Jeep Garage  - Jeep Forum

Jeep Garage - Jeep Forum (http://www.jeepgarage.org/forums.php)
-   Engine Performance/Intake/Exhaust (http://www.jeepgarage.org/f183/)
-   -   Oxygen Sensors and Their Role in Engine Management--A Primer (http://www.jeepgarage.org/f183/oxygen-sensors-and-their-role-in-engine-management-a-primer-20300.html)

jeepgcoman 03-15-2011 08:21 PM

Oxygen Sensors and Their Role in Engine Management--A Primer
 
I am doing this thread due to my recent experience with the Oxygen Sensors (O2) on my Hemi WK. I’ll explain how and why I became very interested in this, and the results of my research and actions. This is more or less a "LOTS OF THINGS YOU NEVER WANTED TO KNOW ABOUT OXYGEN SENSORS, AND THEIR ROLE IN ENGINE MANAGEMENT."

This will be quite long and a lot of it will be in bullet statements, with explanations or comments on some. So, sit back and read, ignore, go to sleep, or close the thread. I promise though that, unless you’re an absolute wizard on these systems, you’ll learn something, right along with me. Also, since fuel prices are once again skyrocketing, this might be a good opportunity to familiarize ourselves with some of the things that affect the fuel economy, emissions and the performance of our Jeeps, or any of our vehicles for that matter. But, also be aware that while much of this may apply to other makes/models, some things may also be quite different from others. This is not meant to be all inclusive information, but focuses on items/areas I found to be of interest to me, or something I should perhaps be aware of for future reference. Besides, to cover everything would take days.

This all started when I recently had major exhaust system work done…custom tubular headers and a complete custom 3 in. Magnaflow Cat. Back system. After it was completed I decided I would monitor the system with my DashHawk to insure that everything was working properly and there were no indications of exhaust leaks or sensor issues. I feel that I have a pretty fair knowledge of most automotive concepts and systems, although I never really paid too much attention to "modern" engine and fuel management systems because, "they always worked fine" for me. I thought I knew enough about the returnless electronic sequential multi-port fuel injection (that’s a mouth full) open and closed loop operation, and knew what O2 Sensors did, but not so much how and why they did it. It was kind of an "out of sight, out of mind" thing. This is where my curiosity really began though. At this point I should also mention that I have another Hemi and DashHawk equipped vehicle which came in handy for direct comparisons in the initial phases of troubleshooting. It conclusively pointed me in the right direction.

I have always had a screen set up on the DashHawks to monitor all four O2 Sensor voltages and the Catalytic Converter temperatures, but never paid much attention to them, how/why they worked, or what all the readings and indications meant. When I started regularly monitoring the upstream (before Cats.) and downstream (after Cats.) O2 sensor systems I found that the upstream left (1/1= Bank 1, Sensor 1) O2 Sensor voltage fluctuated quite a bit while the upstream right (2/1=Bank 2, Sensor 1) Sensor was quite stable. Because the left one was cycling so much, I immediately thought that I had an exhaust leak on that side and the other (right) side was working fine. Also, both the downstream sensors (1/2=Bank 1, Sensor 2 and 2/2=Bank 2, Sensor 2) were quite stable too, so I thought they were also working fine. After all, "stable is good and fluctuating is bad", right? The downstream readings were sending a non-cycling rich (higher millivolt) signal to the PCM, as was the 2/1 Sensor. This is when I decided that I should do a little research to find out what all these readings and numbers really meant. Boy, did I get a big surprise. Turns out that the 1/1 sensor was working pretty good except for being a little lazy, the 2/1sensor was virtually inoperative and both the rear sensors (1/2 and 2/2) were working fine.

I decided, since I had just done my 60K service, I might as well change all four of the sensors. They weren’t very expensive….~$30 each, or $120 for all four. My rationale was that if one is bad or going bad the others are probably close behind. I opted for Bosch sensors, since they were about the only ones I had heard of and I knew that Robert Bosch’s engineering gang were the ones that invented them. This turned out to be a poor decision, at least in my case. I don’t know if the same would apply to anyone else though.

