1987 No power to fuel pumps

[A1Stack]

Hey guys, I have an 87 Bronco II that I purchased in non running condition. No power to fuel pumps. I was able to get them to kick on by jumping the 2 relay connectors, so I can rule out bad pumps and any wiring issues further back. I ran a voltage test on the relay plug, I’m getting the correct power and grounds on all the pins except for the pin that I believe is supposed to power on with the ignition turned on. I had my wife crank the engine while I checked for voltage, nothing. Anybody else had this problem? Could it be the ignition switch, or maybe a bad computer? Additional notes: I have replaced the relay, and the intertia switch is good.

 

[RobbieD]

Depends on which relay that you're jumping connections on.

Power from the ignition switch turns on the EEC relay, and then the computer grounds the fuel pump relay to turn it on.

If it's the fuel pump relay that you can jumper to make the pumps run, then it could be the computer.

If it's the EEC relay that you can jumper to make the pumps (and everything else) to run, then the ignition switch could be the problem. It's fairly common for the ignition switch to wear out on the first generation trucks, and it isn't too hard to check.

Removing two screws from underneath will let you remove the steering column plastic trim peices.

Now you can look at the electrical part of the ignition switch. Check for a gap on the switch between the plastic and metal parts. Wiggling the wires or the plastic part will help show if the two parts have loosened. It will look like this:

If the switch is tight, you can also meter the switch wires to confirm that it's not the problem, before moving further down the circuit to troubleshoot.

If the ignition switch is bad, you can replace it, or try strapping it back together (like the one pictured).

Welcome to TRS.

 

[A1Stack]

Depends on which relay that you're jumping connections on.

Power from the ignition switch turns on the EEC relay, and then the computer grounds the fuel pump relay to turn it on.

If it's the fuel pump relay that you can jumper to make the pumps run, then it could be the computer.

If it's the EEC relay that you can jumper to make the pumps (and everything else) to run, then the ignition switch could be the problem. It's fairly common for the ignition switch to wear out on the first generation trucks, and it isn't too hard to check.

Removing two screws from underneath will let you remove the steering column plastic trim peices.

Now you can look at the electrical part of the ignition switch. Check for a gap on the switch between the plastic and metal parts. Wiggling the wires or the plastic part will help show if the two parts have loosened. It will look like this:

View attachment 108009

If the switch is tight, you can also meter the switch wires to confirm that it's not the problem, before moving further down the circuit to troubleshoot.

If the ignition switch is bad, you can replace it, or try strapping it back together (like the one pictured).

Welcome to TRS.

It’s the fuel pump relay that I jumped so that answers my question. Must be a computer issue then. Is there a way I can test that before buying a new one?

 

[RobbieD]

It’s the fuel pump relay that I jumped so that answers my question.

Key on, three pins on the fuel pump relay should have +12 volts; grounding the fourth pin (Tan'L Grn wire, which is also on the EEC self-test connector) will make the relay "click" and the fuel pumps run. If it does do this, then it's not getting the ground from the computer (EEC).

Must be a computer issue then. Is there a way I can test that before buying a new one?

About the only check you can do to the computer itself, is to open it up and look for blown capacitors or corrosion on the circuit board. There are several threads on here with pictures showing what the blown caps will look like.

 

[A1Stack]

Key on, three pins on the fuel pump relay should have +12 volts; grounding the fourth pin (Tan'L Grn wire, which is also on the EEC self-test connector) will make the relay "click" and the fuel pumps run. If it does do this, then it's not getting the ground from the computer (EEC).

Perfect, I’m almost certain a new computer will fix this problem. Thank you for your prompt reply!

 

[bcschief]

Fuel pump or pumps will only run under certain conditions. When you turn the key on the PCM will command the fuel pumps for about 3 seconds to prime the system and then shut off the pumps, when you crank the engine, it will again turn on the pumps as long as it see's engine rotation thru the PIP signal from the distributor, when it no longer see's the PIP signal it will shut off the pumps. The power for the pumps goes thru the fuel pump relay, the fuel tank selector switch if equipped with dual tanks and the inertia switch, so any one of those could cause the pumps not to run even if the PCM commands the pumps to run.

 

[rusty ol ranger]

Perfect, I’m almost certain a new computer will fix this problem. Thank you for your prompt reply!

When mine failed to power the fuel pump i was able to get a fuel pump code from the ECM.

Code 95 maybe? Dont remember the number.

Anyways chances are its the ecm