Difference in ECUs...?

[TigerDan]

I'm curious about the differences in 14CUX ECUs over the years. I know the EPROM chips are different, but disregarding the chip are there any other real differences, upgrades etc. between say a 1989 ECU and one from 1995? If you took an early 3.9 ECU and plugged a later 4.2 chip into it, would it behave exactly the same as a later 4.2 ECU? I believe I read somewhere that the early ECUs had the chip soldered in so I suppose if that's true, it wouldn't be as simple as just plugging one in...

 

[cmb]

Here's what I know:

Most early ECUs (with the "PRC" part numbers) have the PROM soldered in place. It's only in a socket on later units -- I believe this includes all "AMR" ECUs, and I've heard that some later PRCs have socketed PROMs as well.

Note that 1989 model year NAS Land Rovers used the 14CU system, as the 14CUX wasn't introduced until 1990. The 14CU lacks the wiring in the harness used by the external fault code display module. It also lacks the wiring used by the "tune resistor" (intended to allow selection of the fuel map), although this doesn't matter because the NAS firmware disables support for the tune resistor anyway. NAS firmware is hardcoded to use map #5. The 14CUX systems also use updated fuel injectors that offer slightly better fuel economy.

I've never tried to swap a 14CU PROM into a 14CUX system, but I can't think of any reason it wouldn't work. Most of the upgrades over years of 14CU(X) production (such as the improvement for cold-weather start) are handled by the firmware in the PROM.

--Colin

 

[TigerDan]

'K, thanks for that...I was under the impression that the switch from 14CU to 14CUX came a year earlier, in '89 corresponding with the introduction of the the 3.9...but in looking at my '89 parts truck it doesn't have a code display module or the connector to plug one in, so it does look as though I was mistaken in that assumption.

 

[ptschram]

They are interchangeable, however, the 13 and 14 CU had different wiring for the A/C circuit when compared to the CUx.