Surge, engine light flashing

[TruckerKevin]

07 Liberty, 154,000 miles. I am the new owner, just bought it.

After a week of owning it, the check engine light came on. Took to Oreillys and it showed the O2 sensor 2nd bank? was the culprit. They offered me a Bosch, after reading here that Jeeps don't like Bosch I passed, and never replaced it. The engine light came on once more, then went off for a few days. But my Jeep always ran good. Frankly, I forgot about it.

Today I noticed a surge. About mid range throttle. At first I thought the transmission wasn't shifting, then realized it was the motor. Giving it gas it was fine, but cruising at 1500 rpm it "cuts" and surges. And it got constant.

Then when I stopped and at idle, it began running somewhat rough and the check engine light came on then started flashing. I pulled over, took the battery cable off to clear it and the light went away but it still surges (but idles fine now?)

I am just posting this as I am a new Liberty owner and was hoping someone knew something in particular that these cars suffer from before I go part swapping. Would a bad 02 sensor probably be the culprit?

I have not had the codes read since that first time but the engine light is now "off"

 

[GunnerSchenck]

Not 100%, but here's my $0.02.

Doesn't need to be a jeep specific issue to be going bad.. sounds to me like your o2 sensor is bad and telling your pcm to cut back on fuel and causing a lean condition where you're not getting enough fuel delivery..
If it's running rich, it may still cause a bogging issue, but would likely start to clog up your cats with unburnt fuel.
Your o2 sensor is much cheaper than the cats are..so I'd hop on it before other issues arise.
The wiring to the 02 sensor on that bank runs under the engine and the loom around it cracks, becomes brittle, deteriorates and falls off.. might wanna look at the wiring to the o2 sensor while you're at it since your problem seems to be intermittent.

P.s. of course, a Mopar part would be the best fix.

But I could be wrong, and will await somebody else to chime in..

 

[renegade 04]

It could still be a bad o2 sensor, but i think the surging is a bad throttle position sensor.

 

[Phil + Neela]

I had this same problem. Your "downstream" O2 sensors are bad and need replacing. They are an integral part of the fuel/air ratio management feedback loop. Without good feedback from the sensor, the computer defaults into a rich mixture. This mixture will work at low RPMs but you will lack speed and power while destroying your catalytic converters.
Replace your O2 sensors that are on the far side of the catalytic converter and you'll be all set.


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[tjkj2002]

I had this same problem. Your "downstream" O2 sensors are bad and need replacing. They are an integral part of the fuel/air ratio management feedback loop. Without good feedback from the sensor, the computer defaults into a rich mixture. This mixture will work at low RPMs but you will lack speed and power while destroying your catalytic converters.
Replace your O2 sensors that are on the far side of the catalytic converter and you'll be all set.


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Actually the "down stream" O2 sensors have zero effect of fuel/air mixture.There sole purpose in life is to monitor the catalyst efficiency. The "upstream" O2's are the ones that tell the PCM to increase/decrease the injector pulse width.

Oh and that "default" cold start up fuel/air map will not damage the cat's in anyway on a well maintained vehicle,also the performance is barely effected.You just spend a little more $$$ on gas and produce a little more pollution and why we have heated O2 sensors so they start working faster to fine tune the fuel/air mixture.

 

[Phil + Neela]

Actually the "down stream" O2 sensors have zero effect of fuel/air mixture.There sole purpose in life is to monitor the catalyst efficiency. The "upstream" O2's are the ones that tell the PCM to increase/decrease the injector pulse width.



Oh and that "default" cold start up fuel/air map will not damage the cat's in anyway on a well maintained vehicle,also the performance is barely effected.You just spend a little more $$$ on gas and produce a little more pollution and why we have heated O2 sensors so they start working faster to fine tune the fuel/air mixture.

...everything you say makes perfect sense.

My only counter example is that I had the aforementioned symptoms which were corrected by replacing the downstream O2 sensors.

So now I'm a bit confused.


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[TruckerKevin]

Thanks for all the replies.

I think what I am going to do tomorrow is replace both o2 sensors anyway out of maintenance. They have probably never been replaced. And inspect the wires.

I also so happen to have a junk 3.7 that came out of another liberty with a rod knock. I can pirate the tps sensor from that and see what happens.

I have really been fearing a bad valve. From all the google searches thus far I see that these 3.7 motors had a valve design failure that has also caused similar symptoms. I sure hope not!

 

[JasonJ]

Whoa whoa whoa... everybody hold on a second.

