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Mike S., Chevy Mechanic
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Experience:  ASE Certified Master Technician
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Chevrolet S10: 1989 Chevy S10 2.5L/5 spd Fuel pump doesnt

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1989 Chevy S10 2.5L/5 spd

Fuel pump doesn't engage when ignition is turned on. Truck will crank when gas is poured in carb but stops when its burned up.

I've replaced the fuel pump. Is there a universal switch or inertia switch for this model that could keep the fuel pump from engaging?

There is a relay that turns the fuel pump on for a few seconds when the key is turned on then when the engine starts, the oil pump switch keeps power to the pump when the engine is running. Below is the circuit for the fuel pump, first make sure the fuse is good and then check for power at the pump when the key is turned on and the engine is cranking.


Fuel Pump

Wiring Diagram For Chart A-5 - Fuel Pump Relay Circuit Diagnosis






Customer: replied 5 years ago.

i'm not able to view the image.

Customer: replied 5 years ago.
Relist: Answer came too late.

Here is a better look.


So, first of all check with a 12 volt test light or voltmeter, the ECM B fuse 10a (hot at the time). If ok, then also make sure you have voltage at the orange wire at the relay. There is a prime connector, you could jump 12 volts to that to see if the fuel pump runs. It doesn't show the wire color but they are usually red. That would check out the relay and wiring to the pump.

If it runs when using the prime connector then the problem may be the ecm and/or wiring from it to the relay. Now remember, the fuel pump usually only comes on for a few seconds when the key is first turned to run, unless the engine is cranking and the oil pressure builds up enough to override the relay. So, have someone else turn the key to run and check for voltage along the dark green/white wire for 2 seconds. Also, check for voltage on the gray wire leading to the fuel pump if the relay is activating.

Customer: replied 5 years ago.
Where is the relay located?
Left front inner fender.

It appears as there are 3 of them. If any are the same part number you could swap with one and see if the fuel pump runs to quickly check if it's just the relay that is bad. From the diagram, the relay is on the far left looking at the bracket.



Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 7368
Experience: ASE Certified Master Technician
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Customer: replied 5 years ago.



This vehicle only had two relay switches where the diagram showed three, but I changed it out and it now is running great.


Thanks very much for your help!

You are welcome and thank you!