I have an 88 MJ with a 5 speed. I’m having an issue with bucking above 2,000 RPMs. After testing, replacing and cleaning almost ever sensor and ground I checked the MAP sensor. I got the following specs:
A to B 4.01 volts
A to C 5.00 volts
A to B hot at idle .99 volts (S/B 1.5 to 2.1)
I figure great the MAP is bad and this will fix the problem. I put a new sensor in and to my surprise I get the same readings. With the MAP pigtail still back probed I stared messing around. I ran another ground straight to the battery but it made no difference. Then, I crimped the vacuum hose going the MAP and noticed that less vacuum gives a higher voltage reading. So, I tied the hose in a loose knot to until I got the voltage from A to B and idle to 1.35. I took the truck out for a test drive and it ran way better, not perfect but the MAP sensor was still out of spec. What would cause a high vacuum? Has anyone seen this before?
A to B 4.01 volts
A to C 5.00 volts
A to B hot at idle .99 volts (S/B 1.5 to 2.1)
I figure great the MAP is bad and this will fix the problem. I put a new sensor in and to my surprise I get the same readings. With the MAP pigtail still back probed I stared messing around. I ran another ground straight to the battery but it made no difference. Then, I crimped the vacuum hose going the MAP and noticed that less vacuum gives a higher voltage reading. So, I tied the hose in a loose knot to until I got the voltage from A to B and idle to 1.35. I took the truck out for a test drive and it ran way better, not perfect but the MAP sensor was still out of spec. What would cause a high vacuum? Has anyone seen this before?
