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ECU differences; adaptation...


Wondering if '93-'95 420 with a correct WOT '92 ECU will run EXACTLY the same (prior to exploding at WOT) as the later non-WOT ECU? Despite significant differences with CR, cams, and whatever ignition else?

And, after an ECU change, will just driving the car over time end up at the same idealized adaptation point as forcing the issue via the LED pushbutton or blinker box? Over how long?


.036 Hoonigan™, E500E Boffin
Staff member
The late engine will run basically the same with the early LH module, however the adaptation values will usually be different by a decent amount, with richer adaptation compared to the "stock" module. Same on both 4.2L and 5.0L engines, btw. Generally somewhere around 5-7% difference IIRC?

But yes, eventually the adaptation will happen even if you don't reset to mean values. Depending how far off they are, could be a couple hundred miles, or a couple thousand. Resetting speeds up the process and should keep it to the couple hundred ballbark (i.e., within a tank of fuel, give or take).


.036 Hoonigan™, E500E Boffin
Staff member
Clearer, yes, but is your "basically" different from my "EXACTLY"?
Yep. Different, somehow. If early (WOT) vs late (non-WOT) were EXACTLY the same, the adaptation values would also end up the same within ±1% or so. Since the difference is 5%+ as seen on multiple different engines, something is different in the programming. Doesn't affect power or fuel economy, or anything else that I can see, besides the minor change in adaptation numbers. I doubt we'll ever learn more without getting a Bosch LH engineer to fill us in on how these things really work.