I got a 1993 dakota with the 3.9, 200,000 miles on it. When i first got it a few years ago, i was getting 16-20 mpg pretty consistantly. Then all of a sudden it dropped to 9-11 mpg. Never lost any power, still runs great but the exhaust smells funny, like its rich and its a very strong smell. No check engine lights ever come on. No smoke. No cat converter. Recently replaced plugs, wires, cap and rotor. Replaced air filter also. What should I do next?

 

O2sensor could of failed, I also have a 93 3.9, and I've never seen a check engine light, did u manually check for codes? Key in ignition, on off on off on off on, wait and count slow flashes then fast flashes for codes?

 

Thanks for the reply, i found some codes stored in there. Turns out i got 51 for oxygen sensor stuck on lean position, 21 for oxygen sensor circuit, 32 for EGR system, and 12 for memory standby power lost. What does the code 12 do?

 

Don't worry about code 12. Pretty much comes up all the time (it's supposed to mean battery disconnected within last 100-or-so key-on's, but, it usually appears all the time).

 

my 90 also has bad mileage, checked codes (first time ever) see blinking check engine light but what am i looking for in the blinks, all look the same to me and all run together?
don't mean to hijack here but my issue is like posters.

 

OP- Probably need to replace O2 sensor. My mileage increased when I did mine. And from the codes, that's a good bet.

-There is a good write up in the FAQ.

 

Pulled EGR valve out and found the stem was locked up. Put a new one in and it works good now. Still gotta do the o2 sensor yet.

 

Having the same gas mileage problem with my step-sons Dakota. have replaced the egr and the map sensor but it has not helped the mileage at all. Will try the o2 sensor next I guess. Extremely frustrating for a first semester college student spending all his money on gas, he only gets about 7 mpg.