DME differences for early/late S2s

[Mark944na86]

I've discovered that the Bosch DME changed on the S2 midway through 1990:

Porsche 944S2 1988 - 1990 Bosch #: 0 261 200 195
Porsche 944S2 1990 - 1992 Bosch #: 0 261 200 458

OK, so what happens if you put a chip designed for the later unit into the earlier one? The reason I'm asking is that I was considering buying a Weltmeister chip, but it is unclear whether it was designed for the early of late DME unit. It's advertised as a 90-92 chip, which would indicate it was designed for the later DME, but the Weltmeister site only indicates Weltmeister only seems to make one S2 chip, and it is for the 89-90 (i.e. earlier) DME!

ProMax Motorsport http://www.promaxmotorsport.com/ at the very least make two separate chips for these different DME units; it's not clear that other manufacturers do.

Anyone know what the story regarding differences/interchangability is? Obviously don't want to buy a Weltmeister chip that won't work, or will cause damage.

Mine is the earlier DME, BTW.

-Mark

[Dantilla]

Sometimes parts and part numbers get updated.

The spare fuel pump relay I keep in my 944 has a 993 part number.

I'm not aware that there were any changes. They may be interchangeable.

[944 Ecology]

The difference has to do with the ballast resistors on the injectors.

The injectors are different for the two types of DME boxes.

This "should" not affect whether or not the upgraded chip will work in either box... that said, I would have to see empirical evidence that a chip "upgrade" makes a big difference on any normally aspirated engine without a lot of extra engine work.

gb