Troubleshoot Fuel Pump

Troubleshoot Fuel Pump and Fuel Injector

The electric fuel pump is the heart of every electronic fuel injection system. Let’s review the basics of this critical fuel injection part. The function of the fuel system is to store and supply fuel to the cylinder chamber where it can be mixed with air, vaporized, and burned to produce energy. The fuel, which can be either gasoline or diesel is stored in a fuel tank. A fuel pump draws the fuel from the tank through fuel lines and delivers it through a fuel filter to either a carburetor or fuel injector, then delivered to the cylinder chamber for combustion.

Usually located inside or near the fuel tank, the fuel pump’s job is twofold:

1) To push fuel from the tank to the injectors, and

2) To create sufficient pressure so the injectors will deliver the correct amount of fuel under all operating conditions.

The pressure developed by the pump, as well as the volume of fuel it flows, must both meet the vehicle manufacturers’ requirements or engine performance, economy and emissions will suffer.

The amount of fuel pressure required for a given application will vary depending on the type of injection system (L-Jetronic, CIS, Motronic, etc.), the flow characteristics of the injectors and the engine’s fuel requirements.

For example, certain Audi models with Bosch Motronic require 55 to 61 psi (3.8 to 4.2 BAR) of static pressure measured with the engine off. By comparison, a BMW may require 43 psi (3.0 BAR) on some models or 48 psi (3.3 BAR) on others. The differences may not seem like much, but a few pounds of fuel pressure can have a significant impact on engine performance and emissions.

Why Flow & Pressure Are So Important

A fuel pump that doesn’t meet the OE minimum fuel flow or pressure requirements for your car can cause driveability and emissions problems.

A weak fuel pump or one that can’t generate enough pressure can upset the calibration of your fuel system. This may cause the engine to run lean or starve for fuel under load, causing symptoms such as hard starting (hot or cold), poor idle quality, hesitation or stumbling when accelerating and a loss of high-speed power.

Low fuel pressure can also be a cause of lean misfire at idle and under load, which causes a dramatic increase in hydrocarbon (HC) emissions. A car experiencing this kind of problem usually won’t pass an “enhanced” emissions test that measures exhaust emissions under simulated driving conditions on a dynamometer.

Low fuel pressure and/or lean misfire can also trigger the engine warning lamp on 1997 and newer cars equipped with OBD II (on-board diagnostics).

So, if the original fuel pump is weak or has failed, it’s important to make sure your replacement fuel pump meets all OE fuel performance specifications.

Why Fuel Pumps Fail

Electric fuel pumps run constantly, so after many years of service they can experience wear in the armature bushings, brushes and commutator. Pump vanes, rollers or gears can also wear causing a gradual loss of pressure and flow.

Accelerated wear may also occur if sediment or rust gets past the inlet filter sock. In some instances, a pump will fail because contaminants entered the pump and jammed it, causing the motor to overheat and burn out.

Your fuel pump relies on fuel passing through it for lubrication and cooling. Consequently, fuel starvation can be another factor that accelerates wear and may even cause pump damage under certain operating conditions.

Fuel Pump Diagnosis

If your fuel pump stops working (no noise, no line pressure), the first thing that should be checked is the pump’s voltage supply and electrical connections. An open relay, blown fuse or loose wire may be all that’s preventing the pump from working. Low battery voltage can also reduce the pump’s ability to generate pressure by reducing the speed of the pump motor.

Measuring static output pressure and fuel delivery are the two standard diagnostic tests that can be used to determine a pump’s ability to deliver fuel.

Static pressure is measured with a gauge attached to the fuel rail or teed into the fuel supply line with the engine off and pump energized. Fuel flow is measured by disconnecting the fuel supply line, energizing the pump for a specified number of seconds (engine off) and measuring the volume of fuel delivered into a container.

If static pressure or the volume of fuel delivered is less than your car manufacturer’s specifications, your fuel pump needs to be replaced. Replacement would also be required if the pump’s check valve has failed (inability to hold residual pressure in the system after the ignition is turned off).

A Few Important Things to Remember

Heed the following repair tips when installing a new fuel pump to avoid problems:

Tip #1: Whether a fuel pump is mounted inside a fuel tank or externally, the inside of the tank should always be inspected and cleaned if rust or debris is found in the pump or filter. Replacing a pump without cleaning a dirty tank will doom the new pump to premature failure.

