Air/Fuel ratio gauge

[MightyMaro666]

Ok i just got an air/fuel ratio gauge and im not sure if it will work on my car? As you all know there are 2 o2 sensors on an LS1 and i dont know how to hook it up to both sensors of just to do it on one. Also will this gauge mess with the signals going to the computer???

[wolfdogs]

Re: Air/Fuel ratio gauge

Originally posted by MightyMaro666
Ok i just got an air/fuel ratio gauge and im not sure if it will work on my car? As you all know there are 2 o2 sensors on an LS1 and i dont know how to hook it up to both sensors of just to do it on one. Also will this gauge mess with the signals going to the computer???

off subject:

ever heard of NATC?

located in Silver Springs?

i spent 1 week a month out there for 13 years in my job. The Ormsby House and places in Reno are my second home

[Joe 1320]

Two ways to do this. Since the gauge taps into the 02 sensor wire and you have two sensors, you'll either need two gauges to observe in real time or a double pole switch to go back and forth between the two sensors. The latter you'll only be able to observe one sensor at a time.

[N20LT4Bird]

I haven't done this, but I suppose you could install another sensor right before your CAT and dedicate it to your guage. This way it would get a reading of the total exhaust. Probably not as accurate as two guages, but maybe more cost effective and easy to read??? Just a thought.

[Injuneer]

The gauge isn't going to supply much in the way of useful info, so I wouldn't agonize over the install. When I had one, I just installed it with a single pole-double throw switch, so I could watch either side. Eventually I replaced it with a ScanMaster, which I still use.

PS: There are 4 O2 sensors on your LS1.... make sure you wire it to the pre-cat sensors. Don't cut into the sensor wires, splice into the vehicle harness wires somewhere between the PCM and the sensor plug. Make sure your connections are extremely sound... you are working with millivolts.

[N20LT4Bird]

Why do you say the guage isnt going to supply useful info??

[Joe 1320]

Originally posted by Injuneer
The gauge isn't going to supply much in the way of useful info, so I wouldn't agonize over the install. When I had one, I just installed it with a single pole-double throw switch, so I could watch either side. Eventually I replaced it with a ScanMaster, which I still use.

Fred, I use a scanmaster as well as an air fuel gauge on my GN. I have to say that the gauge reponds much quicker than the scanmaster. I do prefer to read the actual output in millivolts, but the scanmaster just doesn't sample as quickly as a real time digital bar graph gauge. That's why I use both.

[Injuneer]

Niether of them can respond any quicker than the O2 sensors, and there is a delay and a hysteresis in their response.

For N2OLT4Bird:

The gauges use the stock O2 sensors. These narrow-band sensors are intended to be accurate ONLY at 14.7:1, +/-0.1 units of A/F ratio. And, in closed loop, sensor output is varying over a huge range. As a result, at part load, part throttle, all you will see is a psychedelic light show, with the gauge swinging rapidly from full lean to full rich and back.

At WOT, you will typically be running an A/F ratio in the range of 13:1 for an NA setup, 12:1 for a blower and even richer for N2O. This puts the stock, narrow band sensors in the 800 - 1000mV range. They are not accurate at these levels. The curve of millivolts vs. lambda is extremely flat.... it takes a large change in lambda (A/F ratio) to make a tiny change in mV's. But, at these mV levels, the sensors are extremely sensitive to operating temperatures..... a small change in operating temperature can cause a large change in mV output, masking major changes in A/F ratio.

The biggest value of the gauge is to identify impending sensor failure.... slowing response, readings always on the lean or rich side, etc. And, it will show you a complete fuel failure... the "rich" LED will be replaced by the "lean" LED, but by then it will probably be too late in a power adder motor.

Finally, few of the meters are actually "calibrated" in A/F units, and simply indicate lean-normal-rich in fairly wide bands.

[Jay 02 TA ws6]

Originally posted by Injuneer


At WOT, you will typically be running an A/F ratio in the range of 13:1 for an NA setup, 12:1 for a blower and even richer for N2O. This puts the stock, narrow band sensors in the 800 - 1000mV range. They are not accurate at these levels. The curve of millivolts vs. lambda is extremely flat.... it takes a large change in lambda (A/F ratio) to make a tiny change in mV's. But, at these mV levels, the sensors are extremely sensitive to operating temperatures..... a small change in operating temperature can cause a large change in mV output, masking major changes in A/F ratio.

Can you buy other, wider band sensors then?

[Injuneer]

You can buy wide band sensors and wide band meters. A wide band sensor is not compatible with a factory PCM, so you could not replace the stock sensors. You would have to add another bung, as suggested above.

