Fooling the Computer for Better MPG

[Ecomike]

I tried yesterday and today to monitor what temp CL starts, but the lm2 showed it staying in OL(even though it had went to CL and 14.7). I'll try resetting the lm2 and have the afr, cts, and OL on the same screen so I can at least tell by the afrs the exact temp it does this(I can record too, but should be able to catch it live). The lm2 does have it's limitations: I usually can monitor 4 obd2 parameters at once in addition to the afr(you can set priorities, etc)--any more and then it's too much for it to process and then you don't get accurate live data.

IIRC my son's Ford 96 Taurus goes CL in under 30 seconds from a cold start, if the sensors are good and working. But my memory could be faulty on this. I do recall reading that OBD-II and early HEGO O2 sensors were introduced so that cars could go closed loop in less than 30 seconds of engine start up to avoid air pollution since Cat converters need more than 30 seconds to get up to proper operating temperature.

I doubt the Cat or engine coolant gets very hot in 30 seconds.

What surprised me is that a lack of a working CTS sensor holds it closed loop.
Looking forward to seeing your posted results!

 

[Harlee&Tahoe]

What surprised me is that a lack of a working CTS sensor holds it closed loop.
Looking forward to seeing your posted results!

With RENIX if ECU doesn't read CTS, it will simulate by defaulting to ATS and add 1/2* every 85 revolutions

 

[Ecomike]

What surprised me is that a lack of a working CTS sensor holds it "closed loop".

This was a typo, should have read "open loop"

 

[Ecomike]

With RENIX if ECU doesn't read CTS, it will simulate by defaulting to ATS and add 1/2* every 85 revolutions

Interesting, sorta confirms my actual readings. I ams till surprised that OBD-II does not have a way around the loss of CTS. Maybe because it uses a MAF sensor, and does not use a ATS? Or does the OBD-II have a ATS? It may vary between brands.

 

[xjtrailrider]

Interesting, sorta confirms my actual readings. I ams till surprised that OBD-II does not have a way around the loss of CTS. Maybe because it uses a MAF sensor, and does not use a ATS? Or does the OBD-II have a ATS? It may vary between brands.

My 2 96's and '00 do not have a Mass Air Flow Meter, they do have ATS. I know that when my CTS went bad in my 96 trail rig my mileage went to crap but still no code was thrown. I found it by using the scanner to watch data streams on different sensors to see where my problem was. My CTS was reading -70 degrees.

 

[Ecomike]

My 2 96's and '00 do not have a Mass Air Flow Meter, they do have ATS. I know that when my CTS went bad in my 96 trail rig my mileage went to crap but still no code was thrown. I found it by using the scanner to watch data streams on different sensors to see where my problem was. My CTS was reading -70 degrees.

That is an excellent example of why one needs to check sensors directly and not just look for codes, and not assume that a lack of codes means these little delightful little gadgets are working correctly.

Makes me wonder what would happen if it read 200 F all the time?

 

[stevieb]

Now I need help!!! Getting fed up with Fuel consumption started to look at sensors. While xj was idling removed CTS plug. 1st thing AUX fan came on, 2nd thing check light came on. put plug back fan went off. at least i know if CTS dies AUX fan will go on but now don't know how to cancel check light. it is a 96 xj. now the other thing.
when testing the o2 sensor must i earth to the body or what? i am using a digital meter but the readings i am getting are running around so much that i can't actually say what it is. it even runs into the negative. i have the meter set at 0.00 setting. is that right?
there are 4 wires as i said. grey, white, white, black. what is what???

 

[Ecomike]

Now I need help!!! Getting fed up with Fuel consumption started to look at sensors. While xj was idling removed CTS plug. 1st thing AUX fan came on, 2nd thing check light came on. put plug back fan went off. at least i know if CTS dies AUX fan will go on but now don't know how to cancel check light. it is a 96 xj. now the other thing.
when testing the o2 sensor must i earth to the body or what? i am using a digital meter but the readings i am getting are running around so much that i can't actually say what it is. it even runs into the negative. i have the meter set at 0.00 setting. is that right?
there are 4 wires as i said. grey, white, white, black. what is what???

