Bad gas mileage 1993 Dakota

salb203 · #1 12-17-2005, 05:43 PM

Hi Folks,
I am hoping someone can help me here. I have a 1993 Dodge Dakota pickup with the 3.9 liter V6. I used to average 18 MPG with it but now I am lucky if I get 9 MPG. Financially this is killing me. I have 125,000 miles on it. If I floor the gas pedal, the exhaust comes out black. On the rear of the quarter panal where the exhaust pipe it is black. I have changed the plugs, cap, rotor, wires and air filter. It is running real rich. Fuel pressure is 35 pounds. Any ideas?

Thanks,
Sal Brisindi

360DakotaPwr · #2 12-18-2005, 03:10 AM

How does it idol?

92dakota318 · #3 12-20-2005, 03:15 PM

check your O2 sensor (s). thats your best bet.

JDakota92 · #4 12-21-2005, 01:26 PM

Ditto on the O2 sensor. After that, check temp sensors, but go after the O2 sensor first.

salb203 · #5 12-23-2005, 06:13 PM

Thanks for the tip on the O2 sensor. I will check it out this weekend. BTW, to respond to the first reply, the idle is a little rough.

Regards,
Sal Brisindi

JDakota92 · #6 12-23-2005, 07:57 PM

When was the last time the fuel filter was changed? Air Filter? Also how do the plugs look? Fouled? Answering these questions would be good as well.

salb203 · #7 12-25-2005, 04:47 AM

I did not replace the fuel filter but airfilter, sparkplugs, cap and rotor are new. Plugs were black. Fuel pressure was at specs (about 35 pounds). Does anyone know where the O2 sensor is on the Dakota with the 3.9 liter V6?

Thanks,
Sal

360DakotaPwr · #8 12-26-2005, 03:36 AM

Ok, if you are spitting out lotts of black stuff, then I agree with the O2 sensor idea, however they rarely go bad, its mainly a gimmic for the dealer to get you to spend more money. If you have access to a scanner then you can be sure. Hook up the scanner and read O2 reading, if it switches from lean to rich and back and forth then it is ok if not then it is stuck.

The sensor is on the Y pipe on the right hand side where the two pipes from eich manifold meet into one. Has four wires going to it and takes a 7/8 wrench or socket to remove it.

Sneezer · #9 12-29-2005, 12:54 PM

I have found that O2 sensors do go bad, especially on high mileage engines. In addition, the Bosch ones frequently fail within a year. I have had much better luck with NTK, which was the OEM for Dodge up until the last couple years.

salb203 · #10 01-02-2006, 11:36 AM

Thanks for all your help guys, my buddy has a scanner, connected it up and it showed the O2 sendor was shorted, sure enough there was an exhaust leak that melted the wires. Replaced it with a new one, tightened the exhaust. I will update this forum with a miliage report as soon as I use the truck this week.

Regards,
Sal