Mpg

[Mudderoy]

I've noticed that when I clear the computer I get better gas mileage for the first day, or so. I wouldn't say it is an amazing change, but noticeable. I'm assuming there is a sensor that is giving bad information but how would I find out which? No codes are being displayed.

[xj4life2]

I had a thought but checked with the boys out back and I was actually correct (proud of me ) its because the computer is re learning and will stay to the lean side untill it does. Once it goes into closed loop operation and has re learned it will go back to normal operation and MPG will drop slightly. remember that the computer and system is looking for the perfect 14.7 to 1 ratio and tends to start to learn at below that to avoid a over rich condition.

[Mudderoy]

I had a thought but checked with the boys out back and I was actually correct (proud of me ) its because the computer is re learning and will stay to the lean side untill it does. Once it goes into closed loop operation and has re learned it will go back to normal operation and MPG will drop slightly. remember that the computer and system is looking for the perfect 14.7 to 1 ratio and tends to start to learn at below that to avoid a over rich condition.

I bet you know the answer to this one too. What voltage should the O2 sensor nearest the engine (upstream?) average? Mine fluctuates between .7 and .8 volts while driving about 60 mph. I've been told this means it is running rich. I've never been able to confirm this with any researching I've done on the Internet.

http://xjtalk.com/images/special/o2_graph.jpg

http://xjtalk.com/images/special/o2_data_capture.jpg

[xj4life2]

Should be between .4 to .6 and switching . We look for a real smooth pattern between the switches. I spoke to our lead tech and his first question was how fast is you scope? and what is the time frame ? what is it at idle ? But yes you aren experianceing a rich condition. It may be fooling the computer if its fast enough. let me know

Ps the second o2 is fine as it is following the first

[Mudderoy]

Should be between .4 to .6 and switching . We look for a real smooth pattern between the switches. I spoke to our lead tech and his first question was how fast is you scope? and what is the time frame ? what is it at idle ? But yes you aren experianceing a rich condition. It may be fooling the computer if its fast enough. let me know

Ps the second o2 is fine as it is following the first

I wouldn't say the OBD II scanner I have that is collecting this data and sending it to the laptop via BlueTooth is extremely fast, however I would expect the readings to be an average of the true information. In other words if the average is high so is the real data. But I dunno really.

Here is another run, but I graphed most of the sensor data recorded. It to shows the O2 upstream sensor running rich.

http://xjtalk.com/images/special/EngineO21_Test1.jpg

http://xjtalk.com/images/special/EngineRPM_test1.jpg

http://xjtalk.com/images/special/EngineTemp_Test1.jpg

http://xjtalk.com/images/special/EngineSpeed_Test1.jpg

http://xjtalk.com/images/special/EngineTiming_Test1.jpg

http://xjtalk.com/images/special/EngineIntake_Test1.jpg

If I sit still and just rev the engine I do NOT have a run rich situation!!!

http://xjtalk.com/images/special/EngineO21_Test3.jpg

http://xjtalk.com/images/special/EngineRPM_Test3.jpg

Let me know if I didn't answer any of the questions. Thanks so much for looking at this. I've been spending about 3 years on this issue. I'm getting about 12 mpg and I think I could improve that to 14 to 15 mpg if I can find the answer to this issue.

[Thomass]

What voltage should the O2 sensor nearest the engine (upstream?) average? Mine fluctuates between .7 and .8 volts while driving about 60 mph. I've been told this means it is running rich. I've never been able to confirm this with any researching I've done on the Internet.


perhaps this will help explaining the voltage.. ??

Oxygen sensors are essentially chemical generators. They work by constantly measuring the oxygen content inside the exhaust manifold and comparing it to the air outside the engine. If this comparison shows little or no oxygen in the exhaust manifold, a voltage is generated. This voltage is then sent to the fuel injection computer, where it is received and based on the voltage, the fuel injection computer makes the necessary adjustments to change the overall fuel-air mixture of the engine. When the oxygen sensor measures the correct mixture, the voltage drops and it sends the appropriate signal to the computer to stop adjusting the mixture. This is a non-stop exchange of signals between the sensor and the computer, and it is constantly making adjustments depending on the needs of the engine. When the sensor fails, it stops sending voltage to the fuel injection computer, and usually the computer interprets this as “ok, we aren't’t getting a signal, so we better enrich this engine as much as we can”, hence a rich running engine.

