Well, I posted this in the Bronco forum, but I figured I might get a good answer here, so here I go, please help!!!!

88 302 Bronco, aod, pushbutton transfercase. GT40P heads, Comp cam, headers, (though those shouldn't be a factor).

Here's what I'm having problems with, periodically, the Bronco will jump to what I am assuming is a 'safe mode.' I am thinking something is getting power to ground. The oil pressure gauge and temp gauge peg hard right, the RPM's peg below 0. The windows switch stop working, the check engine, and red 'engine' lights comes on. It has happened several times, I try and trace it down, and after a while, it goes away. Last night, I made it go away by starting the truck with the test wire hooked up, which, if I remember correctly, resets the computer.

When this has happened, the truck has cranked the starter on it's own, even without an ignition wire on the starter solenoid, I have to disconnect the battery to make it stop. Also, when this happens, the alternator case has power going to it, which of course arcs with the mounts when I reistall it.

What I have replaced: computer (it was used, no huge investment), connectors on the alternator, both battery cables and starter cable, ignition switch, starter solenoid.

I have also had the battery, alternator, and starter all checked, though I'm taking the alternator back as it's only producing 11.85 volts right now.

My theory: Some electrical component, which has both ground and power running to it, is eventually overheating, and failing, crossing the power and ground, and sending power through the ground in the whole system. Somehow, giving it some time, or reseting the computer seems to help it, but it comes back later (normally a very inconvient time). I believe this because it seems like, when this happens, and I get it running again, sometimes, the oil pressure gauge will float right at the 'H' line, and as soon as there is an electrical demand (rolling up windows, pressing brake i.e. brake lights) the gauges peg and the truck dies.

I've tried pulling codes, but there is nothing.

Some things that might help: currently, my oil pressure and water temp gauges peg to the right when I shut off the truck, I can't remember if it did that before all the problems. Also, I found an aftermarket keyless entry system called "My Valet" model 710T, it seems wired up correctly, though there is a small switch coming off of it with two grey wires and according to a website I found with one, it is equipped with a "starter killer active/passive", though I don't believe this has anything to do with my problems as I compeletely disconnected the unit and it didn't change anything. Also, I disconnected two ground wires that were bolted under the dash, one goes to the keyless entry, the other is a black wire that attaches to the headlight switch case, and the lights still work with it disconnected?

Anyways, that's all I can think of to put in here, I hope someone can help me, I'm no wiz with a volt-o-meter and really need some direction here!

Any and all help is appreciated!



EDIT: Another thought that came to me, before all this happened, replaced my cap and rotor and wires, and have since been shocked everytime I played with my timing. I replaced the lower cap portion and that didn't help, I think I'm going to look there, but I thought that might be significant.

 

Your truck cranks the engine without the trigger wire hooked up to the starter solinoid???? Wow, sounds like you need to call ghost busters....

Can you unhook all your non-stock electrical items, such as stereo systems, keyless entry, whatever, and see if it goes away? What I am getting at here, is try to unhook everything that is not REQUIRED for the truck to run. Then, if it goes away, start hooking them back up, one at a time, a week or so at a time, to eliminate the problem.

I would also check under the truck along the frame, looking for any wires that may have been eaten by chemicals such as fuel and oil, maybe causing a short when the conditions get just so.

I really don't see any way for the truck to crank itself if the small wire from the ignition switch is not hooked up to the relay, it just seems electrically impossible, especially since you said you changed the solonoid. I'm not saying you are wrong and its not doing it, i'm just stumped on what would cause that. That relay just passes the wire straight from the battery to the positive post on the starter, activated by the ignition switch. Crazy.

Also, check all your ground connections, any you can see I would remove, clean and reasseble with contact grease to prevent future corrosion.

Okay, I'm done for now. I'll think some more about it and let you know if I come up with anything.

That's strange.

 

It sounds like you have a grounding problem along with possibly a few others. You said you replaced both battery cables, so we can assume you bolted the - battery cable to the proper stock location down low on the engine block.

