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Discussion Starter #1
I need to know how to test my eec test relay next to the fuel pump relay. My fuel pump decided to not run while trying to start after fueling up at the gas station. I ran a wire from the battery to the fuel pump and it ran so the pumps not bad, and everything else has power. It has to be the fuel pump relay or the eec test relay thing right? :scratchhe

BTW this is on a 4.9
 

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I need to know how to test my eec test relay next to the fuel pump relay. My fuel pump decided to not run while trying to start after fueling up at the gas station. I ran a wire from the battery to the fuel pump and it ran so the pumps not bad, and everything else has power. It has to be the fuel pump relay or the eec test relay thing right? :scratchhe

BTW this is on a 4.9
take another relay out and swap it. also look at the terminals on the relay sometimes if you clean them up a little with a wire brush it will work again. It doesnt always have to look corroded either. On the farm trucks at work it happens all the time a dull film coats the terminals and causes them to not work correctly.
 

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connect a wire to the two biggest sockets on the harness where the relay plus in. Do that to the eec and fuel relay.

since you're pre 90 you have two fuel pumps, one on the frame, one in the tank.
 

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or it could be the wire going from the relay to the pump... but id lean more towards the relay... always carry spares
 

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Discussion Starter #5
Thanks guys. I just had one of my friends come pick me up. I left the bronco at the gas station (we pushed it into a parking spot and its a 24/7 station) We're going to take a crack at it again tomorrow. were going to go back prepared with some tools and such, I might buy the relays just in case I need them and if I don't it wouldn't hurt to carry spares
 

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Thats a great idea! I know what I am adding to my travel tool kit next!!!
 

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Discussion Starter #8
I still haven't been able to get this fixed.... I need to get this thing out of this parking lot! Can anybody hook me up with a wiring diagram for the wiring between the fuel pump on the frame rail and the relays and stuff?? I am assuming it will not work to wire the pump straight to the battery just to get it home? I guess the pump isn't supposed to run all the time? But I really need a wiring diagram and we could probably figure it out. I've been searching for one everywhere and can't find one!
 

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actually i believe they do run all the time, i think it is just during start up that it cycles. The fuels pressure system runs on a return line so it is able to run all the time maintaining flow and pressure not by modulating the pump. If it was mine I'd jump the relay to get it home but make sure you have a way to kill the power to it if ya have to.
 

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Discussion Starter #11
actually i believe they do run all the time, i think it is just during start up that it cycles. The fuels pressure system runs on a return line so it is able to run all the time maintaining flow and pressure not by modulating the pump. If it was mine I'd jump the relay to get it home but make sure you have a way to kill the power to it if ya have to.
I do have a switch that i can hook to a wire and run it from the battery to the fuel pump, but the only reason I haven't tried that is because I didn't know if it mattered how many volts the pump got because I didn't want to risk frying the fuel pump. That is going to be my last resort to at least get it to the town where i'm living, its broke down at a truck stop between my home town and where i'm going to college/living

are both fuel pumps running?
I honestly haven't checked the rear fuel pump, but we have power past the relay under the hood, and the inertia switch seems OK, but yet theres no power to the pump. I also don't know how the rear pump is wired into the system...
 

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I had a similar situation with an 86 i had. It was intermittent over months, came and went at will and sometimes was fine for a long time. eventually it would start though and i never figured out what it was, you could hear the pump was not cycling at start up. The body was beyond saving and i just drove her till the end, funny thing is it was the body that ended it for that truck rusted away so bad it just wasnt safe anymore so i parked it. Sorry i cant be of more help good luck with it.
 

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Discussion Starter #14
I would connect a wire after the relay and to the pump, it would seem there is a break in the wire and this will bypass it and work like factory.
We tried that, but when I touched the wire to the fuel pump all it would do is arc a little and then the relays would click but the pump still wouldn't run. :scratchhe

We may not have been hooked to the right wire on the relay?

My friend found a wiring diagram today so we should be on the right track but if all else fails we will run a wire from the battery straight to the pump with a kill switch on it just to get it home
 

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Discussion Starter #15
So I bought a new fuel pump relay and that didn't change anything. What voltage values are each of the fuel pump relay wires supposed to have? The wire going from the relay to the inertia switch (brown in color) was only reading .009, but all the other ones read just under 12 volts. I did mess with the inertia switch and reset it, but that didn't make any difference either. I am about to give up and bring it to a shop :cry
 

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All you had to do was get 2 small pieces of wire and by pass the eec and fuel relay. You didn't have to go and buy a relay. As long as the power wire has 12v with the key in the on position it should be able to work correctly. Make sure the fuel cut off switch's button is depressed. It's above the brake pedal. If it is, I would say the fuel pump on the frame is bad. Test it and see.
 

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just get a fuel pump and replace it. it's not that expensive. i did 3 weeks of diag on mine just to find out it was the pump that puked. while you're at it, change the fuel filter.
 

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Discussion Starter #18
All you had to do was get 2 small pieces of wire and by pass the eec and fuel relay. You didn't have to go and buy a relay. As long as the power wire has 12v with the key in the on position it should be able to work correctly. Make sure the fuel cut off switch's button is depressed. It's above the brake pedal. If it is, I would say the fuel pump on the frame is bad. Test it and see.
I just bought a new relay so that I new for a fact that it wasn't bad. So does the fuel pump actually run 100% of the time that the truck is running? Or does it click on and off? That is why I didn't bypass the relays cause I figured that it would probably screw something up.

just get a fuel pump and replace it. it's not that expensive. i did 3 weeks of diag on mine just to find out it was the pump that puked. while you're at it, change the fuel filter.
The fuel pump is good, I just replaced the fuel filter and frame rail fuel pump this spring, and I have already ran a hot wire from the battery to the fuel pump and it worked fine. If the fuel pump is not running, then the fuel filter shouldn't have anything to do with it.

I gave up and had my brother come pick it up with a trailer so I can work on it in the garage or the shop where he works. It should be easier to work on with out wind and snow
 

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Bypassing it won't hurt it. If you just replaced the pump it might still be good. Search on fuel pressure regulator. If that checks out (no fuel in vac hose). I would say the fuel system is fine. When you turn the key to on, the fuel pump will buzz for a second then turn off. But runs 100% of the time when the motor is running.

Start looking at ignition if the pump is priming. ignition control module, distributor, corrosion on the eec, or ??? Pull codes too, that will help you in the right direction.
 

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IIRC, I had a mustang do this to me years ago. There was something about the wiring or pcm that prevented the grounding of the fuel pump relay when the TFI module and stator went bad. Check your ignition module or put on a spare.

As a quick check, see if your fuel pump relay clicks on for a few seconds when the key is cycled to on. You should feel it pull in when the ignition switch is turned on.
 
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