I have a 1997 F250 Light Duty with the 4.6L engine. I seem to have replaced just about everything and I thought I was done having problems with the truck. Well, I was welcomed with the sight of the alternator/battery light and a spiking voltage a few days ago. So, I parked the truck and removed the alternator, and purchased a new one. Before I install it, I noticed a sensor or something with a two wire harness directly under/behind the alternator. There would pretty much be no way to get to this without removing the alternator or maybe the intake manifolds as it is in the tunnel between the cylinder banks and below the intake manifold. It is held in place by 2x 8mm bolts.

Since I have replaced just about everything on this truck, I figure this part will be the next thing to go after I put the alternator back in place. I am not exactly sure what this part is but was going to take it out and bring it to a parts store with me to see what it is and possibly replace it for good measure. The top 8mm bolt was easily removed but the lower one is more difficult. I was able to get a small 8mm combination wrench into the tight space and loosen the bolt until it hit part of the engine just behind the main belt pulley. I could not loosen it anymore and it almost seems like the intake manifold must come off to get to this. Before I waste more time/money, what is this part exactly? I cannot seem to find it on any diagrams and everyone at the parts stores can't figure out what I am talking about. I am guessing it isn't likely a problem but figured that since everything else has gone wrong and this is kinda hard to get to, I might as well fix it too. Someone told me it might be a knock sensor but it doesn't look like the pictures I looked up.

I have already replaced the temp sending units that screw into the coolant passages as well as the crank and cam position sensors so I know where those are.

Thanks.

 

I just completed a head gasket replacement on a 97 4.6 Windsor on Aug. 8th but can't picture the sensor you are describing. I remember connecting wires to 2 sensors behind the Alternator. 1 is located on the plastic plenum on the bottom of the intake manifold and the other is on the left front of the engine block, just below the separation line between the block and head on the valley side of the block. It seems like this sensor was the thread in type, I don't remember screws like you describe. There is a 3rd sensor on the floor of the valley directly under the intake but it's in the center of the block, hard to see with the intake attached and it plugs into the wiring harness on the rear of the engine. It's also the thread in type.

 

I went around to parts stores and no one knew what I was talking about so I went to the Ford dealer. They didn't know what I was talking about until I took them a picture and they found it on the parts diagram. They could tell me the part number and the price of the part, but not what it did. I took the part number and did some looking. This is the actuator for the IMRC or Intake Manifold Runner Control. I believe it is called the Intake Manifold Tune Valve. Basically it adjusts airflow depending on engine RPM to optimize gas mileage and power but is an overly complex system that tends to get gunked up and cause trouble.

After all this, I believe my IMRC is stuck in the high speed position or is intermittently sticky as I get extreme hesitation and then the truck starts runnign normally when it has been sitting. I have dumped Seafoam and other cleaners through the throttle body in the past and might have seen some improvement from these. I am going to do some more of this to try and free the butterfly up.

For those who have tried to clean the IMRC without taking everything apart, what do you suggest using and how successful do you think I might be. This seems to be something that isn't completely stuck so it might be repairable this way right now. How high do I need to get the RPMs in order to actuate this device? I was thinking of holding the throttle open to between 3500-4000 RPMs and spraying some cleaners through the throttle body or a vacuum line.

Thanks.