Carrera DME unit question...

Rick Lee · Rick Lee's Garage

In trying to teack down my fuel mixture problems, I'm starting to think it may be related to the DME unit. My car is an '87 and I am still using the original '87 DME with the newly installed '85 engine. DME units have different part numbers for each of those years, though the Autothority chip from the '85 fit in my '87 DME.

Ditto for O2 sensor. Different part numbers for each year. Could this be a/the cause of my rich running?

ChrisBennet · ChrisBennet's Garage

Richard,
Pretty much the only thing that changed was the idle speed ('85=800, '87=880rpm) and a little more advance. I forgot, what was your mixture problem?
-Chris

targa911man · targa911man's Garage

Doesn't the chip control all the engine functions? Unless the 87 DME box is wired differently from the 85, it would seem to me that the 85 Autothority chip would be better matched to the 85 engine than the stock 87 DME chip. Also, Richard I seem to remember we had a problem with the adapting/soldering of wires for the new O2 sensor when we put it in. Have you checked to see if the sensor is working? (Not that I know how you would do that.)

Doug E · 03-20-2003, 02:31 PM

Do you have the car back now or is it still in the shop?

Rick Lee · Rick Lee's Garage

Car is still in the shop and Stan is having me compile all the info I can on the new engine and possibly mismatched components before he racks up labor charges finding more of them out for me. Dan, I have heard from others (including Wayne) that the aftermarket O2 sensor can be a problem. Marc has had no problem with his. I have a friend at the dealership who says any 3-wire VW O2 sensor will work. There's not much of a consensus on this and the Bosch one is an expensive gamble. Dunno about mine, but it's on the list to be checked. I may have to ask Rob to send me the original '85 DME to try out.

Joeaksa · 03-20-2003, 05:03 PM

If you need one, I have a extra 85 DME unit. Its worked fine in three cars so far.

Joe

Rick Lee · Rick Lee's Garage

Thanks Joe. This gang never ceases to amaze me. Lemme do some more checking first before I go with your DME. Just out of curiosity though, in what cars other than a 1985 Carrera did your '85 DME work?

ChrisBennet · ChrisBennet's Garage

The '84 through '89 DME's are functionally the same. I run my 1989 "spare motor" with my 1986 DME. Are you using the stock '87 chip in your '87 DME?
-Chris

Rick Lee · Rick Lee's Garage

Quote:

Originally posted by ChrisBennet
The '84 through '89 DME's are functionally the same. I run my 1989 "spare motor" with my 1986 DME. Are you using the stock '87 chip in your '87 DME?
-Chris

Chris, I'm using the Autothority chip from the '85 engine in my '87 DME. I've heard from others that DME from 84-89 are the same. Why do they have different part numbers then?

Dutchie · 03-21-2003, 03:48 AM

Richard they are the same. There are a few things different on the early dme. The Eprom for the new versions has 28 pins vs 24 for the old. However you can mod an early version dme to 28 pins easy, and it will function the same way as the later models. The only diffrences are that the old dme used onboard memory and the new ones (28 pins) use the memory on the eprom. Not that i,m so wise

i read all this on http://frwilk.com/944dme/ hope it helps.

Cheers,

Ed

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by Richard LeSchander
Chris, I'm using the Autothority chip from the '85 engine in my '87 DME. I've heard from others that DME from 84-89 are the same. Why do they have different part numbers then?

The boxes are functionally the same but internally different.
'85 DME's usually have a 24pin/2K Eprom
'87 DME's usually have a 24pin/4K Eprom or 28pin/8K eprom.
See my chart DME data chart

I modified my '86 24pin/2K DME to use 24pin/4K ('87 style) Eproms and it runs fine with either my old stock 2K chip or my custom 4K chip. In other words, the '87 4K box will run the old '86 2K chips. I haven't looked at an actual '87 board so I am not positive that my mod to make my 2K box a 4K box is exactly the same as what the factory did.

I hope this helps,
Chris

Dutchie · 03-21-2003, 04:20 AM

Nice info on your chart Chris tnx

i found an eprom programmer than handles the eproms of the later types. Now i,m looking for a way to real time edit one and make changes while driving. Maybe Steve can help me out with that one.

kepperly · kepperly's Garage

Does anyone know if there is any advantage using an 88 or 89
dme in an 87? the change from 24 to 28 pin eprom would to a novice seem like more "computer "power?

Quicksilver · 03-23-2003, 09:53 AM

Quote:

Originally posted by kepperly
Does anyone know if there is any advantage using an 88 or 89
dme in an 87? the change from 24 to 28 pin eprom would to a novice seem like more "computer "power?

It would more like having the Declaration of Independence printed on 2 pages to get more political clout out of it.

The ROM just has numbers in it. It doesn't make any difference what is holding them.

Wayne

Steve W · Steve W's Garage

Power wise, probably not, though I have heard the advantage of the 28 pin eprom is a better idle. The 28 pin eproms were programmed with a idle speed of 880, while the earlier eproms were set at 800 - although one could program the earlier eproms to idle at 880 also. Don't really know if there is any advantage to this for earlier cars, it may have been raised to accomodate for the g50 tranny and clutch of the later cars. I will attempt to perform this mod , and program a new 28 pin chip identical in mapping to what I am running now, some time in the coming weeks, and see if there is any difference.

kepperly · kepperly's Garage

Steve W.
When you get this done I would be interested what the outcome would be to see if it works.

keith epperly

silverc4s · silverc4s's Garage

It won't be possible to reprogram the EPROM while underway, if at all- It would require a FLASH memory chip to do that. Not invented yet in this era...

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by silverc4s
It won't be possible to reprogram the EPROM while underway, if at all- It would require a FLASH memory chip to do that. Not invented yet in this era...

It's possible. You just use an Eprom emulator.
-Chris
Link to Xtronic emulator

Quote:

Eprom Emulator Adapter for emulating 2716-27256 Order I-Emulator $99.95
Order info
Not recommended for new applications instead use the ROMutator

A static RAM that acts like an EPROM 2716 - 27256 Instant programming time - often used to work with car computer chips. Simply, plug the emulator into the programmer, plug the cable to the ROM socket and you can change memory locations while your equipment is powered up. The emulator comes with its own software that allows editing in Hex and ASCII.

Steve W · Steve W's Garage

I wouldn't reprogram the eprom while driving anyways. There is a lot thought and time involved with remapping eproms and I would not remap a new chip in real time.

Dutchie · 03-24-2003, 01:40 AM

Quote:

It won't be possible to reprogram the EPROM while underway, if at all- It would require a FLASH memory chip to do that. Not invented yet in this era...

I can a buy a sytem here that does just the thing, but it costs 2000 euros

Offcourse Steve is right about the thought and time needed to program it. I was thinking of making a number of configurations at home and try them out. I guess stopping the car while doing this is the best thing to do Steve you,re right about that

What i meant was writing it in flash like Chris said, sometimes my english is just not good enough to explain what i mean

Ed