l28et fuel management
I spent a lot of time researching options to control fuel delivery in my l28et for the Sinister s30 project. Xenon’s website is a great resource overall, and answered the majority of my questions, but I had trouble finding a concise explanation as to what common fuel management choices were available.
First off, if you’re putting an l28et into your own s30, you’ll need to decide if you’re going to keep the stock fuel tank or not. The stock tank is un-baffled, so fuel sloshes around when cornering, accelerating, or braking. If the tank isn’t full, the fuel pickup will sometimes run dry and won’t deliver fuel to the engine.
If you don’t mind replacing the stock tank, make sure you get a baffled tank. These essentially have doors that keep a small amount of fuel at the pickup so the fuel pump never runs dry. Many s30 owners install baffled fuel cells, which are the ideal solution but are time-consuming and require a welder to install.
If you’re keeping the stock tank without modifying it, you’ll need two fuel pumps and a surge tank. The surge tank is a small container (less than a gallon) that holds fuel. The first fuel pump feeds the surge tank, and the second pump pulls fuel from the bottom of the fuel tank into the engine. This is a simple, economical option if your stock tank is in serviceable condition. I’ll be using an old 1.5liter fire extinguisher as my surge tank, and I’ll post up a diagram of exactly how it works later. For now, you just get a picture of the extinguisher.
The third, more uncommon option is to fill your stock tank with a sponge-like foam. The foam holds fuel and keeps it from sloshing. It reduces lateral weight transfer and is relatively inexpensive, but render conventional fuel gauges useless.
The final option is to keep the stock tank but add baffles. I can’t come up with a compelling reason to do it unless you’re really into keeping the car looking completely stock. You’ve gotta be pretty OCD to care what the fuel tank looks like, though.
280zx-t ecu is pretty much a paperweight that uses electricity. For most cars, it’s better to unplug the o2 sensor, which feeds information that would be absolutely critical to any other car. The z31 ECU is pretty much plug-and-play and will improve mileage somewhat. There are aftermarket ECUs available, such as the Wolf, which come highly recommended, but are expensive ($1000+ USD).
I came to the conclusion that the ideal solution is to install MegaSquirt, but it’s a time-consuming ordeal. First, you’d have to decide which version of MegaSquirt to purchase. There’s MS1, MS2, and MS3, and there are various versions of software that can be run on each. Without getting into too many details, my recommendation is a pre-assembled MS2v3. It’s worthwhile to purchase a relay board, a cable to connect the two, and another cable to run to the engine itself. You’ll still have to connect all the wires to the correct sensors and inputs, but it’s a straightforward affair. You can get away with building the whole thing for around $400 if you don’t value your time very highly and have a moderate amount of experience with soldering, but I highly recommend the pre-assembled kits.
The most crucial sensor on for fuel delivery is the air measurement sensor. The stock AFM (air flow meter, uses a flapper to measure air being sucked/pushed into the engine) is inferior to a MAF (Mass Air Flow sensor, measures air density/velocity), which isn’t quite as good as a MAP (Manifold Absolute Pressure, measures how much pressure is in the intake manifold). MS2v3 comes with a MAP sensor built-in, and can accurately read up to 15psi of boost.
The second sensor that’s important to note is the o2 sensor. It measures the amount of unburned oxygen that leaves the engine, and the ECU adjusts the fuel map based on what information the o2 sensor offers. I’ve heard from several people that the stock 280zx-t ecu goes a little crazy with an o2 sensor plugged in and they recommend removing it for better performance and mileage. It’s strange and contrary to normal logic, but it’s become common knowledge at this point. That’s just one more reason for me to dislike the stock ECU even more.
If you’re installing megasquirt or making a major change to your engine configuration, you’ll want to borrow or buy a wideband o2 sensor. A wideband displays just how rich or lean your fuel/air mixture is. It’s much more useful than a traditional o2 sensor that essentially only tells you if you’re rich or lean.
The more accurate the information you’re feeding into the ECU, and the more information you’re feeding it, the more accurate it can be. The faster and smarter the ECU, the more precise the end result will be. There’s a big difference between accuracy and precision, but you want both, not one or the other.
Fuel management is where you’ll gain almost all the mileage gains on an older efi car. There can be significant performance increases as well if you end up fine-tuning your setup and spending a respectable amount of time getting it right.