How To Make Fuel Pump Run Continuously
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The Fuel pump is considered the heart of the engine. Nothing in your vehicle will be more annoying than a malfunctioning fuel pump.
Often people notice issues related to the fuel pump since information technology is the part that feeds the engine.
Problems related to the fuel pump will never become unnoticed since information technology directly manifests into vehicle driving issues.
So, the fuel pump glitches shall be diagnosed as early every bit possible to go along the wheels moving. Otherwise, information technology would result in makes blunders during usage.
Often people experience that the fuel pump runs continuously with key ON and it is due to issues like bad ECU, incorrect wiring, faulty/stuck fuel pump relay, malfunctioning crank position sensor or cam sensor, bad oil pressure switch, ignition switch short, defective airflow metering sensor, or wiring connection mix-up upshot.
If you are experiencing simillar issue, and so y'all are not solitary. This is ane of the most frequently reported problems that people oft face.
Hither in this article, we will become to know the details for the cause of this constantly priming fuel pump and the solution to prepare it.
Table Of Contents
- 1 How Fuel Pump Priming Works?
- 2 Fuel Pump Runs Continuously With Fundamental On? (9 Causes And Solutions To Fix It!)
- 2.1 Bad ECM
- two.2 Faulty/stuck fuel pump relay
- two.three Wrong wiring
- two.4 Refit fuel pump relay and fuse
- 2.5 Faulty crank position sensor or cam sensor
- ii.6 Bad oil pressure switch
- 2.7 Ignition switch short
- 2.8 Lacking airflow metering sensor
- two.9 Wiring connection mix-upward
- 3 How To Test The Fuel Pump Relay?
- iii.i Continuity test
- iii.2 Resistance examination
- 3.3 Voltage exam
- 3.four Beep sound Exam
- 4 Conclusion
How Fuel Pump Priming Works?
If yous are observing that the vehicle battery is frequently draining off and can hear fuel pump operating sound from the back of your vehicle even if the key is in ignition on condition, then probably it is associated with the constantly priming fuel pump which endlessly draws electric current from the battery until it dies.
Before we talk about the reasons for the subject field problem, we shall first understand what is fuel pump priming and how it functions?
Last time, i wrote an article on fuel pump primes but no fuel pressure level on pump outlet. You may go through that article if you want to understand fuel pump priming function in particular.
The fuel pump priming is a function that is incorporated in most of the in-tank electric fuel pumps which ensures that the pressurized fuel is available at the engine injector inlet at whatever given time.
Before we kickoff cranking the engine, when the key is in ignition on position, the vehicle ECM (Electronic Control Module) grounds the fuel pump relay to fclose the power supply circuit to the fuel pump to run the fuel pump for 3 seconds.
Subsequently iii seconds, the ECM cuts off the power supply to the fuel pump by switching off the ground to the fuel pump relay, until the engine motility is detected past the crank sensor.
The crank sensor sends signals to the ECM to activate the fuel pump when the engine starts running. This sequence is pre-defined and programmed in the ECM.
This ensures that the fuel pump runs and maintains the fuel supply hose under desired pressure and ready for fuel injection before the beginning of the engine crank.
This is required for the atomization of fuel upon injection into the engine manifold for ensuring proper combustion.
But many times the fuel pump keeps on constantly priming and the fuel pump won't shut off with the primal in ignition on position after the preset timing.
If the fuel pump stays on with key on, the first thing you lot would do before it kills the bombardment overnight is to remove 1 of the battery terminals to shut off the fuel pump.
But it is frustrating to practice this temporary fix on daily ground and yous may accidentally finish upwardly screwing another electric parts of your vehicle.
Fuel Pump Runs Continuously With Key On? (9 Causes And Solutions To Gear up It!)
Below are the probable causes for the fuel pump to run continuously with key on. Y'all may endeavour to figure out what is causing this problem later analyzing each root cause in your vehicle for taking further class of action.
