Fuel pressure test

[tribal599]

In the Mountaineer/Explorer 99 workshop manual it states that in order to relieve the fuel pressure the electrical connector to the inertia fuel switch must be pulled to disable the fuel pump. To get to this IFS you have to pull away the carpet and door trim to get to it on the passenger side. So my question is can I pull the fuel pump relay instead? They both disable the fuel pump. What is the difference between the two? Thanks

 

[colintrax]

There's no difference, pull whatever you want to disconnect the fuel pump. The inertia switch is easy to get to, no need to pull the carpet. Make sure you crank the engine over for a second after you pull the relay or switch to actually remove fuel pressure.

 

[bobinyelm]

Why not just pull the fuel pump relay? It's #5 inside the black relay box just behind the battery under the hood. Takes 30sec to reach it.

If you have not ever removed a relay, just wiggle it back and forth as you apply upward pressure and it will come right out.

It's indexed, so you cannot insert in incorrectly when re-installing it, BTW.

Here is a photo of the box in my 2000 Explorer showing Relay #5 in relation to the others. The firewall is to the right, and the battery to the left in the photo.

Click (or Copy/Paste): http://screencast.com/t/WUvYMUM0O

Click to enlarge:

 

[tribal599]

Why not just pull the fuel pump relay? It's #5 inside the black relay box just behind the battery under the hood. Takes 30sec to reach it.

If you have not ever removed a relay, just wiggle it back and forth as you apply upward pressure and it will come right out.

It's indexed, so you cannot insert in incorrectly when re-installing it, BTW.

Here is a photo of the box in my 2000 Explorer showing Relay #5 in relation to the others. The firewall is to the right, and the battery to the left in the photo.

Click (or Copy/Paste): http://screencast.com/t/WUvYMUM0O

Click to enlarge:

When i remove the relay, then connect my fuel pressure gauge to the test port on fuel rail, I would put the relay back on so I read pressure KOEO mode?

 

[colintrax]

When i remove the relay, then connect my fuel pressure gauge to the test port on fuel rail, I would put the relay back on so I read pressure KOEO mode?

KOEO does not apply to you, that's OBD1. Your truck is OBD2. But fuel pressure has nothing to do with OBD. Although to test fuel pressure it is technically K (key) Ô (on) E (engine) Ô (on) but that's improper nomenclature.

If you're trying to test fuel pressure you have no reason to release fuel pressure. Just screw the gauge onto the Schrader valve, start the truck, and see what the gauge reads.

The only reason to release fuel pressure is to disconnect something. Say replace the fuel filter, fuel injectors, pump, or lines.

 

[bobinyelm]

Well,, pulling the relay and running the engine until it stalls will help you get zero pressure so you can connect the gauge without spraying fuel all over, but you don't need to.

To check your fuel pressure, just jump relay base terminals 3 and 5 (the two inboard ones aligned fore and aft) together with the gauge connected. This will turn the pump on (even with the ignition switch off-you can hear it running) and you can test your pressure.

It's good to also check the pressure w/ the engine running and using fuel, though.

 

[tribal599]

Well,, pulling the relay and running the engine until it stalls will help you get zero pressure so you can connect the gauge without spraying fuel all over, but you don't need to.

To check your fuel pressure, just jump relay base terminals 3 and 5 (the two inboard ones aligned fore and aft) together with the gauge connected. This will turn the pump on (even with the ignition switch off-you can hear it running) and you can test your pressure.

It's good to also check the pressure w/ the engine running and using fuel, though.

Thanks guys. I'll remove relay, connect gauge, plug relay, turn key on for three seconds and then turn off, watch gauge stabilize in the 40-65 range as per workshop manual. Then turn it on again and do a leak down test. It's my first time so i'll play it safe.