Oxygen Sensor output voltages?

[Ecomike]

Thanks very much Mike.... That definitely gives me a direction to go in. I had not checked os sensor functionality at cruise and will double check
the EGR....

You are getting close looking at that data so hang in there. The only one left is that CO at idle, and it has droped 50% both times with prior repairs, so they did help already. Like I said, I think a small EGR leak at idle may be the culprit. but make sure the O2 sensor heater is getting voltage too.

Good luck.

I am off to work on replacing my brakes Vac booster for inspection this week!

 

[nickguy]

Good luck with the brakes. I did do a quick test at 2k rpm and sure enough the voltage to the sensor drops to the 2.5 volt range now. Egr next. Thanks again Mike.

 

[Ecomike]

Good luck with the brakes. I did do a quick test at 2k rpm and sure enough the voltage to the sensor drops to the 2.5 volt range now. Egr next. Thanks again Mike.

At 2K rpm the O2 sensor gets hot enough to read properly even if the O2 sensor internal heater is not working. Did you check for the 12-14 volts on the large diameter, third, O2 sensor wire, before going after the EGR?

 

[nickguy]

you know I did. I get about 13.5 v. As I mentioned before at first I thought that was the problem until I figured it is wired into the fuel pump circuit and does not function with just the ignition on. But with the engine running and the os sensor disconnected I get the appropriate voltage. Am sure the heater circuit is good. Have pulled the EGR valve and am in the process of cleaning it up. Still just 4.89 volts at idle though...

 

[Ecomike]

you know I did. I get about 13.5 v. As I mentioned before at first I thought that was the problem until I figured it is wired into the fuel pump circuit and does not function with just the ignition on. But with the engine running and the os sensor disconnected I get the appropriate voltage. Am sure the heater circuit is good. Have pulled the EGR valve and am in the process of cleaning it up. Still just 4.89 volts at idle though...

Sounds like your on the right track then. If the EGR does not fix it, then I would suspect a leaking, or multiple leaking injectors at idle. Don't forget their is an electric solenoid that activates the EGR, but it sure sounds like a stuck open, just barely stuck open EGR.

If it was a poor combustion problem at idle (low compression, or poor spark...etc.), I would think it would show up at higher rpms too, so I kinda rule that out.

 

[nickguy]

Removed EGR valve... pretty dirty but I think functional... Threw a new one on... Pulled the fuel rail and injectors, and pressurized. One injector leaking. Replaced EGR and as I have no idea of the injector's history decided to treat the XJ to a new set reasoning that they will be always useful.

Hooked up the voltmeter and lo and behold.... same results.

Now that I have ruled out most stuff I was intrigued about what ecomike said about the heater circuit.... I get 13.5 volts to the circuit with the sensor unplugged and the engine running but I tested while hot and connected and got a steady 1.5 v... For grins I hotwired the heater circuit to the o2 sensor and I finally achieve oscillation.... (don't even go there
So what appears to be happening is that the heater circuit is being shut off at idle when it actually needs to be on.... Am in the process of troubleshooting that circuit focusing on whatever mechanism the ECU uses to turn it off and on or indeed figuring out it it needs to be on all the time. More to come but I finally feel like I have avenues to explore. One that may be the case is a previous owner disconnected AC and I am wondering if the ECU thinks it is actually on as according to the RENix manual it goes to open loop when the AC is on. More to come.

 

[Ecomike]

Sorry to hear the first two did not work, but a leaking injector was sure to wipe out a good cylinder shortly, so it's good that you found it!

I'd bet that it's 1.5V at cruising too on the attached heater voltage. The O2 sensor gets hot enough at cruising from engine exhaust to work. The built in heater is there for idle operation as the exhaust does not keep the O2 sensor hot enough at idle.