Tip #2: If you’re replacing an in-tank fuel pump, always disconnect the battery to prevent any unwanted sparks. Then drain the tank before removing the tank straps and opening the pump’s retaining collar. Keep all flames and sparks away!

Tip #3: When installing the new fuel pump, always replace the filter screen and use a new O-ring or gasket for the sealing collar.

Tip #4: Do not “test” a new pump before it has been installed by jumping it. Running a pump in a dry condition with no fuel to lubricate it risks damaging it. Do not run the pump until fuel has been added to the tank. Also, replace any braided or rubber fuel lines that are flaking or cracked with the correct type of EFI hose.

Your Fuel Injection Parts Shopping List

Here is the list of fuel pump related parts you should consider when performing work on your car’s fuel pump – some of these are subcomponents of other parts listed so you may not need to purchase the individual components. Also, not all cars are equipped with everything listed here:

– Fuel Pump (new not remanufactured and meeting OE specs) –
– Fuel Pump Check Valve –
– In-Tank Feed Pump (if applicable) –
– Fuel Filter(s) –
– Fuel Pressure Damper –
– Fuel Pressure Accumulator (if applicable) –
– Fuel Distributor –
– EHA Valve (Differential Pressure Regulator) –
– Fuel Injectors & Fuel Injector Seals –
– Cold Start Valve (if applicable) –
– Fuel Injector Holders (if applicable) –
– Frequency Valve (if applicable) –
– Fuel Pressure Regulator, Preset or Vacuum –
– Warm-Up Regulator, Electric (if applicable) –
– Fuel Pump Relay(s) –
– Fuses –
– Temperature Sensor(s) (Fuel Injector Computer) –
– Thermo-Time Switch (Cold Start Valve through ECU) –
– Throttle Position Sensor (Throttle Switch) –
– Position Sensor(s) (Crankshaft, Flywheel) –
– Oxygen Sensor(s) –
– Knock Sensor –
– Air Flow Meter (Air Mass Sensor) –
– Auxilliary Air Valve (Idle Stabilizer, Idle Motor) –
– Idle Control Unit (if applicable) –
– Fuel Hose (Bulk or Preformed Hose) –
– Breather Hose (Bulk or Preformed Hose) –
– Intake Boot(s) –

DIY: How to Replace Your Electric Fuel Pump

What you will need:

  1. Ratchet wrench set with deep sockets and universal joint
  2. Penetrating lubricant
  3. Hose clamp pliers or screwdriver
  4. Fuel line disconnect tool
  5. Soldering gun or iron
  6. Fuel pressure gauge
  7. Manual pump and hose for draining fuel tank
  8. Approved storage container for storing fuel
  9. Bolt or wooden dowel to plug fuel line from fuel tank
  10. Jack and jack stands
  11. New fuel pump
  12. New flange “O” ring
  13. Oil or white lithium grease

Replacing your non-electric fuel pump

Fuel pump replacement is pretty easy. If you can replace a thermostat, you can replace a fuel pump.

This is for a 64 Classic with a 195.6 in it, but applies to almost every engine (at least the older ones, don’t know beans about electric fuel pumps) (V8s will have the pump in a different location – front of engine? but the procedure is the same)

First thing to do is get the new fuel pump. This can be a big problem if you’ve got vacuum wipers – you may have to special order it.  The pump will come with a gasket in the box. The only other thing you need are a few wrenches and maybe a pair of pliers and a screwdriver. You also need gasket scraper or other sharp-edge tool. A good idea when replacing a pump is to replace all the rubber hoses at the same time, and the fuel filter for good measure.

Rubber hoses (they’re actually neoprene, but that’s harder to spell) are used as “shock absorbers” in the fuel system to allow for different vibrations for the fuel tank, line, and engine. There will be at least two sections of rubber hose, possibly as many as four. We’ll start back at the fuel tank and work our way forward. Crawl under your rear axle (may need to jack the car). Look for the fuel tank. On the forward side of the tank, there will be a small tube sticking out. There’s also a wire connected here – this is to your fuel level sending unit (other end is to your dashboard’s fuel guage). As long as you’re under there, make sure this wire is connected nice and tight. From the metal tube out of the tank, there will be a section of rubber hose. This connects to the main (metal) fuel line which carries the gas up to the engine bay.

