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Garage Band

FAST’s wide-band sensor helps our supercharged LT1 really dance to a different tune.

Story Andy Bolig - April 05, 2012 10:00 AM

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This is the heart of the matter. The design and engineering of the wide-band sensor allows for a clearer view of the air/fuel ratio, even beyond 14.7:1. 

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The tools of the trade. At idle, our Tech1a shows that the ECM is adding fuel while the FAST wide-band meter shows an air/fuel ratio of 13:1. These two tools allowed us to safely tune our engine’s fuel for more performance and better fuel mileage and driveability. 

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Our Vortech supercharger kit was engineered before computers took over EVERY aspect of our cars’ operation. Increasing fuel pressure mechanically was adjusted by changing out these discs. 

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There are several different ratios available from Vortech. The complete kit allowed us to make slow changes as we leaned out the fuel. 

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Our MAFTranslator has allowed us to fine-tune the A/F ratio at 500 rpm increments and under three different load settings (low, mid, high). We can adjust the fuel leaner or richer in percentages by typing in the amount (up to 60% +/-) at the desired rpm. The MAFTranslator adjusts the signal going to the ECM to compensate for the changes. Works great and allows for tuning of our ECM without having to burn another chip for each change.

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These two charts illustrate the differences between wide-band sensors and narrow-band units. Notice how volatile the line becomes as the air/fuel ratio nears 14.7:1 on the narrow band while the wide band sensor carries a gradual curve, allowing you to see more than whether or not the engine is close to stoichiometric. Image: Bosch Auto Parts

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These two charts illustrate the differences between wide-band sensors and narrow-band units. Notice how volatile the line becomes as the air/fuel ratio nears 14.7:1 on the narrow band while the wide band sensor carries a gradual curve, allowing you to see more than whether or not the engine is close to stoichiometric. Image: Bosch Auto Parts

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Using a wide-band air/fuel meter to help tune our cars has become as important of a tool as wrenches

There are so many reasons why a properly tuned engine should be the goal of every enthusiast. No denying that they run better, but they also run much cleaner and they use less fuel as well. 

Our ’85 Corvette has a non-factory LT1 with a Vortech V3 (T-trim) supercharger installed. There are a lot of modifications to the install and if we were using the cumulative-performance-parts math technique, everything should have added up to about 1,000 hp with all the “added parts”. Sure, that’s a little bit of an exaggeration, but in reality, our combination was still much less than it could have been without some final tuning 

The later model GM ECM that we are using has helped make our LT1 a great running package when it comes to driving around town. Its capability in making changes, even when only receiving input from the factory-style narrow band O2 sensor, is to be commended. We’ve already put quite a few miles on our car and have seen upwards of 28 to 29 mpg on the highway. Driving around town, the car did pretty well also. The problem arose when we decided to push the envelope and go into boost to get more performance from our LT1. For those asking, “Why didn’t you go with a newer aftermarket ECM?”

At the time, this was the best of both worlds. We wanted all of the dash functions to still operate (fuel mileage/average, range, etc.) which meant that we couldn’t go past 1989 technology, and by using a crank trigger instead of the Opti-spark, this ECM allows that to happen. What it doesn’t allow is a flashable tune. We started off with a tune in the “chip” that was close, but conservative, and we would sneak up on it from there.

We’re using a newer, LS-style MAF sensor, so we needed something to convert the frequency signal from the newer MAF to the voltage-based signal that the ECM could understand. We’re using a Gen-II MAFTranslator from Full-Throttle Speed and Style to allow that to happen. It also allows us to make changes to the “tune” at various rpm and load settings. The newest aftermarket ECMs can overcome many of these hurdles, but they weren’t available when we built the car. 

The car has run great up until the engine would go into boost. At that point, the ECM was in a realm that it never was intended to participate. There were components to help the ECM speak the language of boost, but in reality, there were some finer points lost in the translation. The factory oxygen sensor in the exhaust pipe does OK for keeping the engine relatively in tune, but as you get closer to that edge of performance-tuning, you need a more stable means of reading exactly how the engine is running or needs tuning. That’s where the wide-band sensor comes in. 

The difference between a wide-band sensor and the factory narrow-band sensors, like what is found on our ’85, can be summed up in one word: resolution. “Narrow-band” means simply that. The area where the sensor recognizes variations in oxygen levels is very limited (narrow). As the air/fuel ratio goes further and further away from Stoichiometric (14.7:1 or one “Lambda”), the window that the narrow-band sensor is able to resolve is greatly diminished. Wide-band sensors, on the other hand, operate in more of a linear fashion, allowing for better resolution of the air/fuel ratio, even as the mixture continues to go lean or rich. This wider view of your engine’s air/fuel ratio is beneficial as you are tuning your ECM because it helps to show if you are hitting the “sweet-spot” but also how far you are from hitting it. The benefits of having a wide-band oxygen sensor have also been reinforced by the aftermarket, where several of the newer engine controls systems are now utilizing wide-band technology. 

