Title says it all my o2 sensor will sometimes goto 0 when idling and stay for a few mins between 0-.5v in my logger but no check engine light ? Should I swap it? Does it cause any problems? Thanks

Also my isc will either slowly drop to zero or rise to 120 I set it to 30 grounding everything but when I in ground it drops to zero or goes to 120 slowly

Do you have a wideband? What is it reading while the O2 sensor is acting up? Your O2 sensor should cycle when you are in closed loop mode, either at Idle or when you're cruising...

Just went through the same thing last week. I swapped my exhaust manifold gasket, bolted every back up, and o2 didn't cycle. It cycled fine prior to me doing any work. After some searching and reading peoples threads I decided to just fork over $40 dollars for a new o2 from Napa. Swapped in the new one and it's cycling again.

As for your ISC get a multimeter and test the voltage. My old ISC didn't have the behavior yours is having but I could never get it down to anywhere near 30. Tested it and one of the pins was displaying 0. Swapped it out with a good tested good one. Another issue I had with the ISC was the ISC driver chip per ECMLINK was shot. That was another reason my ISC was not able to adjust accordingly.

Those were my issues that is similar to what you're experiencing.

Good luck.

I read about O2 sensor performance issues degrade over time and by installing a new one even did not solve the dreaded problem from running rich to even starting and dying problems. The sensors are designed to send the rich/lean signals by reading the Oxygen content in the exhaust stream to the ECU. Some vehicles have 2 sensors one before the cat and one after the cat; some have 4 sensors but the principal still remains the same. These upstream and down stream sensors send this data in milliseconds (MS) to the ECU then it does its calculations based on the information given adjust the fuel to air ratio. The problems is over time our wiring that is now 21 years old does not flow electricity as it did when the wire was new. Even a slight delay of a few mill-seconds and will set the check engine light or store a trouble code. This is due to the fact that the ECU see's there is a delay in the response from the O2 sensor then it suspects there is a problem and the MIL illuminates. So the solution I read was to reprogram the ECU with a different emissions specifications so that it would not falsely flag a delay in the signal sent to the ECU to indicate an inaccurate component failure. Basically you have to reprogram or re-flash the ECU to not throw the code just because there is just a slight delay in MS that the ECU cannot compensate for.

As for O2 sensor reading make sure the vehicle is warmed up and watch the voltage, when your driving as opposed at idle. There is a range for the voltage and any scanner or data logger you should be able to read live sensor data streams and compare the vehicle data to sensor specs. The scanner I use can show me the voltages and data streams reading in MS so you may come across a different value depending on the scan tool or logger you use. If the sensor is original go ahead and get a new Mopar/Mits sensor do not buy cheap aftermarket alternatives. You also say you have an ISC problem you have 2 problems you need to fix one then the other. It is best to fix one problem first then off to the next. I know one thing about ISC's they can test good and you still can have idle problems. It is best to go ahead and invest in a new one and a new O-ring that goes with it. Best of luck!

Thanks for the replys everyone! I'll be picking up a new isc btw in the next few days , I'm also checking my ignition timing

Hopefully everything goes well and can figure out why my o2 stops oscillating sometimes it literally goes to 0v and bounces between .05 for minutes Its random either cruise or idle

I've idled at 500 rpm to 2000 (when my idle position switch was shot ) I'm on he quest for the golden idle of 750 and a perfect o2 readings ,

Also idk if this is something to know but I haven't swapped to a nt fpr yet will that affect much? I was runninnf 390cc with a nt ecu for a 1yr an a half let's say I was running super bee rich I've got 240 cc injectors now I also have the fpr solenoid hooked up still and I deleted the resister pack when I swapped to 240cc injectors,

thanks for the replies

Derail20T said:

Do you have a wideband? What is it reading while the O2 sensor is acting up? Your O2 sensor should cycle when you are in closed loop mode, either at Idle or when you're cruising...

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No wide band is there a point where it should stop cycling?

Sound to me like your ecu is bad open and look for burned capacitors or leaking. And disconnect your o2 sensor and use a multimeter to see if it cycles but never should hit 0. If it cycles unplugged most likely your ecu is toast.you can still check harness to be safe for shorts or loose connections.

inthemidst said:

Sound to me like your ecu is bad open and look for burned capacitors or leaking. And disconnect your o2 sensor and use a multimeter to see if it cycles but never should hit 0. If it cycles unplugged most likely your ecu is toast.you can still check harness to be safe for shorts or loose connections.

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Hmm let's hope not my ecu was rebuilt when I bought the car costed 200$

o0GuitarKid0o said:

No wide band is there a point where it should stop cycling?

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Yes, when you are not idling or cruising. Basically if you are reving up the engine or accelerating the O2 won't be cycling because you will be in open loop mode. When you are in closed loop the ecu looks at the mas sensor to adjust Fuel based on airflow into the engine. It also looks at the O2 sensor signal as feedback and fine tunes the amount of fuel being injected accordingly. The ecu is targeting stoichiometric 14.7 a/f ratio. This is why the O2 cycles. If the O2 senses a lean a/f mixture the ecu adds Fuel, when it sees a rich a/f mixture the ecu will reduce the amount of fuel.
In open loop the ecu takes information from the mas sensor and injects a specific amount of fuel according to the current airflow. It looks at tables based on rpm and load and adds a predetermined amount of fuel. It does not look at the O2 sensor for feedback in open loop. The O2 sensor will still transmit a signal but the ecu doesn't use it to help target a specific a/f ratio. This is why the O2 doesn't cycle in open loop mode.

