Grand Cherokee 2000 getting Extremely bad millage @ 14.5MPG from 17.5MPG within 1 month.

Don't tell me, let me guess, you buy your auto parts at Cut Rate? YOur hair blonde, too? God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com

likely O2 sensor is starting to fail and causing the engine to run rich.

Do you have kids are are they borrowing your Jeep? :)

Are you using the same gas station, and does your state switch blends between summer and winter.

Thanks, I bought an expensive PDF repair manual for the Jeep. Will look it up..

Thanks again for your input.

Then get the spark plugs your engine calls for. Champions! God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com

O2 is a possibilty. Might check ECTS (engine coolant temp sensor) as it sets base line for mixture. Also my wifes 2000 Cherokee with a 4 banger and a stick runs noticably better, smoother and gets better MPG too in warmer months with 89 or better octane fuel in it.

----------------- TheSnoMan.com

i vote on the O2 sensors as well, i've had prior experience on 2 chrysler vehicles with the O2 sensors with exacttly the same symptoms. poor fuel consumption (in a very short time), black inside the tailpipe and black exhaust under WOT.

on one of these vehicles (where I had the problem w/in the first 20k miles) it wasn't a bad sensor but the wires had been routed too close to the exhaust manifold and burned through.

On your 4,7 these are pretty easy to get to but you need the special socket (I got mine at Napa) to R&R. iirc there are three of these ... one on each side ahead of the quick light-off cats and one more downstream of the single main cat.

to my knowledge there isn't a good way to diagnose them as a component, maybe the scan will tell you if you need to replace all three, my guess is that at least the two upstream sensors should be replaced.

reboot

Yea.. I forgot the clip on the side of the I6 is notorious for pinching and melting the O2 sensor.

As for testing, you can do it with a torch and possibly with the DRB, but there isn't any real good test for a lazy sensor.

while back I connected my scope to the sensor and pulled a few waveforms. ..and all I can find on my compooter is sparkplug waves... :( bah. Wonder where I saved those...

Champions are crappy spark plugs, Bill.

See Wilson, I told you everything Bill says is useless.

In article , wilsonb wrote: #So far have; #Replaced all Sparks with E3 Are they copper core plugs as spec'ed in the service manual?

/herb

The weirdest thing has happened recently. Grand Cherokee 2000 getting Extremely bad millage @ 14.5MPG from 17.5MPG within 1 month. Computer jumps back and fourth with MPG 19.5 then jump down to 13.5 then back up to 14.5.. and it's noticeably guzzling gas like crazy. (Has 1000,000miles) 4.7lt, 2wd, V8 So far have; Replaced all Sparks with E3 Cleaned Air filter Put good gas cleaner in tank a few times now. Use regular gas Have take to Chrysler Dealer and they have no clue. (Will call back tomorrow and ask why they didn't do a full Scan on it when I had a 'full' check done on it.) I checked the exhaust and there is a black grid out of it, maybe gas running to rich? Sensors off? Fuel filter?

Any else have this or ideas?

Thanks so much..