No Reading on Fuel Pressure Tester When Cranking or Ignition on

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diagnose fuel pump

Diagnose Fuel Pump

If the fuel pump is not delivering adequate fuel force per unit area and volume to the engine, the engine may non start or run properly. Depression fuel pressure can cause hard starting, a rough idle, misfiring, hesitation and stalling. No fuel pressure will prevent the engine from starting, or will cause the engine to quit running if the fuel pump fails while driving.

Fuel injected engines are very sensitive to fuel pressure level equally well as fuel volume. Low pressure will cause starting and driveability problems. A pump that can deliver adequate pressure but not enough book may allow the engine to first and idle ordinarily, but it will starve the engine for fuel and cause a loss of power when the engine is under load, accelerating hard or cruising at highway speeds.

Engine Cranks But Will Not Start

A dead fuel pump can prevent an engine from starting, but so can a problem with the ignition organization or the engine itself (such as a broken timing chugalug).

The get-go affair to check would be spark. This can be washed by connecting a spark plug tester to a plug wire while the engine is cranking. The tester must be grounded to the engine block for a practiced electrical connection.

CAUTION: Do not touch any of the spark plug wires while the engine is existence cranked or you lot may get a bad shock!

If an engine has a coil-on-plug ignition system, and it is possible to remove i of the coils, do so and identify a spark plug in the finish of the coil. Then place the ringlet and plug then the plug is touching metal on the engine.

If the ignition organisation is working properly, you should see a series of sparks while cranking the engine. No spark would betoken an ignition trouble such every bit a bad crankshaft position sensor, ignition module or ignition coil.

Adjacent, check the timing belt if the engine has an overhead camshaft and safe timing belt. The belt is usually enclosed inside a plastic comprehend on the terminate of the engine. Removing a couple of screws from the cover and pulling the cover back should allow you to see the belt. If the belt looks okay, and turns when the engine is cranked, compression is probably not your problem. Timing belts can jump fourth dimension if they loosen up or if the cogs on the underside of the belt become damaged. It'south as well possible for the overhead camshaft to seize or intermission if the engine has run low on oil or has overheated. Only if the cam gear turns when the engine is cranked, that's probably not the trouble either.

CAUTION: Continue your fingers away from the chugalug and gears while cranking the engine!

If ignition and compression are both OK, that leaves a lack of fuel as the most likely cause of the no start. Merely is it the fuel pump or something else?

Possible Causes of a Fuel-related No Start:

ane. A dead fuel pump (could be the pump, pump relay pump fuse or a fault in the pump wiring circuit)

two. A plugged fuel filter

three. Low fuel pressure (weak pump, restricted fuel line, low voltage to the pump or a defective fuel pressure level regulator)

If the pump runs and generates normal force per unit area to the engine, just the engine nevertheless does not start, the problem may be:

i. No voltage to the fuel injectors (blown injector fuse or bad relay)

2. No pulse signal to the injectors from the PCM (no crank or cam sensor input to the PCM, or a bad commuter circuit in the PCM, or a wiring harness problem)

3. A shorted fuel injector (robs voltage from the other injectors so none will operate)

fuel pump gauge

Fuel Pump Checks

One of the first things to cheque is the fuel pump. Does the pump run when the engine is cranking? The pump should make a little noise. No noise would tell you the pump is not spinning.

On nearly vehicles the pump is energized by the PCM via a relay. When the ignition key is beginning turned on, the PCM energizes the fuel pump relay for a couple of seconds so the pump volition run to build upwards pressure level. The PCM and so shuts off the fuel pump relay (which turns off the pump) if information technology does not receive an rpm signal from the engine indicating the engine has started after cranking. The pump circuit too may be wired though an oil pressure switch and/or an inertia condom switch that kills the pump in case of an blow. Refer to the wiring diagram to find out what is involved earlier jumping to whatever conclusions.

A bad fuel pump relay will prevent the fuel pump from running. Locate the fuel pump relay in the engine compartment (information technology is usually in the power heart). Remove the relay and shake information technology. If you hear anything rattling inside the relay, the relay is cleaved and needs to be replaced.

To test the fuel pump, bypass the relay to route ability straight to the fuel pump. If the fuel pump runs when the relay is bypassed, the problem is a bad relay or a fault in the wiring excursion that provides power to the relay. Bypassing a relay can be tricky because you have to know which terminals to jump. So earlier you endeavor this procedure, you must await upwardly the fuel pump wiring diagram for your vehicle in a manual or online.