First of all, other than a half mention of a bank 2 O2, no one here can possibly know what part is causing this. HE HAS NOT PULLED THE DTC'S YET!

Sure, it could be the Bank 2 sensor 1 O2, except that the OP hasn't said that the original O2 fault was for an upstream O2, could be a downstream O2, and as tj said, those do not play a significant role in adjusting the fuel mix. They are for emissions monitoring of the catalytic converter efficiency... there's even a code for it, P0420 Catalytic Converter Efficiency below Threshold.

So guessing is fine, but it's just that. Kevin, before you go throwing parts at this thing, or extra O2 sensors and TPS's that you may not need, please pull the trouble codes and verify the fault before anything.

Once you know the exact DTC, you can diagnose this more accurately and save yourself some money, but more importantly save effort and time. You may find that there are new, different, or more DTC's stored than the one originally O'Reilly's reported.

 

[GunnerSchenck]

After a week of owning it, the check engine light came on. Took to Oreillys and it showed the O2 sensor 2nd bank? was the culprit.

I agree that he should check the codes as well before buying any parts, even stop at AZ and have it done for free. But he also stated he'll be taking the TPS off a donor engine, so won't be losing money there either.

 

[TruckerKevin]

OK I will tomorrow. The original code was bank 2 o2 sensor. And now I think of it, the donor engine is out of an 03, mine is an 07 so I bet the tps is different. Ill post the codes tomorrow.

 

[sota]

Actually the "down stream" O2 sensors have zero effect of fuel/air mixture.There sole purpose in life is to monitor the catalyst efficiency. The "upstream" O2's are the ones that tell the PCM to increase/decrease the injector pulse width.

Oh and that "default" cold start up fuel/air map will not damage the cat's in anyway on a well maintained vehicle,also the performance is barely effected.You just spend a little more $$$ on gas and produce a little more pollution and why we have heated O2 sensors so they start working faster to fine tune the fuel/air mixture.

I'm going to disagree with you on the first part.
I had what turned out to be damaged wiring to the downstream O2 sensor and it most definitely caused problems with engine management. AFRs would go bonkers past a certain point of throttle application because of faulty data being sent by that sensor. I didn't want to believe it myself because as you said the downstream *should* only be used to monitor the catalyst, but the fact that immediately after replacing the damaged part and NOT clearing the computer first, the vehicle ran perfectly.

 

[TruckerKevin]

I did a little more reading and came across this interesting tidbit of information. Wether it is correct or not I do not know, but it makes a lot of sense to me. (Also I am a truck driver and I am out on the road today so I can't do anything pertaining to my jeep until I get home tomorrow. But I do appreciate the folks that are helping me try to figure this irritating problem out!

snip/if your downstream sensor is "toast" you may want to look into the catalic converter because if it is clogged or the honeycomb inside is damaged it can restrict airflow to the second (downstream) oxygen sensor and confuse the computer making it throw a code/check engine light. the upstream sensor should be the first to go in a normal situation because the converters main job is to convert carbon dioxide into h2o to lower emissions. therefor the upstream sensor is constantly surrounded by dirty air making it work more. this is normal and should be the first of the two to go. typically when that one goes bad change them both. if the downstream is "bad" well it probably really isnt bad but the catalic converter that is bad./snip

 

[turblediesel]

Apples and oranges but my Ford acted the same as your Jeep until I put a new oxygen sensor on it.

 

[JasonJ]

I did a little more reading and came across this interesting tidbit of information. Wether it is correct or not I do not know, but it makes a lot of sense to me. (Also I am a truck driver and I am out on the road today so I can't do anything pertaining to my jeep until I get home tomorrow. But I do appreciate the folks that are helping me try to figure this irritating problem out!

snip/if your downstream sensor is "toast" you may want to look into the catalic converter because if it is clogged or the honeycomb inside is damaged it can restrict airflow to the second (downstream) oxygen sensor and confuse the computer making it throw a code/check engine light. the upstream sensor should be the first to go in a normal situation because the converters main job is to convert carbon dioxide into h2o to lower emissions. therefor the upstream sensor is constantly surrounded by dirty air making it work more. this is normal and should be the first of the two to go. typically when that one goes bad change them both. if the downstream is "bad" well it probably really isnt bad but the catalic converter that is bad./snip

Eh.... A lot of assumptions in that statement, wherever you got it from. Firstly O2 sensors "dont work hard"... the read the amount of residual Oxygen in the exhaust gases and convert this into a voltage of a pre-specified range and report it to the PCM. Dirty exhaust air may physically clog and cover the sensor ports in the O2 sensor... but it won't make it "work harder". It's a chemical compound in the gases converted to an electrical signal kind of reaction, there is no actual "work" being done. It isn't making an effort to do anything.