Two of the wires should be ground wires. I am guessing the white ones. With all power off probe the white wires, and ground the other probes on Ohms setting. Should be less than 1 ohm, if those are the grounds and if they are properly grounded. The gray or white wire should read a steady battery voltage with the other meter lead grounded, meter set for DC volts. The last wire should be the 0-1 volt O2 sensor data wire.

A bad ground on any of the 2 ground wires, no battery voltage on the third wire with the engine running will cause O2 sensor to not work properly.

You can not check the fourth wire with a digital meter, requires an analog, old style needle meter to read the actual O2 sensor output. The out put is a variable alternating DC sin wave, 0-1 volts, and it can be seen on an analog meter set to DC volts of about 0-10, or 0-5 volt range. If it does not alternate, if it stays at a fixed voltage, it has a problem. Check the other wires first. The battery voltage to the one wire on the O2 sensor goes through a relay!!!!, which can go bad too!

Also common is for the O2 sensor wires to rub, burn and short on the exhaust manifold.

 

[1bolt]

1) There's no MAF on any 4.0 they are all speed density maybe you meant MAP?
2) Be careful what advice you accept on checking the O2 sensor... If it's not warmed up it wont be cycling back and forth between rich and lean and will be fairly steady. If there are other sensor problems such as a dead coolant temp sensor or a blown o2 heater element fuse, or the throttle position sensor is off... You guessed it the o2 sensor reading wont cycle back and forth, none of which indicate that the o2 "has a problem" So if you follow certain advice you might end up replacing your o2 for no reason.

3) check the fuel economy rating at the EPA gov site of the 2007 Wrangler 2 door, equipped with the 'modern more efficient' overhead cam, rollerized 3.7L V6 Minivan engine...
4) look at the Wrangler TJ with 4.0

In fairness I believe the 04 and 05 TJ EPA rating was under the older, (since changed slightly to supposedly be more accurate and representative of real use) rating method. But this still means the 06 TJ is using the same rating system (which is probably why it lost 1 MPG from the 05 TJ. Yes I know the JK is a little heavier, but it's also supposed to be more aerodynamic...
Lets not forget that the 3.7 has the advantage (in a apples to apples fuel efficiency comparison) of being smaller displacement.

So roughly 1mpg difference between the efficient 3.7 L and the old dinosaur outdated obsolete 4.0 push rod antique "tractor engine", and maybe not even that much in the REAL WORLD where the 4.0's big time torque advantage will translate into better MPG on winding, hilly, slower speed roads. Or when pulling any kind of load.

 

[Ecomike]

1) There's no MAF on any 4.0 they are all speed density maybe you meant MAP?
2) Be careful what advice you accept on checking the O2 sensor... If it's not warmed up it wont be cycling back and forth between rich and lean and will be fairly steady. If there are other sensor problems such as a dead coolant temp sensor or a blown o2 heater element fuse, or the throttle position sensor is off... You guessed it the o2 sensor reading wont cycle back and forth, none of which indicate that the o2 "has a problem" So if you follow certain advice you might end up replacing your o2 for no reason.

No I was asking what the OBD-II 4.0, newer jeeps were using, MAP or MAF. I was not sure if they had stayed with the MAP all the way to 2002.

Those are some EXCELLANT points, and it seems the issues vary some from Renix, to OBD-I and to OBD-II as to which other sensors, and types of errors can keep the closed loop mode off line, and keep it in open loop.

Might be worthwhile to start a discussion, investigation, and data table as to just what can keep the 3 different ones in open loop, thus making an O2 sensor look dead in a direct O2 sensor test!

Everything I have read says the closed loop mode should activate in less than one minute, as ours have HEGO's, heater is built into the HEGO to get the O2 sensor up to operating temp in about 30 seconds.

Still for poor MPG's, I would start with testing the O2 sensor to see if it is getting into closed loop, then go from there.