• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

What would cause poor city mileage?

C

clunk

NAXJA Forum User
Location
West Kootenays, BC (canada)
I have not had the greatest city/slow speed mileage since I bought my jeep. My highway numbers are 26 MPG, my city numbers are barely 14MPG. (I'm in Canada so my calculations are a little different, and higher than those of you in the states).

My jeep is a 1990 with AW4 and around 103k on the original 4.0l engine. It is bone stock beside a set of LT235 all terrain tires. I run 30PSI in the tires.
I have some intermittent lifter noise (which I have now gotten used to), run 89 octane gas and new muffler/tailpipe a few weeks ago. The plugs, wires and cap were all replaced around 8000km ago. 02 sensor looks to have been replaced by the previous owner not too long ago (going on looks alone here though). The jeep runs pretty well besides the occasional lifter noise. I'm not sure why my city mileage is so poor, I do live in a very, very hilly city though (think little san fransisco).

The one thing I can think of is that the knock sensor is busted. I broke it while trying to get at the block drain plug while changing the coolant. Since it still runs the same as it did before, I havn't bothered buying a replacement. I didn't notice a decrease in performance or gas mileage since it broke, so I doubt this is the problem.

Any insight, or is this normal mileage for a jeep in a hilly area? I'm really, really happy with the highway numbers but since alot of my driving is in the city (up and down the hill), I'd like to improve it as much as possible.
 
i would definitally replace that knock sensor, thats one of the computer inputs and it can really protect your engine.
i'm not sure if that would contribute to your gas milage. mayme the computer goes into a "safe" mode and runs rich in low speed.....
 
My 90' gets 12mpg in power mode and 17mpg in comfort mode(city). Try switching to the comfort mode if you haven't already.

The more i run between 45 and 65 mph the better the mileage, 35mph kills my mileage.
 
Driving in the city might be your problem, its like !!!1.

Also driving up hill in stop and go rush hour traffic does little for improving gas mileage.:eek:

The knock sensor retards timing to avoid engine damage if the engine starts to knock. If it is not knocking and pinging with hot engine trips up hill you don't need it.

Not having a knock sensor does not hurt mileage as evidenced by your incredible, invious 26 mpg highway mileage. Wanta trade????

I would recommend sticking to down hill trips on the highway at 4 am and 60 mph when there is no traffic if you want great mileage. Otherwise its time to buy stock in oil companies or get your own oil well.

By the way, I am pretty sure we talked about your lifter noise before, FYI, my 2 year old, loud as hell, first cold start of the day lifter noise is now completely gone. :clap:Between MVO, Lucas, and finally an attempt at slowly switching over to synthetic oil (tried a 50/50 blend, but it sprang too many leaks....long story, back to using dyno oil now) where I ran a 50/50 blend for about 2000 miles, I finally got rid of the lifter noise on mine. I am using 20W50 dyno oil with 1 quart of Lucas now and no more lifter noise.:clap: I also solved the last of my other problems and the engine is running perfectly now, so stick with the additives, and maybe try a quart of mobil 1 synthetic as an additive to loosen up and clean that sticking lifter.

With 26 mpg highway, I would leave well enough alone! Jeeps get lousy mileage in the city and when run under 40 mpg. The TC does not lock up until after about 42 mph, and it does not shift into 4th gear until about 40 to 50 mph, depending on acceleration.

How steep are the hills?

clunk said:
I have not had the greatest city/slow speed mileage since I bought my jeep. My highway numbers are 26 MPG, my city numbers are barely 14MPG. (I'm in Canada so my calculations are a little different, and higher than those of you in the states).

My jeep is a 1990 with AW4 and around 103k on the original 4.0l engine. It is bone stock beside a set of LT235 all terrain tires. I run 30PSI in the tires.
I have some intermittent lifter noise (which I have now gotten used to), run 89 octane gas and new muffler/tailpipe a few weeks ago. The plugs, wires and cap were all replaced around 8000km ago. 02 sensor looks to have been replaced by the previous owner not too long ago (going on looks alone here though). The jeep runs pretty well besides the occasional lifter noise. I'm not sure why my city mileage is so poor, I do live in a very, very hilly city though (think little san fransisco).

The one thing I can think of is that the knock sensor is busted. I broke it while trying to get at the block drain plug while changing the coolant. Since it still runs the same as it did before, I havn't bothered buying a replacement. I didn't notice a decrease in performance or gas mileage since it broke, so I doubt this is the problem.

