Tom M'Guinn

For you DME gurus out there, I'd like to better understand the function of the DME fuel management under wide open throttle. As I understand it, the DME moves to the WOT fuel map once the TPS a certain amount (over 65%?). If so, is it true that, once in the WOT fuel map, there are only 16 (or so) levels of fuel on the map, and that the level of voltage on the ARM signal determines which of the 16 fuel levels get delivered. If so, does anyone know what those AFM voltage break points are?

fast951

Tom, the WOT is a single row array. The index into it is RPM not voltage. The number of rows varies between stock and aftermarket chips..

Tom M'Guinn

If the DME is indexed to rpms at WOT, and not the AFM signal, then how do piggy-back controllers adjust fuel at WOT, given that they all seem to intercept the AFM signal and adjust up or down?

fast951

The values in the WOT array are used as variables in a formula. The signal is another variable...

Tom M'Guinn

So... is this right: At a given RPM at WOT, the DME will (a) check the AFM input voltage (and other sensor inputs presumably), (b) look up the fuel number on the EPROM's WOT fuel table corresponding to that RPM, and (c) calculate the injector duty cycle using all this data, based on a formula programmed into the DME. I assume the formula used to calculate the duty cycle is hard coded, and not part of the EPROM (that is, the formula itself, rather than the fuel array that helps feed the formula)? Does the same basic theory apply at idle?

Tomas L

As I understand the workings of the DME, your description is correct.
The formula is in the program code for the microprocessor, which along with all data maps is located in the EPROM. IIRC the only thing that is hardwired in the DME circuits is the lambda sensor signal levels for rich and lean mixture.
Yes it does apply at idle to, with the addition that at idle it also takes lambda sensor input in account if code plug is set for closed loop operation.