Vacuum Module ID & Problem

[MJWenrich]

I have been hearing a constant motor noise from under the hood and traced it to a vacuum motor behind the passenger battery and in front of the radiator fluid reservoir. I disconnected hoses one at a time to determine if there was a leak in a hose but the motor continues to run. At the bottom of the unit there is open nipple but plugging it with my finger does not change anything and I don't see an unused hose lying in there. Thought it was for the windshield washer fluid but after disconnecting the electrical to the problem unit the washers still work. Different motor. My Haynes manual does not tell me what this unit is or the function. Maybe for the A/C? Any ideas to help me? The motor vibrates, is rubber mounted and is pretty loud inside the truck.

 

[Bob4x4]

on the 04?

 

[MJWenrich]

Yes. I guess I assumed being on the 3rd gen forum that would be understood but I should have clarified.

 

[Bob4x4]

probably the vacuum pump if it is running constantly at key on check for a vacuum leak first

 

[sag2]

I could not find anything for the wiring for the vacuum pump in service info. Hope it isn't the pump as they list for $300!

 

[cerberusiam]

Vacuum motor for the cruise control, that is all it runs. Disconnect the line that runs up along the cowling and plug the fitting it comes form, if the motor still runs the internals have failed, yes, it is an expensive little bugger.

 

[MJWenrich]

Thanks for identifying it. The cruise still works. Does that make sense?

I disconnected that line this morning. And the others and taped over them. The unit still buzzed right along.

Is it dealer only with no aftermarket?

 

[cerberusiam]

You can't just disconnect the line, you have to plug the vacuum line inlet on the pump to see if it is just a line failure or a pump failure. A small enough crack in the lines somewhere will still develop vacuum enough to run the components but cause the motor to run constantly. Generally there is a line or plastic fitting cracked between the motor and the cruise control unit somewhere allowing air into the system.

 

[MJWenrich]

Okay. I will disconnect all the lines and tape over the plastic inlets/outlets and see if the motor stops. Strangely, there is a larger nipple on the bottom that has nothing connected to it. It's about 3/8 line size. I placed my finger over it while the pump was running and did not detect vacuum. I was thinking it might be some kind of relief valve. But I will cover all of them and see what happens.

 

[cerberusiam]

The nipple on the bottom is probably the discharge and moisture drain. If you live in a buggy environment they built nests in it and plug it up, the wolf rats and mice chew the lines off and wiring harnesses, in the garage. LOL!

 

[MJWenrich]

I plugged all the lines and it still won't shut off so I guess the unit is bad. It does make vacuum so I suppose that is why it is still a functioning CC unit. Thanks for the help and I will go in search of a replacement unit.

 

[MJWenrich]

Internet search revealed this is a problem unit on other brand trucks over many years. Namely Ford. According to one supplier, the way to check your unit is as Cerberusiam suggested. There is more than one company making a replacement part and I chose to go with the Dorman 904-214 based on reviews. $50 from Rock Auto plus about 5 bucks to ship. Local O'Reilley wanted $89. I can wait for it to get here. So thankfully I don't have to step up to the $300 model.

 

[cerberusiam]

The $90 is probably close to OE quality and Dodge just over prices it. The Doorman is a cheaper model but for $50 bucks you can buy a couple before the ROI gets out of hand.

 

[MJWenrich]

I priced the same Dorman model at O'Reillys and it was simply more money. No good guy discount. But you are correct. Now that I know what it is I can replace it if it becomes a problem again. One review said one of the nipples broke on install but all the others (about 40) were positive.

 

[MJWenrich]

Update. With the new pump installed I have determined that the problem was the pump...but probably caused by my ignoring the constant running for a year. That was apparently because of a problem at the cruise control servo. Would anyone know if that part is servicable?

 

[DonFitzwater]

I doubt the cruise servo is serviceable.

 

[MJWenrich]

In another thread on the same subject, sort of, cerberism gave me a link to moparparts for the vacuum module. Sure hope it works to stop this problem.