PDA

View Full Version : 96 XJ troubles hot starting


96_z71
05-01-2012, 04:10 PM
Brothers 96 cherokee 4.0 is having troubles hot starting sometimes as well as check engine light and even shittier than usual gas mileage. Have to give it gas to get it started and keep it running for about a minute then it sorts itself out (when hot). Smells like its running really rich. Scanner says code for secondary o2 sensor, which I thought was only there to detect if the cat's working, not altering fuel trim. Recently did a tune up, as well as primary o2 sensor and cleaned all the throttle body sensors. Any ideas?

yoda604
05-02-2012, 10:52 AM
secondary o2 sensor reads the lean/rich in your fuel and tells the computer to make the adjustments. Start there. is it backfiring as well? what kind of code reader? can it give you any readouts, or just codes?

96_z71
05-02-2012, 12:23 PM
I thought that was the primary o2 job and secondary just senses if the cat is functioning. Just able to read codes haven't datastreamed it yet

Chopstick
05-02-2012, 01:52 PM
Doesn't sound like a huge problem. Did u replace the secondary o2 sensor or just the first one? In my obd1 (I know yours is an obd11) when my u2 sensor breaks or fails that's how my truck runs and you'll notice the lack of fuel mileage completely. If the only codes that your getting is the o2 then replace it.

I hate typing that much on an iPhone. How's your plugs, leads, cap an rotor? Fuel rail isn't leaking?

yoda604
05-02-2012, 02:03 PM
I thought that was the primary o2 job and secondary just senses if the cat is functioning. Just able to read codes haven't datastreamed it yet

nope they both do the same job, and feed back to the computer. So if one is new and the other is all old, they're both going to be feeding back to the comp with different readings and fighting for the adjustment. that's probably why when it's warm it sorts itself out. Also check your vacuum lines and MAP sensor. The MAP sensor can fail and throw no codes.

96_z71
05-03-2012, 03:19 PM
nope they both do the same job, and feed back to the computer. So if one is new and the other is all old, they're both going to be feeding back to the comp with different readings and fighting for the adjustment. that's probably why when it's warm it sorts itself out. Also check your vacuum lines and MAP sensor. The MAP sensor can fail and throw no codes.

Good to know, thanks. Gonna change out the o2 tomorrow and see what happens, failing that I'll clean out the map sensor...again.

WagoneerXJ
05-04-2012, 09:42 PM
My gf's 97 TJ would do this once in a while. Not Always when it was hot though. Turned out to be a bad cell in the battery, was screwing with the computer.

96_z71
05-04-2012, 09:49 PM
Threw a new post cat o2 in er today, no more check engine light, got it good and hot, tried a few hot starts and it started mint.

96_z71
05-04-2012, 09:50 PM
My gf's 97 TJ would do this once in a while. Not Always when it was hot though. Turned out to be a bad cell in the battery, was screwing with the computer.

Never thought about the battery. Does look pretty old so it wouldn't hurt to throw a new one in as well.