As soon as I replaced the sensors the PCM almost immediately set P1128 and P1129 Diagnostic Trouble Codes (DTC’s). The DashHawk was indicating that the upstream and downstream wiring had been switched. I knew that wasn’t true so I started researching what those codes really meant. Along the way I discovered, through other DCX forums, that O2 Sensor problems were quite common on Chrysler vehicles. Anyway, P1128/P1129 really mean that closed loop fuel status is not being achieved in a timely manner on either engine bank. In my case it was because the heaters were not heating up the sensors fast enough.

I discovered, thanks to my parts guy, that the original factory ones were made by NTK, a division of NGK. I ordered both NTK upstream sensors, changed them, and now all it well. Turns out that the Bosch sensors were too slow heating up and would cause the transition from open loop to closed loop to be delayed, or not happen at all due to the codes being set. The heat up threshold is ~40 seconds. More than 40 seconds would set a DTC and not allow the fuel system to switch over from open loop to closed loop until much later (or not at all) than the PCM required. The upstream sensors when cold with the engine off are what I will call "parked", and indicate 1.270 volts on the DashHawk. This was true with all upstream Bosch and NTK sensors. The sensors need to get below about 1.0 volt (I think the book says 900 mV) before they begin oxygen sampling. It would take ~47 seconds for the Bosch 1/1 sensor, and ~37-40 seconds for the Bosch 2/1 sensor to reach this point. By contrast the NTK’s reach this point in ~7-8 seconds. Closed loop is achieved at different times based on engine temperature and other sensor inputs, and with the Bosch sensors would take up to one minute fifteen seconds, or would display an error code (8) for the fuel status indicating closed loop was not achieved. The NTK’s would take no longer than ~35 seconds to warm up and transition to closed loop.
 
