A buddy bought a 99 (I think) dually. He said it is low on power. We were looking at something under the hood on my truck and he noticed that I had something he was missing.....the entire MAP Sensor and wiring/tubing is missing. Would this cause his lack of power? If nothing else I would think where the MAP line plugs into the spider would be leaking boost pressure???

Thanks.

 

Check engine light will be on and all fueling/boost will be effected.

Yes, the power will be effected because its effecting the fueling.

 

That is not good. Definitely cause some performance problems. So at the spider is it just capped or left open to atmosphere. Either way need to fix before driving any more. Can you see the wires cut. I can't imagine anybody would do that.

 

Just to help you out.... I changed my low pressure pump and in the process broke off the plastic nipple off my map sensor leaving a intake Leak and only would assume a boost leak as well. Truck has no power and really poor acceleration but idles well...hahah...thought this was a helpful situation that could help another out. if you wonder if it working or not? its simple.... unplug the sensor did you loose any performance? it should run like cr#p. if it feels the same very good possibility you have a bad map sensor. you should see a tremendous difference in power between plugged in and unplugged.

to answer your question it is 100 percent his problem.. you got to have one or I beleive it might run in some type of limp mode.

hope this helps.

 

evilinkchris had the same problem...


The tube had broken off in the map sensor and the PO tried to fix it using a straw from a WD-40 can.

We replaced the MAP sensor along with the rubber hose and he was good to go again.

Inspect the map sensor, check the hose to the plenum for cracks or loose connections, replace either as needed.

 

I've heard wd40 and duct tape can fix anything. Never considered using the straw, that dude needs McGyver points for creativity, even if it didn't work. On another note, map sensor hose works well for removing/installing glow plugs.

 

I'm just curious... how do you know if your map sensor has gone bad? I'm assuming AE would pick up a code for that?

Drake

 

It would...

Your truck really wouldn't go anywhere fast since it can't tell how much boost the engine is putting out. If it can't tell how much boost is there, it can't release the right amout of fuel.

 

Was having a low power issue with my new 7.3 at the bottom end from take off and then it would slowly pick up and eventually take right off. That's a problem where I live because in order to get out in to a traffic lane you have to get on it from a dead stop or wait for a long opening which generally doesn't happen until evening. Anyway, I was reading this thread and thought I may as well unplug my map sensor and see what it does.. It made a huge difference! I now have full power at low end and the truck is snappy again. The down side is that there is now a check engine light so I ordered a new map sensor and we'll see how that goes. The PCM must put in some default values in case of a loss of signal from the sensor. What's strange is it acts exactly opposite of what some had said would happen previously in this thread. I had just done a EBPV delete and rebuilt the turbo with a wicked wheel on the new engine and I had replaced a faulty PCM...just for background in how I got to where I am. I do believe I may replace the wicked wheel as I can barely hear it doing anything but I will probably set up a boost gauge before I do that..

 

@GromOne , ensure there is no dip or depression in the rubber hose that goes from the intake spider to the MAP sensor. It should be a continuous and gentle slope from the MAP down to the intake spider. We have seen a couple of instances in the past where oil vapors would liquify in the tube and create an intermittent vacuum in the hose.

Below is proper hose routing and installation in pictures.

Here is an image of my MAP line post T4 install with the Riffraff OCR:



Here is an image of my MAP line with the OEM spider and OEM MAP sensor connection, which I assume is what you have:



In addition, this is what the PC/ED volume in the Ford Service Manual has to say about the MAP sensor.



Lastly, make sure you are using only Motorcraft sensors. The 7.3L is a picky SOB when it comes to sensors and valves.

 

This thread gets multiple points for being zombie thread. Multiple times. 👍🏻