hey all,

2000 xj sport 149,000mi; no lift, stock rim size - bought in june. been getting about 10mpg since then so I changed out o2 sensors, spark plugs, 4-hole fuel injector upgrade, cleaned out throttle body -- runs great but i'm averaging 8mpg now, what gives?

I flashed the pcm after the upgrades and read it takes 50~ cycles for the computer to adjust to your driving patterns. It's been about a month since I did all the upgrades and I've been driving fairly regular. Is there anything else I should check to fix this?

 

 

You need to get an OBD2 scanner so that you can see what your fuel trims are doing. They can be had on amazon for about $20 these days (search BAFX OBD2 Scanner).

It does not take 50 cycles for your fuel trims to adjust. It takes about 30-seconds to 5 minutes. If it is getting 8mpg it is probably not running great. It is probably running very rich, or 1 or more cylinders are not igniting.

Is the check engine light on?

 

fuel injectors are the bosch ones, they were refurbished and looked fairly clean and pretty much brand new. o2 sensors are NTK as well as spark plugs - the regular copper ones. I was originally going to go with champion but I was reading around that 00/01 like NGK better?

I have an OBD reader, I'll check to see what it says when I get home, thanks. What should I be looking for with the fuel trims? no check engine lights, used to have the cylinder 3 misfire but it was the heat soak issue which hasn't been back in a while after the recall fix

 

check pre cat 02 sensors when looking at obdii. it should be oscillating regularly between high and low voltage. do you have an exhaust leak, is your fuel gauge accurate? does your cat look ok? your coolant temp sensor at the thermostat housing may be sending bad information to the computer too, get the obdii and see what the computer is telling you your temps are (normally it will be a different reading than the gauge, between 0-10degrees lower)

 

repaired an exhaust leak a couple of months ago, should be good unless it's gotten bad again. how can I tell if the fuel gauge is accurate and if my o2 sensors are oscillating regularly?

 

I just meant to make sure your fuel gauge is reading properly when you're on empty and calculating your mileage. I'm sure you've done this just throwing it out. should be getting around 19-20 gallons to fill up on empty.

on obdii app you will see a voltage reader for your o2 sensors. I can't imagine new, oem stock ngk sensors are bad though

 

If the O2 sensors are NTK and new and the plugs are straight copper, there's no exhaust leak, etc. I'd most definitely check the coolant temp sensor.

Get the fuel trims, temps and O2 voltage readings and provide all that data. If it isn't obvious to you when you get the data, there are plenty of folks (like Jordan) that are very knowledgeable about what should be reading what under what conditions and can help you decipher it.