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66-96 Ford Broncos - Early & Full Size
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Need Help Troubleshooting!

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So it has been a while since I have posted on this forum but i've owned a few fords since then. ;)

Alrighty, so I just moved way up north to Washington from Texas. My lady and I moved up here to be closer to her family and better opportunities, well there has been an agreement on me and my lady's grandfather, Del, he has 1989 F150, 4x4, Single Cab, Swb, with a hopped up 351.

So Del has been telling me the problems on this truck and it kinda has me lost diagnostically but I do want to ask questions about this darn thing. Del decided to take the old 351 block out did some work to it and put it back in. Well shortly after he started to experiencing weird problems with it. When you turn the key into the on position, the fuel pump runs constantly and will cause the truck to not want to start.Like the fuel pump should shut off after a couple of seconds but doesn't stop. He replaced the the fuel pump and the computer more than once.

It'll run strong for a little while and start having problems, Del unplugged the battery for 10 days, hooked it back up and it started right up. He said something about letting the capacitors release all the data. Once again, it would run strong for a good bit and then just die. Well I got to put my hands on it and all I did was unplug the fuel pump relay, turned the key on, and the fuel pump never made a sound. I connected the relay back in, turned the key, and the fuel pump run constantly and didn't start.

My guess is that I need to probably backtrack that wiring and check for a bad ground? Any help is appreciated!

If I left anything out, i'll try to update this.

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Yo Yeti,

 It's likely the EEC Relay (BROWN CONNECTOR) is hanging closed; If the EEC relay goes bad, it could be sending the signal to the fuel pump relay to turn the fuel pumps on; One easy test for this is: Without the key in ignition, bump the starter over @ the starter relay using a screwdriver. If it is the EEC relay, the truck will start without the key in the ignition..."

You have ruled out the FP relay hanging closed.

MIESK5 NOTE; from Ford EVTM;

When the ignition is switched to the ON position, it turns the EEC Power Relay on. The EEC Power Relay provides power to the EEC-IV processor and the control side of the fuel pump relay. Power for the fuel pumps is supplied through a fuse link  attached to the starter relay (battery side). From the fuse link, current flow is through the fuel pump relay and Inertia Fuel Shutoff (IFS) switch to the fuel pumps. The IFS switch is a safety device used to shut off the fuel pump in the event of a collision. If the IFS switch is "tripped," it must be reset by depressing the white or red button on the top of the switch. The fuel pump relay is controlled by the Powertrain Control Module (PCM).

When the ignition switch is turned to the ON position, the fuel pumps will operate. If the ignition switch is not turned to the START position, the PCM will shut the fuel pumps off after approximately one second. The PCM will operate the fuel pumps when the ignition is in the START position to provide fuel while cranking.

After the engine starts, the PCM will continue to operate the fuel pumps unless the engine stops, engine speed drops below 120 rpm, or the IFS switch is "tripped."


Wiring Diagram in an 89

Consider  EEC & Fuel Pump Relay Swapping to Bosch Style Relays & Color Codes in all pre-'92 EFI Bronco & F-series; "...Working on ONE relay at a time, remove the terminals from the stock connector & discard it. I collected these Bosch-style sockets in junkyards, but they're available at most parts stores, from Ford, or several online suppliers like RJMInjectionTech.com as crimp-on kits for a near-factory look. Being careful to connect the wires to the proper terminals (using the list below), securely connect the old wires to the terminals of the new sockets. Try to keep the wires the same length so there's not a huge ratnest. EEC PWR 30 - Y (battery always 12V) 87 - Bu, DB, R (out to EEC) 85 - Wh/LB, R/LG (12V in from ig.sw.) 86 - Bk/LG, Bk (ground); FP: 30 - Y (battery always 12V) 87 - Pk/Bk, Br, DG/Y (out to inertia sw.) 85 - R (12V in from EEC PWR relay) 86 - T/LG, LB/Or (ground from EEC)...It's OK to reverse 30 with 87, or 85 with 86 on either relay. It's possible to just use common insulated flat blade terminals to connect the bare wires to the relay terminals without a socket, but it's not as secure or convenient. Now the truck will be MUCH more reliable, and can use the cheaper, heavier-duty, more common ISO relays that are easier to swap. Tape up the harness & secure the relays to a safe mounting location. Not all relays have mounting tabs like these, but the sockets or harness can be zip-tied to something solid..." @ http://www.supermotors.net/registry/media/507187

Here is the 1989 EVTM, Emissions & Pre-Delivery Manuals, Partial via mrnewland1 in Google Drive @ https://drive.google.com/drive/mobil...?usp=drive_web
Slow scrolling for me with lousy Comcast service.. Find page # of item desired in contents, then flip screen flip down like spinning a bearing (a no-no) then stopping periodically to see which page you're on.

Free registration for some wiring diagrams (86 through 96) and Technical Service Bulletins, (80 through 96), same as by Ford @ BBB Industries- Premium Alternators, Starters, Power Steering Products @ http://www.bbbind.com/free-tsb/


Here are some PCM KILLER perpetrators and other causes:
Old leaky capacitors, see https://www.fullsizebronco.com/forum...ore-codes.html by jowens1126
Smell around the PCM. If it smells like dead fish, it's bad. 
Bad Intel 8061 chip or bad Intel 8361 memory chip
Bad Voltage Regulator, ee http://www.fuelinjectedford.com/images/eec085.gif by Ryan M
Burned PCM printed circuit board circuits (brown burn marks). 
Water damage from cowl leaks, ESPECIALLY if you you have wet carpet or mat near driver kick panel; or on PCM Connector due to a bad hood seal near cowl panel, viewable with hood up.
The alternator could be generating an AC voltage spike due to bad diode(s),
Bronco was jump started on reverse polarity.
Overheated PCM.



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