Until recently, the cheapest wide band sensor/meter combo I had found was the MoTeC Professional Lembda Meter - a mere $1,000. Recently I saw a unit for about $360 that appeared to be authentic.

LM-1 Wide Band A/F meter

MoTeC PLM:



MoTeC Professional Lambda Meter

There is also a do-it-yourself kit wide band setup.... not familiar with how well it works.

D-I-Y Wide Band project

[N20LT4Bird]

Wow, its interesting you say that the readings arent accurate and/or fast enough to make a difference. I am kinda big into the dodge turbo scene and all of those guys do their tuning with an air fuel guage. When they (and I say "they" because I havent done this yet) start boosting above the levels of where the logic module stops adding fuel they rely on the guage to help dial in the correct amount of fuel to add manually. Is there a better way to do this besides the 360 dollar meter you mentioned???

[Joe 1320]

One of the instruments I feel is critical in a max effort forced induction application is an exhaust temperature gauge. Tuning by that along with A/F mixture will prevent meltdown.

[Jay 02 TA ws6]

Originally posted by Joe 1320
One of the instruments I feel is critical in a max effort forced induction application is an exhaust temperature gauge. Tuning by that along with A/F mixture will prevent meltdown.

That's a great suggestion... it makes sense since leaner = hotter...

What temperature range would the exhaust be in for optimal power on a stock motor?

The A/F mix I am shooting for should be 14:1 correct?

I am interested in this because I am going to be playing around with LS1edit next spring... I am running "pig rich" remember ?

[Injuneer]

Even exhaust gas temp (EGT) alone isn't a perfect solution. You need to arrive at the optimum setup for your particular engine by dyno tuning, using a wide band sensor, and an extremely experienced eye for reading the spark plugs. My engine spent several days on an engine dyno before we were satisfied that it was set up correctly. I have an EGT sensor on #7 primary. Now, after verifying the tune with the engine in the car on a chassis dyno, and verifying the tune at the track, we have a pretty good idea where EGT should be. But there is no one "ideal" EGT reading for all setups. EGT again is very sensitive to the type of thermocouple you use, and EXACTLY where you locate it.

I think in the forced induction setups, EGT is a very good way to track A/F ratio, as Joe points out. A friend of mine is building a 1,500HP Vortech blown 383 SBC, and his 2" custom headers have an EGT bung on each header primary tube.



Jay 02:

You have to tune A/F for two different conditions. At idle and part load, you want to maintain exactly 14.7:1. That is the stoichiometric A/F ratio.... in theory each molecule of hydrogen and carbon in the fuel has the proper number of molecules of oxygen to combine with, so that the products of combustion include only carbon dioxide and water. In actuallity, even with this "ideal" A/F mixture, combustion is not perfect or 100% complete, and you will have some oxygen that doesn't combine with the fuel, and the exhaust will contain trace oxygen (what the O2 sensor picks up) and a small amount of carbon monoxide and some unburned hydrocarbons.

But, 14.7:1 is the A/F ratio the PCM is designed to control to, because that is the A/F ratio that yields the lowest combined total of the emissions carbon monoxide (CO), unburned hydrocarbons (HC) and oxides of nitrogen (NOx). That yields the exhaust composition that the catalytic convertor is designed to handle best. And that gives you a fairly decent fuel economy. So..... at part load/part throttle driving, you want the PCM to correctly control A/F to 14.7:1.

For max power and max torque, 14.7:1 is too lean. Classic carb tuning aimed for A/F ratios in the range of 12.8:1 to 13.2:1 for max torque and max power. These seem to work as well for modern EFI setups. But I have seen people get results with mixtures as rich as 12.5:1 or as lean as 13.5:1. But in general, look for something around 13.0:1.

The problem with the LT1 tuning is that when you go to WOT, and the PCM enters "power enrichment" (PE) mode, it uses a fairly complicated formula involving tables that consider several sensors in the engine, and the PCM calculate a variable A/F "target" value. Typically, the LT1 PCM stock programming targets a PE value of 11.7:1, and that is way too rich for optimum power. That is the value you want to change with programming.... tweeking the PE tables to get closer to 13.0:1. In a stock LT1, there might be 10-15HP in that adjusement. Not sure about LS1's.

But if your control system, including all the sensors, is healthy, the ignition system isn't causing excessive misfires and there are no exhaust leaks before the O2 snesors, there is no reason for the engine to run "pig rich". That would indicate you have one or more of the problems I mentioned.