Oxygen Sensor (O2) Gee Whiz Information

Below is much of what I learned about the oxygen sensors. It is, by no means, all inclusive and is only as good as the research articles I used. I guess that means that there may be some errors. Feel free to comment, correct or criticize me on anything you may question or find wrong. I have also tried to put them in some sort of order that makes a little sense.
--O2 sensors were first installed on Volvos in 1976-77 and the system was called, Lambda Sond..
--While Lambda is the 11th letter of the Greek alphabet, it is also another name for the oxygen sensor. When the system has reached "lambda" (1.0) it is at stoichiometric air/fuel mixture. Above 1.0 is lean (more oxygen, less fuel) and below 1.0 is rich (less oxygen, more fuel).
--Stoichiometric (14.7/1 air/fuel mixture) is when an ideal (iso-octane) fuel is used it will completely consume all of the air and fuel in the mixture. This will provide the best mixture for economy and lowest emissions, but NOT THE MOST POWER. The most power is achieved at ~12.8-13.2/1air/fuel ratio. My Hemi Jeep runs rich (as do almost all stock vehicles) at about 11/1 air/fuel mixture at Wide Open Throttle (WOT).
--So, Lambda 1.0 and stoichiometric mean the same thing, and this ratio is what is needed for the best economy and lowest emissions, but will not provide the best performance.
--Our Jeeps are equipped with four, 4 wire, heated, narrow ratio (band) air/fuel O2 sensors, two near the exhaust manifolds in front (upstream) of the catalytic converters, and are identified as, 1/1 is the front left side, and 2/1 is the front right side. The other two (downstream) sensors are located aft of the catalytic converters and are identified as 1/2 which is the rear left side and 2/2, which is the rear right side.
--In closed loop fuel status THE FRONT TWO SENSORS (1/1 and 2/1) ARE THE PRIMARY INPUTS that tell the PCM what mixture they are sensing. This, along with other sensor inputs are used by the PCM to make closed loop mixture adjustments, by changing the fuel injector pulse width. The object is to keep it as close to 14.7/1 air/fuel ratio as possible.
--Some of the other critical sensors are the Manifold Air Pressure (MAP) Sensor, the Throttle Position Sensor (TPS), the Ambient Air Sensor (AAS), Engine Coolant Sensor (ECS) and the Intake Air Sensor (IAT).
--The rear O2 sensors (1/2 and 2/2) are used solely to determine catalytic converter efficiency. If their indications mirror the front sensors, after the cats. have warmed up to at least 600 degrees F, the converter is not working properly and needs to be replaced. Since the converter’s job is to burn any unburned fuel, further reducing emissions, the rear sensors will normally show a richer (less oxygen) mixture, meaning that most of the air/fuel mixture has been burned off.
--O2 SENSORS:
--are relatively inexpensive…~$30-50 each.
--are made by a number of companies. Some of the more common ones are, Bosch, NTK and Denso.
--ARE PROBABLY THE MOST IMPORTANT PCM INPUT DEVICE IN DETERMINING ECONOMY AND EMISSION LEVELS. Even today, not very many people are aware of their presence, or the importance they play in engine performance and pollution control. Some surveys indicated that ~95-99.7% of all vehicle owners were not even aware that their vehicle had oxygen sensors.
--that are failing do not necessarily display a Malfunction Indicator Light (MIL) or set a DTC. A sensor may be lazy/sluggish, or biased rich or lean.
--are mini voltage generators, and the readings they generate and send to the PCM are expressed in millivolts (mV). The normal range is ~100-900 mV. At startup, on mine, the voltage is ~1.270 volts, and quickly (with the NTK sensors) drops to the appropriate range..
--mV indication of ~450 mV is approximately the midpoint and indicates about a 14.7/1 air/fuel ratio. Below 450 mV indicates a lean condition and above 450 mV indicates a rich condition.
--indicating the lower mV reading mean that more oxygen (lean) is in the exhaust gas. The higher mV reading indicates that more fuel (rich) is in the exhaust gas.
--are vented to the atmosphere through the wiring connectors and insulation. This type of venting, rather than using a hole in the sensor body, reduces risk of water, dirt or other debris from contaminating and possibly fouling sensor and causing it to fail.
--provide feedback to the Power Control Module (PCM) during closed loop (idle, low load, light throttle) fuel status. During initial cold and at Wide Open Throttle (WOT) operation the fuel system is in open loop status, and their feedback is ignored by the PCM. Instead the PCM uses preprogrammed fuel tables and other sensor inputs to determine the air/fuel mixture. Closed loop operation uses other fuel tables.
--once warmed up, normally "cycle, or flip flop" continuously and alternately from rich to lean to rich passing the 450 mV point in both directions. The number of times it cycle sare called crosscounts, or the number of times it passes the 450 mV point. The number of times this crosscount occurs varies with the type/brand of sensor and over time becomes slower with age/contamination. The more crosscounts, the more precise the mixture control.
--upstream and downstream all work the same, but the downstream ones SHOULD NOT have any crosscounts once warmed up and should be relatively constant somewhere above 450 mV.
--are installed on all newer vehicles today.
--should last between 50-100K miles
--wear out slowly (become lazy/sluggish), similar to spark plugs, so may not be noticeable until a DTC has been set or economy has degraded significantly.
--are easily contaminated which can render them "lazy/sluggish" or inoperative.
--effectiveness will deteriorate or fail if exposed to such things as lead,, phosphorus, EXCESSIVE OIL, WATER, silicone sprays/gasket sealers (unless certified to be O2 sensor safe), some fuel additives, road salt, dirt, or mishandling. The amount of moisture and oil that gets by the inferior Positive Crankcase Ventilation (PCV) system on the 5.7 Hemi’s would, IMO, be cause for concern for premature O2 sensor and/or Catalytic Converter contamination and deterioration. Not regularly checking/changing the PCV Valve could aggravate this. IMO, Hemi owners should always check the PCV Valve and behind the throttle body butterfly at each oil change.
--have a host of DTC’s that are associated with the many different malfunctions that can occur with them.
--are not easy to check without special On Board Diagnostics, Generation II (OBDII) test equipment. If you have a ton of miles on your ride, get lousy fuel economy, and know they haven’t been changed, it’ll be cheaper to replace them than pay to have them tested. As I said, mine were failing at 60K. They can be tested with a voltmeter that is capable of reading millivolts but again, IMO, would not be worth the effort.
--that have completely failed will usually indicate a rich condition and, if not replaced in a timely manner, could cause the overheating and failure of the Catalytic Converter on the affected side. For us Hemi guys, if it is rich enough at light throttle to change the fuel injection status to open loop, the MDS will also become inoperative.
--are among the leading cause of emission test failures due to high Hydrocarbons (HC) and/or Carbon Monoxide ( CO). Surveys have shown that anywhere from ~40-70% of emission test failures were attributed to defective oxygen sensors.
-- LAZINESS OR FAILURE CAN CAUSE UP TO ~10-15% INCREASED FUEL CONSUMPTION, emissions test failures, driveability issues such as surging and/or hesitation, and overheating and failure of the Catalytic Converter.

