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How do i test my fuel pump to find out if it is bad or not ?

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Spray quick start. If it starts then you know its fuel related. Then turn key on while someone listens to the pump thru the filler neck. It should run for about 2 seconds then shut off, If you hear it, and the car starts with quick start then the pump failed. If you do not hear it you will need to verify you have a 2 second 12v pulse on the green or grey wire at the connector. If you have the signal then the pump is bad. If no signal then you either popped a fuse, relay. or the PCM failed. Go to mitchell1diy for wiring diagrams and procedures. .

Posted on Jul 21, 2010


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I have a 2002 gmc yukon will start then die out i can hear my fuel pump charging could my fuel pump be bad ?

Could my fuel pump be bad ????? Rather then guessing , i suggest you test fuel pressure to know for sure . Videos on youtube showing how . You will need to buy a fuel pressure testing tool . (55-62 psi) VIN: (V, T,U)

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Have a 1990 Chevy Silverado pickup 350 Put a new fuel pump fuel filter screen fuel pump relay Fuse electronic control module cap rotor new injectors. Injectors won't spray but they have power. Fuel pump...

Disconnect the wire connection to the fuel pump, turn it on and test for 12V (or whatever your car battery voltage is) at the leads coming from the battery. If 12V is present the problem is the fuel pump. Test the continuity of the pump circuit at the same time (no power on for this test). set VOM to resistance attach to both leads going to pump. If reads 0.00 continuity is OK. If no reading pump circuit is open, pump motor is bad. I have had them bad right out of the box. Good lesson to learn whenever possible, ALWAYS bench test new parts before installing.

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2001 acura mdx wont start. cant hear fuel pump.

going backwards, ? (yes, i to check volts first) but...
you check fuel pressure cranking, (is press in spec or not?)
the FSM covers this, 1/.2 the cars only get pump activation,,
cranking and running, never just key on (the fsm shows this fact, i didnt look for you)
Yours is older loop system, not dead head.
there are 5 test just for the pump, (actually more)
pressure cranking and running, (leakdown test and injector balance tests and shut test for loop version) on V6 that 6 +4 ,10 total tests.
once the gauge is in place we do all 10s tests on v6.

ok say my pressure spec. is 40psi cranking and i get 10.?

spec: 32-40 running, pSI, vac, hose conn. (cranking will be more)
in loop systems the cranking pressure is about 10 PSI more.
after it starts, the vacuum sucks pressure from say 50psi to 40.
(its also altitude compensating)

Voltage checks, (any voltmeter)
use a voltmeter to see if full power reaches the pump.
i check voltage and its 8v. (bad) cranking volts can be near 11v due
to battery load, 200amps or so... what i do is measure battery crank
voltage and expect same to pump , using the 0.5v rule. (drop)
the connector over here to pump is all corroded. ,,
fix that and bam, now full presssure
or i find a bad fuel pump relay, replace that and bam.
or i find 0v, to pump.
i find relay bad. (simple tests on relay) (its not bad ECU)
ok i find 12v. at pump. so what is wrong?, i check my fuel pressure
regulator at the fuel rail, its stuck wide open because the shunt test
passed (one of 4 tests above) so new reg and bam, 40psi to rail.
i can test the reg with my hand vacuum tool that all shops have.
i can see pressure, running and cranking and check fuel pressure
with no vacuum (50psi?) then pump it to say 20 "hg (simulates idle)
and see 40 pSI, and check the diaphram for leak down.
my reg was bad.
there are other tests:
1: fuel pump current. (if excessive, its a bad pump)
2: scope test or use a current probe on pump and see it spiking
like made, , it has bad commutator and will die so.

there great videos on all this at. Duane's site.

check the pump cranking

do not hot wire the fuel pump relay
if you slip 1/.8" you blow up a nice $400 ECU, (or more)
the ECU drives this relay (with a transistor, you dont want to explode)
if you feel compelled to hot wire things, disconnect the pump
and hot wire that.
now the relay.
it has 4 pins 12vdc in, 12vdc out to pump (contacts)
and 2 coil pins.
you put your meter to coil pins (across) i get 12v to coil cranking and running, that is the ECU working right
i get 12vdc in and zero out the contacts, the relay is bad.
lets say you see 3v out, that can be a shorted pump. or wire grounded out to pump. I check the current with my amp clamp and see 15amps
the pump is bad. most draw 4-6amps. normal.
i keep an open mind, what is bad, its only the pump 1/2 the time
or less. maybe 1/3? (reg, pump, wires and friends)
corroded connectors big time...some even burned up.

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What's the fuel pressure ? Hook up a fuel pressure gauge an test it yourself . fuel regulator ??? It's a fuel pressure regulator . I was starting rough and I had a diagnostic done. "They" said it was the fuel regulator.
Hard starting - not starting rough . What year is the truck , what engine does it have . If they don't know for sure what's wrong you better try another repair shop that know's how to diagnose .
Electrical problems can lead one to believe the fuel pump is bad . Doing voltage drop testing on the electrical circuit is a very good test.
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Plus doing current testing can pin point a bad fuel pump .
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Whole fuel system

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You can make a jumper from a wire with stripped ends or even a straightened paperclip. Jump the circuits on the right side of the fuses for best results
For a 1979-84 240, jump fuse circuit #5 to #7.
For a 1985-93 240, jump fuse circuit #4 to #6.

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