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All right, started up the truck the other morning and its idling like it has a wicked vacuum leak. Then the IAC kicks in and it revs up to about 2500 and hangs there for a while and slowly starts coming down. I pop the hood and start checking for vacuum leaks and any loose wires. Pull a plug wire and check spark, good. Start pulling connectors from sensors one by one and nothing changes. I can even hold the throttle open and unplug the IAC and let it idle, like crap at 1000 rpm. Try to drive the truck and at first it seems OK but then starts falling on its face off and on, bad enough to not be able to drive across town to the shop.
Borrow my sisters car and head to the shop and pick up a scan tool,fuel pressure tester, noid lite, and some other crap. Get back to the house and I can't communicate with the PCM. I can talk to the ABS, Airbag, and GEM but not the PCM. Hook up the noid light and the injectors are firing. I have fuel pressure. Logically it must be spark related cause a computer would suck.
Head to the store and pick up plugs, wires, and coils. As I'm pulling off the old plug wires most off them are coming apart and the electrodes on the plugs are skinnier than Kate Moss. Get everything put on and still doing the same thing.
EGR right. If the EGR is stuck open it would be like a big vacuum leak at idle. Pull the gasket off and head to the shop and make a block off plate. On the way home i grab some MAF cleaner and Carb cleaner. Block off plate doesn't work. Cleaning the MAF doesn't work. Spray carb cleaner all over trying to find any vacuum leaks, nothing.
I pull the harness off the PCM and check continuity between it and the DLC. Eerything checks out allright. I notice that the check engine light isn't on either.
Replace the Cam sensor just because I've heard lots of bad stuff going on there and they are cheap. (And once you figure out its not on the head its easy to find, right.) No fix.
Had a friend from another shop (I mostly work on old cars) check it out. His scan tool didn't hook up. (I even tried a third scanner) He ran all the same vacuum, sensor checks I did. He was perplexed. HE talked to a couple ford mechanics he know and they all agreed that PCMs rarely go bad.
But as I sight here typing this, I am starting to think it is.
Its not plugs, wires, coils, CMP, or EGR. Those are all replaced or blocked off.
I can unplug the IAC and rpm instantly drops and either dies or stays at whatever if my thumb is on the throttle.
Its not the MAF, O2s, IAT, or TPS those can all be unplugged and the truck can be driven with the same power/ no power results.
The timing belt hasn't slipped or skipped a tooth. Again, can drive it with power no power and it idles almost smooth at 2500 with just the occasional sputters.
Fuel problem? Probably not. Noid light said the injectors were firing. It idles smooth when you ( or the truck) raises the rpm, and you can drive it with power no power.
Usually when an input/ sensor goes bad the PCM will go into Failure Mode (FMEM). Might drive a slight bit funky and you can't go over 40ish, but it idles fine and drives nonetheless.
And it was perfectly fine when I drove it home the night before.
Get those Brains working!!!!!
Sorry this is a long post. I'm glad I found a Ranger forum!
Borrow my sisters car and head to the shop and pick up a scan tool,fuel pressure tester, noid lite, and some other crap. Get back to the house and I can't communicate with the PCM. I can talk to the ABS, Airbag, and GEM but not the PCM. Hook up the noid light and the injectors are firing. I have fuel pressure. Logically it must be spark related cause a computer would suck.
Head to the store and pick up plugs, wires, and coils. As I'm pulling off the old plug wires most off them are coming apart and the electrodes on the plugs are skinnier than Kate Moss. Get everything put on and still doing the same thing.
EGR right. If the EGR is stuck open it would be like a big vacuum leak at idle. Pull the gasket off and head to the shop and make a block off plate. On the way home i grab some MAF cleaner and Carb cleaner. Block off plate doesn't work. Cleaning the MAF doesn't work. Spray carb cleaner all over trying to find any vacuum leaks, nothing.
I pull the harness off the PCM and check continuity between it and the DLC. Eerything checks out allright. I notice that the check engine light isn't on either.
Replace the Cam sensor just because I've heard lots of bad stuff going on there and they are cheap. (And once you figure out its not on the head its easy to find, right.) No fix.
Had a friend from another shop (I mostly work on old cars) check it out. His scan tool didn't hook up. (I even tried a third scanner) He ran all the same vacuum, sensor checks I did. He was perplexed. HE talked to a couple ford mechanics he know and they all agreed that PCMs rarely go bad.
But as I sight here typing this, I am starting to think it is.
Its not plugs, wires, coils, CMP, or EGR. Those are all replaced or blocked off.
I can unplug the IAC and rpm instantly drops and either dies or stays at whatever if my thumb is on the throttle.
Its not the MAF, O2s, IAT, or TPS those can all be unplugged and the truck can be driven with the same power/ no power results.
The timing belt hasn't slipped or skipped a tooth. Again, can drive it with power no power and it idles almost smooth at 2500 with just the occasional sputters.
Fuel problem? Probably not. Noid light said the injectors were firing. It idles smooth when you ( or the truck) raises the rpm, and you can drive it with power no power.
Usually when an input/ sensor goes bad the PCM will go into Failure Mode (FMEM). Might drive a slight bit funky and you can't go over 40ish, but it idles fine and drives nonetheless.
And it was perfectly fine when I drove it home the night before.
Get those Brains working!!!!!
Sorry this is a long post. I'm glad I found a Ranger forum!
Went back to the store where I got it and they sent it out to another store to get flashed. 
Turned the key on and COMMUNICATION!!!!!!!! Checked to make sure I had all the other sensors plugged in and went to start it. 
It took a few minutes to get the cylinders cleared out but it has ran flawlesley since. I even put 250 miles on it yesterday and I think my gas mileage has even improved. 
