Downstream O2 sensor needed?

Hey, I have a little problem with my 96' cherokee. have had it since day one.

Heres the symptom: Hard start/long crank when hot,sometimes hard to keep running.

Ok, so now to get specific.
-Jeep will start right up in the morning or after sitting for 4+ hours.
-If i stop at a gas station, turn the jeep off, come back out and try and start it, it acts like its flooded and long crank.
-When it finally does start it wont stay idleing, i have to double foot it untill I get on the road again.
-If I jab the throttle it acts like it wants to die(dont know if thats related)
-It did this before i took the Cat and o2 sensor off.
-Jeep does have a rod knock.


My Thoughts:
Im thinking that one or more injectors are stuck open causing the flooding situation. i also noticed that the oil smells like gas and is very thin, which makes my think that the gas is washing down the cylinder walls and getting in the oil(which is why it will start after sitting for a while.)

But could it be that i messed up by taking the o2 sensor off and the computer is just dumping in too much gas? :dunno:

Things I've checked:
-Battery
-Alternator
-All filters
-No codes in computer


Hopefully someone out there has had the same problem, or knows how to fix it.

Thanks alot,
-Nick

Re: CAT & O2 sensor needed?

blacklabel000 said:

Heres the symptom:
-Hard start/long crank when hot,sometimes hard to keep running.
-When it finally does start it wont stay idleing, i have to double foot it untill I get on the road again.
-If I jab the throttle it acts like it wants to die(dont know if thats related)

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The Cat are O2 sensor are required if you want it to run right. What are your gas MPG's ?

The symptoms you describe point to a bad battery, a loose connection, or a corroded wire.

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) or when the battery goes bad and needs replacing.

Your symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal.

The ECU will relearn the idle settings after a short period of driving and the engine will start and idle normally. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem. Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body.

If the symptoms reoccur, you need to have your battery load tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC) and using fuel injector cleaner should be part of your routine preventative maintenance.

Re: CAT & O2 sensor needed?

blacklabel000 said:

My Thoughts:
Im thinking that one or more injectors are stuck open causing the flooding situation. i also noticed that the oil smells like gas and is very thin, which makes my think that the gas is washing down the cylinder walls and getting in the oil(which is why it will start after sitting for a while.)
sounds VERY likely- gas in oil is classic symptom as is a failed converter



But could it be that i messed up by taking the o2 sensor off and the computer is just dumping in too much gas?
since you say it was doing it before you removed them, doubtful
:dunno:


Thanks alot,
-Nick

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Were it mine, I'd pick up a fuel pressure gauge and verify it's rapidly losing fuel pressure on shut down. You can pull the rail and look for drips or you can pinch the return line to eliminate other locations for bleed down.

Re: CAT & O2 sensor needed?

Tim: i like the suggestion about the IAC, ill take care of that along with the throttle body tonight.

What you are saying about the battery would only make sence if the jeep would do it every time (hot or cold) i started it. and thats not the case, it only acts up when hot.

Same with fuel pressure.....

Gas mileage is horrible, dont know exactly what it is, but i cant expect it too be great with a jeep on 35s....


-Nick

Re: CAT & O2 sensor needed?

First things first you need an o2 sensor. And I don't see how it is possible you are running around without an o2 sensor and it isn't throwing a code. Without an o2 sensor it is going to run hella rich.

Re: CAT & O2 sensor needed?

blacklabel000 said:

Tim: i like the suggestion about the IAC, ill take care of that along with the throttle body tonight.

What you are saying about the battery would only make sence if the jeep would do it every time (hot or cold) i started it. and thats not the case, it only acts up when hot.

Same with fuel pressure.....fuel can cause an over-rich condition when it leak and slowly leak past the rings (diluting the oil) until the fuel is no longer in the cylinder enriching the mixture (as would be the case if it sat 'til cold)

Gas mileage is horrible, dont know exactly what it is, but i cant expect it too be great with a jeep on 35s....


-Nick

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blubullett said:

First things first you need an o2 sensor. And I don't see how it is possible you are running around without an o2 sensor and it isn't throwing a code. Without an o2 sensor it is going to run hella rich.

