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Troubleshooting the fuel pump circuit



By: BigBabyLou

So you say your car doesn't start because you don't have fuel to the injectors?
And I assume you cycled the key on and listened for the fuel pump priming whine and didn't hear anything?

First things first: check the main fuse by the battery. It's a single fuse in a plastic fuse holder. It might actually look a little like an unplugged connector. It will have an orange wire and a red wire going to it. (on older models, the wire color might differ)

Next thing you can check is the fuel pump relay. It looks like the fan (or MAF) relays and is located in the engine compartment, on the firewall, in the corner right by the brake booster.
Unplug the relay.
Identify the wires on the connector:
- an orange wire (might be actually pink/black on some old models) that supplies 12V power
- ared wire (or could be also orange on some models) which you can ignore right now
- a grey wire (or tan/white on older models) which powers the fuel pump
- one thinner black/white wire for the ground
- one thin green/white wire from the ECM

(for simplicity, I will stick to the newer wire colors - please substitute them with your wire colors if you have an older engine model)
Wiring diagram

Measure the voltage (or use a test light) on the main orange wire. If you don't see 12V, you have power supply issues. Check the wiring.
Check the ground on the black/white wire. It is often a problem.
Using a paperclip, jumper the orange power supply wire to the grey fuel pump feed wire. Does the fuel pump turn on? Likely a relay issue or ECM wire problem.
If you replace the relay and the problem persists, try testing the green/white wire for voltage. Stick a test light in it and turn the key on. Does the light light up for two seconds? Cool, the ECM wire is ok then. Whew!

If the fuel pump didn't turn on when you jumpered the grey and orange wires, you might have a problem with either the pump or connector C313.
Of course, it's easier to check the connector first. So jack up the back of the car and put it on jackstands securely. Reach above the differential, there is a 3-prong plug on the wall behind the rear seats. Unplug it and clean it. Plug it back in and test the pump again. This connector is constantly exposed to dirt, water and road grime so it does get dirty even inside.
You can put ground on the black wire and 12V on the grey wire (on the connector on the tank side). If the pump STILL doesn't run, measure the resistance between the black and grey wire. You should see only a few ohms (up to 20). If you see something like 10 kilo-ohms or in general a big number like that, the fuel pump is very likely bad.

Hope this helps.
Lou


 
 

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