That being said, yes, a faulty converter can cause the downstream O2 to report erroneously. However I'd rather replace a $40-$80 O2 sensor any day than an $800 catalytic converter without more evidence of failure. That is NOT the part you want to just toss at the car to see if it fixes it.

I'd say that you need to know the exact DTC before doing anything else. If the fault code says Bank 2 sensor 2 voltage out of range, or no output, or states that the heater circuit is malfunctioning, then it's likely an O2 issue.. if it is reporting that catalyst efficiency is below threshold, then it MIGHT be the converter.. but it could be a faulty O2 sending the voltage reading that indicates a bad converter when it's really not.

Once you know the DTC, there are specific tests that can be done to determine which is the more likely scenario.

 

[LibertyTC]

BTW- What brand of o2 sensors should be purchased?
57960[/ATTACH]"]

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Jeep will likes these! :gr_grin:

 

[TruckerKevin]

What you said JasonJl makes a lot of sense. Please hold that thought, I will be back tomorrow with my findings!!!

 

[tjkj2002]

I'm going to disagree with you on the first part.
I had what turned out to be damaged wiring to the downstream O2 sensor and it most definitely caused problems with engine management. AFRs would go bonkers past a certain point of throttle application because of faulty data being sent by that sensor. I didn't want to believe it myself because as you said the downstream *should* only be used to monitor the catalyst, but the fact that immediately after replacing the damaged part and NOT clearing the computer first, the vehicle ran perfectly.

A bad downstream O2 will not directly effect the fuel/air mix,it does however force the PCM to use a different fuel/air map to lower emissions without the cat's being monitored.Also if the downstream O2 wires are grounding out it can cause a limp mode.

There is alot of bad info on the internet about OBDII and how it operates and what causes what and what fixes what.Once you get into OBDII,I mean really into it, you would be amazed at what it can do.You will also find that every automaker has a slightly different spin on what it can and can not do and what you can and can not access without a OE level scanner.

GM is the most accessible regardless of year,make,or model.

Ford can be tricky unless you can understand mode 6.

Chrysler is hit or miss depending on year and who actually owned them at the time.

All foreign manufactures,regardless if they are built in the US or not, are hit or miss with nissan being the most cryptic.

 

[TruckerKevin]

Well, I stopped at Oriellys on the way home tonight and had the codes pulled.........No codes!
I guess I should not have cleared them yesterday

But the surge is still there at mid range throttle around 35-45 mph. Not as bad mind you.

I guess I will change the plugs tomorrow and tinker around with general maintenance and keep driving it until the engine light decides to come back on.

 

[GunnerSchenck]

GM is the most accessible regardless of year,make,or model.

Ford can be tricky unless you can understand mode 6.

Chrysler is hit or miss depending on year and who actually owned them at the time.

All foreign manufactures,regardless if they are built in the US or not, are hit or miss with nissan being the most cryptic.

GM seems to be make their information the most accessible all the way around.
Shoot I mean even when it comes down to collision repair information.. seems to be the only manufacturer that doesn't make you pay to know where to section what joints, where they use what foams, etc..
Just technician friendly.. I've had more luck when it comes to hyundais and Nissans than trying to finding ford info. Seems if you don't pay for access to their database, you've gotta hit or miss it yourself.
Even redoing the last maxima I did, you were able to find sectioning locations (even though I just went with the factory seams on the front rails) but the next thing I go to do, ford fiesta.. nope, hop to the payment boiii

That being said, about the o2 sensors, I completely understand what you're saying about the downstream sensors, but if an upstream sensor causes a rich condition.. you're saying all that extra unburnt fuel makes its way out the exhaust as pollution? That's the only thing I've ever read that you posted that I've found questionable.. I'm not saying you're wrong, as you're obviously plenty knowledgeable and experienced.. just defies a decent amount of experiences I've run into.
So just to clarify, you're saying in no way will a bad o2 sensor, regardless of up or downstream, will cause a condition that will eventually clog up a muffler, then mid cat, then cats? And from there cause sticking exhaust valves, etc..???

 

[illegal_groundz]

is the check engine light flashing ..??? and if so how many time does it flash be it stop ..should be about 12 times ...my jeep did the same thing and it was also throwing ramdom misfire code to ..mine was the cats ..let it run for a bit and look and see if the cats are glowing red if not go to the back of exhust and see if you smell sulfur ...