Ok, so I bought my '99 F150 4.6L XLT a few months ago and the CEL was on when I bought it so I knew there was going to be some work for me to do. I don't have any history on the truck but have managed to work out all of the codes but one. P0113.

I replace the IAT sensor hoping for the quick fix and had no luck. Next I checked for voltage at the plug and got none. Figuring that there is a break in the line somewhere I used my wire tracer to tone out the wire. What I found has me baffled.

The wire goes from the driver side to the passenger side of the engine compartment where there is a block connecting 2 wire harnesses together. The wire (solid grey) goes into slot 40 on one side and doesn't come out the other. There was never, at any time, a wire there.

This is what I don't understand. The PCM is obviously looking for the sensor data and the sensor exists. I doubt that it came out of the factory this way so I would guess that someone changed out the wire harness??? But if they did how is this wire missing but apparently EVERY other wire is there and working?

Anyway, what I really need to know is where in the PCM do I hook this sensor up? I am working on the assumption that I can just run a new wire from the sensor to the PCM where I hope there is a wire coming out that I can splice onto.

thanks in advance

James

 

Goes to terminal 39 on the computer.

 

Thanks. But since the sensor is a resistor then there isn't a positive and negative right? It just comes in one side and measures the voltage going back to the pcm. So which side should the voltage be coming from and which side is the return side.

I would guess that the imput voltage to the sensor is the gy/r wire and it returns to the pcm on the gy wire. So I should be checking #91? Or do I have it wrong?

 

You are correct, #91 grey/red is the reference voltage from the computer. If this wire had a problem, you would have a whole group of codes, since it feeds many different sensors.

Don't you have any wire left going to the sensor? From your description of the problem, I would assume you already have the grey/red going to the sensor, since the grey red comes from a splice out in the engine area and spreads out to many different sensors.

 

Yes, both wires are at the sensor. The grey one goes to a harness plug (where 2 different parts of the harness are plugged together) and ends there for some reason I still don't understand. The other grey/red wire I haven't traced down...but I guess I should since that is the wire the reference is coming from....maybe it is a bad splice?

 

Find the grey/red at the sensor and put your digital voltmeter on it and then find a good ground. You should have 5v on it if it's good.

Either someone has been messing around with this truck, or I guess it could have been made like that. How did it make it through with a code I don't know. I will tell you a story about a mustang I had that I know must have had a factory miss-wiring.

I found a ad for a 85.5 mustang SVO way back in the 1990's. It had a little body damage, but the price was right. I really didn't know much about the thing, it seemed to run fairly decent for a 4 cylinder.

After I got all the factory manuals, I started reading about the fuel switch on the console. It seems with regular fuel the boost was supposed to be 10 pounds, with the switch in the premium mode the boost was supposed to go to 14 pounds of boost. I noticed the switch didn't seem to do anything. I started checking the wiring, and found I had the wrong books, my 85.5 was wired like a 86. So the dealer was nice enough to let me photocopy the fuel strategy wiring from the 86 book.

I took the complete console out, hooked a battery charger to the wiring, and started taking readings as I switched the switch. It had a couple of relays in the console, and I noticed one of them was not working. That's when I found out the wiring harness had been wired wrong from the factory. Instead of one of the wires being on the common of the relay, and the other on the normally open or normally closed, they had one wire on the normally closed, the other on the normally open. No way this would this have ever worked, and the pin was actually loaded into the wiring plug wrong.

I think the boy that sold it to me knew it had a problem. I bet this thing made the rounds to several people, I wonder if any of the dealers had tried to fix it. I will never forget on my first test ride after I made the change, I flipped the switch to premium, and nailed the throttle, and the boost gauge pegged and I heard this loud whooshing sound under the hood. But I was not going anywhere fast. That's when I figure out the clutch was slipping.

Had to pull the tranny, put a new clutch in it and get the flywheel resurface(it was pretty bad) and boy, that thing would fly then.

 

Ok, I figured out a main part of the problem. At some point someone has replaced the wiring harness with one from (I think) an Explorer. To make it worse there are quite a few spliced wires inside the harness itself. I would guess that this was to make the truck run even though the CEL was on.

I figure, no problem, I will just replace it with the correct one and pulled one from a junk yard out of a 2002 Expedition. The part number on the harness was the same as what I got from fordparts.com so I figured I was good to go.

Wrong. While hooking up the 'new' harness I got to the plugs for the tail light harness and the new harness only had 2 plugs but needed 3 for the tail light harness....and the 2 that were there the pins and wires didn't match up. So now I am lost. How can the harness have the right part number but be the wrong part? Where did I screw up?

 

I thought you had a pickup? A lot of the explorers had amber rear turns that are separate bulbs.

 

I do, 99 F150, and it wasn't an Explorer it was an Expedition. I was told that the F150's and Expeditions were basically the same truck engine-wise. And since the part number on the Expedition matched (and everything else that was left under the hood looked close) I figured it was gospel.

Apparently it wasn't.



just for clarity I am talking about the engine harness that actually plugs directly into the PCM.

 

I am not sure what the engine/computer harness would have to do with the rear taillight harness, except maybe the speed sensor in the rearend.

 

The taillight harness starts at the engine compartment and actually plugs into the engine harness right next to the fuse box.

 

Have you tried it yet? If the engine runs good and all the codes have gone away, possibly the taillight harness can be modified to work.

 

No, there are a couple plugs missing and I would prefer to not have to modify the harness if I don't have to.

I just realized that my truck originally came with a romero engine but someone replaced it with a windsor. could that be causing my problem? I was under the impression that the engines were basically the same except for the flywheel bolt pattern and maybe some other small stuff that wouldn't affect the wire harness.

I am having trouble finding the harness at the local junk yards. The trucks I have seen are different in one of the following ways:

-The AC dryer is in the front of the engine compartment instead of the back
-The tail light harness only has 2 connectors instead of 3
-The fuse block is different. (mine has one but some of the ones I have seen seem to be separated into 3 parts)

I would think that the best route would be to get the first 2 right and either change the fuse block to the 3 separate ones or (and I would actually rather do this) pull the wires from the 3 different parts and hook them up to the one block on my truck. I just need to make sure the actual wires are the same.

Does anyone have any insight into this?

 

You will have to explain this a little more. Your truck came with a 4.6 or a 5.4 liter? And now it has a 351w(5.8 liter)? Give a little more detail on this. I am guessing you bought this truck used and whatever happened with the engine was already done?

 

It originally had a 4.6 romero and now has a 4.6 windsor according to the tag on the valve cover.

And yes, all this was already done to it when I bought the truck used. I have ran into all this trying to get my CEL off.