I have a 1987 bronco w 5.0L EFI. I’ve been having insane problems w fuel pump relay not clicking/engaging. The eec relay energizes and clicks. I have 12volts at fuel relay from the eec relay and the yellow wire which is hot at all times. I have purchased a rebuilt ECU/PCM. They did not need mine so I opened up and it looked good. No discoloration around capacitors. Well I got the refurbished one in truck and still no clicking of the fuel pump relay. I put the old ECU/PCM and still the same. No clicking of fuel pump relay.

I have checked grounds and power thru the ECU/PCM harness at pin holes. These checked fine.

any recs? My fuel relay (and I have purchased 4) all are 5 prong. The original is 4 prong.

I can supply power thru the fuel pump relay harness to run the fuel pumps.

thanks.

 

The key for the computer to control the fuel pump relay is the tan lightgreen stripe wire going to the relay. You checked all your power + wires, that is good. But what happens, the coil to the relay is not grounded. So even though it has power, it will not click until the computer provides a ground to turn it on. That is what the tan/lightgreen wire is for.

So if you want to do some testing, find the connector where you plug in the code reader. It will have a terminal in it with the tan/lightgreen wire going to it. It is just for this purpose, to have a place to ground out the tan/lightgreen for testing purposes. Look for the connector over in the pass side hood hinge area. If you are going to keep working on this thing, you need to know how to pull the codes, all you need to do is find these two connectors and get a testlight.

Here's the connectors. In this picture he says the later trucks are located over by the driver's side hinge.





The connector that is larger with the angles on it, that is the one that also has the fuel pump test wire.

 

Thank you. Will try the test that you mentioned I have purchased an obd1 and I can’t get the thing to read. The original harness looked all messed up. I purchased a new harness. Installed. No codes.

yeah. I followed the schematic and still nothing. But will recheck again.

 

Here's a 1986 diagram, it is very similar to your 87 with a few minor differences. You can see the control for the relay comes from "ZZ" and "YY".

 

Here is "ZZ" which is power from your ECM relay. It powers most everything related to the computer, including power for the control to the fuel pump relay through "ZZ". I think you said you had this power? The red wire?.

 

Here is "YY". This is the tan/lightgreen which the computer grounds to turn on the fuel pump relay. You can see it goes to pin 22 on the computer. You can also see where it branches out and goes to the self-test connector, which is the connector where you plug in the code reader.

 

Yes I have power at yellow and red wires (hot at all times and the w ignition). I’ll check in the other.

man. Thank you so much for your help.

 

Many thank again.
I have fuel relay is fixed. I’m getting fuel to fuel rails.
engine turns over. No start. I have spark at distributor. Spark at spark plug. Nothing. Just cranks and turns over. There’s not much suction at intake. Is this usual?

 

Take a testlight and put it across one of the injector wires. Does it blink when the engine turns over?

Also have you checked the fuel pressure. I think your engine should be around 38 psi. I have rigged my own pressure tester by taking the guts out of the test port on the fuel rail(it's just like a tire valve) and then slipped a hose with a hose clamp over the test port and ran that to a pressure gauge. Or you can buy the official fuel pressure tester that will go right on the gauge.

 

I had a loaner fuel pressure gauge from the auto parts store. It would not fit on shrader valve. Going to get another one tomorrow.
I have not used a test light. But will do this as well. I’m not sure what this fuel injector test light it but I will get educated.

thank you.

 

You can get testlights for the injectors called "noid" lights. Harbor Freight even sells a kit. Just to test if the injector is getting a voltage pulse to turn on.

You can also spray some starter fluid or flammable brake cleaner in the throttle body and see if the engine will run on that. If it does you know you are getting spark and are lacking fuel for some reason.

 

Obtained a fuel pressure gauge. I could get pressure up to 30 or so. Then it would drop quickly. Found a leak at the single stage fuel reservoir. No aftermarket part for this. Crazy. Went to 4 salvage yards Saturday. Found one. Installed. Has slight leak but pressure holds better.
I have compression in each cylinder (4-7) at 150. 8 is at 175.
When I pulled the plugs, they were dry. No fuel on them. Bone dry.
I checked the vacuum on the fuel pressure regulator and its holds vacuum well. No leaks.

why no fuel on any of the plugs?

I have pressure at rail.

I measured voltage on the #6 fuel injector and red wire is hot and the other wire does pulse hot. I have not put noids on. The injectors are difficult to remove and I didn’t want to break them. Also the injectors for 1-4 I have to remove manifold. Which looks like I’m going to have to do.

Any thoughts. How do I remove the injector to place noid on them

 

The wire pulsing hot is good enough to know the computer is turning the injectors on and off. Your engine is what they call "batch fire". If you look at the color of the wires on the injectors, all of them have the red wire which is common hot. 4 of them will all have one color wire opposite the hot red, and the 4 others will all have another color opposite the red. They have the injectors divided electrically into 2 groups of 4. But they all fire at once each revolution of the crankshaft. The 1st go round the injectors inject half the fuel the engine needs to each cylinder. Some cylinders get fuel, some don't since the intake valves are shut on some of the cylinders. So the half shot of fuel just lays on the back on the intake valve. When the crankshaft comes around again, all injectors give a half shot of fuel again. If there was fuel already laying behind the intake, this next half shot is applied and then the intake will open and suck it all in the cylinder. I know it sounds crazy, but that is how it works.

None of the above is fixing your problem though. I am wondering when you crank the engine, is your fuel pressure holding around 38 psi? It needs a lot of fuel to start, just like a carbed engine has to be choked. Just to hear it run, you might be able to shoot some ether or brake cleaner down the throttle body, and see what it does. If your fuel pressure is not up to snuff, it still may start for a little bit.

 

Shot some starting fluid, runs briefly. Checked noid lights on cylinder 5,6,7. They light up.
tank was rust. In tank fuel assembly was rusted. I guess that rust process affected injectors. The truck was sitting a good while.
going to order some injectors. The noid lights that fit injectors were GM PFI and Bosch 2. Not the FORD.

THANKS FOR ALL THE HELP!