Oxygen sensors usually put out a very small voltage when measuring oxygen content. Typically, they only put out from 0 to 1.1 volts. All internal combustion engines need a proper air-fuel ratio in order to run correctly.
Gasoline engines need to run a ratio of 14.7 parts of fuel to one part of air. (Air cooled motors typically need to be slightly richer). When an engine has more fuel than it needs, all the oxygen in the cylinder head is consumed and the resulting exhaust gases contain almost no oxygen. This usually causes the sensor to generate a voltage of greater than 0.45 volts. If the engine is running too lean, all the fuel is burned, and the extra oxygen remaining flows out into the exhaust manifold. The oxygen sensor detects the extra oxygen and the voltage signal will drop to below 0.45 volts.. 0.45 volts is usually the voltage where the car is neither running rich nor lean, this is when the car’s mixture is usually perfect.

Oxygen sensors usually generate an output voltage between 0.2 to 0.7 volts. However, Oxygen sensors doe not begin to generate full output voltage until it reaches about 600 degrees F. Some oxygen sensors have a built-in heating element that lets the sensor heat up quicker. Keep in mind that most oxygen sensors work in an open loop until they have reached a certain temperature.
What this means is that until it has heated up, the car will not use the oxygen sensor to measure the mixture, but rather use all the other sensors on the car. The sensor will generate a constant 0.45 volts until it has heated up. Once the sensor reaches a certain temperature, it becomes a closed loop and the sensor starts to generate variable voltage.


if you wish, you can fool the fuel injection computer as i did. i run on highways 25.85 mpg, But, there is a lack of power, running up a hill (3%) will bring my speed down and towing an other car is impossible. But for long distances on smoot roads, it is for me fine. In the mountains i have to reprogram again, back to 14mpg

Thomass :driving:

[4.3LXJ]

What brand sensor are you running Tony? I was using Bosch and couldn't get one so I got another brand, name escapes me right now, and noticed by tail pipe went from black to clean. Power dropped a little too due to the lean mixture I think. But the point is that I think not all O2 sensors are crated equal.

[Mudderoy]

What brand sensor are you running Tony? I was using Bosch and couldn't get one so I got another brand, name escapes me right now, and noticed by tail pipe went from black to clean. Power dropped a little too due to the lean mixture I think. But the point is that I think not all O2 sensors are crated equal.

Bosch. I've suspected the brand for some time, but at $60 each...

[xj4life2]

First of all I agree with Steve on the o2 sensors they are not all equil at all and Bosch is the worst in Jeeps .I have tried many and I always end up back at Jeep for the best in them, Price point sucks but I have to replace them alot less so it works out in the end. As for the graphs we went over them at lenght last night and we have come to a couple of conclusions. If you look at the temp vs o2 you will see that the computer is not comming on till 192* therefore the sensors are not acting correct untill then (open loop) . What t stat are you running ? Secondly the graph that says "new o2" did you replace the o2 then graph that one ? Because it appears to be working as it should. If you print the graphs then stack them you can clearly see when your jeep is in open loop and when the computer takes over (the flatline) and goes into closed loop. Since you don't have much data past that point I can't really say more. My Tech think temp is the issue at this time.

[Mudderoy]

First of all I agree with Steve on the o2 sensors they are not all equil at all and Bosch is the worst in Jeeps .I have tried many and I always end up back at Jeep for the best in them, Price point sucks but I have to replace them alot less so it works out in the end. As for the graphs we went over them at lenght last night and we have come to a couple of conclusions. If you look at the temp vs o2 you will see that the computer is not comming on till 192* therefore the sensors are not acting correct untill then (open loop) . What t stat are you running ? Secondly the graph that says "new o2" did you replace the o2 then graph that one ? Because it appears to be working as it should. If you print the graphs then stack them you can clearly see when your jeep is in open loop and when the computer takes over (the flatline) and goes into closed loop. Since you don't have much data past that point I can't really say more. My Tech think temp is the issue at this time.

This data was gathered some time back. I have gathered data since then but I have not put in the work to graph all the data like I had here. It is possible that I had the 180 degree thermostat installed at the time of these graphs, I don't recall.

I have been considering for some time purchasing a OEM O2 sensor, just one. To replace the upstream O2. With this additional information I think I'll check on it and try replacing it.

The next time I collect data I'll be sure the temp is up before the test.