So either the O2 sensor heater is internally shorted, or there is a bad connection in the jeep wiring or relay that is not allowing enough current to flow to the O2 sensor's internal heater. The bad connection (bad relay contact perhaps?) is acting like a resistor, but only under load, and thus dropping the voltage while under load. It is a dynamic resistance that only shows up under load, or a short in the O2 sensor heater internally.

I think the O2 sensor heater should read about 8 ohms cold across the heater wire(s). If it is about 1 ohm, the the O2 sensor heater is bad, shorted. If it is OK it must be the relay or wiring, or connectors.

Removed EGR valve... pretty dirty but I think functional... Threw a new one on... Pulled the fuel rail and injectors, and pressurized. One injector leaking. Replaced EGR and as I have no idea of the injector's history decided to treat the XJ to a new set reasoning that they will be always useful.

Hooked up the voltmeter and lo and behold.... same results.

Now that I have ruled out most stuff I was intrigued about what ecomike said about the heater circuit.... I get 13.5 volts to the circuit with the sensor unplugged and the engine running but I tested while hot and connected and got a steady 1.5 v... For grins I hotwired the heater circuit to the o2 sensor and I finally achieve oscillation.... (don't even go there
So what appears to be happening is that the heater circuit is being shut off at idle when it actually needs to be on.... Am in the process of troubleshooting that circuit focusing on whatever mechanism the ECU uses to turn it off and on or indeed figuring out it it needs to be on all the time. More to come but I finally feel like I have avenues to explore. One that may be the case is a previous owner disconnected AC and I am wondering if the ECU thinks it is actually on as according to the RENix manual it goes to open loop when the AC is on. More to come.

 

[Ecomike]

One that may be the case is a previous owner disconnected AC and I am wondering if the ECU thinks it is actually on as according to the RENix manual it goes to open loop when the AC is on. More to come.

Where did you see that? That is big news to me????

Tell me more!!!!!!

 

[nickguy]

My apologies...

I have no idea where the AC/open loop presumption came from. I thought I had read it somewhere on this effort but actually think I confused it with the interaction with the idle stepper motor as outlined in the renix manual. So sorry about that it comes from the grasping at straws department.


Good news however. This is sussed. It looks like I had a bad relay. It seems to be my karma to get weird mechanical problems. With the engine running with the 02 sensor unplugged I got 13.5v... at the sensor... with it plugged in however I got 1-2 volts. Reading up on the relay function I learned that it should simply energize the relay circuit while the engine is running. If the ECU grounds out the relay it will turn the circuit off... So I presumed that the ECU was doing just that. Checked the relay and activated it with a piece of wire to ground, while monitoring the sensor, and the relay activated which, if I had been right would not have happened, because it should have already been activated.
So long story short the sensor heater relay was bad. It functioned mechanically and would bridge through 13.5 volts all day. Once load (amperage) came into the picture the thing dropped to 2 volts... Swapped out the relay and with the engine running and the sensor plugged in the voltage at the sensor heater wire had changed to 13.5 volts... swapped to the sensor (gray) wire and my 4.89 volts was swinging between 1 and 4 like it should. Hooray... Off to the emission test but that should be a formality now.

Thanks Mike for keeping me focused on the heater circuit. It made so much sense when you said that if it worked at cruise and not at idle then heater might be suspect. Think if I had got to the relay right away I may have saved some money but all the bits I replaced needed doing. Like so many JEEP issues it was a multitude of problems the only thing that fixed it was to stay methodical and rule out stuff. Just a note to others... If you do not have +12v on the heater circuit at idle there is a problem.

Stuff that was bad or functioning at less than optimum...

1: No CTS due to previous owner being an idiot and stealing the hole for a mechanical temp guage... (there is some thought that the ECU can get by without it but I think it should be there)

2: Leaky fuel injector or 2

3: Cat on the edge..

4: Probably less than optimum plugs and cap and rotor

5: Bad o2 sensor from running rich for so long...

Mike I am very grateful for your assistance. You have RENIX down and are the man. Hopefully this thread helps others wade through this particular problem. One day if I build a renix stroker this experience will prove invaluable.

