Have done a lot of searching and have yet to find a true fix for my wife's truck. So far have changed plugs, wires, cap n rotor, up stream 02 sensor and made sure all vacuum lines were good, and it still throws the check engine light after about 10-15 miles from a reset. For about the first 5 miles after resetting, the truck runs like new but then starts getting the issues back of rough idle and poor acceleration and horrible gas mileage. O2 sensor is throwing the code for being lean but even looking at the O2 sensor, plugs and extreme amount of raw fuel coming out of the exhaust its clearly not running lean. Only thing from my searches that i haven't tried yet is changing the map sensor because i don't want to keep throwing parts at it that aren't fixing it. This has been an ongoing on/off issue, sometimes the light will go off for a few months and then back on for a few months, when the light is on the mpg is 10-12 and off its about 11-13 at best(city driving) Personally a regular cab 2wd Dakota with a 3.9 should get much better as my 96 ram ext cab 4x4 gets 14-15 in the city. If anyone has any suggestions I would be very appreciative as this truck has been driving me nuts for 2 years now.

 

Tested the map sensor last night. Have 5.14 volts between the 2 outside wires, 1.9 voltz on the center wire with motor idling, spiked near 4.3 volts goin wot for a second and around 4.4 volts with just key on(center wire) only thing I could find was something saying 1.5 volts on the center wire but not sure if the volt}es +e out of the norm causing it to run rich but read lean at the o2 sensor?

 

I recommend changing out all your sensors as you hit 120K on your truck it depends on how fast you put the miles on compared to how old it is. My truck didn’t run like new till I changed all them out. Your problem sounds like something that changes with weather that I would say is either the MAP or the Air Temperature Sensor they are sensitive to weather changes but I also suggest changing the TPS and clean the throttle body.

How old is the cat?

 

It's dumping fuel out the exhaust because the computer thinks the mixture is lean.

P0131 is 02 sensor shorted to ground. Check the wiring for damage.

What brand 02 sensor did you use? If it was Bosch, change it.

 

Dan but why would it be intermittent like he says?

 

You mean "first 5 miles truck runs like new?"

Just a guess, it's not running closed loop for the first few miles. Once it warms up it is, then it realizes the inputs (02 sensor) are bad.

I'm not saying it can't be a MAP sensor but there is an obvious fault with the 02.

 

Searched on here and found the ntk was reccomended so that's what I got. can sit in the driveway and idle plus some revs for 30+ min and no check engine light or running bad, only after driving for about 10 miles or so Truck has about 130k on it and don't have a ton of money to be throwing at it right now... which is while its been an ongoing problem too because I can only put so much $ into it at a time. Have traced the wires and haven't found any bad or soaked in oil, checked the computer for oil from the power steering and all those wires were dry and good too. I am a marine mechanic so I'm used to most stuff but o2 sensors are fairly new to boats so this is driving me nuts

 

I installed a new map sensor last night and still same problem after driving 10-15 miles the check engine light is back on. Only getting PO171 now but its still running extremely rich. Any chance the ntk sensor i got from advanced auto was bad?

 

P0171 fuel system lean.

The computer sees that and tries to correct it by making the mixture rich.

I'd still be looking at that O2 sensor.

 

Is there any way the gas cap could be related to the code p0171? Filled put some gas in the truck and started it up and now the light is gone and its running better, or could it just be a coincidence and in reality its taken till now to get a better reading from the new map sensor? (i did disconnect the battery when i installed the map sensor to reset it)