Thanks for taking the time to have a look at this, I feel much more comfortable with the information now that I have it from a trusted source. :patriot:

[Mudderoy]

Well just called, it's $95 so not too bad.

[xj4life2]

Happy to assist any time I can !!!!!!

[Mudderoy]

Well before I started working on the Jeep today, I ran down to the local Chrysler dealer and picked up a OEM O2 sensor.

It was $95 ($103 after taxes). I wish I had checked on this before because so far I've purchased 3 Bosch O2 sensors at $65 each (plus tax).

I removed the positive from the battery and grounded it to clear the computer. So in a week or so I'll throw the OBD II scanner on it and get some readings. With all I've been through on this I fully expect to see NO CHANGE. But eventually I guess you will, just can't give up!

http://lh4.ggpht.com/_b0ViaGso2Ko/TFxccP7HTII/AAAAAAAAAYI/lXtzQtlfIpg/s640/2010-08-06%2013.58.37.jpg

http://lh5.ggpht.com/_b0ViaGso2Ko/TFy0_9LRMFI/AAAAAAAAAYY/rQUcF2ptOi8/s640/2010-08-06%2016.09.12.jpg

[jdougn]

Hope this hasn't been covered but how did you determine that your only getting 12 mpg?

[Mudderoy]

Hope this hasn't been covered but how did you determine that your only getting 12 mpg?

Well I fill up note the odometer, fill up again and subtract those two odometer readings then divide by the number of gallons it took to fill up the tank. I hope that's what you were asking.

[Mudderoy]

http://xjtalk.com/images/special/jeepgasmileage2010-8.jpg

I filled up Friday morning, drove to Creekside wheeled for several hours and drove home. The gas mileage suffered due to the slow speed and duration of the engine running burning gas going little or no where.

[4.3LXJ]

That is not bad for wheeling milage. I get about 11 mpg combined.

[Mudderoy]

Well I think I have several MPG threads on here, I'm just going to add to this one... :P

2504

This isn't A REAL CALCULATED measurement, but until recently I was lucky to see 100 miles at the mid way point. For those of you not following along, my MPG has been at least 1 mpg lower since installing the rebuilt 4.0, sometimes 2 mpg. The only REAL issue is I used to be able to drive back and forth to work 5 days before having to refill on the 6th day, usually Monday. I've only been getting 4.5 days out of her.

So about 192 miles to a 18 gallon tank, instead of 215 to 230.

I think the ECU is slowly re-learning since I removed the 160 degree thermostat and install the 195. Calculated mpg has not improved, but this is the first time I've seen more that 115 miles 1/2 tank in a very long time.

[ArmyGuy45]

Well I think I have several MPG threads on here, I'm just going to add to this one... :P

2504

This isn't A REAL CALCULATED measurement, but until recently I was lucky to see 100 miles at the mid way point. For those of you not following along, my MPG has been at least 1 mpg lower since installing the rebuilt 4.0, sometimes 2 mpg. The only REAL issue is I used to be able to drive back and forth to work 5 days before having to refill on the 6th day, usually Monday. I've only been getting 4.5 days out of her.

So about 192 miles to a 18 gallon tank, instead of 215 to 230.

I think the ECU is slowly re-learning since I removed the 160 degree thermostat and install the 195. Calculated mpg has not improved, but this is the first time I've seen more that 115 miles 1/2 tank in a very long time.

Have you thought about pulling the neg cable on your battery to reset your computer??

[Mudderoy]

Have you thought about pulling the neg cable on your battery to reset your computer??

You know not until I was typing this post did I think... "I should have reset the computer when I swapped thermostats"

I think the apparent increase in gas mileage may mean it has learned anyway so I think I'll leave it be and see where my mileage is after the next fill up.

[ArmyGuy45]

You know not until I was typing this post did I think... "I should have reset the computer when I swapped thermostats"

I think the apparent increase in gas mileage may mean it has learned anyway so I think I'll leave it be and see where my mileage is after the next fill up.

Its ok, I am still learning so you are not the only one.:beer:

[silver_xj]

I'll chime in on this thread. I'm all stock with the exception of a K&N CAI and a Magnaflow catback. Right now im reading 203 and the needle is between the 1/4 and 1/8 tank marks. Mix mostly city traffic driving back and forth to work this week. This is with mid grade gas and sea foam in the tank. I can only hope this is normal before I lift it.