getting roughly 10 mpg on my 2001 jeep cherokee 2wd, changed plugs to champions, new coil pack, previous owner says he changed o2 sensors and injectors with multi nozzle injectors,with what i do not know, these are the codes its showing now, i'll check o2 sensor fuse tomorrow as i didnt know there was one until a few minutes ago, heres the codes im getting

po152, po 158, po155, po161,po141, po135, po443, po300, po304,po138 these are the codes its showing now

 

I have no personal experience but have read a few times gas millage and injector replacement being linked.

 

P0135
Means there is a malfunction in the A/F sensor heater circuit of the upstream bank 1 (sensor 1). A lot of times is the PCM has detected a short in the circuit, or excessive resistance in the heater circuit.

P0138
Indicating the downstream O2 sensor for bank 1 (sensor 2) fails to have a lower voltage output below 1.2 volts for more than 10 seconds indicating a lack of oxygen in the exhaust stream.

P0141
Indicating the Engine Control Module (ECM) has tested the O2 sensor heater circuit and detects a problem with the downstream bank 1 (sensor 2) oxygen sensor heater circuit. A lot of times it is the PCM has detected a short in the circuit, or excessive resistance in the heater circuit.

When the P0141 code is active your system spends too long in an open loop

P0152
Indicating that the upstream O2 sensor for bank 2 (sensor 1) fails to have a lower voltage output below 1.2 volts for more than 10 seconds indicating a lack of oxygen in the exhaust stream or a short to power in the sensor circuit.

P0155.
An indication that the heater element of the upstream bank 2 (sensor 1) oxygen sensor is taking longer than the normal to heat up. the ECM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly.


P0158
Appears when the downstream bank 2 (sensor 2) oxygen sensor located behind the catalytic converter has remained at a high voltage for too long. When an engine is running lean, it means that there is more oxygen than fuel in the exhaust gases. When the engine is running rich, it means that there is more fuel than oxygen in the exhaust gases. If the sensor is working properly it switches from low voltage (high levels of oxygen) to a high voltage (low levels of oxygen).

P0161
Sets when the Powertrain Computer or PCM has determined the downstream bank 2 (sensor 2) Oxygen Sensor Heating Circuit is malfunctioning. This means that the Heating Circuit is using too little or too much electrical power

P0300
Means that the the car's computer has detected that not all of the engine's cylinders are firing properly. This code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring.

P0304
Is defined as a Misfire Detected in #4 Cylinder. ... If it varies beyond 2 percent, the Monitor will set a P0304 code and illuminate the Check Engine Light.

P0443
That the engine control module (ECM) has detected a malfunction with the purge control valve or its control circuit. This could mean an open or short in the valve or circuit.

 

i have the original fuel injectors the original owner gave me, i dont know what kind of shape their in, the story is they are single nozzle and he swapped out for a multi nozzle injectors for better mileage, (shouldve ran away right then)

 

also showed 04>>, >>>>, >>>> what do these mean? also previous owner changed o2 sensors said he had to rewire? i believe he used some generic cheapies, is there a test for the purge control valve? i know nothing about automotive repair any help is appreciated,

 

Ugh... not good news.

With the multiple O2 sensor codes and this statement about "rewiring", what I would do is assume the P.O. completely screwed the pooch.
I would buy 4 brand new NTK O2 sensors. (The 01 always has 4 - the 00 had 2 for federal emissions, 4 for CA emissions) BRAND IS IMPORTANT! The XJ is hyper sensitive to the improper O2 sensors and NTK is the O.E. manufacturer. You should be able to find NTK sensors on Rockauto.com or at your local parts retailer for the same price as other well known brands.

Next I would grab a copy of the 01FSM and get VERY familiar with the wiring diagrams for the O2 sensors. Find as many pictures, videos, etc. online as possible and figure out exactly what's going on with the wiring. You want to know exactly where the O.P. spliced the wires so you have the original colors and then trace each one and make sure it's going to the correct place, that the wire gauge is the same as the original and that the connections are making proper contact.

I would bet that once you straighten all that out, the codes will disappear and you'll be getting a solid 20-ish combined mpg (due to your 2wd instead of 4wd).

Edit - I think the new injectors are a total red herring. Your problem is the "rewired" O2 sensor wiring and (likely) off-brand components. I think even the purge valve stuff may go away once the O2 sensors are running correctly. If not, at least you've eliminated the bulk of the issue and can then focus on anything else.

 

i found a blown fuse for the 02 changed it rest codes, rode around for about 60 miles and no light, hopefully that was it

 

NTK sensors on Rock Auto are pretty cheap. They'll also have the proper connector on them.