Yes o2 sensors do not function cold.

stars said:

...he problems is over time our wiring that is now 21 years old does not flow electricity as it did when the wire was new. Even a slight delay of a few mill-seconds and will set the check engine light or store a trouble code...

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Aged wiring like that which is in our vehicles cannot slow down the flow of electricity as you are describing and have this effect. However, aged wires definitely can introduce a degree of resistance through advanced corrosion and nonconductance through breaks in the wire or failing connectors. Add engine bay heat to the wires, causing them to alter physical form when hot, and you have another issue altogether (and harder to diagnose).

Let us not also forget that the signal from an O2 sensor is in the 0 to 1 volt DC domain. For sh*ts and giggles, throw a multimeter in ohms mode to test the resistance between the harness-side sensor connector and the ECU connector. You'll likely need an additional length of wire to make that reach. Test the resistance of that too so that you can subtract it from the overall value. I doubt it will be much, if any. If it is, you have a wiring issue.

Is this issue only when idling?
What are your fuel trims? Add them to mmcd and take a look. Your L M and H should all be as close to 100 as possible. Report back.

It's kinda during any part . My fuel trims were 116 a while back but I reset the ecu and currently there still 100, I remeber today on a cold start (not that the O2 matters) but it was at a solid .89 v (idle) ,

curt-s said:

Aged wiring like that which is in our vehicles cannot slow down the flow of electricity as you are describing and have this effect. However, aged wires definitely can introduce a degree of resistance through advanced corrosion and nonconductance through breaks in the wire or failing connectors. Add engine bay heat to the wires, causing them to alter physical form when hot, and you have another issue altogether (and harder to diagnose).

Let us not also forget that the signal from an O2 sensor is in the 0 to 1 volt DC domain. For sh*ts and giggles, throw a multimeter in ohms mode to test the resistance between the harness-side sensor connector and the ECU connector. You'll likely need an additional length of wire to make that reach. Test the resistance of that too so that you can subtract it from the overall value. I doubt it will be much, if any. If it is, you have a wiring issue.

Is this issue only when idling?
What are your fuel trims? Add them to mmcd and take a look. Your L M and H should all be as close to 100 as possible. Report back.

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idles not bad I bought a timing light to check ignition timing ,prob do that this weekend my idles still a bit random but decent

So all three (low, medium, and high) trims were all 116?

That's not really good. That means the ECU has been figuring there's a lean condition (through the O2 sensor in closed loop mode, caused by bad pump, injectors, fuel flow rate, or the O2 itself) and dumping in fuel. You were actually pretty close to the maximum it can add.
It should have changed by now and given the age of your components and how things are whacky, I'd take another look at the trims. Rarely, if ever, will it be spot on at 100 if you've given it enough time to change. And I mean rare, and it shouldn't really take long.

There is a ever-so-slight possibility you're being placed in open loop mode much more than normal, which would also cause the trims not to update.. too much and at wrong times and it will throw a CEL, if I recall correctly.

Does your CEL work?

curt-s said:

So all three (low, medium, and high) trims were all 116?

That's not really good. That means the ECU has been figuring there's a lean condition (through the O2 sensor in closed loop mode, caused by bad pump, injectors, fuel flow rate, or the O2 itself) and dumping in fuel. You were actually pretty close to the maximum it can add.
It should have changed by now and given the age of your components and how things are whacky, I'd take another look at the trims. Rarely, if ever, will it be spot on at 100 if you've given it enough time to change. And I mean rare, and it shouldn't really take long.

There is a ever-so-slight possibility you're being placed in open loop mode much more than normal, which would also cause the trims not to update.. too much and at wrong times and it will throw a CEL, if I recall correctly.

Does your CEL work?

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Yup cel works great; and acually it was just the short term that was at 116;but I reset and it hasn't changed , I don't leave home woth out that logger love that thing , I have a o2 I'm just going to swap an see how that is I gotta find a non turbo fpr , I still have the turbo one paired wit the solenoid thanks for the help

curt-s said:

So all three (low, medium, and high) trims were all 116?

That's not really good. That means the ECU has been figuring there's a lean condition (through the O2 sensor in closed loop mode, caused by bad pump, injectors, fuel flow rate, or the O2 itself) and dumping in fuel. You were actually pretty close to the maximum it can add.
It should have changed by now and given the age of your components and how things are whacky, I'd take another look at the trims. Rarely, if ever, will it be spot on at 100 if you've given it enough time to change. And I mean rare, and it shouldn't really take long.

There is a ever-so-slight possibility you're being placed in open loop mode much more than normal, which would also cause the trims not to update.. too much and at wrong times and it will throw a CEL, if I recall correctly.

Does your CEL work?

Click to expand...

Well today I took a look at my fuel trims the ftl was maxed at 139% and the other ones were at 103% so I'm running rich as hell, my o2 was not cycling at all it was just chillin at .05 v on or off throttle so I'm hoping my spare o2 will fix it I guess will have to see