I just filled up 19.756 gallons. I had gotten 286.1 miles out of that which makes for 14.48 MPG. mostly in town on trips no more than 20-25 miles tops.

I had 9MPG when I bought it.
I started with a new EGR the only code it had, then Plenum kit, Timing chain and tensioner, wires, all new sensors on the intake and TB, plugs, cap, rotor, cam and crank sensor, O2 sensor new serpentine belt. I got it up to 19+mpgs
I recently fixed exhaust manifold leaks and broken studs and replaced all pipe and Cat & muffler from the Mani back.
All of that new stuff is under 2 years old.
I just got the exhaust done a few weeks ago and put on new tires. On a 500 mile trip I got 19+mpgs. I don't think anything I installed would have gone bad I used Napa parts. NGK o2 sensor. I have read that it matters if you don't use the exact right brand of wires, plugs, sensors etc. I priced a cam and crank sensor with the dealer and they want north of $120 for one and north of $130 for the other. !!! So that's an o unless its absolutely necessary. It also occurred to me that the tire size might be affecting the odo some T215/75R15 (100/97S)

Any ideas where I should look for the problem? Oh yea I have the Sync set and +1 it wouldn't sit on zero if I tried to get there it would jump up 5 or 6 all of a sudden.
thanks.

 

Quick test on tires is compare speedometer to a GPS to see if they match up. Or use another vehicle and drive a route of 20 miles....do the same with the Dak and see if the miles are the same.

 

According to the FAQ2 T215/75r15 is 27.7"
I can't find any data on what the OE size of tire is.

 

It should be on the door sticker, Onemore94dak.

Or, since it's a 1994 and within the 25 year cutoff, grab your build sheet from Mopar. It also should have it.

RwP

 

Sheesh I thought I had posted already.
Thank you Ralph it is on my build sheet. P215/75R15
I just hooked up the MT2500 and there are no codes. Just to be sure I used the key too. Only a 55.
All items I could look at in systems seemed to be within normal range except it said the exhaust was rich. O2 was .23-.92 EGR indicated it was working as did the IAT, MAP and Coolant temp sensor. I don't recall the IAT and MAP results if there were any.
I'm wondering is running it with two plugs being of different kind from the other 4 may have a negative effect or if not fixing everything right away after installing the new cap, wires, plugs, coil, O2 sensor may have made them less effective than they would be had I done the plenum and fixed the exhaust before putting in new ones.

 

What are your fuel trims like? Is your truck fuel injected? Might have an injector leaking down. I find it usual that the computer sees a rich condition but cant correct it. If you got a fuel pressure gauge, hook it up. If memory serves me correctly should have a working pressure of like 30-35 psi depending on engine load. (you can look up specs). With the gauge hooked up, cycle the key till you see pressure, and it should be able to hold that pressure without dropping quickly. It will bleed down a little normally, but if it just dives off then you know you have an issue. Usually there is also a specification for bleed down time. maybe this will help, just kind of what I thought it sounds like. Also I find it unlikely that the brand of wires/sensors could cause you this much trouble. Also I noticed a considerable drop in mileage after I lifted my truck, put 31" off road tires on it and loaded it up with gear :-)

 

Thanks Thomas, Thanks I'll do that. I'm keeping it stock since they are supposed to be pretty good as built and I only intend to use it lightly with an occasional load of gravel and the injectors are rebuilt maybe a year old from Motor Man Fuel Injection Supply.

 

So I attached the gauge and it didn't register. ??? Then I took it off and there is not pin to push the Schraeder valve pin down in it. Now I am confused as I am sure I used this gauge to check it once before and it read 32-35psi. Anyway I need a Schraeder vale removal tool as I can't find the one I used to have so I can check the fuel pressure for drop off. I'm not driving it as I have a brake issue in another thread here. Too many things to do at once right now. Good thing I have an extra rig.

 

I took the gauge back to the store and they exchanged it. I hooked it up and the pressure sat at 32-33 for the whole time it was hooked up no drop off. So its not leak down of the injectors.

 

The fuel gauge just dropped from full to between full and 3/4 on my test drive of about 10 miles. !!!??? I can see the new muffler pipe reducer is leaking some carbon before the muffler (I ran out of O2 with about 2 inches left to weld when I installed it) I'll get that sealed but I don't think something that far back can be affecting MPGs.