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Fuel pump test


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LeeOG
New User

Jan 25, 2021, 6:45 PM

Post #1 of 4 (595 views)
Fuel pump test Sign In

I need to check my fuel pump's functionality. I was first considering to jumper the pump relay slots from batt to pump for just long enough to hear the pump motor running. But, not sure if computer or ECU might preempt such a setup. What about disconnecting the battery and use it as a stand alone power source for the same setup ?


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 25, 2021, 8:31 PM

Post #2 of 4 (580 views)
Re: Fuel pump test Sign In

All questions have to start with year, make, model and engine size.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



LeeOG
New User

Jan 26, 2021, 8:07 AM

Post #3 of 4 (564 views)
Re: Fuel pump test Sign In

OK, the vehicle is an old (1996) Dodge Ram 5.2 liter truck that is rarely driven, but has never failed to start in the last 25 years - except yesterday. The spark is good, but the spark plugs not so much (electrode burned down and 67 mil gap which should be .035) . I simply want to check if direct power to the fuel pump will activate it. And, to accomplish this, I want to disconnect the positive battery terminal (leaving ground connected), and run a direct line connection from the 12V positive battery post to the rely slot pump path. I'm thinking that a 2nd person laying under the fuel tank should hear some pump response. Of course, this says nothing about fuel pressure or current, but this can be checked later. I guess my question concerns the feasibility and practicality of such a test.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 26, 2021, 8:21 AM

Post #4 of 4 (560 views)
Re: Fuel pump test Sign In

That would not be feasible unless it has failed testing through normal means. The fuel pump activates for 2 seconds every time the key is cycled on and then continues during cranking. Trying to jump out the fuel system can be very dangerous as if you put power to the wrong terminal you can easily fry your computer.

The engine has a service port on the fuel rail where you can attach a gauge and then crank the engine. This is the accepted way of testing for fuel.
Just because you hear a fuel pump running does not mean it is working properly. A pressure test is the only acceptable procedure.

You should also be testing for spark and injector pulse as a loss of reference signal would also knock out the fuel supply.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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