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Discussion Starter · #1 ·
Hi everyone.

I have an 89 EB 5.0 / AOD Bronco. The truck has 89k on it and is fantastic shape and well maintained. I have been having one heck of a time with my truck just shutting off the fuel pumps when it is really hot out.

I live in Vegas... Yesterday it was 106. I can drive the truck all day long, but when it is time to come home ( 3 days in a row) I have to drive on the highway for about 30 mins at around 65mph. The truck will start to slow down and I can hear the fuel pumps turning off. Until finally the rpms get low enough they just turn off. The truck will start after about 20 mins. However the fuel pumps make odd clicking or really quick intermittent power noises and then it smooths out again.

Now I am a very competent on fords and have already had the fuel pumps replaced just because they were original and almost 20 years old. I have checked the FPR / EEC Relays before, and replaced them and keep the old ones as spares just in case. I have verified that the truck makes correct FP at the rail with a guage. I have replaced the Ignition module with a OEM ford one. (nothing to do with my no power at fuel pumps though)

So yesterday the truck did it again, this time it took me 20mins to get the truck to come back to life again, while I was poking around in the truck trying to get it to start I checked the relays and they were hot and were pushing voltage correctly EXCEPT that on both the EEC / FPR the RED wire that is hot when the key is turned on is only 2.70 volts! All other connections are 12.34volts.

I also attempted to ground the eec-iv tester connector to ground to attempt to have the computer turn on the fuel pumps... no go.

I know the pumps are brand new, the wires are in perfect condition as is the rear tank plug.

My question is about the the red wire that feeds into both EEC / FPR relays being so low. Has anyone had this symptom before? If so what or where does this RED wire come from, what components are down line the wire that might cause the voltage to be so low?

This is driving me bonkers, I am hunting for my schematic for the wiring but just want to know if someone else had this happen?
 

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shibby
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The red is 12v supplied from the EEC power relay, not to it. You'll probably have to check the yellow feed wire supplying the EEC relay from the battery, 18ga brown fusible link. There are fusible links at the battery location and also at the relay location.
 

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Discussion Starter · #3 ·
Thanks for the tip. Now I am a bit confused, as when I tested the voltages for both relays (these are the 2 that are next to the drivers hood hinge) I removed both relays from the plugs and tested the power on the plugs then tested the relays. Without any relays plugged into the FPR/ EEC relay connectors I observed 2.70v on that red wire on both plugs with the key in the run position.
 

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Discussion Starter · #5 ·
thanks for the diagrams. Ok, so more testing... I plugged the relays back into the truck. Tested the RED wires again after turning the key to run.. fuel pump primes for 2 sec, go to test... Full 12+ volts on both plugs.

So I guess the voltage is correct as I see per the diagrams that the RED wire is actually Voltage from the PCM V PWR on pin 37 which feeds virtually everything under the hood lol. I do remember that with the relays on before when my truck died the red was at 12+ as were all the others except the ground of course... but was no fuel pumps.

I traced the yellows from the relays - to the ignition switch, tested the switch and traced all the way back to battery and fuse links.. no problems to report. Everything is great.

Now I have been thinking... what if the fuel pumps are stopping due to heat? This kinda makes sense as it only happens when hot hot hot out and the relays test out with 12+
I know the inertia switch is good as well as I have tested it and also ran a manual jumper on the connector when this died yesterday.. no change.

I guess I will have to wait till it happens again and test the fuel pump connector itself for 12+

I figure if the pumps have 12+ when this is going on and the ground is active, well then it's pretty obvious the pumps are dieing due to heat.
 

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Discussion Starter · #7 ·
So I got thinking..... what if... What if my in-tank pump has died and the only pump to be working is the external pump? Since technicaly the rear pump is low pressure, it's only purpose is to supply the external pump with a continuous supply of fuel, then the external pump pushes it out at high pressure as required for the efi.

If the in-tank pump is bad, then the external is doing double duty, which would explain why the pump just fails to work for about 20mins when ever the truck dies during a hot day. It also may be the reason I think the pump was making weird noises and is louder than I think it should be, but then again it has kinda been that way since they were replaced.

So, I disconnected the 12volt lead to the external pump and cycled the key to the run position... There is no noise from the rear pump, cycle a few more times and attempt to start truck... bleeds of pressurized fuel and dies.

Pull of inlet fuel connector from external pump and aim it into a bottle.. cycle the truck again... NOTHING.... how freaking lame!!! Only a few months old and as far as I know it may have never been working! What sucks worse is the fact the truck has 1/2 a tank in it! Arrrgggggggg

anyone ever encounter this on there bronco?

I am thinking of getting an OEM pump + Sender kit from Bronco Graveyard... its like 180 for it complete with all the fittings oem pump / new harness and plug kit
 

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Discussion Starter · #9 ·
Ok, So I just got done pulling my tank out and the pump and fuel gauge sender. The pump is toast so I will be getting another pump and installing it. But what freaked me out when I got the unit out of the tank is the return fuel line that comes down into the tank has an orange cap and crimp on it! WTF? I can tell this is the OEM unit as it has the ford part # on the top where the fuel quick connectors are, and the cap looks to be original!

I have been scouring the net for pictures of various units and most have no cap on that line, yet some do.. What should this truck have? It has a return fuel line, it was connected to the fuel line.. but apparently it had nowhere to dump it..

I am really confused now.

Here is what my unit looks close to



Notice that where the return line comes down just before the sending unit.. No cap... MINE has a Orange cap and is crimped on from the factory.



That one shows an orange cap on the return line... although unit looks nothing like



Airtex complete unit.. notice the orange cap
If the picture is to small... look at them in my gallery
 

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Discussion Starter · #11 ·
Thats not a cap, if you squeeze it sideways (the long way) it opens up, like a rubber valve.
Like the little orange valve in a vacum tester pump gun.
:)

OK, your correct lol! I was like WTF is that... having an older bronco that did not have that on there I was like thinking it was capped but then the fuel system would have been very upset if it were I suppose.

Thanks for the quick info!

I am off to get my pump.. WOO HOOO!

Oh yeah.. if anyone ever wants to take out the bronco fuel tank, get your self an air gun! It took me about 20mins to drop it.. ( after I emptied it)
Without an air gun, prepare for a workout as the bolts and nuts are usually rusted pretty good. Just remember to use anti seize liberally on the bolts when you go to reinstall them to keep it from happening again
 
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