Rose City GC SRT8 03-17-2011 10:26 AM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Nice writeup. Lots of good info. So how do you get the rear O2 sensors to show "ready" with long-tube headers and not throw a code? That is what I would like to know.

blackpepper 03-17-2011 11:07 AM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
+rep

jeepgcoman 03-17-2011 11:23 AM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
What code or codes are you getting? I can't imagine that, just because you have long tubes (mine are kind of intermediate), there would be a problem with the sampling. I know with long tubes you've had to extend the wiring harness, but that shouldn't cause a problem, if done correctly. What kind (brand) of rear sensors are you using, and are they new or have you had them checked?

By "ready" I assume you are talking about heating up to the point where they start sampling. The rears are used solely to compare mV readings with the front sensors. If the mV readings mirror that of the fronts, the cat is not doing it's job. The rears should show a fairly steady higher than 450 mV output. As far as heating up to the ready point, I don't believe their heat up time is as critical as the fronts, although if they don't heat up completely within a certain timeframe, I am sure they will set a code. The Bosch sensors definitely take quite a bit longer to heat up than the NTK's.

If you continue to have a problem, after exhausting all avenues of correction, you may want to look at the following web site to see if you can eliminate it this way: http://www.angelfire.com/super2/cont...Mil_HowTo.html

Walt 03-18-2011 06:37 PM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Checked the O2 sensors & connectors today when I did the oil / filter change. They look exactly like the factory ones. #*@$% bifocal eyes were so close, I couldn't read the numbers on them. I did see that they are provided with a wiring harness out to the body connector. Therefore, whatever dielectric the dealer's service technician applied to the electrical connection would have been ~8-12" away from the sensor itself....no cause for concern on air vent plugging .

Also, was at the dealer today. They re-set the O2 sensor slow response codes (P0133 / P0153). Service Advisor told me they only use MOPAR. Since Service Manager was out, we didn't have a definitive plan on what to do next.

HEMI ran OK for about 7 miles (including MDS); mpg's jumped immediately. Then it threw DTC P0153. I was by AutoZone, so I re-set it. We'll see what Saturday brings.

Talked to Drew Technologies today about the DashDAQ XL. I'm going to Ann Arbor (after 4/15/11). [No weekdays off until after then.] The Sales Mananger will let me try his before I buy. I like that. Can set up multiple pages either in-situ or with PC help. GPS antenna is a 1" x 1" sensor behind the unit.

jeepgcoman 03-21-2011 08:20 PM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Anything new with the O2's and MDS, Walt? I checked out the DashDAQ on their web site. I see they have a maximum of 10 screens (pages) when using the "Neon" setup. It looks real good, but spendy. I also noticed that there are way more PID's available than the DashHawk, but many wouldn't be used, at least by me. I also didn't see any transmission related PID's, which is fairly important to me.

Walt 03-22-2011 01:44 PM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Quote:

Originally Posted by jeepgcoman (Post 380155)
Anything new with the O2's and MDS, Walt? I checked out the DashDAQ on their web site. I see they have a maximum of 10 screens (pages) when using the "Neon" setup. It looks real good, but spendy. I also noticed that there are way more PID's available than the DashHawk, but many wouldn't be used, at least by me. I also didn't see any transmission related PID's, which is fairly important to me.

