Turbot11

Hey guys,
I am about at my wit's end trying to figure out why my mileage sucks, hope I can get steered in the right direction. I have a 93 Sport, 4.0L, auto, 4WD that's averaging about 12-13 MPG. the vehicle is stock, no lift, only upgrade are the tires, General Grabber AT2's in LT235/75/15 @ 42psi on it. The motor is a 97 4.0L with approximately 40K on a rebuild. What I thought was the culprit was the stock injectors, #5 & #6 leaked at the pintle and were flooding out the cylinders. After reading on here I replaced the injectors with the Neon 703/784 injectors. The engine idled much better and ran smoother, but no increase in mileage. I replaced the coil and have blue/white spark. I replaced the spark plugs after the injector change with Autolite platinum's and 1000 miles later they are clean, no more carbon fouling in any of the cylinders.
After reading on here some more and figuring the O2 sensor was fouled out I replaced it with a new sensor. Again I have yet to see any improvement in mileage, it still averages 12-13MPG, it's slightly better on the highway upwards of 13MPG. I replaced the cap, rotor, wires & fuel filter in spring 2013, New K&N style filter a month ago. The contacts on cap and rotor are burned, I have a new cap & rotor on the way, hopefully that will help. The converter is not clogged and because I am a cheap a$$ I replaced the factory muffler with a glasspack. There are no fuel leaks that I can find anywhere
I don't expect 30MPG out of this thing but how can my 94 2WD 4.0L Auto Sport with 286K on the original engine get 20MPG and this thing 12? From what I have read on here I should be able to expect 18-20. The engine runs beautifully but lacks power in comparison to my 94 and no matter what I do the mileage sucks. Above and beyond the cap/rotor its getting does anyone have any suggestions as to what else I should look into? Any help is appreciated!


Thanks in advance,
Chris

bus driver

Sounds like you're taking care of a lot of the proper maintenance. Change the fuel filter? The engine came out of a 97 but is the gas tank still original? If so, the fuel filter would in the rear of the undercarriage. If the gas tank also came out of the 97, I think the fuel filter is within the gas tank and you can leave it be. Alignment?

Turbot11

Thanks, only the long block is a 97, I kept the original intake & exhaust manifolds when I swapped the motor. The gas tank is original as far as I know, It does have the external filter, which will be replaced again, after this impending snowstorm passes. I am stumped as to why it has no improvement in mileage, it runs so much better with everything I have done to it

Turbot11

I did have an alignment done on it when I put the AT2's on 3000K ago

RTorrez1

Personally I would get rid of the platinum plugs and run Champion copper or NGK copper. The 4.0 seems to run better with the stock plugs. I tried the platinum plugs and only left them in for about a week before getting rid of them. They made my 98 run like crap and didn't help the mileage one bit.

belvedere

Has it ever gotten better mileage? How long have you owned it? Did you do the rebuild?

You've covered all the usual suspects. Low on power and MPG...makes me wonder about things like ignition timing and valve timing.

s346k

what kind of condition is the trans in ? did you reset the ecu after the injector swap?

Turbot11

Thanks,
I would love to run coppers in it, I put in Platinum because I'm up it the northeast where all our environmental friends dictate what the gas is comprised of. I've found the ethanol blend dissolves coppers rather quickly. The gap on the coppers in my 94 went from .035" t0 .055" in less than a year. I wouldn't mind swapping in a set just to see if it improves it any

Turbot11

No, the mileage has always been crappy, I bought it in November 12'. I bought the engine used put it in as a short block, cleaned up the deck and put a new HG on it. I thought about playing with the ignition timing but I thought the ignition timing wasn't adjustable on the 4.0? I know the distributor can physically be turned; but I was under the impression it was like a 4.3 GM where you can twist the distributor and the only change is it stops running if you go far enough. I would love to be able to adjust the timing.

Turbot11

Trans seems to be ok for the most part, sometimes slips a little downshifting. I did not reset the ECU after the swap, how do I reset it?




Thanks

s346k

search is your friend, but this is what I did.

remove positive cable from the battery

ground it (chassis, block, etc) for 30+ seconds

leave the cable unhooked, make sure it won't fall back on the post - then go turn the key forward, but not to start

turn on your headlights for 10+ seconds

turn off headlights and return key to off position

reconnect the cable

BlueRidgeMark

That's odd. I run copper and all our gas is 10% corn junk, and I do NOT see that problem at all. I put on ~30,000 per year.

Maybe you have a spark that is TOO hot?

Turbot11

Maybe, I did replace the coil. It is something else I will have to check. I will try the coppers again and see if that helps too. Mileage has been a little better since the O2 replacement, about 15-16 mpg but still not near 20

93gc40

I have 96 4wd auto on 31 and 14-18 is NORMAL, Is the same I got with stock 215 tires.
1 I would expect the 2wd to get 2-5 mpg better that a 4x4, just due to the extra axle and transfer case.
2. High performance exhaust and intake = more air flow, more air flow means more fuel flow. Neon injectors flow more fuel not less, Swap the packs with a stock muffler I'd bet you pickup 1-2 mpg.
3. 10% mandated ethanol, runs anywhere between 10% and 20% alcohol. You can see a 5%-10% variation in MPG tank to tank, station to station.
4. Then there's the HUMAN factor, maybe your foot has gained weight, common side affect of louder exhaust.

kikstand454

As a side note. Pull your throttle body and clean it and the iac (?) sensor completely. It did wonders for my wife's ford focus.....I need to do it to my xj.
also a full seafoam treatment has worked for me in the past.
I have a '98 4wd on 29"s and I get 19 on the hwy and about 16 in town.
good luck.