One new tool we found recently (see beneath) makes bypassing a fuel pump relay much easier and requires no wiring diagrams or jumper wires. The tool is a fuel pump bypass relay. Information technology is a replacement relay that has an ON-OFF rocker switch on top. All you do is replace your fuel pump relay with the test relay, flip the switch to energize the fuel pump and run into if the fuel pump runs. If the pump works, the problem is a bad relay. If nothing happens, the problem is a bad fuel pump or a mistake in the wiring between the relay and pump. The tool is made by IPAtools.com and comes in a kit that includes vi different relays that fit a diverseness of import and domestic vehicles:

Fuel pump relay bypass tool allows y'all to energize and exam the fuel pump.

Other electrical problems that tin affect the pump include low voltage in the pump'southward power supply circuit or high resistance in the pump's ground connexion. Either may forestall the pump from running or spinning fast enough to generate normal fuel pressure level.

Measuring Fuel Pump Pressure level

Depending on the awarding, the fuel system may require anywhere from xxx to 80 psi of fuel pressure to showtime and run. NOTE: Fuel injected engines are VERY sensitive to fuel pressure level. If pressure at the engine fuel rail is fifty-fifty a couple pounds less than specifications, the engine may not outset or run well, or experience hesitation or stalling problems.

Pressure specifications volition vary according to the type of fuel injection system on the engine equally well as the performance, fuel economic system and emission requirements of that detail model year vehicle. At that place are no rules of thumb. Every application is different, and then always look up the pressure specs when troubleshooting fuel-related performance problems.

When there is too much fuel pressure level, the engine runs rich. This causes an increase in fuel consumption and carbon monoxide (CO) emissions. An engine that is running actually rich also may experience a crude idle, surging and possibly even carbon-fouled spark plugs.

When there is not enough fuel pressure, the engine may not start. Or if it does, it may idle roughly and run poorly. Low fuel pressure creates a lean fuel status that can crusade lean misfire, hesitation, rough idle, hesitation and misfire on acceleration.

To check fuel pressure level, you lot need a gauge and a place to attach it. There are a number of dissimilar checks that tin be made, including static or rest pressure (key on, engine off), residual fuel pressure, running pressure level, maximum or "expressionless head" pressure and book of fuel delivered. The fuel pressure regulator also should be tested, and a fuel pressure drop test performed to check for dirty fuel injectors.

Unlike vehicle manufacturers recommend different test procedures. On many European EFI systems, the OEMs recommend using a static pressure level test with the engine and ignition off. This is done by bypassing the fuel pump relay and energizing the pump directly. Near domestic and Asian vehicle manufacturers, on the other hand, provide a test fitting on the fuel runway then pressure can be checked with the engine running.

If you are working on a vehicle that does not have a pressure test fitting, you volition have to tee a pressure estimate into the fuel line only ahead of the injector fuel runway.

Caution: Before hooking up your pressure level gauge, relieve all pressure in the fuel organisation.

Static Fuel Pressure Examination
With the cardinal on, engine off (or with the fuel pump energized), fuel pressure level should come up quickly and hold steady at a fixed value. Compare the force per unit area reading to specifications. If you get no pressure level reading, check for voltage at the pump. If in that location is voltage only the pump is not running, you take plant the problem: a bad fuel pump.

If you lot do go a pressure reading but the reading is lower than normal, the cause may be a weak pump, a blockage in the fuel line, filter or tank inlet sock, or a faulty pressure regulator. Also, depression voltage at the pump may prevent it from spinning fast enough to build up normal pressure. Check the voltage at the pump. If OK, check the fuel filter and lines for obstructions and the operation of the fuel pressure regulator before you condemn the pump.

Balance Fuel Pressure Exam
When the pump is turned off or stops running, the arrangement should hold rest pressure for several minutes (look up the specs to see how much pressure level drop is allowed over a given period of time). If pressure level drops quickly, the vehicle may accept a leaky fuel line, a leaky fuel pump check valve, a leaky fuel pressure regulator or one or more than leaky fuel injectors. Low remainder fuel pressure level can cause hard starting and vapor lock during hot weather.