Yes, but I'm almost embarrassed to post it. After re-setting the O2 sensor DTC's twice (P0133 & P0153), I went to AutoZone and changed the leaking radiator cap. The coolant temp on the gauge went up 1 tick (to where it was before: 2 ticks below gauge mid-point). No more coolant leaking by & on to the RHS suspension. :thumbsup:

Standby for the amazing part:
MDS started working, mpg's are up, and car runs smoother. What mean this? :confused: Until I got this WK, I used to understand internal combustion engines and mechanical engineering. This thing is more like Einstein's General Theory of Relativity and Electro-Quantum Mechanics. :eek:

Spoke to Drew Technologies. They will let me come down and try the Sales Manager's in my Heep, so I can see how it works. Only unit I saw that gives me lube oil pressure and voltage both. Also need GPS, so it's not that much when everything is combined into 1 unit.

jeepgcoman 03-22-2011 08:10 PM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
How long are you going to have the DashDaq? Let us know what you think. Glad things are back to "normal" for you.

Rose City GC SRT8 03-23-2011 09:50 AM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Quote:

Originally Posted by jeepgcoman (Post 377611)
What code or codes are you getting? I can't imagine that, just because you have long tubes (mine are kind of intermediate), there would be a problem with the sampling. I know with long tubes you've had to extend the wiring harness, but that shouldn't cause a problem, if done correctly. What kind (brand) of rear sensors are you using, and are they new or have you had them checked?

By "ready" I assume you are talking about heating up to the point where they start sampling. The rears are used solely to compare mV readings with the front sensors. If the mV readings mirror that of the fronts, the cat is not doing it's job. The rears should show a fairly steady higher than 450 mV output. As far as heating up to the ready point, I don't believe their heat up time is as critical as the fronts, although if they don't heat up completely within a certain timeframe, I am sure they will set a code. The Bosch sensors definitely take quite a bit longer to heat up than the NTK's.

If you continue to have a problem, after exhausting all avenues of correction, you may want to look at the following web site to see if you can eliminate it this way: http://www.angelfire.com/super2/cont...Mil_HowTo.html

LT headers on the 6.1 SRT8 will throw codes. It's the rear 02 sensors. Some people have had success with antifoulers, but it doesn't work reliably for the 07 and later models. This MIL how-to shows some promise.

jeepgcoman 03-23-2011 03:36 PM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Rose City, do you know what codes are thrown with the long tubes?

Walt 03-23-2011 06:56 PM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Quote:

Originally Posted by jeepgcoman (Post 380856)
How long are you going to have the DashDaq? Let us know what you think. Glad things are back to "normal" for you.

Whoops. New radiator cap just delayed the inevitable. Back to codes yesterday on the way to school after work. DTC P0153 (O2 sensor 2/1 slow response) again. :angry: Went to Advance Auto on the way home from work today (along with 6" of new snow) and reset the codes.

These DTC's only happen on days of the week that end in "y". :brows: Back to the dealer on Friday afternoon........:banghead:

Don't have the DashDAQ XL yet. Will be looking at DashDAQ XL when I go to Ann Arbor on a weekday (not open on weekends). Nothing local. I don't want to buy if it does not do what I want or it's obtrusive on the LHS dashboard. I'm more tactical and visual than Internet evaluative. Incentives to buy on e-bay are $50 cheaper, no state sales tax, and free shipping. Maybe I'll look at the mfgr in Ann Arbor and buy on e-bay....best of both worlds. :)

jeepgcoman 03-23-2011 07:42 PM

Re: Oxygen Sensors and Their Role in Engine Management--A Primer
 
Bummer on the codes again.

Can't wait to read your review of the DD.


All times are GMT -5. The time now is 05:00 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright 2012 - JeepGarage.Org
The Jeep Grand Cherokee Owners Community