Bad ECM
If the fuel pump is constantly priming, then it means that the ECM that is supposed to shut off the power supply to the fuel pump after three seconds of initial priming of pump; is not doing so.
This means either the ECM is bad or the driver in the ECM could exist shorted, otherwise, it would accept ungrounded the fuel pump relay to trigger the fuel pump shut off.
When the fuel pump priming is completed, the voltage to the fuel pump shall be stopped merely due to bad ECM, the fuel pump relay is continuously grounded. Hence the fuel pump keeps on continuously running when machine is off.
You lot may find traces of moisture and burn down marks on ECM. These are the confirmatory signs that the issue is due to the bad ECM and it'south fourth dimension to supersede it with a new one.
If whatsoever of your friends have the same vehicle, then you may try swapping the ECM to confirm that it is the culprit before you purchase a new 1.
Faulty/stuck fuel pump relay
The Fuel pump relay is the part that controls the power supply to the fuel pump and if the fuel pump relay is stuck closed or faulty and then it would send continuous ability to the fuel pump, even when the fundamental is kept in ignition ON position (non engine cranking)
Then the fuel pump would exist constantly priming regardless of the central position if the fuel pump relay contacts go stuck airtight.
Auto mechanics sometimes short the fuel pump relay by putting a fuse or jumper wire between the load side relay blades to fix the problem with the relay.
This keeps the fuel pump running continuously without the basis input from the ECM, after three seconds of fuel pump priming.
With the key in ignition ON condition, the contacts of the relay should be open later the completion of fuel pump priming. If non, it ways that the fuel pump relay is faulty.
Fix for the faulty fuel pump relay
By and large, the ampere rating of the fuel pump relay matches with that of some of the other relays in the TIPM plastic box (Total integrated Power Module houses all vehicle relays).
So endeavour swapping the fuel relay with the same rating and confirm whether the fuel pump stops constant priming.
If yep, then replace the fuel pump relay with a new one. If not, you are not done. The issue lies somewhere else.
Ordinarily, when the fuel pump is reaching its end of life, information technology would draw more electric current which may crusade the fuel pump relay contacts to fuse.
You may bypass the fuel pump relay, if you want a temporary ready to deal with a faulty fuel pump relay.
Or if you keep the relay powered upwards long enough then also this problem may happen. So yous may likewise wait for signs of a failing fuel pump.
Incorrect wiring
Bank check whether the wire from the fuel pump relay to the ECM has become corroded or damaged and is exposed past touching the frame of the vehicle thereby grounding the fuel pump relay permanently.
If then, then information technology would go on the fuel pump relay constantly ON that would requite the fuel pump a abiding 12 V with the key on. Hence the fuel pump won't close off in this case.
If this non-terminate fuel pump running thing occurs once in a while, and so it also indicates that at that place is a false basis in the wire between the fuel pump relay and the ECM due to intermittent contact with the vehicle frame.
Information technology is besides possible that the fuel pump wiring is accidentally plugged into the 12 V supply directly during diagnostic testing past the mechanic and has bypassed the fuel pump relay birthday.
All of the to a higher place incorrect wiring conditions would atomic number 82 to the fuel pump constantly priming problem.
Work around for wrong wiring
Ensure that the electrical wiring from the fuel pump relay to the ECM is routed away from whatever sharp objects to prevent unintended fouling.
This would crusade wear and tear of wiring due to the vehicle vibrations and thus leads to possible permanent earthing of wire.
If you lot detect that the wiring harness is compromised, then fix these areas past roofing brusque pieces of electric tape over the exposed surface area and thereby forestall unintentional footing connexion to the fuel pump relay.
While replacing or repairing the electric connectors and wiring, you need to confirm the fuel pump wires color codes to avert possible wrong wiring. Otherwise, the vehicle won't start as the fuel pump won't become power.
