So I'm troubleshooting a crank no start condition on a 86 F150 with the fuel injected 302, manual trans 4x4. Currently I am not getting power to the fuel pump. I have replaced the pump, the fuel filter, ignition cylinder, and the fuel pump relay.

With everything plugged in as normal, when I turn the key to ignition on the relay clicks on, then immediately clicks off, and the engine just cranks but will not start.

When I jump power straight from battery hot to the power terminal on the fuel pump it kicks right on and the truck starts right up.

I started doing circuit checks on the relay and have 12V at the yellow wire marked always hot in the circuit diagram. With the key on I also have 12V at the red wire that is hot coming from the ECM. This led me to Ohm out the tan and light green wire that is ECM controlled ground, and with the ignition on I have infinite resistance or an open circuit.

This led me to believe that I was not getting a good ground to the relay, so I backprobed the ground wire at the relay and connected it to a good ground. The relay then clicked on and did not click back off, however the fuel pump still wasn't running.

I have to be missing something. Has anyone had any similar issues, or any advice on where to go from here? With batt hot to the pump it starts up immediately and runs like a champ, but I don't want to have battery hot to the pump the whole time I'm driving it!

 

I assume you are using the diagrams here (Electronic Engine Control - ???Gary's Garagemahal) and here (Electric Fuel Pump Control - ???Gary's Garagemahal). But, you didn't say if you have a single or dual tank system.

Anyway, I can't imagine you having two problems. So, let's take one at a time. When you said "ohm out the tan/light green wire", how did you do that? I would use the voltage function and put the red lead on +12v and the other on the tan/light green wire. Then, with the Start or Run the ECA should take the wire to ground and your meter should show 12v.

But, if you grounded that wire, or that side of the relay's coil, and the relay kicked on but the pump didn't run then you have another problem. And I'd bet on the inertia switch being it.

 

It is a single tank, with the low pressure in tank pump and high pressure rail mounted pump.

When i say that I ohmed out the tan and green wire I mean that I measured resistance between that pin of the relay and chassis ground with the ignition in the run position.

i have isolated the inertia switch by shorting the two pins of the connector that goes into it, and still do not get voltage to the pump.

 

Depending on which way you set up your meter you might not get a good ohm reading when the ECA is working properly. The ECA is a solid state device and the direction of the current is important. I think if the red lead is on Ground and the black lead goes to the tan/lg wire it should work. But if you turn them around you won't get a good reading. But, your meter might be backwards from that. And that's why I would use the voltage scale instead of resistance.

 

Gary, what is this ECA you refer to? I suspect that is something peculiar to the 7.5. What we have here is an EFI 5.0. The EEC module controls the fuel pump relay, although I may just be nitpicking.

Anyways, the yellow and red wires correctly have +12 volts and the tan/LG wire is a ground sourced by the EEC module. The relay has been observed to click when a ground is supplied and I may add this tan/LG wire is the same circuit as the fuel pump test point at the EEC test connector. The only piece of the puzzle is what may be happening with the P/BK wire at the relay. This wire should supply +12 volts when the relay operates. I think you are probably correct in that the inertia switch has tripped, (on the firewall inside the cab on the left side of the transmission hump if you are looking for it). When it is tripped, it interrupts the power to the fuel pump from the fuel pump relay which comes from the P/BK wire.

On that short click from the relay, that is perfectly normal when the key is turned on without starting the engine. What is happening is that the EEC module contains a 1 second timer that is constantly reset by PIP pulses from the distributor. If the engine is not turning, no pulses are generated and the timer runs for 1 second and shuts off the fuel pump relay. This is for safety, I.E. shuts off the fuel pump with the engine not running. This is also why there is a fuel pump test pin on the EEC test connector. The idea is to place a ground on the test pin so the relay stays energized with the key on so you can troubleshoot the fuel pump relay circuit. In a pinch, I have driven the vehicle with the fuel pump test jumper in place, but this defeats the safety of the shutoff from the EEC module when the engine is not running with the key on. This can be useful to get you home when you can't find out why the fuel pump is not running, but I would not recommend long term driving in this condition.

I'll add an observation in that the ground for the EEC module is connected at two points. There is a black wire at the battery- post and an orange wire to the engine at the left rear of the intake manifold. The latter is peculiar to the 85/86 5.0 EFI and if it is disconnected, you may have issues with fuel pump relay control.

 

Good observations. Thanks!

 

The orange wire you mentioned sounds like a good starting place. I've already taken the inertia switch out of the system by placing a large screwdriver in between the terminals going into the connector from the relay hot to inertia switch, basically removing it from the circuit and still had no power to the pump.

 

Also, does anyone have a pinout of the 86 ecm, so I can do a resistance check from the wire at pin 22 to the relay?

 

What's wrong with the one on pages 60 and 61 in the link above?

 

They don't have a diagram showing which pin on the actual connector is pin 22.

 

You can't tell from the wire colors?

 

See attached document in post 14...

 

 

1986 EEC-IV Diagram

 

That is awesome. Thank you for the diagram.