Remove the section of hose. Keep in mind that you’re working next to a tank full of gasoline, and try not to let tools slip – you DO NOT want anything to spark down here. Since this one’s the hardest one to change (involves crawling under the car is the only “hard” part) this is the one that everyone “forgets” to do – I’ve often found original factory hosing on this section. This is crying out “replace me! replace me!” if you listen hard enough. The hose is connected to the metal line with hose clamps. If you’re lucky, they’re the new style which are removed by a flathead screwdriver or a nutdriver (3/8″ I think, could be smaller). If you’re unlucky, it looks like a piece of bent coathanger. These are the original hose clamps and are technically know by mechanics as “Jesus” clips, since that’s what you scream when the pliers slip and you pinch your finger. Take a pair of pliers to them, compress the two wires sticking out from them and the clamp expands (doesn’t that sound easy? wait till you try it…). Slide it out of the way for now. When you get the clamps off or loosened and out of the way, take the rubber hose off. Use pliers VERY carefully (don’t squeeze much at all – use the pliers to twist, not to squeeze) and twist the hose back and forth until it rotates freely around the metal line. Then work it back and forth until it comes off. If it’s really on there and does not want to loosen, you can take a knife or razor blade and slit the hose lengthwise and just peel it off. NOTE: Make sure not to score the metal fuel line with the razor blade if you do this. This can cause a fuel leak. Remove hose and old clamps. If fuel starts pouring out of the tank, plug the line with a piece of cork or something (I’ve found a cap to a ballpoint pen works well – right diameter), but it usually doesn’t – a bit splashes out when you take it off, then it stops.

Going up to the engine bay, find where the fuel line enters. For a 195.6, this will be on the passenger’s side of the car, low down. This is also the side with the fuel pump on it. There are different setups of fuel pumps and rubber and metal lines, but most of them have a rubber hose section between the mail fuel line and the fuel pump. Remove this in the same manner as the one back at the tank. From the fuel pump, the gas goes to the carb. There are, again, different setups for this. A typical one has a metal line from the pump over the engine to a very short rubber hose and then into the carb. Sometimes there’s a rubber hose from the pump out, sometimes there isn’t one by the carb. On older fuel pumps, the filter is inside the pump. On newer ones, the filter is “inline” somewhere between the pump and the carb. On 199/232s, the filter screws directly into the carb, then is attached to the metal line with a very short section of rubber hose. Sometimes people put aftermarket filters inline between the pump and the carb – these are usually clear or white plastic, so you can actually see the fuel going through it and see when the filter’s dirty. Your setup will be one, or a combination of these. Inspect the whole thing. Remove all rubber hoses and clamps.

Now’s the time for a trip to the parts store. Easiest thing to do is take along ALL pieces of old hose. At the parts store, they’ll help you get enough new hose to replace them all – they may even cut them to size for you. BE SURE you tell them it is fuel line. Fuel line is neoprene, but vacuum hose line can be just rubber. Gasoline eats rubber, so you want neoprene. Get at least 4 to 6″ extra just in case. Also buy a bunch of hose clamps – remember you need two for each section of hose you’ve got. They’re cheap, so you might as well replace them too, although more and more I see really inferior hose clamps being sold so eventually the older ones might even be better than the new ones. But for now, replace them. If you have one of those plastic aftermarket inline filters, you should replace that now too (they’re also cheap to buy). Also, you’re going to need gasket sealer (see discussion below).

OK, a word about metal lines. These lines are very thin-walled tubing, and you want to be careful whenever doing anything to them because they will crush or kink very easily. And a fuel line with a kink in it is a major headache. You probably don’t need to replace any of the metal lines (unless you slip and crush or kink one) so I won’t go into all that. Just be careful around them – treat them gently. Metal lines either connect to a section of rubber hose, or else they screw in at the end. There will be a brass nut-shaped thing at the end of it that screws into a brass socket on the pump or carb. Get a wrench out and gently loosen this connection. Unscrew it all the way, and it just pops off. If you totally remove the over-engine fuel line, notice which way it threads in there amongst the other lines and stuff, so you can get it back into the right place.

