Tuning Holley 4Di Fuel Injection

These tips apply to the original Holley 4Di TBI system. This is the first laptop computer programmable fuel injection system that Holley offered back in the mid 90's. The files that it writes have the extension  .M16. 

The new Commander 950 systems that Holley now offers appear to be well engineered, true world class EFI systems. These tuning tips do not necessarily apply to the the Commander 950.

For anyone who has struggled with the old system, my sympathies.I have worked with this system since 1995 and have programmed it to work almost flawlessly in my car. This took many hours of trail and error to figure out how the changes affected the functionality of the engine. Now I like the system, even with its shortcommings (although I would really like to step up to a Commander 950 someday).

Holley had had a decent hardware package that used GM sensors and connectors, but it was controlled by a software package that was apparently written by the night janitor - in his spare time - drunk. They even had a data acquisition software that could talk to the system, but didn't offer it to the consumers! I am offering this data acquisition software here as a download for people have this system. If anyone out there has copyright issues with this, email me and I will take it off. And Holley, if you are listening, shame on you for not offering this to us in the first place!

Starting:
On a cold engine, hitting the starter right away seems to put you into an idle mode that takes a few seconds to come up to the high idle speed. Instead, turn the key to ON so that the fuel pump comes on, and then turns off with its internal timer. Now engage the starter and the motor will fire and come up to cold, high idle instantly. 

Idle Tuning:
If you have a cam with overlap that is more than stock, you have probably found that the oxygen correction sends the idle into convulsions as it tries to maintain a stoichiometric mixture on an engine that won't idle with one. To keep the oxygen sensor from interfering with this basic function, set the oxygen trigger voltage to 0 (zero) for Idle only. The zero setting puts the computer in open loop for that RPM range only. As you come off idle, the oxy kicks back in to closed loop and all is good. Once you get the oxy out of the way you can set the idle mixture where the engine is the smoothest. 

In the advance features menu, set the idle to something normal like 750 RPM, then tune the idle with the idle speed screw on the TBI to an RPM that is just above the programmed setting. This keeps the idle air controller from causing the idle to hunt up and down slightly. 

Spark Advance:
This function was troublesome for me. It seemed to interfere with idle smoothness and engine starting. I disabled it and went with a conventional HEI distributor with normal advance features. Maybe you have had better luck. Let me know.

Deceleration Wait State:
Set that puppy to zero seconds. No need to spit fuel into a decelerating engine. I have found this setting to not affect engine smoothness with my setup.

HONDO Data Acquisition Software:
Again, download this saving grace. Unzip these files into a separate directory and run it with the computer hooked up to the ECU.  Select READ_DATA from the menu, and you will have a data display similar to the Holley data panel. Hit the W key to start data logging. The first time you do this, you will be placed in a screen that allows you to set the file name. The default is the date and hour.

Drive off and allow the system to gather data. You can hit the W key as you drive to start and stop the datalogging as often as you want while writing to the same file. Please don't crash while doing this (ok, my butt is covered legally, whew!).

The driving loop should be designed to gather data that is meaningful. Do some steady RPM logs first to get data on cruise performance. Then do some gradual acceleration runs to get data under higher load values. Do some full throttle runs to see what is happening under full load. 

Once you have a data set, go to GRAPH_LINE to see this data represented graphically. Select the file, hit enter and you will see a list of parameters to graph. Hit the space bar and arrow down to select the parameters. For fuel curve purposes all you really need to see is: MAP, RPM, Oxycorr, Oxygen voltage. The fewer items selected, the better the graphs look. Once selected, hit enter to graph. When the screen finishes drawing, hit F7 to rescale the windows to show the maximum data range. 

You are looking for data where the oxygen correction is outside of the 0 to -10 range. If oxygen correction shows a positive value, then the basic fuel map is too lean for that MAP and RPM. Use the Fkeys as shown at the bottom of the screen to move the cursor line to relate values. To zoom into a range of data, move the cursor line to just before the block of data you are interested in and hit F2. Move the cursor line to just behind the block of data and hit F8. This will show that data full screen. To get back to the entire data set view, hit F7.

Fore more sophisticated data sorting and interpretation, you can export the data file into a .CSV format file. This format is readable by spreadsheet programs like Excel. You can use the spreadsheets filtering,  sorting, and graphing functions to rearrange the data  look at it many different ways. 

The best way is to play with it and get a feel for what you are looking at.  This is not a complete set of turn key instructions on how to tune a fuel curve, but if you take your time to understand the system and work with it, you can get it to perform very well.