A fuel pressure gauge will need to be hooked up at least temporarily. The supply side needs 12-21psi and the return side needs 0-3.
Holly makes systems with either a progressive or a 1-to1 throttle linkage. This system uses the progressive linkage. The rear injectors need to be adjusted to come on when the secondary throttle blades start to open. The primary throttle blades need to be adjusted so that the engine will idle mainly on the air going through the throttle blades. The Idle Air Control (IAC) motor supplies some air at idle and increases the air supply when the engine is cold based on the RPM you have programmed for cold running.
I borrowed a laptop from a
friend. It had a dead battery, like
most laptops, so I had a choice between a cigar lighter adapter for $75 or a new
battery for $175. I chose the
adapter. When you are tuning it
helps to have a friend drive. If
you are tuning alone, don’t set the laptop on your vinyl seats because it can
melt them and it blocks the laptops ventilation.
Set the laptop on a piece of cardboard or wood.
above: Some examples of the tuning windows. Their are 11 tuning windows and two graph windows. When the engine is running the cell that the computer is using will be highlighted.
There are over 300 variables to adjust in the program.
Tuning is fun, but it is a long and involved process.
The 02 sensor only makes small adjustments, so you have to get the
mixture close to ideal before it can work properly. The
numbers used in the fuel map are an arbitrary representation of the fuel injected.
Fuel needs to increase with load and RPM.
The program has special graphs that can be used to fine tune for
acceleration and startup enrichment. It can also
change the amount of fuel injected according to coolant and/or air temperature.
For instance if the engine starts to overheat extra fuel can be injected to help
cool it down.
I spent a month fooling with the tuning. I got the freeway cruising set fairly easily, but the city tuning is difficult. I had trouble with it being too rich most of the time and too lean other times. I had to return my friends laptop so I set the F.I. to run slightly rich with the O2 doing its best to lean it out. With a little more tuning I believe that I could further improve my gas mileage.
City mileage improved slightly to about 10-10.5. Freeway mileage went up from 10.5 average to a 12 average. The car no longer smells of gasoline of hot days, and cold starting is much simpler. The quicker cold starts and more efficient cold idle will significantly prolong engine life.
During acceleration the air/ fuel ratio is about the same (12:1) on a fuel injected engine as a carbureted engine. However, during cruise situations the computer can drop the ratio to a more efficient 14.7:1. Once you get on the freeway and start cruising the efficiency of the closed loop system really shines. All around there is a 1-1.5 mpg improvement, but in some situations their can be as much as a 3 mpg improvement.
This installation is much easier on cars that have charcoal canister systems because they already have a return line and a vapor separator. But either way, make sure you have another car to drive for at least a month while installing this system.
I figure that this system will take about six years to pay for itself, so it may not be for everyone. But for the control freak it lets you have complete control of your engines fuel metering and the ability to watch what is going on in real time. This is an enthusiasts dream come true.