NOTE: Make sure you use line wrenches made for these fittings. They grab on 5 sides and will keep you from rounding over a fitting. Also, make sure you put a wrench on the fitting it goes into. Failure to do this is the number one cause of bent lines. If you can’t get the fitting apart, use a little penetrating oil. A steel nut into a brass fitting is real common and they can be a pain to get apart.

So now you should have everything disconnected. Also take a good look at your pump now, to see which connects to what. Making a little sketch can help answer questions later. Oh, a word about vacuum pumps. If your fuel pump has more than two hoses coming out of it, it’s a vacuum-assist pump for your wipers, too. You’ll need to unhook the vacuum line(s) (are there one or two? I forget) and also mark which one went into which connection on the pump. Hint: if you hook it up backwards, it won’t work. Vacuum lines look like fuel lines (rubber hosing) but they just pull off usually (no clamps) so they’re easier to deal with.

OK, so it’s all disconnected. Now you need a wrench. Probably a half inch, as AMC just loved those half inch bolts – you can take most of a Rambler apart with a half inch wrench and a Phillips screwdriver! A socket wrench makes this an easy job. There are two bolts which attach the pump to the engine. Remove these. Loosen one a little bit, loosen the other one, and then just remove them. The pump will now come off the block, although you may have to yank it (old gasket sealer may be gluing it on there). Put it aside. Oh, be careful, it’s full of gas and if you tip it, it’ll all run out, so do this someplace where you don’t care about (hint: not in your wife’s flower bed – it’ll kill the flowers).

Now comes the messy part. Scrape the pieces of old gasket off the engine block. You can use a gasket scraper, or a putty knife or anything with an edge, but if you do be careful – you don’t want to put big scratches and gouges in the block. I like to use the handle end of those wire scrapers (they look like big toothbrushes with copper bristles), since it’s wood and won’t damage the surface. Takes more elbow grease this way, though. Get the surface completely clean – as clean as you can get it. Get ALL tiny pieces of gasket and gasket sealer off it. Spray some carb cleaner on a rag and wipe it off (and the surrounding area) to clean oil, grease, and gunk off the surface. LIGHTLY rub it with steel wool or wire scraper or very fine sandpaper, just to completely clean the surface.

NOTE: You may also use a spray on gasket remover. Spray both sides of the gasket and the engine block, let it set a few minutes, and put the gasket onto the block. It will stay in place.

Now you’re ready to put it all back together. You can do this in either order, lines first or pump first. To put the new pump on: first take a look at the old pump and the new pump side by side. They should be exactly the same. There’s a lever sticking out that goes into the block – this definitely needs to be exactly the same. The pump itself may have minor differences (replacement ones can have a metal bowl instead of glass or other minor things). If the outgoing metal line screws into the pump (no section of hose) then look at the old one – there will probably be a little brass fitting on it that bends it 90 deg. Note which way it is pointing, then remove it from the old pump and put it on the new one. If the threads are stripped anywhere on it, replace it (it’s cheap and any hardware or auto parts store will have one). A word about brass fittings – they’re fragile. Brass doesn’t rust, but it’s kind of soft metal. You can strip the threads on it easily. Tighten it enough so it’s nice and tight, then tighten it a bit more to align it the same way it was on the old one. But resist that urge to overtighten it. If you get it all together and it leaks out of this fitting, then you can tighten it more, but if you overtighten it, it means another trip to the parts store to get a new one. Now get the new gasket out of the box. Fit the pump to the block with the gasket in there (do a dry run of assembling it). The gasket may need to have a little bit trimmed off – I’ve noticed that the gasket is probably also a big 3 gasket and is very slightly different than AMC – on the big rectangular hole in the middle there may be a “flap” of gasket that may need to be trimmed a little. If you’re lucky, the gasket will fit perfectly. Otherwise get a sharp knife and trim off the little flap.

There are several philosophies about gasket sealer, I’ve noticed. “Whatever works” is my motto. Best thing to do is send a plea to this list, compare answers, and go with what sounds right. Or you can ask someone in the parts store what to use AND how to use it and follow their advice. Some people don’t use any sealer, some use sealer and no gasket, some use it on one side, some on the other, and some on both. Personally, I spread a very thin coating on both sides with my finger, but someone will be sure to tell me how wrong this is, I’m sure. Hey, works for me and doesn’t leak. Anyway, ask the parts store guy and go with what he tells you, that’s my advice.

