Exhaust Experiments & Air Fuel Ratio
 

I did an unconventional experiment when I accidentally broke my exhaust nuts & couldn't screw the pipe on. This led me to drive 360 miles without a midpipe, cat & muffler.

The result was the best gas mileage ever. I drove 330 miles before the gas light came on. My previous best was 315.

I put on a highflow cat but took it off because it had a severe drop in mileage. But when I take the whole thing off my mileage goes up..hmm so now its time to tamper with the 2nd O2 sensor.

Its something I don't want to duplicate again but it led me to do to 2 different tests to try out.
The problem with my car is if u lean the fuel too much the 2nd O2 sensor picks it up because theres no gas to burn in the cat. Its all got burned in the more efficient A/F ratio. The 2nd sensor mimics the first sensor & inefficient CAT cel (p0420) is given robbing mileage again

1. O2 Simulator - Trick the 2nd O2 sensor to thinking everything is normal.
https://www.mkiv.com/techarticles/oxy...sor_simulator/

2. O2 Sensor Deadzone - A O2 Sensor that isn't in direct exhaust airflow fluctuates different than the first one in direct airflow.
https://www.k-series.com/forum/showthread.php?t=8833

Im going with the $5 option 2 mod first to see if it gives me more control of the air fuel ration w/o making the CAT mad.

Anyone else dont similar tests?

You can buy an EFIE for around $60-70.

An O2 sensor cycles around 1Xs per second..maybe a little longer? Info usually in the FSM. Cycling too slow is called a "lazy" sensor...sign that it needs replacing.

exhaust selection depends on the car and what exhaust you're putting on. a properly sized free flowing system will have little difference. the stock system tuned for quietness will make some difference, a cheap replacement system will make a big difference.

As for the engine, it depends on the manifold design and how the engine's designed. I had an infiniti G20 that broke the exhaust off before the cat and while highway/high rpm power and mileage was great, you coudln't drive the car under 3k rpms (not that it minded) put the exhaust back on and BOOM, chirp the tires at 2k and accelerating it tops out around 6500 rpm and gets great mileage in town, 1-2 less on the highway

I have a EFIE & A/F Gauge already. The problem is the EFIE lowers the ratio for about a few minutes. Then AF ratio goes back up. Im burning all the fuel before it hits the cat, then the 2nd O2 sensor pics it up and either throws a 420 or re adjust the ratio :(.

Aren't you supposed to put the EFIE on the second sensor?

ZugyNA -

I don't think so. That was not my understanding when I installed mine :

Eagle Research EFIE Online ...
https://www.gassavers.org/showthread.php?t=5036

I think that older cars have only one 02 sensor (pre-OBDII?!?!?!) in the exhaust manifold, so it works better with them. On my car, I think the EFIE works because I can *see* the A/F ratio go lean. My observation is that it cycles up to lean and back down to normal (see post above). I do think that the better setup is an EFIE for each sensor, but I only have one EFIE effecting the exhaust manifold 02 sensor.

Right now I am disabling the EFIE to see what my long term MPG is without it.

CarloSW2

Well....if the second O2 has the final say...it's possible that using the EFIE on it would work? Using it there would tell the ECU that the mix was too rich and over ride the first O2?

Interesting.

ZugyNA -

I think that having an EFIE on both 02 sensors would be best. In terms of dominance, everything I have read about "closed loop" operation implies (to me) that the 02 sensor in the exhaust manifold is the one that is primarily used by the ECU/PCM. The second 02 sensor (again, from what I have read), is helping to maintain the health and efficiency of the catalytic converter.

Hrmmmmmmmm ...

Hypothesis : At least one 02 sensor is needed for closed loop operation.
Test #1 : Disconnect first 02 sensor and see if car is able to go into closed loop operation. Note OBDII error codes. Reconnect sensor. Clear error codes.
Test #2 : Disconnect second 02 sensor and see if car is able to go into closed loop operation. Note OBDII error codes. Reconnect sensor. Clear error codes.

For each test, a failure to enter closed loop implies that the ECU/PCM depends on that sensor for closed-loop operation. If both tests fail to enter closed loop, then both sensors are absolutely necessary for closed loop operation.

Here is another thread by XFi on the same subject :

Just ordered an EFIE - BrightGreen FeverBuster
https://www.gassavers.org/showthread.php?t=4894

I think that someone around here (XFi?!??!) was going to install an EFIE on both 02 sensors, but I can't remember who.

CarloSW2

A lot of it depends on the particular ECU (vehicle) that you are working with? I've read of people having problems with double O2 Dodge trucks...where the ECU over rode anything they tried.

I'd try it on the second O2....though you might get a code if the ECU starts to think the first O2 or whatever is faulty.

I ran an EFIE on a 3 wire O2 '87 Nissan using around 200 mas. Found that the temp sensitivity was to my advantage since the mas increased with temp...allowing a little richer operation when cold. Found it was best to find a place in the cabin that was down low...away from sun and heater/AC flow to get an ambient temp.

The main gains from an EFIE are supposed to come from using them WITH something like acetone or fuel heat....though it's a good idea to get the ECU to cooperate with the EFIE first?