Have a 1997 Dodge Ram with 142K. MIL Light was on the code was for the O-2 sensor. I have replaced sensor, then the TPS sensor code came on replaced that, now my truck is throwing the code p0108 MAP sensor signal voltage high. I have replaced the Map Sensor, still getting code and motor is loping between 600 to 1200 rpm. Both the old and new Map sensors are reading about 5.15 volts. Any ideas what might be causing this.
This is a '97 1500 Sport with a 5.9, Automatic

 

Map code may be due to a plenum leaking..... have you fixed your plenum yet?

and: Welcome to DF!

 

Thanks for the Info, that probably explains the crappy mileage the loud sucking sound and black soot from the tailpipe as well. Not happy about dropping $120 bucks to find out I need to drop more but I guess that's the joy of owning an old truck. I used to think I picked it up cheap. This could really cause the p0108 code?

Thanks for the welcome, guess you'll all be hearing more from me.

 

Update: HeyYou was correct.
I spent a weekend changing the plenum gasket, haven't done anything like this in twenty years. The plenum was blown out in three places. While I was in there, I went ahead and changed the hoses, plugs, cap and rotor. Also replaced some vacuum lines. Broke a plenum bolt at only 6lbs. of torque!!! since it was late on Sunday I wound up reusing the new plenum gasket. Bought all new bolts and reinstalled, truck still ran poorly. Thinking it was because I reused the plenum gasket, I pulled the manifold back out it was fine. Bought new gasket kit and reinstalled everything, still ran rough, Turns out the Catalytic Convertor was also clogged.

 

Might wanna have a look at your O2 sensors as well. Burning oil tends to do bad things to them.

I always enjoy doing a job twice...... NOT!

Is it running better for ya now?

 

I have it going in to the muffler shop tomorrow, but it runs better with the o2 sensor removed. Bringing the new one with me. It actually wasn't that bad the second time around, took less than 3 hours. Having a clue helps.

 

Had a ruptured Charcoal canister as well, I think this may have caused the rest of my problems. The vacuum line was full of carbon pellets right up to the throttle body and the canister was almost empty. Wouldn't be shocked to see some in the Convertor when it gets replaced.
https://dodgeforum.com/forum/2nd-gen...questions.html

 

a buddy of mine with an 85-ish first gen 318 had the canister rupture and suck the charcoal into the carb. it stopped up the idle circuits in the carb but he was able to keep driving it with a foot on the pedal. it made it another 10 miles and then it stopped up the cat completely. i fixed his carb for free, but the cat cost him $$ at the muffler shop.