Willfulone

99 Cherokee Sport

All of a sudden I am getting really bad gas milage.

I was getting 14-16 when I got it

When I lifted it and put in 31s I was getting 11-12

Now all of a sudden I am getting 5-6

The only thing I've done in the last month is put in a new Alternator


Any ideas???

Tks
Will

Gee oh Dee

When was the last tune up? Plugs, wires, cap and rotor if you have them.

Check for codes, just cuz there isnt a CEL doesn't mean it doesnt have codes stored. Could be bad o2 sensor.

Air filter, too.

Extreme cases injector stuck open or bad regulator.

Willfulone

Tks,

I have new injectors - I'll do the 02s while I'm at it

Will

salad

Any codes? No way it's running that rich and not throwing a Check Engine Light.

Unless your tires are mundo flat.

CCKen

Other than bad mileage, how does it run?

Stumble/hesitation at cold drive-away until it heats up?

Does the TC lock up?

Any other symptoms?

Some DTC's are not active and trigger a CEL and will remain stored in the PCM memory. You'll need to use a code reader or scanner to access any stored (pending) codes.

Not all engine systems activities are monitored by the PCM, fuel pressure for example, and won't trip a DTC.

Willfulone

Seems to run fine.

Only way I noticed anything is that I was like, "where did all my gas go"

Then I filled it and started keeping track...

No check engine light.

Have not checked the codes yet

Will

RTorrez1

Like CCKen said "Some DTC's are not active and trigger a CEL and will remain stored in the PCM memory. You'll need to use a code reader or scanner to access any stored (pending) codes." So you should run it over to any parts store and have it checked for any stored codes. It much better to do that before you start throwing money at it. At least that my give you a direction to go. The best thing is they will read the codes for free.

jbsjunk

Do you have a locking gas cap? Someone might see it as an easy target to gas up their Honda.

BlueRidgeMark

How are you measuring your gas mileage? I'm asking because many people think they can "measure" gas mileage by the "I filled it up and used a half tank" method, or other bogus methods.

Any method that uses any information from the gas gauge is worse than worthless. It will lie to you.

The only method that means anything is to track the gallons pumped at each fill by what the gas pump says, and the miles driven by the odometer, and do the math.

If you have non-standard tires, you must do the math to correct the odometer reading.

If you are using any other method, like, "I know how far it is to work and the store and I did it X number of times.", or if you are using the gas gauge as part of your "calculating", you really have no idea what your gas mileage is. You just think you do.

You are fooling yourself and wasting a lot of time and effort chasing problems that may not be a problem at all.

If you are measuring your gas mileage correctly (there's only one way), and you see a sudden change, then you have some troubleshooting to do. A component has failed or gone out of spec. Sudden changes are almost always the result of sudden changes.

Willfulone

I did the math. Miles driven / gallons used.

I did not adjust for the tires, but before this happened I was getting 11-12 MPG
none adjusted.

Then it went to 6

Changed the 02's this weekend

I have 784 injectors sitting on the self for this weekend.

Will

XJ Hero

Did you do a tune up on it urself? Was mentioned before...plugs, cap, rotor, wires. I had a bad cap n rotor on my 99 and my mileage did the same thing. New parts and it did better on gas and ran better. O2s should help u too...mostly upstream though.

F1Addict

The larger tire size accounts for the drop from 14-16 to 11-12 MPG. It's a minor decrease in economy but more because of odometer error due to the larger circumference of the 31" tires.

Besides the other suggestions, I would recommend jacking up each end and spinning the tires to make sure you don't have a caliper or drum dragging.

Willfulone

Fuel injectors going in tomorrow morning

Did plugs and wires 6 months ago

Have not done cap and rotor - never done it before.
Is there a how to some where you could link

Tks
Will

BlueRidgeMark

Cap & rotor? No sweat. They are brain-dead easy to change. You probably don't need a how-to if you're at all handy. One tip - put the new cap next to the old one, and swap the plug wires over one at a time, so you don't get the order mixed up. Get the wires swapped and you'll be pulling your hair out.

So you've got a 50% reduction in gas mileage? Basically overnight? That's got to be a pretty significant component failure somewhere, so you should be able to find it with some systematic troubleshooting. It's not going to be something subtle.

Checking for a dragging wheel is free, so it's not a bad idea. Kind of doubt you'd lose that much gas mileage and not notice something really hot, though.

Demonoid369

Cap,rotor,wires, spark plugs, speedo gear, O2 sensors, catalytic converter, pick up coil, fuel injectors, thermastat, etc... All has been talked about plenty, just search! The fact that you haven't told us what all has been replaced or not isn't going to help us help you. You need to search