• 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.

2001 lost 50% MPG

D

dbMqt49855

NAXJA Forum User
Location
Marquette
Hello,

My 2001 Jeep Cherokee Sport 4WD 4dr SUV (4.0L 6cyl 5M) has lost 50% of it's fuel mileage. I changed my radiator out 2 months ago and the problem seems to have started around then. I am only getting 8-9 MPG and the local dealer has no idea what's going on.

I have heard to try replacing the o2 sensor, pouring seafoam into the tank, etc. I hate to chase the issue without any results.

Any ideas or suggestions?

Thanks!
 
is it related to the radiator? does the jeep achieve the same operating temp as before the radiator swap?
when was the last tune up? (spark plugs, air filter, etc)
clean the throttle body
if the O2 has never been changed, then it is worth the 60$ to do so.

also, when did this start, just recently (last couple of weeks) or in say, october or november, when winter blend was put into the gas


finally, a good fuel system cleaner like lucas, or seafoam would be a good idea.


check for vacuum leaks too
 
Not to mention that a clogged catalytic converter (or converters, depending on whether you have a California- or Federal-emissions XJ) will kill fuel economy. Same goes for a cracked exhaust manifold.

What steps have been taken to troubleshoot this so far?
 
I may be wrong, but I think all 2001's have the CA-emissions style pre cats.

I would check
-For sticky brakes, bearings, driveshafts(Jack it up and check for dragging)
-Remove the fan belt and see if you have a bad component (a ruined a/c compressor will create a ton of drag)

Change-
Both upstream 02 sensors
Spark plugs. (You MUST use the double platinum style plugs, the kind with platinum on both the electrode and ground, because the 01 uses a waste spark style ignition, it wears out copper plugs.)
Run a good fuel cleaner.

My lifted, heavily armored 2001 xj on 32's and 4.56's gets 18 freeway.
 
Be sure that you are "calculating" your actual gas mileage. Gotta do the math.

Miles driven divided by gallons consumed. Extrapolating your mileage by how many miles you get per tank is not very accurate.

And get at least 3 samples before coming to any conclusions.

Fresh NGK plugs for your vintage are a good start to optimizing engine efficiency.

And as mentioned, anyone that owns an 00-01 needs to keep an eagle eye on their coolant reservoir. The #1 symptom of a cracked 0331 head is unexplained coolant loss.
 
10% ethanol can be responsible for around 5% hit on gas mileage, give or take a bit. Cold weather can contribute possibly another 5% depending on how it is driven.

I'm not a big ethanol fan, but it is here to stay to fulfill the oxygenated fuel requirement. I have seen people exaggerate the affects of it, but the studies (independent) that I've seen and there are more than a few, all seem to range around the 4-7% range for a gas mileage hit. I think it is important to let the numbers do the talking here. On these studies, it did depend a bit on the vehicle, as some are more sensitive to the 10% blend than others.

But adding 10% ethanol to cold weather, and your mileage is going DOWN! That much we know for sure!
 
Last edited:
Why did you change the radiator? Did the engine overheat? If so, did you change out the thermostat? Do you have access to an obd2 scanner that'll tell you the engine coolant temp and fuel trims?
 
XJensen said:
Change all four, upstream and down if you got them. They are all used to calculate the fuel to air mixture. One dead one will screw everything up.

Josh
Click to expand...

Don't bother changing the downstream O2 sensors and they DON"T affect the calculation of the fuel mix. They're just there to check the condition of the cat converters.
 
Interesting, but obviously would not be the first time the FSM is wrong. The oxygen content after the cat is highly dependent on the condition of the cat. It's technically not possible to determine if the engine is running lean or rich based on sniffing for oxygen after the cat. Otherwise, all those people who installed downstream O2 sensor simulators after they got rid of the cat would not be running correctly.
 
toates89 said:
maybe your comp is running in cold mode all the time that would kill mpgs
Click to expand...
I was thinking this... did you touch the wiring to the CTS in the thermostat housing while you were swapping the radiator?
 
i would also look at the CTS as the culprit
 
lawsoncl said:
Interesting, but obviously would not be the first time the FSM is wrong. The oxygen content after the cat is highly dependent on the condition of the cat. It's technically not possible to determine if the engine is running lean or rich based on sniffing for oxygen after the cat. Otherwise, all those people who installed downstream O2 sensor simulators after they got rid of the cat would not be running correctly.
Click to expand...

Seems like they went way out of their way to describe the sensor operation differently in the 01 XJ FSM, to get it so wrong.


I will make a call to my brother who worked at Chrysler for all of his adult life to see if he can confirm or dispute the FSM with his engineering coworkers. Will let you know what I find out.

I'm betting that anybody with an 01 XJ, 4 sensor setup who has removed their pre cats, and is using sensor simulators to fake out the PCM, probably ISN'T running correctly.
 
You must log in or register to reply here.

Similar threads

B
2001 XJ dies at highway speed
2
Replies
20
Views
2K
N8N_99xj
N
M
P0432 Code - 2001 XJ 4.0L – Auto – AW4/NP231 – 259K miles
Replies
0
Views
1K
Misternapps
M
Saudade
"Stealth" Vacuum Leak
Replies
1
Views
1K
cruiser54
C
X
XR3Z's vs 19 XF2E's (2001 XJ) and so much more
Replies
5
Views
2K
xcm
xcm
S
Cherokee XJ RENIX 1990 - low power, bad mpg, problem with ignition and timing
3 4 5
Replies
92
Views
10K
szachmat
S
Back
Top