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i am Testing my MAP sensor yesterday with my meter and with the vacuum pump and meter hooked up to the signal wire i can get a steady decrease in Hz while increasing vacuum starting at around 158 at 0” and about 104 at 20”. So I think the sensor Is ok. But I don’t have 5v at the power wire nor do I have 10-12v when I test the ground. I have .004v on the power and 7.75 on the ground. When I run a jumper ground straight to the ground a relay clicks on power dist box but no other affect. When I unplug the sensor while running it idles up, when I bump the gas it dies. So it’s doing something but with no power? I am looking at all things because my E4od is shifting hard 1-2 and 2-1. It now shifts good 2-1 after this. And someone mentioned on a thread somewhere that they had that issue and after all the usual things it ended up being that. I have already replaced the VSS(Motorcraft) PSOM, solenoid block, plug to solenoid block, checked the tone ring, fluid in diff, fluid/filter in trans, I still have a 453 and 332 codes. I took the EGR off, put a block plate and installed a “dongle” in the wiring. Still have the code. But when I plug the valve back up electrically and hook vacuum straight to it the valve opens and the truck doesn’t want to stay running after you put it in gear or coastdown but shifts great all the up and down. I am confused and it seems like I either have a few different things going on or the brain of everything acting up.
I am not sure how you are testing the MAP sensor supply, signal return or output. At least the output, when referenced to signal return, appears correct. As you have found the output is variable frequency.
1992 F Series Engine Control Page 4
Gray/Red wire is Signal Return which goes to PCM Pin 46. There is also a splice for the O2 ground on Pin 49.
Light Green/Black is the signal output to PCM Pin 45.
Brown/White wire is VREF from PCM Pin 26.
There is no 12 VDC feed or output associated with the MAP sensor.
