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by Chirag Asaravala

With wideband oxygen sensor pricing having dropped significantly over the last several years, consumer digital air-fuel meters are more affordable then ever before. For under $500 you can own the same tuning capability that before could only be rented during a dyno session.

It seems so simple that one might wonder if there are any downsides to these devices. The answer is yes. Just about all of the air-fuel meters on the market still lack refinement. They fit in that category of "techy" tuning products, looking like Radio Shack projects boxes with clumsy switches and requiring a laptop to configure. They work well if you are willing to put in the time, but the normal enthusiast would quickly lose interest and


The FAST air-fuel meter has the capability of running single or dual wide-band oxygen sensors. Shown is the dual-sensor kit, PN:17402, which costs about $460.
go back to tuning by SOTP (seat of the pants.) Besides, we'd rather be out tuning the car than behind a laptop tuning the tuning tool!

We recently were presented with a Fuel Air Spark Technologies (FAST) new wideband meter to test. While the unit is marketed for its dual oxygen sensor capability - enabling the separate, or averaged, air-fuel ratio (AFR) reading of both exhaust banks, we were impressed by its design and self-contained operation. There is no need for a PC to get this unit configured. For carbureted engines this is a slam-dunk. Install a couple of oxygen sensor bungs right after the headers and you're on your way to precision tuning your idle, part throttle, and wide open throttle fuel delivery.

However, on an EFI car the appeal of dual-bank AF ratios is immediately soured by the thought of wiring up two more sensors into the exhaust. FAST however has solved this issue. The unit is capable of delivering an analog signal that can be set to simulate a narrowband 0-1V signal. You can have a wideband air-fuel meter which will simultaneously replace your stock narrow-band sensors. Read on, we'll show you how.


The FAST kit comes nicely packed in this padded case. Included are the sensors, wiring harness cigarette lighter power adapter, along with the exhaust bungs and plugs. Getting the unit working is as simple as welding the two supplied M18x1.5 bungs into your exhaust, installing the sensors and connecting the wiring. The on-screen display walks you though the setup.
EFI guys may be cringing at the thought of installing two more sensor bungs in their exhaust system. No worries, the FAST system has provisions for sending a narrow-band signal to the factory EFI computer.

We removed the narrow-band sensors and set them aside. We'll have to connect to the stock sensor harness later on in the process.
It's pretty easy to tell a wide-band oxygen sensor (left) from a narrow band. The zirconium dioxide element in the sensor's tip produces a voltage that varies according to the amount of oxygen in the exhaust compared to the ambient oxygen level in the outside air.

The wide band sensors are installed into the existing bungs. Note the connector, it will not plug right into the factory harness. 		The new wide-band sensors connect to the FAST unit using the provided cables. We'll route them from the drivers compartment through the firewall and over the transmission to the connect up with the sensors.


We've routed our cables and secured them out of the way from the exhaust pipes or moving parts. Make sure to mark the cables to identify the left and right sensor.


The cables are connected to their respective sensors. At this point we could connect the other ends of the cable to the FAST wideband unit and the system would be functional - however since this is an EEC-IV EFI car the engine's computer needs a oxygen sensor signal for each bank, or it will throw a trouble code and run poorly.

Under the heat shrink of each O2 sensor harness are a pair of leads which can be used to deliver an analog output signal. This signal can be in one of three formats, which we show on page 2. Our interest is to use the narrowband signal format which will allow us to feed the EFI computer and replace the stock O2 sensors.
The O2 sensor wiring from the factory harness consists of a ground wire, a 12V lead to heat the narrow-band sensor, and a signal back to the computer. We'll take the leads from the FAST wiring in caption 3 and connect to this factory wiring. More

 
(Air-fuel meter installation)
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In This Article:
With the cost of wide-band oxygen sensors dropping in recent years, more and more enthusiasts are utilizing wide-band devices for tuning their cars. We got a hold of FAST's new dual-sensor kit for installation and review.

 


Fuel injected cars typically use narrow-band oxygen sensors in the exhaust system. The FAST system enables you to replace the stock O2 sensors with the wideband ones and still send out a narrow-band signal.
 
 

 

 
What is a Wideband sensor?
Standard "narrow band" O2 sensors operate between 0 and 1 volts, and are only capable of accurately measuring a stoichiometric air/fuel ratio (e.g. 14.7:1). A richer or leaner condition results in an abrupt voltage change (see Fig 1.) and thus is only useful for qualitative determination. Modern automobiles use this "switch" like sensing at idle and part throttle to make small compensations in fuel delivery to keep the air/fuel ratio near 14.7:1.
Wide band oxygen sensors utilize a more sophisticated sensing element which enable it to produce precise voltage output in proportion to the oxygen in the exhaust (see Fig 2.) As a result a wide band sensor can measure accurately from as rich as 9.0:1 to as lean as free air. Wide band sensors used to be cost prohibitive, however recently their wide spread use has reduced prices to as low at $50.