Having had problems with my 89 F150 302 EFI lately, I took it to the mechanic on Friday to get it sorted out. I gave him my workshop manual and even hooked up a self test light for him while he read the book. We were going to do a KOEO test when he jumps in and starts the truck with the self test hooked up. WTF !!! He knew it was connected. Now there is no power to the HP fuel pump. The only way we can get the pump to run is to jump a lead off the battery to the pump itself. There is no power in the wire from the ecu.
My question is this...If you start the truck with the wires connected up to the self test unit, does that send an unusual amount of power through the ECU and will that damage it. The truck starts if I connect power to the pump directly, but not on it's own. Has this idiot fried my ECU ?
Many thanx.

 

I'd first remove any jumpers and disconnect the negative battery terminal for a couple of seconds to reset the computer.

Verify the Inertia Switch mounted on the driver side firewall inside the cab.
hasn't tripped.

Here's the schematic (Thanks to Subford's CD) of the fuel pump relay for an 88. I believe the 89 setup should be the same.



When you turn the ignition to Run, the fuel pumps should run for about 2 seconds and then shut off because no ignition reference pulses will be found because the engine is not running or cranking.

With the ignition key in Run, at the Fuel Pump Relay you should measure 12 volts on the small Red wire. This 12 volts comes from the ECC Power Relay.

On the Large Yellow wire you should measure 12 volts at all times. It comes from a fusible link that is attached to the starter solenoid lug on the battery side.

The EEC energizes the Fuel Pump Relay by grounding the small Tan/Light Green wire. When the relay energizes, 12 volts from the Large Yellow wire passes thru the relay to the Large Brown wire and then 12 volts is applied to the fuel pumps.

So if you ground the Tan/Light Green wire and start the engine and it runs, I'd say the computer is bad.

 

Thanks f150xlt. Just got computer back from tech. He says there's nothing wrong with it. Looked under the dash and found a heap of melted wires from previous owner. So that's where I'm going to start and find the fuel pump problem.
BUT....some d*ckhead has hard wired the pump to the ignition so it ran all the time, they by-passed the relay which has been removed !!! They have also removed the inertia switch. My question is, will it affect the truck at all if I rewire everything as per diagram, but minus the inertia switch. I just want it to work ok so I can sell it !

 

the inertia switch just shuts off the fuel if you get in a wreck....I would advise to put the switch in, because in a wreck where there might be sparks around and high heat, you dont want a bunch of high pressure fuel blowing everywhere

 

The ECU (EEC) shuts off the fuel pumps if the engine stops running for any reason, a wreck, broken fuel line or any number of things. I would also advise to put the ECU back in the circuit also for the same reasons nighthawk285 talked about above.

Also on an 89 the wire leaving the fuel pump relay may be Pink with a black stripe instead of the brown wire. This wire also goes to pin #8 of the ECU and if not hooked up you will get a code 95 on an 89.

 

On my '89, power wire from pump is red/ black stripe, joins into 2 x brown wires. 1 goes to ECU , 1 goes to tank selector switch.

 

Here's the diagram of the fuel pumps for a 88. 89 should be similiar.

 

I think your red/black stripe is a pink/black stripe wire and the brown wire goes to the Inertia Switch not the tank selector.

 

Mate, someone has played with the wiring in this truck before and anythings possible. Got some bits and truck now fires ok but shuts down after 10 - 15 seconds. Might be inertia switch not being there or pump is not flowing enough. Have to check on weekend. I gotta stop buying things that people have stuffed up !

 

I believe that starting the vehicle with the self-test apparatus wired shouldn't damage anything --- this is called a KOER test (Key Off Engine Running). Are you sure that the self-test jumpers, etc were connected properly?