No power to new fuel pump.


Redranger90

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'90 ranger 2.9 , just replaced the pump and sending unit but the pump won't turn on. I changed the relay , checked the inertia switch, wiring and fuse but still nothing no pressure to the regulator and cant hear the pump. HELP!!
 


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Bird76Mojo

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Use a voltmeter and check for power at the pump, or pump connector. If you've got 12 volts there, then you must have a ground issue or a bad fuel pump. It's not unheard of to get defective parts at the parts store these days.
 

rusty ol ranger

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Could also be an ECM issue.
 

Paulos

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@Redranger90, try bypassing the fuel pump relay and see if the fuel pump runs continuously. You just need a jumper between the two terminals in the diagram (fuel pump test point and computer test ground), ignition on. This only bypasses computer control. If the pump now works, the problem should be in the computer (ECM). If it still doesn't work, it's somewhere in the fuel pump wiring system or fuel pump. The inertia switches can appear to be okay, but not be. With the jumper in and the ignition on, check for power at the inertia switch. No power means the problem is before the inertia switch, if you have power there it means it's the inertia switch or somewhere past it. The diagram I posted is for an '89, but it should be the same for your '90.
fuel pump sys.jpg
Fuel pump relay bypass.jpg
 

Redranger90

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Thank you everyone I have a friend coming over with a digital multimeter and we're going to go through the wiring these diagrams really help I will let you know what I find this evening.
 

Redranger90

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I have a ECM from a 89 2 wheel drive Auto with a c but it's the same engine can I use that on my vehicle
 

rusty ol ranger

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You could plug it in and see if the fuel pump runs. But i wouldnt use it as a total replacement.
 

Paulos

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I'd say you have a good chance of an '88 through '92 2.9, 4x4, manual, non-California ECM's working. But I wouldn't think a 2wd auto would. I don't see anything in the ECM pin out diagram that would indicate a problem to just test it. 4x4 electronic shift may be an issue though.
 

rusty ol ranger

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An auto ECM will run a manual truck but itll idle wrong and have less power and just be quirky in general.

But to test fuel pump operation have at it.
 

Redranger90

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I have a ECM from a 89 2 wheel drive Auto with a c but it's the same engine can I use that on my vehicle
Mine is a 9 4 wheel drive standard without AC
@Redranger90, try bypassing the fuel pump relay and see if the fuel pump runs continuously. You just need a jumper between the two terminals in the diagram (fuel pump test point and computer test ground), ignition on. This only bypasses computer control. If the pump now works, the problem should be in the computer (ECM). If it still doesn't work, it's somewhere in the fuel pump wiring system or fuel pump. The inertia switches can appear to be okay, but not be. With the jumper in and the ignition on, check for power at the inertia switch. No power means the problem is before the inertia switch, if you have power there it means it's the inertia switch or somewhere past it. The diagram I posted is for an '89, but it should be the same for your '90.View attachment 28473View attachment 28474
thanks for the info it helped a lot
 

Redranger90

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Ok guys its fixed. Finally. All electrical checked out with the multimeter my inertia switch is working correctly and I believe it was a combo between unseating and reseating the pins on the ECM and reseating the pins on the pump plug I can't say for sure but after I did those two items it's running again. Thank you to all who commented and give input on my situation.
 


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