I finally got a code PO108 map sensor high input. engine is 5.9 and idle is very rough until it warms up,but still noticeable sitting at stoplight. Have replaced cap,rotor.plugs,wires,coil and IAC. Vacuum holds steady at 19 PSI and compression averages 150. routed wires per TSB. She runs great on the highway or as soon as the throttle opens. Also replaced the catalytic converter. Could this be a lull in repairs? Thanks for any advice.

 

High input? That would imply a problem with the power feed to the map..... not necessarily the map itself.

 

i'm guessing it means the map is internally shorted, and passing a higher than expected range of voltage, probably 5 or 12 volts. you can test with a volt meter.

the map is sort of expensive, about 80-100 bucks. if dollars are short you might get one from a junkyard.

 

The freeze frame data showed 11.2 volts for the MAP. It also threw a cylinder 8 misfire,which was also the cylinder with the lowest compression reading. Other tests for fuel pressure were 48 PSI on the rail. So your saying something else could be causing the code. This condition developed overnight. Truck was running great. Dropped it off to get rear end worked on and when i picked it up it ran like crud.

 

Going to try a new one anyway as i've spent money on worse things and will let you know. I read somewhere in the forum that a map sensor is either good or bad.

 

Map should only be getting 5 volts or so. Sounds like a possible short in the wiring somewhere.

 

Was the pre cat os replaced as well when the cat was? And when was the cat replaced? And has the plenum been checked? A miss fire on 8 is usually clogged cat and/or blown plenum (commonly) by #8. Get a Haynes and a cheap DVM, with those 2 things you can check just about all the sensors before wasting money on replacing them. There is also a small small hose behind the MAP that connects to the TB, that can be broken or not connected.

Oh and btw, if the MAP is checked with a scanner or the plug is back probed, and the wire is not checked/isolated from the MAP itself , it could very well be an internal fault like DHV stated.

 

Truck went into shop today. They said 3 cylinders are at 60,80and 80 rest 150ish. And thats why its idles jumpy. Why would that throw High Input MAP code? do you see relationship? Cat and 02 were done very recent.

 

I might add the mileage on motor is 210,000. But throttle is very responsive ,plenty of power on highway. Anybody trolling out there? The new Map did improve the first start it up jumpiness.. anybody?

 

Did the new map make the code go away?