We had wanted to do some wide-band tuning on our car for some time, but we had several considerations. We have a fuel pressure gauge and a vacuum/boost gauge, so throwing another gauge pod up on the windshield pillar wasn’t really appealing. Also, the fuel mixture is constantly changing pursuant to throttle position, so a gauge with a lot of lights might be great for quick recognition, but not something that we’d want constantly flashing in our eyes as we drove our car at night. Once tuned, the need for instant access to the air/fuel reading is diminished, so a hand-held unit definitely fit the bill. We could install it when we wanted to check-up on our engine’s tune or do some tweaking, but could also keep it safely in its case where we knew it would be safe. 

We settled on FAST’s unit for several reasons. While it is backlit, it doesn’t utilize flashing lights that might tend to distract, but more than instruct. Also, it can either be mounted as a permanent fixture or it can be hand-held. Our computer uses a narrow-band input to regulate the air/fuel ratio and the FAST unit can not only operate in wide-band, but also can transform that information into a narrow format for use in controlling the ECM. We left the original system intact and only used the wide-band readout to show us the air/fuel ratio, but since we have an LT1 which typically uses two oxygen sensors (one in each bank) we didn’t need to install another bung for the wide-band sensor. 

With the help of the MAFTranslator, we were able to get our engine running pretty close in closed-loop, part-throttle operation. Our air/fuel ratio at cruise was a little rich at 13.5:1, but when we stepped on it and went into boost, the engine would go pig rich. Our Tech1a scan tool would tell us that it was going rich, but we already knew that from the blackened tailpipes. Truth be told, we simply “didn’t go there” and just drove it around peaceably, enjoying the fuel mileage. But we knew there was more under the hood. 

We were delving into uncharted territory, so we hooked up the wide-band and the Tech1a so that we could watch the air/fuel ratio and keep an eye out for any engine-damaging detonation. Also knowing the block-learn numbers at a given operating state let us know how closely we were to being “in tune”. Driving at cruise, our block-learn was hovering right around 126, where 128 is ideal. If the number is lower, the engine is running rich and the ECM is pulling out fuel. If the number is higher, the ECM is adding fuel to richen the mixture to achieve 14.7:1 (stoichiometric). Everything looked good at cruise, but we didn’t install a supercharger to only drive our car at cruising speed. 

The heart of our system is a Vortech LT1 kit. It was designed for around five pounds of boost and our kit (an older version) doesn’t have an intercooler for the relatively low pressure produced by the original A-Trim supercharger. What it does have is what Vortech calls an “FMU” or Fuel Management Unit. This is basically an auxiliary fuel pressure regulator. Where the factory regulator works on vacuum, the FMU works on boost, increasing the fuel pressure as boost increases. You can adjust the ratio that the FMU increases the fuel pressure by changing out metal plates inside the unit. Since our system was designed for a stock application using 24-lb injectors, it had a relatively high ratio, which we found out once we tore it apart to be 10:1. Our engine has larger 30-lb injectors, and coupled with the increased boost pressure (around 10 lbs), that was entirely too much fuel. We didn’t know exactly what ratio we had, and we didn’t know what we would need, so we ordered a complete FMU recalibration kit from Vortech. 

With the wide-band and Tech1a in hand, we went in search of boost and horsepower. We found half of that – boost. If we got anywhere near wide open throttle, the fuel pressure would spike to 90 psi and the injectors would shut down. That was way too much pressure. The air/fuel ratio went immediately to 9:1, the lowest reading available on the wide-band. We needed to install a smaller disc in the FMU and having the kit (p/n 6Z270-010) allowed us to gradually change the settings until we found the right ratio. Leaning out an engine’s air/fuel ratio is best done in small, gradual steps. Go too far, too fast and you could lean your engine out excessively. Not good, especially under boost.

Using the kit as a reference, we found out that we had a 10:1 ratio, so we opted for an 8:1, then a 6:1. Finally, we leaned out the system with the 4:1 ratio disc and we started to get a positive response from the engine. Things were still a little rich, but we could at least work with it within the MAFTranslator to bring it into line. Swapping out the discs was very simple and makes tuning a system utilizing an FMU a breeze. Just go slow, keep an eye on air/fuel ratios and watch for knock in the cylinders. 

With the wide-band air/fuel gauge, the Vortech FMU calibration kit and a scanner to watch for damaging knock conditions, we were able to bring our little ’85 Corvette around to a stout street performer. The air/fuel ratio is still a little on the rich side under boost, but we can continue to tweak it a little at a time with the MAFTranslator to get it right where we want it. 

Using a wide-band air/fuel meter to help tune our cars has become as important of a tool as wrenches and until they change away from internal combustion engines, they will remain pertinent to engine tuning with carburetors or EFI. What was once only available to high-dollar tuning shops has become accessible to about any garage, even yours. 

For Your Information:

 

Fuel Air Spark Technology

(877) 334-8355

 

Full Throttle Speed and Style

(586) 294-4404

 

Vortech Engineering

805-247-0226

 

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