Running Fuel Pressure Examination
With the engine idling, compare the judge reading to specifications. Fuel force per unit area should exist within the acceptable range given by the vehicle manufacturer. If low, the problem may be a weak pump, low voltage to the pump, a clogged fuel filter, line or inlet sock inside the fuel tank, a bad fuel pressure regulator, or nearly empty fuel tank.

Dead Head Pressure
This checks the maximum output pressure of the fuel pump. With the render line pinched shut, the pump should produce two times its normal operating pressure at idle. If the pressure rating does not go upward with the render line blocked, the pump may non be able to deliver plenty fuel at college engine speeds. Possible causes include a worn pump, depression voltage at the pump, a plugged fuel filter or inlet sock in the tank, an obstructed fuel line or virtually empty fuel tank.

Fuel Book Test

A fuel pump that delivers normal pressure may still cause driveability problems if it can't deliver enough fuel volume to meet the engine's needs. A fuel book test may therefore be the all-time way to evaluate the pump's condition.

A fuel volume test measures the book of fuel delivered over a specified interval. This exam can exist done past connecting a fuel flow gauge into the fuel supply line, or by disconnecting the fuel return line from the fuel pressure level regulator and connecting a hose from the regulator to a large container. Caution: Make certain in that location are no open sparks or flames nearby while doing this test!

With the engine off, energize the pump and measure the book of fuel delivered during the specified interval of time. As a dominion, a practiced pump should deliver near iii/4 to 1 quart of fuel in 30 seconds.

Causes of depression fuel volume delivered include a worn fuel pump, a plugged fuel filter or inlet sock in the tank, obstructed fuel line or nearly empty tank. Don't forget that low voltage at the pump can besides preclude it from running fast enough to generate adequate fuel catamenia. The pump'south supply voltage should be inside half a volt of normal organisation voltage. If it is low, cheque the wiring connectors, relay and ground.

Fuel Pressure level Regulator Tests

This exam checks the operation of the fuel force per unit area regulator to make sure it changes line force per unit area in response to changes in engine vacuum. This is necessary to maintain the proper operating pressure behind the injectors and to compensate for changes in engine load.

With the engine running, disconnect the vacuum hose from the pressure regulator. Every bit a rule, fuel system pressure should increase 8 to 10 psi with the line disconnected. No change would indicate a faulty pressure regulator, or a leaky or plugged vacuum line.

Also, when the vacuum hose is asunder from the regulator, bank check the inside of the hose for whatsoever wetness that would bespeak fuel is being sucked into the hose. There should be none. If the inside of the hose is moisture, it means the diaphragm inside the regulator is leaking. This will cause a drop in fuel pressure, and let fuel to be sucked into the intake manifold upsetting the air/fuel mixture. If the diaphragm is leaking, supplant the regulator.

Fuel Pressure Drop Test

This test measures the drop in static system fuel pressure when each injector is energized. The amount of pressure driblet for each injector is and then compared to see if the injectors are dirty and demand to be cleaned or replaced. This test requires an "injector pulser" tool to energize the injectors.

To perform this test, turn the key on or energize the fuel pump for a few seconds to build upward static pressure in the fuel arrangement. Then turn the key off, pulse ane injector for the specified fourth dimension and annotation the pressure drib for that injector. Turn the key back on to rebuild static pressure and repeat the test for each of the remaining injectors.

An injector that is pulsed 100 times for 5 milliseconds should produce a minimum pressure drop of most 1 to 3 psi, and no more than than 5 to 7 psi, depending on the awarding.

The divergence in pressure drop between all the injectors should be two psi or less. If you lot see more than three psi difference betwixt the highest and lowest readings, the injectors are dirty and demand to exist cleaned or replaced.

If you encounter no pressure drop when an injector is energized, the injector is chock-full or lacking and needs to be replaced. If the pressure gauge needle bounces, the injector is sticking.

After cleaning, echo the test to encounter if cleaning did the trick. All injectors should bear witness about the same corporeality of pressure drop (less than ii psi deviation) and no more than seven psi drib at 100 pulses for five milliseconds. If in that location is no change in the readings or the driblet exceeds these limits, the injector(due south) need to be replaced.

