My 92 Bronco finally has a "problem" 351W, E4OD,4.10's... The motor is completely untouched 171K miles. It now has one of those mysterious electrical gremlins. A week ago it died on the wife in the middle of a left turn. She called the tow truck and me, when I was on the phone with her, it started back up and drove home. I put the code scanner on it and KOEO I got code 111, and 512,514. When I tried a KOER test it started by raising the idle and then locked at about 1500 rpm's and gave me a constant beep, no matter what I did, I could not get it out of this mode. Had to shut down and restart, then the code scanner would do nothing but beep. I drove it on Sunday without incident, back and forth to church 2x and around on errands, no problems. Monday, it got me to the corner before it died, I turned off the key, waited a minute, started it again and off I went to work and back without a prob...Tuesday, same as Monday. Wednesday, started, then about a mile down the road, seemed like it was running on 7 cylinders, even popped a few times through the intake. I read a number of posts and decided to replace the TFI, this did absolutely nothing, and I am still unable to get codes from it any more, as soon as I hook up the code reader, it turns on the CEL and locks into a constant beep, KOEO & KOER. I am stumped, I have a complete 5.0 Mustang Injection system in the garage that I can borrow some components from, but I would like to do it in an organized way, please give me any input that you may have seen on this type of problem. I have searched the forums for the 512 code and cannot come up with any better explanation than ECU keep alive voltage missing. Do I need to troubleshoot the 12v side or the 5v computer side.

Al...

 

First thing I would do is check the basics, make sure none of the ground screws for any of the electronics are rusted out, brackets broken, broken wires, etc.

Not an expert with this particular EFI system, but that description makes me think that the ECU isn't properly grounded, or has a short somewhere in the wiring. You may want to disconnect the main ECU connecter, and with a test light check for continuity in all the wires. Odds are a piece of insulation rubbed off somewhere and a hot wire shorted to ground. That would usually end up frying the ECU, also, causing those sorts of symptoms. Good luck with the bronco.

 

The keep alive power is a constant 12V that the computer uses to keep its memory. It could also be due to a bad ground as well. It sounds like it could be happening when some lateral g-forces are put on the wires or the computer, so it very well could be a short. It may have even killed the computer now, since you can't get the codes anymore. I'd start by trying to trace down a short in the power wires for the EEC.

 

Just to make things even more complicated I tried tinkering with it last night. When I turn the key on normally I can here the fuel pump for about 2 seconds, then a click and the sound goes away. Now I can here the fuel pump run as long as the key is on. I will be checking the grounds and voltages this weekend. has anyone seen a specific sensor that would short like this.

 

It's most likely a power or ground issue, not an issue with a particular sensor. The fuel pumps should shut off after 2 seconds, there is some reason they are not turning off. Try sending a PM to fefarms and see what he thinks about the situation. He is very knowledgable about Ford engine computers and could probably help you more than I can.

 

Heres and update... I checked as many grounds as i could find, all good. Started the screwdriver tap method of troubleshooting. I went into the main fuse/relay panel under the hood. there are 4 relay in a row, not sure there names, when I tapped on the one closest to the fender the fuel pump cycled like normal and the truck started. I replaced all four relays, $10.59 each @ FORD. Now the bronco starts and runs and drives. I can now get the codes during KOER test. Now I am stuck t/s the code 332, egr flow insufficient, I replaced the egr position sensor out of haste, $32 down the drain, going to get a vacuum pump this afternoon and test the egr valve.

Al...

 

I believe that you had a bad EEC relay.

 

Ahhh, the dreaded EGR codes....I have experience with those....

33 means either the EGR diaphgram is broken or the EVR doesnt supply vacuum. Since you replaced the EVP, you can rule out a bad EVP.

If you try to apply vacuum on the EGR valve and the air just blows through, it's bad. I know mine is....I'm still trying to get it off the pipe, it's really stuck on there!

 

Ya, I agree about the dreaded EGR codes. The Position Sensor fixed my mustang, thought I might get lucky twice... Could it be possible the exhaust/cat has gone south? Not that I want to do the exhaust now, but it sticks out in my mind. Does anyone know what thingie on the engine controls the egr valve and how can I find it and check it. I have not seen a vacuum diagram worth 2 cents anywhere for the Bronco. All I can see is the EGR vacuum line going into a large harness and I don't really want to break into it if I can pinpoint the other side first...

 

The EVR (EGR Vacuum Regulator) controls the opening of the EGR valve. On my 302. its to the back, right side of engine, near the Fuel Regulator. Its where the TAB/TAD solenoids are. You should see a small gray 'cap' on it. Looks Like this:

To test it, leave engine idling. On the EVR, you'll see a wire harness that plugs into it. It has Two wires. One is +12V and one is 'Pin 33'. Pin 33 is the left wire. Backprobe that wire and ground it. At this time, the engine will stumble or possibly stall.

If it doesn't, the EGR valve is leaky, really dirty or the EVR doesn't supply vacuum.

To isolate the culprit, try this:
On the EGR valve, there is a vacuum line that goes to it. Unplug it. At idle, there should be little or no vacuum on it. Ground Pin 33 again and put your thumb over the vacuum line. You should feel it sucking your thumb.

The sucking indicates the EVR is good, but the EGR valve is bad. If there is no sucking, the EVR is bad.

Edit:
Forgot to mention....Make sure that the Vacuum Line from the EGR valve to the EVR is not broken or leaking.