 

Good deal the "rewire" job probably has a bad part in it.

 

I am very happy for you to hear about this!

The only thing it sounds you need to worry about now is WHY did this fuse blow? I am certain that fuse did not blow for no good reason (double negatives used)... This problem is going to come back if the real reason and primary fault goes unidentified, and does not get fixed.

'Re-wired' oxygen sensors? What was this all about? I wonder.. someone did not know what they were doing when they put their mechanics hands on this Jeep.

If you know someone who can help you out who is also good with vehicles and electronics? I say get ahold of them next, and have them try to help you with the wiring problems your Jeep has right now. Oxygen sensors and all of the many different parts of their circuitry is not an easy task to go trying to handle all on your own, if you are not familiar with these things.

If you study the oxygen sensor circuits and you want to attempt and try fixing up the messed up wiring yourself.. and you need help in any way? Please let me know via messaging!

 

The whole system - The fueling, air, and everything about the PCMs memory; Everything will now have to begin resetting itself back to normal. Do not expect an immediate increase of mpg or anything, until after at least 200+ miles goes by (one full tank of gas)...

There may be some small engine perfomance running conditions to occur while the system goes about resetting itself. It should not be anything major.. but, it is normal and is a common thing to have happen after something like this goes on like it did with your Jeep.

 

Super glad to hear it was (hopefully) just a blown fuse.

It's a reminder that as silly as it seems, it's always best to check all your basics before assuming a larger problem.

I would still suggest that you at least double check the "rewiring" of the O2 sensors and ensure that the sensors themselves are NTK brand. They may not throw a code if they are not, but if you're interested in the maximum possible fuel economy (which is basically still 1/2 the mpg of a Corolla ) then you'll want the NTK. Cruiser54 (one of the top guys on here - tens of thousands of posts, over a decade running a Jeep dealership service dept) specifically recommends the NTK and considering his authority on the subject and experience, it's always wise to listen to his advice.

 

i found a blown 02 fuse changed it out, cleared the codes spent the day riding around, 105 miles and no CEL 60 miles on the 1st tank of gas got 11.3mpg, 45 miles on a fresh tank and just guestimating about 2.5 gals so im thinking roughly 18 mpg on highway running 70 to 75 mph, isnt that still pretty low mpg?

 

the sensors should be branded with the brand name?

 

They're usually printed on the part. The NTK sensors seem to have a look that's distinct (they're a little narrower bodied). Hit Rockauto.com and see the pictures.

As far as mileage, 18mpg on the highway is generally pretty "normal" for a properly running XJ.
The optimal mileage XJ is a 2wd Manual transmission. When driven extremely economically (like a grandma, smooth easy acceleration, zero unnecessary idling, strict adherence to the speed limit -- meaning 65mph on the highway), these XJ's can get a combined mpg in the low twenties (like 20/25).
With a 2wd and an automatic, when driven extremely economically, I'd expect like 17/22.
I have a manual XJ, but it has 4wd, so I have achieved 20mpg combined. This is not typical, just my "best" mpg - at this time of year in New England I do a lot of excess idling, so I'm getting like 14-16 combined.
Bear in mind this is all assuming a completely "stock" XJ running perfectly.

The biggest factor in MPG is the component behind the steering wheel. If you're driving aggressively you're going to take a hit on MPG. You mentioned doing 70-75 on the highway, this is not "lead foot" level, but it's certainly more aggressive than the "grandma" level I'm referring to.

Also bear in mind what the other posters have mentioned about the computer adjustments. You have to get a good couple hundred miles of driving data for the computer to adjust the ignition to the optimum performance.

Fuel quality is a factor to. The quality of the fuel actually varies depending on the time of year and wintertime fuel is generally "crappier" than summer blends. Then there's the ethanol content - higher ethanol means lower performance in the simple tractor engine used in our XJ's.

If you want a pretty accurate MPG rating without fancy analysis equipment, I'd wait until you've driven another 100 miles or so, then fill the tank with a reputable brand fuel (Exxon/Mobil, Shell) from a quality station. Reset your trip-ometer to zero. Drive as smoothly and as un-aggressive as you possibly can with a 50/50 mix of highway driving and "city" driving. After a couple hundred miles of driving, fill the tank again from the same station (same pump even) and do the math. If you get 20 or above, you're in good shape and unless it's under 18, I'd say there's nothing to worry about.
That's the way I do it if I'm trying to get a rough idea of my MPG. Basically you're trying to control as many variables as you can easily control and is a good enough approximation for comparison.