Skwerl

This is a bit long, because I probably should've asked a while ago, but bear me out..

A few months ago my DME in my 88 non-S fried. I ordered one from Vertex, a DME rebuilder in Florida, but they sent out a 24-pin unit, probably from an 86 or 87. I realized it was a different box because the 28-pin Guru chips I had taken out of my fried box would not fit in the rebuilt one Vertex sent me. After looking into it, it looked like this shouldn't be a problem. The 944 FAQ indicates that the other pins really didn't do anything anyway, and were probably added in case of future upgrades. A thread search here gave me similar answers; a 24-pin box should work where there was a 28-pin, provided the car is not an S.

Incidentally, I had called Vertex about this, and they thought that because I had a 28-pin car it must have been an S, but I backed off on their offer to send me an S DME. The 28-pin Guru chips I had were labeled 26/6, and the other S markers did not seem to be there. (The brakes, for one, seem to be the same size. As far as the engine number goes, supposedly the one surefire indicator, I cannot find it on my engine. Does anyone have a clear photo of EXACTLY where that is, because I don't see it.) In other words, Vertex thought I had an S, but it doesn't look that way to me. It would, however, explain the following problems adequately:

One thing I noticed was a dramatic drop in performance on the 24-pin DME. I have appropriate Guru chips in it, but the difference is noticeable. The boost just doesn't seem like it hits as hard, and overall the car feels much slower. I used to chirp tires in 3rd, and now I have trouble doing it in 2nd.

Second, I just failed emissions. I have a feeling the two problems are related: the lack of power and failing on hydrocarbons emissions.

So basically, my questions are: for an 88 non-S, should a 24-pin DME from, say, an 86, work without issue? If so, what are the symptoms of a non-S box in an S car? It doesn't seem likely that I've had an S this whole time without realizing it, because the person I bought it from was an enthusiast and did not sell it as an S. Should I pressure Vertex into finding me the correct 28-pin non-S box, or does it matter?

Thanks for any help/info.

Lorenfb

"So basically, my questions are: for an 88 non-S, should a 24-pin DME from, say, an 86, work without issue? If so, what are the symptoms of a non-S box in an S car? It doesn't seem likely that I've had an S this whole time without realizing it, because the person I bought it from was an enthusiast and did not sell it as an S. Should I pressure Vertex into finding me the correct 28-pin non-S box, or does it matter?"

Bottomline: The DME needs to be converted to utilize the 28 pin EPROM. The 28 pin
EPROM had improvements in the u-code over the 24 pin EPROM (32K vs 64K). That's
why the larger EPROM was used. The 968 used a 256K EPROM. You should've asked to have
your original DME repaired, especially when you have a special chip.

Skwerl

Is there a way to convert the DME easily, or would I be best off just trying to get the original 1988 28-pin computer? Thanks for the response, btw.

Skwerl

bump

Jfrahm

If you explained that you have a 28 pin non-S DME I would think the rebuilder would supply the correct part. They must be confused and think there are 24 pin DME's in 1988 non-S cars, which is not correct. It should be possible to make the car perform exactly the same with a 24 pin DME and the correct chip, but if you liked your 28 pin chip I suggest getting the correct DME for it and put it back into service.

Your performace issues might be also be due to bad gas, boost leaks, etc. but regardless I would start with the correct DME and the chip you like and go from there.
-Joel.

Ken D

Actually, it's somewhat correct.
https://rennlist.com/forums/944-turbo-and-turbo-s-forum/191609-chips.html

Like awilson40, I have a 24-pin DME in my 88 non-S. It has never been replaced. Found out the hard way after ordering 28-pin Vitesse chips. John was very understanding. Lesson learned, when ordering chips for '88 non-S open the box first!

Agree with your post, just swap the box for the correct version.

Lorenfb

"Is there a way to convert the DME easily, or would I be best off just trying to get the original 1988 28-pin computer? Thanks for the response, btw."

Just borrow someone's 28 pin DME box and copy the jumper settings at the end
of the EPROM socket. It's very simple and shouldn't take more than 10 to 15
minutes. You also need to replace the EPROM socket, another 10 minutes.

Good Luck

Skwerl

Thanks!

Now for the longshot question of the day: does anyone have their 88 DME out and would be able to tell me what the jumpers look like?

It looks like in the 86 it's 8704, 8705, and 8706.

Skwerl

Scratch my last post. I don't know what's going on. Those jumpers I posted are from another 86 box I have, but they're different from the ones from the DME I've been using. I guess the 86 I got off eBay was from an NA, maybe.

The one out of my car has B707, B703, and B704 (a longer one that stretches over B705...and it also has B1, if that's a jumper.)

Skwerl

Sorry to post so much to this thread..

I found this site:
http://members.rennlist.com/messinwi...TimPolzin.html

Is that information valid for a 951 DME? Meaning I need to jump B700? Of course, it's not so simple because it says to move 702 to 703, but I already have one on 703.

Lorenfb

"5) All of the semiconductors on the digital board are standard “off the self devices” with the exception of S700 (the CPU in the 84 to 86 with custom programming) and S100 (which is a custom op-amp which reads the flywheel sensors and generates an angular velocity)."

The #5 above is in error, as the injection driver I.C. is NOT a standard part but also
custom Bosch device.

Also, #5 should read, "reads the flywheel sensors and generates an
angular velocity AND TDC POSITION)".

Lorenfb

Some on this forum think that the 944 doesn't use a 64K EPROM (8K X 8 - 28 pins) and
just a 24 pins EPROM (4K X 8), which as mentioned, are jumper selectable.

Please advise those otherwise!