Fuel Organisation Scan Tool Checks

If you have a scan tool that can display OBD system information, look for a fuel pressure PID. Compare the fuel force per unit area reading confronting specifications to see if information technology is in range or not. You tin also compare the scan tool pressure reading confronting the actual reading on the vehicle with a gauge to see if they are the aforementioned. If the judge reads higher, the vehicle may have a bad fuel pressure sensor. A low fuel force per unit area reading would confirm a weak fuel pump, low voltage to the fuel pump or a leaky fuel pressure regulator that does not permit the organization to develop and concord normal fuel pressure.

You can likewise expect at Long Term Fuel Trim (LTDT) and Brusque Trim Fuel Trim (STFT) values to run into if the engine is running lean. A normal range is usually plus or minus 8 or less. A STFT value greater than 8 or a LTFT value greater than ten would tell y'all the engine is running lean, possibly due to low fuel pressure level or a weak fuel pump. Just think that lean readings can also exist caused past engine vacuum leaks and other weather.

Fuel pumps can as well be tested with a professional person level browse tool that has bidirectional capabilities. On the scan tool diagnostics carte, there may be an choice to run a fuel pump self-examination. The test allows you to energize the pump to see if information technology runs, and to test the operation of a variable speed pulse-modulated pump.

You can also utilize whatsoever scan tool or lawmaking reader to pull fuel-related fault codes from the PCM.

Fuel System Scope Tests

Past connecting a Low Amps probe to the fuel pump'southward voltage supply wire, you tin can view the pump's current waveform on a digital storage oscilloscope (DSO). The telescopic pattern will reveal internal clothing in the brushes and commutator that may non show up in a traditional pressure or book test.

Observing the waveform will show if the pump'southward amp draw is normal for the application or is high or low, and if the pump is operating at normal speed or is running deadening. Problems such as a bad spot on a commutator or a curt or open in the armature also will be obvious in the waveform.

A "good" electric fuel pump waveform volition generally seesaw back and along with relative consistency and minimal variation betwixt the highs and lows. A "bad" waveform will show big or irregular drops in the pattern, with large differences between the highs and lows.

Fuel Pump Replacement

Click Here for Data on How To Supplant A Fuel Pump

You lot Replaced the Fuel Pump Only the Engine Nonetheless Won't Showtime

If the fuel pump is running and delivering normal force per unit area to the engine, and the engine has spark and compression, but will not start, the fuel injectors are probably not opening. The PCM uses the trigger signal from the crankshaft position sensor, and/or camshaft position sensor to pulse the injectors. The injectors should receive battery voltage when the key is turned on, and the PCM commuter circuit provides the basis connection to energize the injectors.

The beginning check would exist to check for voltage at the injectors when the key is turned on. No voltage? The problem could be a blown injector circuit fuse, a bad fuel injector power relay, or a fault in the wiring harness to the injectors. The injector fuse and relay are ordinarily located in the relay box or power distribution eye in the engine compartment.

If the fuse is okay, endeavour swapping the relay with another to encounter if that gets voltage to the injectors and so the engine volition first. No modify? Then the PCM may non be pulsing the injectors, or there may be a shorted injector that is robbing power from the circuit preventing the other injectors from opening.

TIP: Try unplugging the injectors one at a time and cranking the engine to see if it will beginning. If the engine starts when a item injector has been unplugged, that'southward the shorted injector that needs to exist replaced.

TIP: You can also measure the resistance of each injector with an ohmmeter. Unplug the injector and measure the resistance between the two terminals. If resistance is outside specifications (high or low), supervene upon the injector.

Professional technicians use a tool chosen a NOID lite to bank check injector pulses. The tool detects digital signals in a circuit and flashes an LED light. No flashes from the injector circuit when cranking the engine would tell you the PCM is not pulsing the injectors. On newer gasoline direct injection (GDI) systems, however, a NOID light is no help.

If the injectors appear to exist working, but the engine is all the same not starting, the engine may exist flooded with Also MUCH fuel (remove a spark plug to meet if it is moisture). Let the engine sit down awhile, then try again, or concord the gas pedal all the style downward when cranking to put the PCM into the "Clear Flood" mode when starting the engine.

NOTE: Difficult starting problems are sometimes the outcome of an improper starting technique on the part of the driver. On a fuel injected engine, DO NOT push or pump the gas pedal when trying to starting time the engine. This just puts the engine into the Clear Flood style, which volition cut off fuel to the engine temporarily making it even harder to start. Just crank the engine without touching the gas pedal.

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