Hey all, I've been lurking through the old posts and I have a question.

What inputs tell the ECM to turn on the fuel pump relay?

My situation:

1989 F150 XLT Lariat 302 Manual trans. dual tanks.

I bought this about a year ago, unfortunately it didn't run that well when I got it, but I got it for a steal so... When it does run it is real rough idle and acts like it isn't getting enough fuel or too much. Fuel rail pressure test was 15 psi with the KOEO and with the fuel test point grounded it slowly rises to 40 psi with KOEO. I was able to pull a code off the computer of 24 which is a ACT/IAT sensor. The EEC relay and the Fuel Pump relay are both working.

Today I'm going to replace the fuel regulator(just for insurance) and fuel filter. Then if that doesn't help I'm going to ohm out the ACT/IAT sensor.

It seems like I have chased the problem to the regulator or to the negative side of the fuel pump relay coil that goes to the EECM. I'm wondering if the EECM is not telling the Fuel Pump relay to turn on(it does come on for two seconds when the key is on, but doesn't seem to come back on).

I've been fighting with this for a couple of days and need to get this truck running, it is my wood getting truck and winter is a comin'.

Do you guys have any ideas? I would appreciate any and all help.

 

ok well I replaced the fuel filter and the regulator but no difference. pump is running so wiring must be good. gonna try a fuel pump next.

 

I'd hate to see you throw expensive parts at this blindly. Before you replace the pump, try pulling it out of the tank and get a pressure reading straight from the pump with the KOEO. You should be getting more than 15 at the fuel rail, but it could be due to clogged fuel lines. If you still get the same 15 directly at the pump, you have confirmed a bad pump and good lines at the same time.

 

I replaced the high pressure pump and also found out that the front tank pump isn't working, also a brake line blew out on my first test drive !!

Now I get to do some brake line work.

how hard is it to replace a front tank pump?

 

Wow did I get into this deep. Ok I've replaced both wheel cylinders and both calipers including pads and most of the brake lines (rusted through). Friday I did compression test and found one cylinder (#8) with 30 psi compression!!! I tore into the motor and found the exhaust valve missing a piece. I've replaced it now along with head and upper end gaskets, thermostat, belt and headers (old manifold was cracked and leaking bad). It also gave me a excuse to remove ALL emission junk, in Iowa we don't care about passing smog test.