My '98 (5.0 V8) keeps complaining about 'intermittent IAT'. Quite easy to see on a scanner that the temperature reading jumps to something around 340 once in a while. This is consistent with a shorted sensor, except that there is nothing wrong with the sensor, or even with the wire harness --.the IAT pin on the PCM just takes a nose dive to ground whenever it feels like. This is intermittent, so on-demand diagnostics is not finding anything, of course. Not the usual suspect, but I am quite confident that the problem is internal to the PCM. Will hate to throw an otherwise good box away, but without the benefit of a schematic there isn't much I can do in there. So here is my question: when ordering a new one, do I have to provide the calibration code, or does one buy a generic one and then program it?
You need a PCM specifically for your 5.0. The PCM has everything programmed into it at the factory. Everything is stored in a rom type chip that retains its programming, much like the bios on your PC, even without power. After you put it in, you can go to ford and have them flash the latest version of the 5.0 software into it if you like.
Have you thought about getting one from a wrecking yard? Much cheaper. There are quite a few late 90's Explorers out there that died in accidents with good PCM's.
You might need to get a PCM from a 98. I am not sure if a 99 or 00 PCM can be used in a 98. Given how far you have gotten on the diagnostics, I am sure you can figure that out. I would think they would be interchangable unless pinouts got changed. Maybe someone here knows more....
Thanks, Ross. Great advice. Just a follow-up question that came to mind: If it comes pre-programmed for the engine, how about the axle ratio (mine is
3.73)? Does this thing want to know how fast I am moving, or just how fast the transmission output shaft is turning... And what about 4WD vs RWD? (mine is AWD, actually). And while we are at it, how about tire size? That's going too far, for sure. Sounds like I need a crash course in engine management that goes a bit beyond the Probst book that I read 10 years ago...
And by the way, I happen to know something about non-volatile memories - Got an EE degree and quite a few years of experience in that field ... Wouldn't mind putting my hands on a PCM schematic. Any clue where to find it?
You are going to exceed my knowledge level of PCM's pretty quickly. Others here will probably know more......
I believe the PCM relies on the speed sensor on the transmission, there is no compensation for tire size. If you do a radical tire size change my understanding is you have to use a different vehicle speed sensor, or buy an aftermarket electronic device that corrects the output. So, changing axle ratios would result in the same answer.
There is software available that will let you monitor your PCM in real time and select the various sensors you wish to monitor, such as oxygen sensor voltages, etc. The pricier the better the software (in general), and manufacturer specific, unless you cough up the big bucks like a repair shop.
There are also some programming tools available for changing variables in the PCM tables. Don't know anything about them, but I've seen some messages from people with turbos / superchargers that revise EGR output levels to control ping, etc. Kind of like programming your own speed chip. Expensive I suppose.
On the late 90's vehicles there are transfer case sensors as well as vehicle deceleration sensors for ABS, and many others, but in general none of those feeds back into the PCM to modify vehicle behavior, they are there for the functioning of the particular system they are part of. The auto transmission is the only one that is really integrated I think.
However, the new 2006 Explorers now have an antirollover system. You can see that the sensor inputs are now being incorporated into vehicle behavior in a more integrated way - if you are cornering too quickly the rollover system starts applying brakes using programmed logic, reducing engine throttle, etc. Won't be long and you will drive by a roadside sensor that will poll your car for its speed, issue an electronic speeding ticket, and bill your mastercard.
I have not seen a reference to a circuit diagram anywhere. Proprietary stuff I suppose. There must be something available however. Would not think you could create the software / programming tools without it.
I noticed you had gotten pretty far in your electical diagnostics and thought that was a little unusual........
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.