I have a 96 Bronco Eddie Bauer with a 5.8 and have a couple of issues. It normally idles a little high, and won't shift into overdrive untill you hit about 55-60 and let completely off the throttle. It's throwing a check engine light and the O/D light flashes intermittantly. I had it checked and the only code it throws is P0664. Anyone got any ideas, cause AutoZone didn't.

 

OBD-II Codes beginning P06XX are internal software errors and critical memory failures within the ECM. The "fix" for something of this nature is a Ford technician or a new computer. Usually codes of this nature are a result of a shorted power supply within the ECM. Wish I had better news. There is always the outside chance that the ECM's memory can be "reflashed" but again, the is proprietary Ford software and would need to be done by them.

 

Figures. Nothing else it could be? What about the tranny? Would it cause that too, or is that a different issue? How hard is it to find a ECM for this particular model, and what if anything interchanges. Thanks for the help. One more thing. I just put straight dual exhaust on this truck, but i couldn't hook up the third o2 sensor, the one between the cat and the muffler. how important is this one, and can i install it in one side or the other of the exhaust without any side effects, or will i have to install some sort of crossover?

 

Ok, I have limited information on the OBD-II system but here's what I DO know.

P01xx are fuel and metering codes
P02xx are the same system
P03xx are ignition and misfire codes
P04xx are auxiliary emission codes (your third O2 sensor should fall into this set of codes).
P05xx are speed, idle control and other miscellaneous input codes
P06xx are internal memory and module control software function codes

It is possible that the transmission codes fall under this set of codes as well. EEC-IV electronic trans. codes are stuck out on the high end of the numbering system and Ford may have opted to do the same thing with them when they made the move to OBD-II. Again, my knowledge of OBD-II is sketchy compared to EEC-IV so you might want to dig a little deeper before you assume the ECM has failed.

If you are not getting a code for the third O2 sensor there may not be a problem with it missing HOWEVER if code P0664 DOES have something to do with memory and software within the ECM it may not be storing or "remembering" any other codes right now.

Like I said, I wish I had a better scope of knowledge for OBD-II to better assist.

 

O.K., I have to make a correction. I listed the wrong code. The original CEL was a P0443. That is what is causing my high idle. Since the exhaust work, I now have a 0102,0136,1401. All related to the "third O2" being disconnected. You mentioned the 04xx codes relate to that, and I looked at the sensor, it's kind of nasty looking and blackened on one side. Other posting I've read say that code is related to a purge valve not working or working improperly. "Evaporative Emission Control System Purge Control Valve Circuit"or"EVAP Canister Purge Control Solenoid or Valve Faulty" Thanks for any help you can provide.

 

Yes, in fact 0443 is indicative of a faulty purge valve circuit. You can check the purge solenoid for resistance... this will tell you if it has failed or not. Resistance should be between 40 and 90 ohms across the terminals of the purge solenoid. If you disconnect the solenoid you can also make certain you have battery voltage (12 VDC approx.) at one of the two wires in the harness with the key on. Check for voltage between one wire at a time to a good ground or the negative battery post. As long as one wire has battery voltage with the key on, the problem is not likely to be in the wiring but rather a failed solenoid. I'm not 100% certain of the location of this solenoid on the '96 models but on earlier models the vacuum line that it connects to comes directly out of the throttle body. You should be able to trace the vacuum line back and find the solenoid.

 

OK. Now here's a new twist. I found the purge valve, and just on a whim, disconnected the electrical harness. That fixed my fast idle, it ran like a top. I also noticed that it stopped my O/D light from flashing as well, so it does have something to do with the tranny. It still doesn't want to shift into O/D until I let off the throttle though, so maybe if I replace it that will correct my issues. The bad part is, the purge valve on this truck is the expensive one that noone carries that you have to order. Any idea why it affects the tranny?

 

So the solenoid is stuck OPEN. The open solenoid is causing your "vacuum leak" which is causing the high idle. Now as to the reason why this would miraculously "cure" the tranny issue, that's a puzzlement. There is no real correlation between the two. Engine RPM's are the closest relationship and the PCM will compensate for higher RPM's for shift parameters.

In thinking about it, the open solenoid may be shorted and causing a "draw down" in the voltage back through the VREF power supply. Low VREF signal caused by ANYTHING can adversely affect any number of sensors and systems. The MLPS uses various resistance values to "tell" the PCM which gear is selected. If the VREF voltage is being drawn down due to a fried solenoid, then all of the values coming back to the PCM through the MLPS will be proportionately affected. This will "confuse" the PCM into thinking there is a problem somewhere else because the voltage is off but not off by enough to throw a code. Try replacing the solenoid. It could be the root of the problem.