Skwerl

So, Dan P, you're saying you have a 24-pin turbo non-S box that you swap into your 28-pin turbo-S car and it runs fine? Now I'm confused, because I could buy that a 24-non S and 28-non S might swap without problems (although that's where I'm having a problem), but a 24-non S with a 28-S? Surely there's a difference between the S DME and the early turbo non-S DME?

The reason I'm pretty certain that the DME is the problem is because the performance drop was quite noticeable, and, since I still had the fried original before I sent it out to recoup the "core charge," I tried it briefly and the performance was back again. The fried one worked, but only for about 20-30 minutes before it overheated and shut off.

And I admit it gets confusing throwing all these 24s and 28s and S's around!

Lorenfb

"I was wondering if an 89 DME (I put the "S" in quotes because it's really a turbo S, but not designated as such), also having 28-pin EPROM, is the same DME except for the chip

...meaning, at the Porsche factory in late 1988 the only difference between the S DME and the non-S DME if you opened it up was the different chip."

Both of your statements are correct. Porsche/Bosch did the same thing in '88 & '89
with the 911 3.2s. My 3.2 has a 64K EPROM (28 pin) in it, and as a result has an
overall better running. They used the same Bosch & Porsche part numbers, so it's
not easy to tell the difference without opening the DME unit. That's why you received
a 32K box. You probably should have requested that your box be repaired.

944Fest (aka Dan P)

Yes, Skwerl, that is correct. When I first got my car a friend who has access to modded chips and does some of his own told me his 86 turbo chip was better than his 89. He told me to get an 86 box, and we could use that. I did and it works fine. When I finally had a chance to dyno the car, I made a run with the 86 box, then swapped the 89 box in (with a modded chip) and ran within 1 hp of the previous. I left it that way and have a backup waiting to go. (sorry, she's not for sale)

Skwerl

Well now I just don't know what to think. I guess I'll go ahead and ask for an 89 DME if they can't find an 88 non-S and then switch out the chips, but maybe it will turn out that somehow it's not the DME causing my problem. At least by having the right box, one link in the chain can be ruled out as the problem. Thanks again to everyone for their help.

944Fest (aka Dan P)

I will note that I'm not talking about stock chips here, maybe since my 86 chips were "cranked up" they would have comparable fuel/boost maps to go with an 89 turbo, who knows. If I were you I'd seek another turbo owner in the area and borrow his box and try that. That is what I've done in the past with guys who have issues. Then again, not everyone has turbo pals who don't mind DME swapping. I do know a guy near St Louis who just bought a nice 86, he's new to the Pcar game. If you want a local pal, look him up. His handle here on Rennlist is SS 951. (Scott S.) (I'm not saying he is going to lend you his DME, in fact I'd be willing to bet you he doesn't know where it is- yet)

rcarpen22

Skwerl, you're saying you have a 24 pin DME box from an early car? I happen to need one of those so if you want to sell it let me know via PM or something.
Thanks

Dal Heger

The 951 computers are all the same with the exception of the number of pins on the chips. The early 951 (24 pin) and the late 951 (28 pin) code is the same, the extra 4 pins were never used. You can burn an early program on a late chip and visa versa. The DMEs are the same. The programs for the 951 and the 951"S" are different, but can be interchanged if you so choose. All of the aftermarket tuning can be applied to either chip (24 or 28 pin). Like I said, the 4 "extra" pins were never used. They switched to the 28 pin chips for "later expansion" possibilities that never occurred.

Dal.

rcarpen22

So what happens if you put a 24 pin chip in a late dme and leave the extra pin holes empty? Also, on which end are the unused holes?

Tom Carson

http://frwilk.com/944dme/88_to_86.htm

rcarpen22

Wow, so according to this web site you can plug the 24 pin chip right in w/o any other mods. Has anyone actually done that? I'd be curious to know if someone has successfully tried that.

Tomas L

There seem to be some misunderstandings here.

The 24 pin DME uses 4 kilobyte memory inside the microcontroller and 4 kb in the external 24 pin EPROM (type 2732).
The 28 pin DME don't use any memory inside the microcontroller and instead uses an 8 kb EPROM (type 2764).
The content of a 24 pin EPROM should be the same (with the reservation for tuning for different engines) as the content in the upper 4 kb of a 28 pin EPROM. The lower 4 kb in the 28 pin EPROM should be the same as the code inside the microcontroller (at least function in the same way, it's hard to check if they are identical since we cannot read the content of the microcontroller).

The jumper shown on Frwilks site instructs the DME if it should use code from the internal memory (plus the outside EPROM) or if it should only use external memory.

If you change chip size you have to change the described jumper at the same time.
I'm not sure if it's possible to go from 28 pin to 24 pin since that requires that the lower portion of the code is programmed into the microcontroller by Bosch. I have no idea if they did that when the code was not used anymore.
The other way around should work fine though.

I hope this also explains why the statement that the four extra pins never were used is wrong.
My guess of why they made the change is, that it was to enable them to upgrade the software after the DME was manufactured. If Bosch discovered an error in the program code they could just recall the cars and have the EPROM changed, with the 24 pin DME they have to change to a completely new DME if the problem was in the code stored in the microcontroller.

Tomas

Lorenfb

"There seem to be some misunderstandings here." - Tomas L -

I don't think so, since it's been clearly stated for the last month on this thread!
Also, other threads on this forum have provided insights into this issue too.

Tomas L

Now I don't understand? Are you saying that these posts are correct or are you just being a troll?