91 Bronco VERY strange problem
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
Well, it's back to the original problem. I pulled fuse and breakers one at a time and none of them made the lights go out or the pump to stop running. Under the hood I pulled the relay marked for Tow Package and the lights went out but the pump still ran. Under the back I found where someone before I owned it had done some rigging for the trailer plug. I cleaned up all that mess and taped it up and now the lights work fine and don't stay on when they are not supposed to. I guess this second electrical problem just happened to show up at the same time as the first problem. But, the original problem is still there. I did pull one spark plug and it's dry but it's also very black and sooty as if the last 2 miles I drove it home were very rich. Like I said before, it's a daily driver and it ran great before this stange fuel pump running and non starting problem. The EEC relay and fuel pump relay triggers the fuel pump to shut off after a few seconds, correct?
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
The EEC gets power via the relay whenever the key is on. The fuel pumps get power via the relay whenever the ECM tells it to close.
My gut tells me that you are looking at two different problems, and that's why a lot of the symptoms don't fit in with your observations and you keep saying to yourself "this doesn't make any sense."
In my mind there are two things you need to do. One, put a fuel pressure gauge on this thing and find out what your fuel pressure really is. Sticking your finger in the shrader valve is not a valid test.
Two, pull the codes with a paper clip, running fuel pump or not.
Here are some different (and easier to follow) instructions:
http://broncodata.com/tech/codes.htm
My gut tells me that you are looking at two different problems, and that's why a lot of the symptoms don't fit in with your observations and you keep saying to yourself "this doesn't make any sense."
In my mind there are two things you need to do. One, put a fuel pressure gauge on this thing and find out what your fuel pressure really is. Sticking your finger in the shrader valve is not a valid test.
Two, pull the codes with a paper clip, running fuel pump or not.
Here are some different (and easier to follow) instructions:
http://broncodata.com/tech/codes.htm
Thread Starter
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
Andym, I tried the test you suggested. Since it doesn't start I could only do the first test. When I hook up my test light it comes on right away with the key off, but it's weak. When I turn the key on it comes on bright and stays there. It never blinks at any time key on or key off, just a solid light. As for checking the fuel at the fuel rail I was only verifying that I had fuel, I knew it wasn't a valid test for pressure. But even if the pressure wasn't good it still doesn't explain why the pump runs constantly. If the truck were out of fuel it should still shut off after a few seconds.
Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
pull the wiring plug that connects to the pump. make sure its clean and perhaps add some dielectric grease.
if the plugs are dry then the injectors are not openning up. locate the fuel injector relay if there is one and test/replace if necessary. you might also post this issue over at FSB, i think ive read this issue on some others rigs just cant recall the fix or symptoms completely
if the plugs are dry then the injectors are not openning up. locate the fuel injector relay if there is one and test/replace if necessary. you might also post this issue over at FSB, i think ive read this issue on some others rigs just cant recall the fix or symptoms completely
Thread Starter
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
SOLVED!!! Since I've tried just about everything else and nothing worked I went back to my original theory that the computer took a dump. It was just too weird with so many problems arising all at once. I know it's not the correct one for the 91 Bronco but I got a chance to try a used junkyard computer marked for 1995. What did I have to lose, it didn't run now. I put in the computer, hooked up the battery, and turned on the key. The fuel pump didn't run at all as I had it unhooked at the crash switch. I tried the electronic overdrive button and it now had the light turn on and off and this didn't work with the old computer. I turned off the key and hooked up the fuel pump wire. I turned on the key and the pump ran a few seconds and shut off. I turned the key and the engine started right up. I drove around about 4 miles and it runs and shifts great.
Posting Guru
Joined: Dec 2003
Posts: 1,205
Likes: 0
From: Ontario
Not often the computer goes.
I am happy to see you found the problem and fixed it, as for the door problem I'm sure it's not that big of a deal now that the no start no run problem is solved LOL.
I would suggest it would be a great night to take the family out to dinner in the nice running Bronco
Food, Family, Friends and a nice drive in my Bronco always puts a smile on my face.
Cheers, Rick.
I would suggest it would be a great night to take the family out to dinner in the nice running Bronco
Food, Family, Friends and a nice drive in my Bronco always puts a smile on my face.
Cheers, Rick.
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Thread Starter
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
Well, I had to drive it to work instead although I'd have rather gone to dinner. In all the years of working on things I've never had to replace a computer in a Ford. I have replaced them while seaching for other problems that wasn't caused by the computer but the computer has never been bad, until now.
Posting Guru
Joined: Apr 2005
Posts: 2,018
Likes: 0
From: Longview, TX
You deserve a nicely framed certificate and photo for the hallway for finding the problem. Call yourself The Supertech Award or something similar. Put it next to the Indy or Nascar driving photo.
Thread Starter
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
B4hntn, I'm just happy I found it and I didn't have to pay someone else to do it. Being the mechanic, carpenter, electrician, plumber, and everything else there wasn't any chance of that anyway. I've still got to figure out that weird door lock problem. Isn't there some sort of relay or relays somewhere for the door lock system?
Posting Guru
Joined: Apr 2005
Posts: 2,018
Likes: 0
From: Longview, TX
Looking at Haynes wiring diagram for a 91, I see no relays, just the two switches. See page 12-49 lower left corner. The first item of interest I see is two black wires going into the left switch first then the harness goes to the right one. If they are grounds or positive. They should be the same. I think I would check each of them first. One is used to lock the other to unlock.
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
B4hntn, the weird thing about the door locks is that the electric door locks only work going down and only work with the passenger side switch but it puts both sides down. I've tested or changed the switches and the lock actuators and everything is ok. If I put 12V to the drivers side actuator both sides will go up and when I swap the hot and ground they both sides go down. If I put 12V to the passengers side actuator both sides will go up and down. So it looks like since I can put 12V it either side and it makes both sides work the wires in between both doors have got to be complete.
Posting Guru
Joined: Apr 2005
Posts: 2,018
Likes: 0
From: Longview, TX
I have looked at the diagram awhile and the light bulb has not come on yet, meaning I don't understand the circuit so you may want to start a new thread on this if someone does not come along with suggestions. Do you have Haynes?
New User
Joined: Jan 2008
Posts: 1
Likes: 0
My 95 bronco has a similar problem. Mine is intermittent thoough. If the fuel pump shuts off after a few seonds the engine wil start. If it runs continously the engine will only start sometimes but will run really bad. I have changed the fuel pump relay, and regulator. The fuel pressure is 41 psi. I really don't want to fork out the bucks for a new computer if I am not sure that is the problem.
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