Hows it going? this is my first post, and i could use some help.

I have a 89 Full size bronco and i'm having some fuel problems.

Problem:
Fuel pump wont run with key on.
If i run a power wire from the fuel pump relay to the positive side of the fuel pump, the it runs, but all the time so long as the key is on.

Things i have replaced:
High pressure Fuel pump, Fuel pump Relay, Fuel filter,

 

Always start with the error codes from the ECM, they can point you in the right direction. Could be corroded connection on the relay, or under the hood, or could be the ECM.

 

Do you have power at the connection at the fuel pump? If not then check the wiring.

Worst case scenario the PCM is defective.

 

i'm not too sure how to check the codes on the ECM, but i do have power to all connections involving the fuel system

 

Check here Ford Fuel Injection for answers to troubleshooting by pulling EEC-IV fault codes.

The ECM/PCM is the absolute LEAST likely cause for the problem. If the truck will run, this unit is fine end of story.

Welcome to FTE and the Big Bronco Forum.

 

Awesome website Grey! Now that I have fuel prob cured, will use it to troubleshoot the EGR. Pump and a new relay and a can of contact cleaner did the trick for my '91.
Good luck with yours skalrim, I bought a Haynes manual for my bronc, they tell you how to get the codes with a voltmeter, Also have a list of what the #s mean. For $15 or so it's a good tool to have.

 

ok got the codes.

code 96: Fuel pump secondary circuit failure. The EEC did not sense battery voltage on the Fuel Pump Monitor circuit

code 67: Neutral safety circuit failure

im not really sure what they mean, but thats what i got so far.

 

With the key on,check for voltage at the Grn and yellow wire, if there is none, check the fusible link near the relay, mine was covered with tape and heat shrink tubing. If there is power there, possibly a broken wire in the harness somewhere along the frame.

 

I would start with replacing the neutral start switch.

 

bump my post

 

check the wiring, maybe both those circuits are in the same loom and are having the same problem at the same point.

 

Code 67 - MLP circuit failure. NPS circuit failure. (manual trans only - clutch engagement switch failure).

Start by making absolutely certain the MLPS (E4OD transmission only), or neutral safety switch (all other automatic transmissions), or the clutch engagement switch is working properly. Disconnect wiring harness and cycle transmission from a moving to non-moving gear using an ohm meter to check continuity across the neutral contacts of the switch if you have an automatic. Or do the same but cycle the clutch in and out if you are dealing with a manual transmission. If this component checks out ok and ONLY if this component is ok then move on to the procedure below.

Code 96 - fuel pump secondary circuit failure/ high-speed fuel pump circuit failure.

Ok, There is no real interpretation required here. With the ignition OFF one terminal of the fuel pump relay should have battery voltage (approx +12VDC) If the terminal with the YELLOW wire (in your 89) does NOT have voltage repair the circuit between the relay and the battery/pin 1 of the ECA. If the terminal with the YELLOW wire has battery voltage, turn the ignition ON and check for voltage at the terminal with the BROWN wire. It should be the same voltage as the YELLOW has. Leave the meter connected and turn the ignition OFF and ON a few times to be certain the ignition switch is actually doing its job. The voltage should swing from battery voltage to zero each time the ignition is turned OFF and vice-versa. If this does NOT happen, move on to the RED wire terminal of the relay. This terminal should behave the exact same way as the BROWN wire should have... voltage with the key ON, none with it OFF. If it does, replace the fuel pump relay. If it does NOT, replace the ECA (computer).