The first thing to make sure of, is any small grounds that may have been left out. A lot of fuel injected Fords had small ground wires that are hooked into the large - wire at the battery. Some of these small ground wires are very important computer grounds. And sometimes these ground wires have small disconnect plugs in their length that can corrode and cause a intermittent ground connection.

There are also small ground straps here an there that go from the engine block to the sheetmetal on the firewall and the radiator support, etc. With all the engine work that was done, I can see some of these not getting hooked back up.

The sparking with the alt brackets, and the seemingly total failure of some of the interior electrical leads me to believe you have a serious lack of grounding. The engine is mounted in rubber mounts, so some sort of provision needs to be made to get the large ground of the block over to some of the sheetmetal.

You are on track too about the system trying to find grounds through components. This is exactly what happens, and is why crazy things can happen when components do not have a good ground return path.

 

Also when you replaced the starter solenoid did you put the battery cable and the starter cable on the same stud? If so the starter cable goes on the other big stud. The rest as Franklin2 says is more than likely ground problems.

 

Thanks everyone for their replys, I appreciate everyone trying to pinpoint this one, I'm going to shed some, but not all, the light on the situation, and some of ya'll were close.

Okay, I chased stuff around, and around, following cable after cable, and when I was checking a free ground wire I found (bolted to the firewall, engine side, right above the ignition coil, has no home if anyone has any ideas, it's a thick one and the end looks like it goes into a connector of sorts) I noticed that I was getting some funny readings from that wire to the block. As it turns out, the body had 1.7 volts running through it, the block had none. So, I hooked up an extra battery cable I had and ran it from the ground post to the body and now there is only .07 volts running and my gauges stopped pegging out. It started making sense why, when I turned the key off, the gauges would peg, as they were still getting current through the body. I am guessing (no expert here) that somehow, with enough voltage running through the body, it would go through the ground in the starter solenoid and kick it over, it's the only thing I can figure.

Anyways, the truck is acting like it's suppose to, though this doesn't tell me where my body is getting the power from. I messed with the wires under the dash A LOT, sometimes it generated a resoponse in the gauges, sometimes not. I ran aftermarket gauges through the firewall, but I used grommets. I'll keep checking, but atleast for now, that extra ground has helped out a great deal!

Thanks everyone!

 

Sounds like you need to run more grounds as the body should be zero volts to ground. The power in the body comes from just about everything and that is normal for it to do that. But you still have to get the body to 0 Volts.

I do not believe the ground bit with the Solenoid. One end of the coil in the Solenoid is ground and the other end goes to that small stud on the Solenoid, so with the wire off unless the Solenoid was welded closed it can not crank the Engine.

 

I don't know about the solenoid(starter relay) thing either, but whatever was going on, hopefully it's fixed now. I wasn't sure the bad ground was causing everything, but hopefully it was.

As far as the .07 volt reading you have now, it's probably good enough, though if you scraped the metal clean where you bolted the wire, it may improve(go lower).

I would imagine you have found the correct factory ground wire("I was checking a free ground wire I found bolted to the firewall, engine side, right above the ignition coil, has no home "), and that the other end may have gotten lost during the engine work. You can install another solid piece of wire to duplicate this wire, and bolt it somewhere on the engine block, or you could go to the junkyard and possibly find the other missing end on an engine and buy that piece so it will plug in like the factory had it.

This is where the 1.7 volts on the body was coming from; You have certain things in the truck that have power all the time, like radio and computer memories. You may have gotten an even higher reading if you had the door open with the domelight on. So the battery + current is running to these devices that are on all the time. The current runs through the device, and the other side of the device is grounded to the body. The current's main goal is to get back to the battery - to complete the circuit. But it can't get there because the body is not grounded. So it looks for the next best way to get to the battery -, and it may find it is best to go backwards through a certain component, and eventually find some sort of path back to the - battery terminal. So the 1.7v you where reading was actually in the middle of the wierd path that the current was struggling to take to get to the battery -.

 

Thanks everyone, I'm learning alot, electrical was never my fortay. If I learn of anything else, I'll let you know, but otherwise, hopefully this is it!