Refit fuel pump relay and fuse
Fifty-fifty though it may sound strange every bit it looks, many times simply pulling out the fuel pump relay and the fuses and plugging it back, helps in shutting off the fuel pump with key on.
This is because the electric parts are ever sensitive to clay and grit particles. Unclean and dirty contacts often lead to this kind of erratic behavior.
Faulty creepo position sensor or cam sensor
The ECM sometimes receives a crank RPM indicate even when the engine is not running, in example of a faulty crank position sensor.
Once the ECM senses crank rotation signals, and so the fuel pump would continuously run on irrespective of the key position (ON or start).
A malfunctioning creepo or cam sensor may false the fuel pump and it won't close off. So it is advisable to inspect the creepo position sensor and replace it with a new one.
Bad oil pressure switch
This is provided equally a backup in case the fuel pump relay fails. Either one can activate the fuel pump.
Commonly, the oil force per unit area sending unit has 3 wires. Orangish, Grey, and Tan. If it does, then pull off the wiring connectedness to the oil pressure switch, when yous experience the issue of the fuel pump continuously running with key on without cranking the engine.
If the pump shuts off, then it'southward the oil pressure switch that keeps the fuel pump constantly priming.
Your vehicle may either have residual oil pressure which supplies to the fuel pump or the oil pressure switch is stuck airtight or it is the bad oil pressure level switch that keeps the fuel pump constantly priming.
And so yous would need to supersede the oil pressure switch with a new one to gear up the issue. The oil pressure switch is commonly located above the engine oil filter.
Ignition switch short
If the fuel pump stays on with key on, then probably the ignition switch is shorted and is feeding the power supply to the fuel pump fifty-fifty the car is off.
Put the key in the ignition switch and shake it a bit and run into if the fuel pump shuts off. Oft if there is an internal short and the fuel pump would constantly prime and won't close off. But if nosotros wiggle the ignition switch, information technology may help in breaking the unintended contact.
If you measure 12 V at the ignition fuse with the ignition switched off, so the Ignition switch is probably faulty and it is fourth dimension to supercede it with a new ane.
Defective airflow metering sensor
In erstwhile vehicles, nosotros take this vane airflow metering sensors (VAF) to measure the volume of airflow through the engine. This airflow sensor works by sensing the motility of the jump-loaded flap which is continued to a potentiometer past a lever arm.
This arm converts the flap movement into voltage signals for sending it to ECM to control the air-fuel ratio forth with other vehicle sensors input.
The airflow sensor has a safety switch for the electric fuel pump relay. The air period through the sensor activates the fuel pump.
This safety switch shuts off the fuel pump in case of an accident scenario (when the engine is not operating, so no air flow) to cut off the fuel supply.
In case of a defective airflow sensor or if the safe switch connection on the airflow metering sensor plate is plugged off so the safety switch volition exist closed, then the fuel pump won't shut off with primal on.
So ensure that the condom switch is plugged in. Generally VAF are non serviceable, but y'all may attempt removing the sensor housing and utilize some electronics cleaner to clean the rheostat contacts. This may reinstate the VAF to regular operation if the contacts are not worn-out, but it would be no assistance if the sensor has a faulty electronic parts or a damaged flap.
Wiring connection mix-up
Ensure that the fuel-pump related wiring connections are not mixed upwards. For example, if the airflow sensor connectors and the cold start injector connectors are confused for one another, then the swapping would issue in neither performing ok.
So you would take trouble cold starting the vehicle and at the aforementioned time, the fuel pump won't shut off and run continuously (since the airflow sensor has a safety switch that cuts off the ability to the pump)
How To Test The Fuel Pump Relay?
Often it is the fuel pump relay that attributes to the problem of continuously running fuel pump with key on, then it is worthwhile to understand whether the fuel pump relay is the actual root cause of the trouble or something else by performing the below set of tests.