Any insight, or is this normal mileage for a jeep in a hilly area? I'm really, really happy with the highway numbers but since alot of my driving is in the city (up and down the hill), I'd like to improve it as much as possible.
Click to expand...
 
I'm in a small town, so there isn't much stop and go traffic (5 lights in town, that's all). Problem is, I like at the top of a 12 block hill..so that's where I'm guzzling the gas.

I found I was getting some pinging with 87 octane gas, but with the 89 it seems to have cleared up. I'll replace the knock sensor this winter when I have time and heated shop space, but for now it seems to be holding okay as long as I keep it on the 89 octane.

I had read your posts on eliminating the lifter noise, and Ive tried just about every additive out there, to not much avail. My biggest improvement came after using a can of rislone additive, which seems to have cleaned out the offending lifters a little. The lifter noise went from close to unbearable to alot less frequent. Now, in the colder weather I am finding that the noise is subsiding with every degree the temp. drops. I think next summer I will feed the old beast 10w40 to thicken things up since it seems that the lifter is bleeding out too quickly..I don't think the thing is plugged any more, it's just having a hard time keeping pumped up in the hot summer temps with 10w30.
I have run a quart of ATF through the crankcase just before an oil change as a last ditch effort to clean anything out, to no avail. I *may* pull the head off this winter and replace the lifters, but I doubt I'll do it if the noise keeps decreasing at the rate it is. I also know the timing chain is making some noise, so I may be hearing a combination of the two..that is also getting replaced this winter.

The 26 MPG is an imperial measurement also, so it's not quite as good as it sounds.


Ecomike said:
Driving in the city might be your problem, its like !!!1.

Also driving up hill in stop and go rush hour traffic does little for improving gas mileage.:eek:

The knock sensor retards timing to avoid engine damage if the engine starts to knock. If it is not knocking and pinging with hot engine trips up hill you don't need it.

Not having a knock sensor does not hurt mileage as evidenced by your incredible, invious 26 mpg highway mileage. Wanta trade????

I would recommend sticking to down hill trips on the highway at 4 am and 60 mph when there is no traffic if you want great mileage. Otherwise its time to buy stock in oil companies or get your own oil well.

By the way, I am pretty sure we talked about your lifter noise before, FYI, my 2 year old, loud as hell, first cold start of the day lifter noise is now completely gone. :clap:Between MVO, Lucas, and finally an attempt at slowly switching over to synthetic oil (tried a 50/50 blend, but it sprang too many leaks....long story, back to using dyno oil now) where I ran a 50/50 blend for about 2000 miles, I finally got rid of the lifter noise on mine. I am using 20W50 dyno oil with 1 quart of Lucas now and no more lifter noise.:clap: I also solved the last of my other problems and the engine is running perfectly now, so stick with the additives, and maybe try a quart of mobil 1 synthetic as an additive to loosen up and clean that sticking lifter.

With 26 mpg highway, I would leave well enough alone! Jeeps get lousy mileage in the city and when run under 40 mpg. The TC does not lock up until after about 42 mph, and it does not shift into 4th gear until about 40 to 50 mph, depending on acceleration.

How steep are the hills?
Click to expand...
 
Sounds like you do need the knock sensor. It would allow you to use 87 octane again. I used Rislonene on my first 2 cars in the 1970s. You might also look for causes of the pinging, as I am told it should run 87 octane all day long with out pinging.
 
Ecomike said:
Sounds like you do need the knock sensor. It would allow you to use 87 octane again. I used Rislonene on my first 2 cars in the 1970s. You might also look for causes of the pinging, as I am told it should run 87 octane all day long with out pinging.
Click to expand...

I'm certain that the pinging with 87 was due to the missing or malfunctioning knock sensor..the 89 stops the pinging as a temporary fix but I'll be replacing it soon enough. I have also read of people not running the knock sensor for years with no problems, but I don't really want to take the chance in the long term. Ive put probably only 500km's on the heep since it broke (I drive a company truck 800km's/week..so the jeep gets off easy!). I might stop at the wrecker on my way home and see if I can snag one, since the dealer wanted over $100 for one.
 
You must log in or register to reply here.

Similar threads

O
0331 Strikes Again...?
Replies
11
Views
297
Ol Blue
O
D
Temp Gauge Reads High With New Senosr
Replies
15
Views
1K
TheDXJ
T
U
Any Bad Sounds From This '96?
Replies
0
Views
1K
Undone
U
B
Jeep xj surging
Replies
11
Views
428
Bmfinney
B
O
Rear Brake Noise Question and Hepl Please
Replies
5
Views
369
asymptonic
A
Back
Top