I got a vacum tester today and decided I'd check my MAP sensor because I'd hoped it was bad, which would explain my poor gas mileage. The plenum is fine, thanks for thinking about it I also did a bit of searching through the search feature, which would probably work better if the word MAP was recognized... DOH!

Before the rain and hail came, I was able to connect my tester and pump it to the amount spec'd in my haynes manual. I read an output voltage of 1.45 volts, and then I had to put things back together and run for cover.

Haynes says the voltage should be less than 1.8 wolts, but I'm reading specs that say it should be 1.5 to 2.5 volts at an idle condition.
So my question is, which is correct? Is 1.45 volts ok?

 

According to the FSM, the zero pressure reading should be .5 volts. Full scale should be 4.5 volts.

 

on DT you put that youre getting 1.45, which is correct this thread or that one? there was a thread awile back that started in the dak section where a few guys got new maps even without codes and they experienced better mileage and acceleration and faster starting, they said that the diaphragm in the map hardens over time,

you also mentioned that you have hesitation and roughness, is this when you 1st take off with light throttle, then clears up? my truck has been doing that with no codes

 

Thanks, I need to clean this thread up too. Holiday rush..I apologise.

My voltage at an "idle condition" vacum is 1.45. Haynes states anything below 1.8 volts is ok, yet I find internet sites that claim hot idle voltage whould be above 1.5 volts.

I also have an occasional smell of gas when the truck is at operating temp. A visual inspection dosn't show any gas leaks. I am reading that this occasional smell is symptom of a failing map sensor.
I also have some roughness and hesitation when the PCM is transfering from open to closed loop as it warms up. The TPS tests ok through its range. The IAT is good, and everything else from plugs to 02 sensors are fairly new. The map sensor is the only factory item left

I was able to (after almost pot of coffee) track down the Dakota threads relating to the map sensor last night. While the evidence was compelling, I always prefer a bit of hard data, and when the voltage data I have conflicts, thats even worse. I could spend 70 plus dollars on a new sensor but if it only increases my power (which probably is until the PCM relearns it) thats not worth it.

I also read HankLs' article on his scenic trip and map sensor readings. I'd love to know if my reading is within spec or not.

 

what about your evap purge solenoid? it controls the fumes coming from your charcoal canister and it can cause rough running and gas smell

 

I know that was an issue on earlier 2nd gen rams, there was a recall, because my '97 was part of that.
I need to see if there's a test I can run. It passed the last time I had the truck smogged but that was '07
Thanks for the idea. If I can find a test that I can do I'll try it.

 

something about blowing in the ports and one you shouldn tbe able to or sumthin like that

 

I believe on bionicdodge that I was told anything from 1.4 to 1.8 volts was good at idle. A higher voltage being due to the lesser vacuum that some of those guys with larger cams run.

 

Thats what I wondered, thanks Aims!

Guess I'll be looking elsewhere for the problem.

 

the evap purge solenoid works like a check valve, pull it off and try to blow through it. if it doesn't plug up one way then its stuck open. don't hold me to it though, thats what i read on another thread.

when my truck is running, my evap purge solenoid has a constant clicking noise and you can feel it clicking if you put your finger on it. i assume that its normal because i don't have a long starting issue or gas fumes. and i believe that clicking noise is the solenoid opening and closing to allow the gas fumes to flow into the intake in short bursts.