Fuel pump relay usually has got 4 pins (3 or 5 pins is also not uncommon). Out of these iv pins, 2 pins are from the control side (input voltage (86) and ECM footing (85)) and 2 pins belong to the load side (fuel pump (87) and bombardment voltage (30)).
The pin names are usually printed on the fuel pump relay and the naming convention may vary from one manufacturer to another. But they are always self-explanatory.
Unplug the fuel pump relay which is located under the vehicle hood within the TIPM plastic box (sometimes too called ability distribution eye) and connect leads to the wiring terminals sitting beneath information technology and plug the fuel pump relay to offset testing.
Continuity test
Set the multimeter for the continuity test and connect ane end of the multimeter probe to i of the load side atomic number 82 (87) and connect the other probe to the other load side (xxx).
If the excursion is continuous, yous would hear a beeping sound and would mean that the circuit is short and demand to supercede the fuel pump relay.
Resistance exam
Set the multimeter to read the resistance across circuits. Measure the resistance across the above 2 load points (87 and xxx).
If the multimeter reads any resistance like nothing or in hundreds or thousands instead of showing infinity.
And so information technology again confirms that the fuel pump relay is shorted and needs replacement.
Voltage test
Peg the negative atomic number 82 of your multimeter (or the end of your test light) to the load side battery terminal (30) and connect the positive lead of the multimeter to the load side (87) of the relay connector.
At present turn the key on (don't crank the engine). If the multimeter read 12 5 (test light come on) for 2 secs, and then go out or does the low-cal stay on?
If it comes on and stays on and the multimeter continuously reads 12 V, then it ways that a default ground is established between the fuel pump relay and the ECM.
So irrespective of the central position the fuel pump won't shut off, then await for simulated ground betwixt ECM and relay and prepare it off.
Beep sound Test
To isolate the fuel pump relay from other probable issue areas like ECM and wiring harness, this examination can exist performed to confirm a standalone consequence in the fuel pump relay.
Connect the two probes of the multimeter to the load side leads (87 & xxx). Then connect the basis lead of whatsoever 12 V power supply to the command side ground (85) of the fuel pump relay.
While you touch the 12 Five trigger of the external power supply to the control side (86) you lot would hear a clicking sound from the fuel pump relay which ensures that the coil and the switch contacts are working perfectly. If not, y'all would need fuel pump relay replacement.
If you are performing this test on vehicle level, since the control side connections are already available, you lot demand to but do the load side connections every bit explained above and check the fuel pump relay.
Decision
The ECM monitors all signals from the various sensors and the relays. Information technology is the key component that allows the vehicles to perform various interconnected operations finer with pre-defined logic.
Each OEM has its own fashion of controlling the vehicle components with dissimilar criteria to operate the ECM with varying input/output signals from the concerned components.
To determine the power supply to the fuel pump and to confirm that the engine is running, some manufacturers may use just the fuel pump relay and creepo position sensor input, whereas others may monitor reference pulses from the ignition module or indications from the oil force per unit area switch, or airflow sensor prophylactic switch.
Vehicle manufacturers constantly come up with artistic means to revolutionize these systems.
The pre-divers fuel pump priming process fourth dimension is controlled by the ECM via a grounding and un-grounding of the fuel pump relay and fuel pump constantly priming outside the boundary conditions of the ECM is the possible result of defective ECM, fuel pump relay or the wiring ground fault.
Hope the above information would have enhanced the knowledge about the troubleshooting of the fuel pump and would help you in fixing the problem of the fuel pump running continuously with primal on.
Happy Motoring!
References
https://forum.classicmotorworks.com/index.php?topic=25632.0
https://www.thirdgen.org/forums/tpi/45792-when-key-fuel-pump.html
https://www.s10forum.com/threads/fuel-pump-wont-shut-off.802689/
http://forums.pelicanparts.com/porsche-911-technical-forum/880250-fuel-pump-runs-constantly-primal-only-non-started.html
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