differential, then support the vehicle with a jack stand. Yeah, this means two lifts to raise the rear of the car.
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West Seattle Mafia 9:22PM (8/03/2006)
My 1995 Ford Van needed a fuel pump at 38,000 miles and I did it in the street without too much trouble. It was a $700 repair at the dealer and I did it for $150+ curb time. The main difference in my case was that the dealer insisted on replacing everything in the tank - not just the motor. Sending unit, float, lines all as one unit. I was able to buy just the motor at Schucks for $95.
One thing that I did learn from dealer was that the only time the parts guy saw pumps dead this early was on short haul delivery trucks and taxis that were driven with mostly empty tanks of gas. (Being submerged is a coolant.) Turns out my van had been previously a hotel shuttle. So the when gas hits $4 a gallon and most people drive around with 1/4 tank and put in $12 every 3 days - it's gonna be a good time to be in the fuel pump business.
Man, seeing the underside of your car reminds me of why I don't miss Massachusetts sometimes. Most shops out here would be speechless to see hardware that rusty.
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len simpson 9:32PM (8/03/2006)
been there, done that, several times. my question is--- u r gonna take care of the salt water termites while ur under there, aren't u?
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Eric Bryant 9:44PM (8/03/2006)
Phil,
I can definitely respect the concern over placing an abnormal load on the rear axle, but I can say that I've seen rear axle failures for only two reasons - a rather severe crash, or way too much air (the latter being somewhat common with young kids and half-ton 4x4 pickups).
Your comments about starting with a submerged pump, as well as West Seattle Mafia's comments, brings up an excellent point that I didn't address in the article - the importance of fuel as a coolant. The pump needs a steady supply of fuel around it to maintain a reasonable operating temperature, and running the tank too low deprives it of this. It also makes the pump work somewhat harder, which means that running most vehicles down below the 1/4-tank mark (or thereabouts) is a good way to shorten the life of the pump.
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Eric Bryant 9:47PM (8/03/2006)
Len,
This car is a $950 winter beater, so it's unlikely that I'll do anything to save the body. I hate to let a car waste away like that, but I don't think that the effort is justified in this case.
Now, twenty years from now when I'm looking high and low for a savagable '91 Caprice wagon, I'll likely be second-guessing this decision ;)
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wes virtue 1:51AM (8/05/2006)
Ahh fuel pumps do I know a lot about fuel pumps.
You see I have issues with this kinda of technology that is inherently poorly designed. Made to fail in other words. Bought a Carter replacement pump for my 2000 safari 8mths back only to have it fail again. They could not replace it under warranty until the rep looked at it.
Well he looked at it and said nope cant do it but because of a distribution snafu I lucked out and it was replaced under warrantee. The rep said that the tank was not cleaned hence it was the fault of the installer. Yada yada yada. Talked to my buddy the volvo mechanic he mentioned that oh by the way "dont buy carter fuel pumps they only last a year or so.
So if these fail because of dirty gasoline how do you make sure that the quality of gasoline is clean enuf to prevent this. It must be noted that these pumps were not long ago $1200cdn plus install. Their cheaper now but it's still between $8-900 installed. There is no way to prevent this. The older 12Lbs systems were not any way near as fussy and dirt cheap to fix(pardon the pun).
It should also be noted in preventive maintaince besides the tank full thing that it's important to replace the filter regularly because a clogged fuel filter (metal partiles and all) will overwork then overheat the pump and shorten it's life.
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m 5:56PM (8/06/2006)
for the record: I have a '91 Toyota Previa, and my Haynes repair manual specifies lifting the rear using the jack at the differential.
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West Coast Service Drriver 6:35PM (8/08/2006)
My company van (Chev Astro) has had 2 pumps go out. Both times it went to the shop (Pep Boys) it went in with 1/2 to 3/4 tank of fuel. Both times it came out with less than 1/4 tank. The mgr. told me, "Well they HAVE to drain the tank or it's too heavy to handle." I guess they just drained the gas on the ground so it wasn't there to put back in! My point; if you go to a shop make sure THEY know YOU know how much $3.10 per gal. gas is supposed to go back in the tank!
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Jeff 11:30AM (8/09/2006)
Nice writeup. My buddy and I recently replaced the fuel pump in my S-10 and we found that the easiest way to go about it was to remove the bed and not even mess with jacking the truck up or trying to remove the tank. I believe it was 8 bolts and unhooking a couple of harnesses and we had the bed off in about 20 minutes. Then it was a piece of cake to pull the fuel pump out.
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Cheryl 4:37PM (8/09/2006)
Thanks for the nice writeup, we're replacing the fuelpump for the second time in our suburban in a year. We thought much as one of the first posters, that gas at 3 bucks a gallon should be saved and reused, and boy did we find out the hard way that it was a dumb move for us... because the nasty gas that burned up the pump in the suburban now has the grand prix running like a heap of junk. So be careful in trying to save money, boys and girls.
The problem as I see it was buying gas at the cheapest place in town, which was the local grocery store which shall remain nameless...
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Rob 1:23AM (8/10/2006)
With respect to the fuel tank, how do you remove the fuel?
I have been looking for an easy to remove the fuel in the event I need to gather up more gasoline for my portable generator in the event I have a very long power outage. I always considered that the gas in my cars could act as a back up supply, however, I have not looked into 'how to get the gas out of the tank'.
Your help would be appreciated.
This situation applies to a 2006 Impala and a 2003 Expedition.
thanks,
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Scott Hiller 3:34PM (8/20/2006)
I have a 2001 GMC Savanna van that had a noisy pump, and after looking at $300 for a complete unit,I found a new pump/motor on Ebay for $70. Dropping that nearly 6 ft. long tank looked daunting, so I cut a 12" square in the floor with a sabre saw. 2-1/2 Hrs. total time. Did this job in early spring, van ran great, started using 10% ethanol from Ma. ,now getting the double startup crap.
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NEBTEK2002 4:40PM (8/20/2006)
Expect things to get worse with Big Ethanol's chief cheerleader Mike Johanns as Ag Secretary.
When he was Nebraska's governor he tried to ban all sales of gasoline not tainted with this stuff. Thankfully, our usually- useless Legislature woke up and stopped this.
The only community close to being a city in this state, Omaha, is located on the border with Iowa which wasn't having any of this nonsense and whose gas stations stood to siphon off millions in gas taxes.
Of course, Iowa's governor is in the pocket of Big Meatpacking and is giving free healthcare to that industry's illegal alien workers-- absolving the "poor" multibillionaires of their responsibility to provide worker benefits. Hopefully, he won't find that Big Ethanol pays better.
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