Austin Healey Electronic Fuel Injection - Page 5

Idle Air Control


Idle Air Control (IAC):  The IAC is actually a stepper motor that opens and closes a valve which lets air into the injector blocks, bypassing the SU throttle body.  The ECU controls the IAC to allow constant engine speed during closed throttle body operation.  This valve is particularly active during engine warm up when the SU throttle bodies are in their full closed position as the IAC continually adjusts the amount of air to try to hold the idle speed constant.  All the injector blocks are connected to the IAC through flexible tubing to a common IAC manifold.  When the IAC opens it allows air to all of the injector blocks.  The IAC is mounted on the IAC manifold and should be mounted reasonable close to the injector blocks.  However, there is flexibility in the positioning since the IAC manifold is connected to the injector blocks through flexible lines, however it is best to keep the lines the same length (mine are at 18").


Idle Air Control


Engine RPM and timing (RPM):  The ECU is looking for some very specific information concerning engine rpm and the engine timing.  To accomplish that, we took a GM High Energy Ignition (HEI) distributor and had it machined to fit the Austin Healey.  There are a number of advantages to using a GM electronic distributor: 1) first and foremost, it is directly plug compatible with the GM ECU, 2) it is a pointless magnetic impulse distributor, 3) it is a higher energy than the stock Healey, and 4) the ECU can control its advance, eliminating the need for distributor weights and vacuum lines.  The ECU, through the distributor connectivity, has full view of the engine RPM and the timing advance.  The timing was set at an initial setting of 10° B.T.D.C., and then the ECU handles the advancing of the timing dependent on the engine needs.  The GM distributor was indexed so that the number one cylinder places the electronic plug-ins on the back side of the distributor (away from the engine).  This almost hides them from sight and adds to the stealth element.  The modified GM distributor drops right into the old Healey distributors spot and allows full use of the Healey's mechanical tach drive.  While some GM HEI distributors have the coil integrated into the distributor cap, we used the older version which has the coil mounted remotely from the distributor.  The advantage of this is that the distributor maintains an "old" distributor look, again maintaining the stealth factor.  The GM coil is plug compatible with the distributor.  Even though the coil looks like a newer coil configuration, it can be mounted in an inconspicuous place to keep it out of view.


Oil Pressure Sensor


Oil Pressure Sensor (OPS) (included in mine but optional):  The OPS is simply a low oil pressure switch.  If the OPS transmits a low oil pressure indication (below 2-7.5 PSI) to the ECU, the ECU will shut off the fuel pump.  This is designed as a safety measure to keep you from frying your engine should you loose engine oil pressure.  I have converted from the original oil filter canister to a spin on oil filter.  The side benefit of doing this is that the aluminum housing provided in the spin on conversion kits (Moss, DWM, among others) is the perfect place to drill and tap for an OPS.  While I was at it, I also drilled and tapped for an oil temperature sensor.  The stock oil pressure fittings are left in place.