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assuming the downstream O2 sensor was removed, there would be no change in mixture, but I would expect to see a "catalyst below threshold" or "O2 sensor circuit" code

Re: CAT & O2 sensor needed?

Have you checked the fuel filter?? Sounds more like it's starving for fuel rather than getting too much!

Re: CAT & O2 sensor needed?

yes i replaced it the other night, along with the air filter, oil change, cleaned TB and IAC sensor.(wow did that make a difference!)

there are still no codes in the computer though?

Re: CAT & O2 sensor needed?

If you don't have a code or check engine light with a removed O2 sensor, it could be that the ECM itself is bad. If the computer cannot detect a fault, it will not throw a code.

Re: CAT & O2 sensor needed?

Does your check engine light come on when you turn the key from off to on without starting it? If it doesn't then someone removed the bulb and you won't know when you have a problem.

Re: CAT & O2 sensor needed?

blubullet-yes it does, there were no codes stored when i hooked a scanner up to it.

keeponjeepin-from what ive understood, when an ECM goes bad, everything starts messing up. isnt it all or nothing?

if im wrong let me know.
thanks,
-Nick

Re: CAT & O2 sensor needed?

blacklabel000 said:

blubullet-yes it does, there were no codes stored when i hooked a scanner up to it.

keeponjeepin-from what ive understood, when an ECM goes bad, everything starts messing up. isnt it all or nothing?

if im wrong let me know.
thanks,
-Nick

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From what I've been told that's not always true. But, I may have been misinformed.

Re: CAT & O2 sensor needed?

Depends on what goes bad.

I'd put a cat back in it and toss a new o2 sensor on it, it can't really hurt.

Another thing to check - might need a new upstream sensor. What I would do is buy a new sensor, install it in the upstream opening on the downpipe, take the old sensor and install it downstream after the new cat. The downstream is not as important as the upstream, which tells the engine computer whether it's running rich or lean and by how much.

Before spending any money on parts though, you should check the battery voltage, as well as the voltage from the frame/body to the negative battery terminal (should be very close to 0), and the fuel pressure.

Re: CAT & O2 sensor needed?

i appreciate all the info you guys are giving me here very much.

thats a good call with swapping the sensors, hopefully the upstream hasnt rustwelded itself on there like every other one out there.

Bat voltage has been checked its at a good 11.46 when jeep is off. and 13.5 when running. No parasitic drain anywhere either.

If your oil is saturated with fuel you need to fix that first.

Injectors, synch sensor in the distributor, fuel pressure, MAP, MAT, PCM, o2 sensor, exhaust leak upstream of the o2 sensor--those are the things that need to be checked for flooding like you are describing.

Note that you could have more than one issue at work here.

Rather then start a new thread I figured I would ask here.

'96 4.0 aw4 np231

The CEL came on and gave me, Bank 1 Sensor 2, as the fault. I gather that sensor 2 is the cat o2? XJ was sluggish and did not respond to throttle input. Thinking clogged cat and/or bad o2?

I ordered a new Cat and o2. Just want to make sure Im on the right path. Thanks

RadioShackSpecial said:

Rather then start a new thread I figured I would ask here.

'96 4.0 aw4 np231

The CEL came on and gave me, Bank 1 Sensor 2, as the fault. I gather that sensor 2 is the cat o2? XJ was sluggish and did not respond to throttle input. Thinking clogged cat and/or bad o2?

I ordered a new Cat and o2. Just want to make sure Im on the right path. Thanks

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Sounds good to me as far as being on the right track. Did it give specifics about the sensor, like voltage too high? No input? etc etc?

P0138, I think was the code. Im guessing but have a picture at home so I will have to check.

The Code Scanner said somethig about heated wire. Does that make sense?

RadioShackSpecial said:

P0138, I think was the code. Im guessing but have a picture at home so I will have to check.

The Code Scanner said somethig about heated wire. Does that make sense?

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Yes, but in that case, check the fuse!

Will do, I know its under the hood but any specifics as to which one? Other then look for the blown fuse, lol.