2.9 eec

[chavo6723]

I have been having alot of problems with my engine running rough and not running at all. I have been digging through wires and relays. I cracked open my eec to find that pin 46 was fried. I know multiple things run to this pin since it is a signal ground. What could cause this to burn up so it doesn't happen again when I get a new one.

 

[franklin2]

Look at the oxygen sensor wiring. Make sure the wiring is not melted near the exhaust pipe.

 

[rusty ol ranger]

Honestly it was probably fried from within the ECM.

Pop it open and have a look

 

[franklin2]

Here's your old thread on this subject.

Thread '2.9 eec'

Jan 24, 2026

I have been having alot of problems with my engine running rough and not running at all. I have been digging through wires and relays. I cracked open my eec to find that pin 46 was fried. I know multiple things run to this pin since it is a signal ground. What could cause this to burn up so it doesn't happen again when I get a new one.

• chavo6723
• 2.9 eec eec computer emission rough idle and running
• Replies: 14
• Forum: 2.9 Liter Forum

 

[chavo6723]

I put a new 02 sensor connector on before all this happened. Could the new connector be pinned wrong? Does anyone know which wires will go to the heater and which one is the signal wire? I got 3 wires on a 4 pin connector.

 

[franklin2]

I put a new 02 sensor connector on before all this happened. Could the new connector be pinned wrong? Does anyone know which wires will go to the heater and which one is the signal wire? I got 3 wires on a 4 pin connector.

Why don't you leave the O2 sensor unplugged and run it like that for awhile and see if the problem comes back. The truck will run with the O2 unplugged, it will just throw a code for it and use the factory fueling tables stored in the computer to run the engine.

 

[SenorNoob]

That works.^

Half the guys in town are convinced having the O2 unplugged makes more power. They're nuts but it does run.

 

[chavo6723]

I will give that a try. I need to get a new eec first.

 

[chavo6723]

I got three wires that go to the 02 sensor. Grey/yw that is from ignition switch. DG/P which goes to pin 29 on eec. And BK/LG that sties into eec relay, ground, and pins 40 and 60 on eec. Can anyone tell me which ones go to the heater wires and which one is the signal wire.

 

[franklin2]

Signal wire is DG/P which goes to pin 29.

The heater wire is the Grey/yellow that comes from the ignition switch.

The question is, are you sure which wire is which on your new O2 sensor?

The O2 sensor is like a battery. It generates it's own voltage when it gets hot enough, to pin 29. It does not need power.

The ignition switch power wire is for the heater only. It just heats the O2 sensor up quicker so it starts generating a small voltage quicker.

The ground is common for both the signal generated and the heater element.

 

[chavo6723]

Yes i am certain of each wire that comes from the harness on the truck. Even my book mirrors the wires. I am just not certain which wires are for the heater (2 white wires on sensor) and which wire is the signal wire. (1 black wire on sensor).

I know for sure the GREY/YELLOW wire is one of the wires to go to the heater. (2 white wires on sensor)

What i dont know is what the other 2 wires connect to on the sensor. They both connect to the eec in some form.

 

[SenorNoob]

Signal wire is DG/P which goes to pin 29.

Is that not the answer you're looking for?

 

[chavo6723]

So the black/LG wire is the other end of the heater?

 

[chavo6723]

Now that I figured out that my wiring to the 02 sensor is good and it has nothing to do with pin 46 getting fried on my eec. The only thing I can see is that 12v from the ignition switch is making it's way ether from the neutral sense switch or the clutch engage switch.
The map, act, ect, and tps all run on 5v.
Can someone correct me if I'm wrong and tell me how to check to see if I'm getting any back feed.

 

[franklin2]

Looking at the diagram more carefully, pin 46 is not a "ground" at all. That may be a term you would commonly use, but according to the diagram it is a "common" or "return" for the 5v. This is interesting, I don't know if you can take a meter and go from the 5v supply to any ground and get 5v, but looking at the diagram, I am thinking you can't. Unless pin 46 is tied to ground inside the computer.

This would be something to check with a meter. Is pin 46 tied to the real ground inside the computer? If it is, this could be a problem if in all your black/white wiring, that the wiring was tied to ground somewhere. That would give other components the opportunity to use pin 46 as a ground when they shouldn't.

Your next step might be to unplug the computer plug, and take a ohm reading from the black/white common 5v wiring to chassis ground. According to the diagram, it should not be connected. If it is, you will have to find out where. If you find it, this may make your problem go away. That connector "C1984" in the diagram is the EEC test connector ground. So it's just a place to test things, and it would be a good place to check and see if the black/white is tied to chassis ground somewhere.