no codes being thrown, but I'm getting 8-10 mpg on a 92 v6 2wd.

 

How many miles on it? When was the last time it had a tuneup? Do you have the kegger type manifold? If you do, have you fixed the plenum? How old are your O2 sensors?

 

bought it at 210k. just changed the oil because plugs and air filter look ok. not sure what a kegger type manifold is, but here are some pics and a video, btw, wouldn't a code be thrown for 02 sensor??:


Engine bay

Spark plug condition

Truck start up and exhaust (Turn up sound)


This was on a cold start.

 

A code won't necessarily be thrown for a sluggish / out of calibration O2. And they're only rated for 60,000 to 100,000 miles, so if those are factory, that's one of the FIRST things I'd do.

And yes, you have the kegger. Peek down into the throttle body (opening it with the motor OFF), and see if there's any oily residue in the bottom. If there is, most likely the plenum gasket is blown, so time to replace it. Might want to consider some Volume Reduction Plates - Marty Fletcher has had some really good luck waking the old kegger up with them, and they can be installed with JBWeld: http://utawesomeperformance.com/apps/search?q=VRP

New plugs, cap, rotor, wires - I'd do all four as a baseline. Be sure to check out the TSB on plug wire routing ( http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm ). Yes, I know it says 94+, but I'd honor its wiring diagrams anyway.

RwP

 

Stuck my finger in and THIS came out. Just looks like carbon buildup. I’ll replace the o2 sensor and work my way to the wires and plugs.

 

Stuck your finger in ... what?

That finger won't reach the bottom of the plenum.

RwP

 

Here's whats down in there:


Vid 1

Vid 2

 

VID1 shows a pretty bad oil coating.

Your plenum gasket is blown. Or sucked.

I'd fix that before I sweated much else for the gas mileage; you're running way off spec with that much of a non-metered leak. It's helping to keep the plenum vacuum down, causing the ECU to enrich the mix, causing excessive gas consumption.

RwP

 

Replace you 02 sensors.

 

In vid one that black spot at the bottom should all be clean metal. You can just replace the gasket and do it again the next time or you can put in one of the new aluminum plenum plates to permanently fix it.
I ran out of gas in my 3.9 at 150 miles on a full 22 gallon tank That is 6.8mpg. I had no gas gauge at the time. My plenum was almost clean just a tiny bit O oil but I went along with the word of folks on here and the other threads I have read and did a Hughes engine plenum kit.
I got 385 hwy miles out of the next tank. Yes I ran it out on purpose, I carried a gas can. That was around 19mpg. I drive mostly in town and I get 14-16 mpg depending on the last time I changed oil plugs etc. Some guy on here claims he gets 23mpg on his 3.9 motor. I don't see how I will get that unless I rebuild. Apparently the v8's get better mpg than the 3.9

When I did the plenum I also had the intake (it looks like half a keg split top to bottom) tanked, replaced all of the sensors in the intake and Throttle Body new water pump and timing chain adding in the TSB tensioner and the coolant hose elbow buried under all that stuff you take off. The water pump timing chain and the elbow are must do's to me since they are old and so hard to get at its best to do them when you have all that stuff off anyway. Keep track of where the bolts to the water [ump go and use painters tape to make labels for the wires and other connections you disconnect. Ditto bolts etc. Change the oil after you do the other work.