i need to know where it is and what it looks like on a 1991 silver anniversary edition bronco with 5.8L engine and auto trans. a part number would be really helpful too.

 

You mean the computer itself? Should be under the dash, drivers side of cab with LOTS of wires going to it.

 

ok i have a white plastic module with lots of wires and one plug, a black plastic module slightly larger with lots of wires and 2 plugs, and a brass colored metal box largest of all but when i opened it it just said anti-lock braking system. and it only has one plug. there is another box behind the trim piece that is under the glove box and it has a little white button on it that when you press it, it illumintates a red LED it has a lot of wires going to it too and 2 more plugs. i need to know exactly what it looks like. "a bunch of wires going to it", doesn't help me at all

 

EEC-IV is the entire engine control system and its sensors and control devices. The main computer in the system is the PCM (powertrain control module). It is located behind the passenger side kick panel below the dashboard in front of the door. The EEC-IV system includes ALL of the sensors and solenoids that control engine functions in a vehicle equipped with that system so the answer to your first question is... all over the place. The part numbers are numerous but the PCM is specific to the engine, transmission, and model year of the truck.

The white module is the 4WD shift module. The black module should be the PCM.

 

ok the one under the passenger side kick panel has a white button on the side of it that has a red LED right below the button that lights up when you press the button. if i am understaning you correctly this is where error codes are stored when there is a malfunction in the computer system. it also has a heatsink on it. i thought this could be what i was looking for now my question is can it be tested to see if it is still good? can i do it myself and what do i need to test it if possible? if i am getting error codes on it what are the chances that it is actually bad?

 

Just curious, what makes you think the PCM is bad? Your bronco, like mine, should have the TFI-IV ignition system. If you are looking for the ignition control module (ICM), it is a grey plastic piece with a fairly large (6 wires or so) plug that is attached to the side of your distributor.

 

well the codes don't clear out of the pcm when i unhook the battery for as long as a month. the codes i get are 51, and 54 which are ect and act which i have replaced. i don't know for sure if the pcm is bad or not but i was just wondering if there is some way to check it out to see if it is possible to eliminate this item as part of the problem. this bronco starts fine and idles up as it cycles and as soon as it idles down it shudders like it wants to die and the tach drops to nothing. it may barely stay running while it does this once or twice but it always dies after one or 2 shudders. i have replaced the entire ignition system and the entire fuel system. i haven't changed the map sensor but it is the only sensor involved that i have not changed out. i don't know where else to look besides the PCM. if there is something i have overlooked that would cause these symptoms by all means let me know. i have 1000 bucks in parts in it right now and i am tired of chasing my tail.

 

Have you check the connectors to these two sensors? If the wiring harness is shorted between the sensor and the PCM, then the PCM is still getting an erroneous signal from one or both of these sensors.

Somthing else you may check is the IAC. I know it isn't showing up in your codes but the symptoms you are describing are exactly what is SUPPOSED to happen when the IAC is disconnected or it fails.

 

i haven't replace it but i did pull it off and thoroughly clean it. i also disconnected it and i didn't get any different reaction from my engine. do you think this could be the culprit? i am willing to try anything at this point.

 

I think greystreak got it, really sounds like IAC. If you can test it, my manual says you should have about 10.5 volts supply from the PCM in the plug for the IAC, and the resistance in the valve should be 7-13 ohms.

 

IF you see no change when the IAC is disconnected, then you definately have an IAC problem. The throttle plates alone won't let enough air through to hold a decent idle. The IAC needs to let air through to maintain idle, hence the name Idle Air Control valve/solenoid.

 

I just replaced my IAC and it made a big difference in idle and overall driveability in my truck. I thought that it was fine before, but it's even better now (I changed it because it dropped idle when the compressor kicked in).

I did it the old fashioned way, I read and asked a couple of questions. I didn't touch the computer or even get codes. For me, it's easier to ask a few q's and buy one part at a time, maybe my intuition is good from working on cars for so many years but it usually works.

I gave up on codes when my check engine light was becoming annoying at one time, and it always said 02 sensor no matter what and I changed it three times and the truck was running perfectly. It now has a factory Ford 02 sensor instead of aftermarket, which seemed to shut it up for the most part.

My check engine light comes on once every few months, I just turn the truck off and restart it and it's gone. If it runs fine, and passes emissions with no problems (actually it is very clean) then what's the problem anyway?

 

this is an ongoing thing. i tried it the methodical way too. just picked one part at a time and started changing stuff out. when i bought this truck it had been stolen at one point and was pretty abused. i rebuilt the motor because of a knock that turned out to be a flat cam lobe. the oil pressure was nonexistant and one of the cylinders had 2 broken rings. i put about 1000 bucks in the motor and now that that is good to go i really need to get it broke in. and of course it won't run. i am just your average shadetree and i like to work on my own stuff. i have never had a problem like this before where i just couldn't throw some parts at it and get it going. i have gradually changed out so many items in the past year that i feel like i have a new truck. i am sure someone out there can relate. i just gave up tonight after almost 3 weeks of it taking up every second of my free time. and it still isn't any better than it was when i started it for the first time after i dropped the motor. i am one of the most stubborn people i know but i feel beaten. i give up.

 

Some thoughts.... how would a failed iac cause an ect/act code? Also i think he said it idles up and down with compressor engagement. That would tell us the iac is working, how well??? Before you condem the pcm make sure those codes arent setting for a good reason. If both of those circuits are shorted, grounded, or open they would set those dtc's as soon as the engine starts. Normally it is unlikely to get two dtc's at the same time in 2 different circuits but in your case might help you to diagnose the problem. You said the motor was out or had been gone throught and both of those sensore are fairly near eachother. How about tracing the wiring quickly down the harness. Do maybee both circuits share a common ground that is either not tight or cut? Any change that when the motor was put together both circuits were pinched under a bracket and are grounding out?


Just my 2c's but randomly throwing parts at something has never solved my problems. I'd check the ground first and a good visual check of both circuits before even using a meter to check ground resistance and pin out voltage.

Hope it helps.

Oh yea, once you get this thing running please explain what the box with the heat sink and led is. Im thinking that is the "Kitt" knight rider intelligence module???

 

Have you double checked everything? A lot of electrical connectors needs to be unplugged for a rebuilt. If you have not done so yet, double check your electrical wiring on the driver side fenderwell (the ones that look like salt/pepper shakers) Mine has four connector from the engine. Disconnect battery (A MUST!), get some contact cleaner and a pointed pick. Disconnect connectors with the male connectors exposed, place the pointed pick on top of male connector (prying out, expanding the connectors) just a little...now. If you over expand it, close it with a long nose plier. After you've expanded the connectors, spray some contact cleaner in both connectors and dry. Then plug them together.....