So get the gasket all gooped up, and put it on the block or on the pump (depends which side is sticky) and then put the pump on the block. Get the bolts started right away. The pump may not want to go all the way on right away – you are fighting the spring that holds that lever down. This is OK, just keep tightening the bolts evenly (tighten one a bit, then the other). Or, if you really want, during the dry run, you can manually turn your engine until the cam lines up perfectly with the lever in the down position. But that’s not really necessary. Tighten it evenly until you’re sure it’s really on there good. Don’t have the torque figures handy for this one, but it’s not that high torque – maybe 20 to 30 ft./lbs. Someone correct me if this is wrong. Don’t break your wrench on it, but be sure they’re tight, how’s that?

Now replace the hoses. Cut each one to length with razor blade or other sharp implement. I usually cut mine about an inch longer than the replacement, then just stick them further onto the metal fuel line to take up slack. Remember it’s easier to cut a hose down a little bit than to find out it’s just a little short. Here’s another handy hint: put the clamps on the hose before you put the hose on. Otherwise you have to take it off and start over! Think about the placement of the clamps when you put them on – which side do you want facing you so that they’re easy to tighten and remove? Anyway, slip the rubber hose on both sides, position the clamps about a half inch to an inch from the end of the rubber hose and tighten them down. Don’t over tighten these too much either. When I see the rubber sticking out a little bit from the little slots in the hose clamp, it’s tight enough (this may sound confusing but it’s obvious when you’re actually doing it). Hook everything back together and you’re done!

NOTE: Get a small tube of silicon grease and put a small amount on the metal tubes. It will be much easier to get the rubber tubing on it and if you need to take it apart, it will not stick as bad.

Read the gasket sealer package to find out how long you have to wait until you fire the engine up – usually at least overnight. When you first start it, it will take cranking it for awhile as the pump has to prime itself the whole system’s dry and so it takes awhile to get from the tank to the carb. When it starts up, let it run and go check the system. Look for any fuel leaks anywhere, and tighten things up if they need it.

NOTE: If you carefully fill the float bowl of the carb (usually through the bowl vent), the car should start up and run long enough to prime the pump. You may want to wait until after you run it before you change the fuel filter. You will undoubtedly get junk in the lines when you do this and you may as well let the old filter catch it.

That’s it! It’s really pretty easy, actually. Even if you replace all the hoses, it shouldn’t take more than a couple hours, even for a first time. Average trips to the parts store during this job: 2.5. But then your mileage may vary.

Electric Fuel Pumps

Electric fuel pumps are almost always located inside the gas tank. This helps prevent vapor lock and keeps the fuel pump cool. The pump is a turbine type hydraulic unit directly coupled Fuel is used as a lubricant and coolant for the motor. The reason electric fuel pumps are used in an EFI engine is that they can produce the high pressures needed for proper fuel management. Typically an electric fuel pump is capable of putting out about 90 psi of fuel pressure. A check valve is incorporated in the fuel outlet to hold pressure when the pump is not running and a pressure limiter valve is located on the pressure side of the fuel pump housing with a return passage to the fuel inlet side to keep fuel pressure within specs.

When the rotor disc rotates, the rollers are pressed outwards by centrifugal force and act as a circulating seal. A pumping action is created by the circulating rollers that draw in fuel at the inlet port and force the fuel through the outlet port into the fuel system.

When the pump is shut off, the check valve in the fuel outlet will close, therefore prohibiting the fuel from returning to the fuel tank via the fuel pump. The check valve will therefore maintain a pressure in the fuel lines called the “rest pressure”.

The maximum fuel pump pressure (not fuel system pressure) is dependent on the calibration of the pressure limiter. If the fuel pump pressure exceeds a preset limit (for example a clogged fuel filter), the pressure limiter will open a by-pass to the fuel inlet side of the pump.

The fuel pump is mounted along with the fuel tank sending unit and care must be taken when removing the pump/sender assembly so as not to damage the sender unit.

Some vehicles have an access panel to get to the fuel pump without having to drop the tank. You should check the appropriate service manual to see if your vehicle has an access panel. In general Ford and GM do not have these panels and most Japanese cars do. Also, some Chrysler cars do have these panels and some don’t. Again, be sure to check the service manual for this information. If you can’t find out, just write me and I will tell you if the tank needs to be dropped or not.


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