 

[nickguy]

Mike you totally called the high resistance relay... I did not read this until just now and had had to go find out for myself. Nice one!

Sorry to hear the first two did not work, but a leaking injector was sure to wipe out a good cylinder shortly, so it's good that you found it!

I'd bet that it's 1.5V at cruising too on the attached heater voltage. The O2 sensor gets hot enough at cruising from engine exhaust to work. The built in heater is there for idle operation as the exhaust does not keep the O2 sensor hot enough at idle.

So either the O2 sensor heater is internally shorted, or there is a bad connection in the jeep wiring or relay that is not allowing enough current to flow to the O2 sensor's internal heater. The bad connection (bad relay contact perhaps?) is acting like a resistor, but only under load, and thus dropping the voltage while under load. It is a dynamic resistance that only shows up under load, or a short in the O2 sensor heater internally.

I think the O2 sensor heater should read about 8 ohms cold across the heater wire(s). If it is about 1 ohm, the the O2 sensor heater is bad, shorted. If it is OK it must be the relay or wiring, or connectors.

 

[Ecomike]

Glad to hear it is fixed.
It was definetely and unusual one.


Be sure to post you new emissions inspection data!

 

[nickguy]

RESULTS= PASS!!!


Quite a marked difference... Interesting that the cruise showed improvement as well. Thanks again Mike.



Cruise Limit HC PPM = 200 me 88 = PASS
CO % = 1.5 me 0.08 = PASS
Idle limit HC PPM = 220 me 53 = PASS
CO % = 1.2 me .02 = PASS

 

[Ecomike]

Mine just passed too:

2263 rpm, 26 PPM of HC
698 rpm, 68 PPM of HC

CO was .29% at 2363 rpm
CO was .35% at 698 rpm

CO2 14.0 to 14.1 %

NOx not tested, it's a 4X4.

Interesting to note that my HCs were lower than yours, but my COs were a lot higher than yours.

 

[nickguy]

RESULTS= PASS!!!


Quite a marked difference... Interesting that the cruise showed improvement as well. Thanks again Mike.



Cruise Limit HC PPM = 200 me 88 = PASS
CO % = 1.5 me 0.08 = PASS
Idle limit HC PPM = 220 me 53 = PASS
CO % = 1.2 me .02 = PASS

Two years later without any modifications wanted to document the actual robustness of a properly tuned RENIX

Cruise Limit HC PPM = 200 me 50 = PASS
CO % = 1.5 me 0.12 = PASS
Idle limit HC PPM = 220 me 16 = PASS
CO % = 1.2 me 0 = PASS

Love that 0 idle emission result.

 

[nickguy]

two years later...

Different engine

Cruise Limit HC PPM = 400 me 192 = PASS
CO % = 3.00 me 0.94 = PASS
Idle limit HC PPM = 400 me 1176 = FAIL
CO % = 3.00 me .71 = PASS

Initial test. O2 sensor is working fine and cycling. Must have a bad plug or injector will report when diagnosed. I also had a very dirty air filter but could still see sun through it. All the HC readings are much higher than 2 years ago though. astronomical on idle and fourfold at cruise. And emissions standards are much lower.

 

[nickguy]

Number 1 cylinder down to 60 psi.. All others > 140 psi. No blowby. Head coming off.

 

[nickguy]

Number 1 cylinder down to 60 psi.. All others > 140 psi. No blowby. Head coming off.

So did not update this but the head was the problem. #1 exhaust valve had pretty much destroyed it's seat the head was essentially scrap. Head had been rebuilt once and other seats were pretty much toast. Pulled a head with 175k from a pick and pull did a rebuild and the I do not have to worry about any kind of overheating problems any more. It is night and day. The fact that my cooling system was build perfect to compensate for the bad head is now really paying off. It incredibly stable. The emission test helped me narrow it down. Once I saw really high HC it made me realize that the replacement engine I had installed had a head problem.