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1987 3.2 Carrera Motronic DME questions, optimisation?

Not sure if this is opening a can of worms from some of the posts I've found in the search function (About chip modifications specifically, some heated words there!!) but I have some questions about the Motronic DME ECU used in the 1987 onwards 3.2 Carrera both RoW and USA specification. I am considering optimising the Motronic unit in my own car.

My vehicle is the M298 version for Australia, which basically means it's the USA specification 9.5:1 compression catalysed 930/25 engine with connector terminal 10 connected and jumper terminal 28 installed on the harness.






I've searched the web and this forum but have been unable to find the answers to a few questions so hoping someone can help me.

My car has the Motronic ECU 911.618.111.20 (Bosch 0 261 200 082) and being a 1987 ECU has the 4K chip. I have read on this forum that the 1989 model year ECU has the "Best" performance being its mid range mapping is further optimised over the 1988 and earlier Motronic units.

1. Apart from buying a new ECU, how does one convert the 1987 ECU to run the mapping of this 1989 unit?


2. In Australia, 98RON pump gas is freely available. Bearing that in mind, is there any reason why I wouldn't run the ECU 911.618.111.18 (Bosch 0 261 200 078) which is for the high compression leaded engines?

I assume this unit has more aggressive mapping for fuel enrichment and ignition advance over the M298 specification ECU. Does anyone know? Note: according to the Porsche Technical Specification Book however (Scan of which appears below) the ignition advance at least for performing an advance test appears to be the same irrespective of high compression or catalysed engine Motronic units, weird!)




I am unsure if this leaded high compression ECU mentioned above would be compatible with a catalyst. I suspect it isn't however if one considers the wiring diagram scan, see pins 23 and 24 on the ECU, you can see that this is the terminal for the 02 sensor. At the end of the harness, it is mentioned these terminals are bridged for a unit with no catalyst and the bridge is removed (And the 02 sensor installed for catalyst operation). Note, no mention is made of the ECU applicable to this connection.




3. Does anyone know if this leaded ECU is compatible with a catalyst?

4. Of course, for competition purposes only!..... does removal of the 02 sensor (And replacing it with the associated bridge) change any of the mapping within the DME?

Thank you for any suggestions on how to improve this vehicles performance in the 2,000 to 4,000 rpm range especially, which I thought was pretty good, until I drove a RoW version from the same year. The mid range performance of this leaded version was superior, especially with regards to mid range torque and transition from light throttle openings.

I think that's about all for now and I thank those that have given their time freely to make this forum such an amazing resource.

Regards,

Carl.
Old 08-17-2014, 10:31 PM
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Best advice would be obtained from Steve Wong at 911chips.com.
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Old 08-18-2014, 04:09 AM
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The simple answer is: You should get a stock ROW '89 chip. It has the best mapping of the stock chips. And then there are all sorts of performance chips. Do a search and you'll see a lot of write-ups about the various offers. With regards to ECU hardware there are two major variants out there:

- ECUs with the O2 sensor electronics in place
- ECU's without the O2 sensor electronics in place

To check, you'd best open it up and check the bottom PCB. See here for a European ECU without the components, the empty area is highlighted. This ECU would not process the O2 sensor signal and thus not run in closed-loop no matter what.



Converting from non-O2 sensor electronics is a little more involved but can be done. It's just a lot of work.

The other variant is whether the ECU has the 24-pin socket or the 28-pin socket for the EPROM. Really early boxes had the EPROM soldered in. If it's the 24-pin version this can easily be converted to 28-pin. Then a jumper gets installed to make the ECU run off the EPROM. This will allow running the latest '89 stock chip and a host of aftermarket chips.

Ingo
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Old 08-18-2014, 05:11 AM
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And here is the ECU with the O2 sensor components in place. Note the two raised calibration resistors. This is what you'd find in all U.S. versions and most later R.O.W. versions as well. My guess is Bosch later just made this to reduce variants.

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How about a NoBadDays DualChip for 964 or '95 993
Old 08-18-2014, 05:18 AM
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Question on table labelled 28 above. I have an '89 Carrera that was purchased in Illinois when new. It's now a CA car brought in by previous owner and subsequently sold through CA dealer.

It has the M240 option. I noticed the fuel trim is set at pos. 4 in table 28. I had heard previously that it should always be set to pos. 0 (stock). I reset it from 4 to 0 a while back.

What should it be? Will it even make a difference. I know it reduces advance above 4K rpm. Is that what your really want for a car that runs on premium gas in CA now?
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Old 08-18-2014, 08:51 AM
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Position 0 is the preferred best performance. It does not alter fueling nor ignition.

In Summary: An 89 DME with a 8K chip and the switch in pos 0 is the very best stock 3.2L factory tune.

Quote:
Originally Posted by big911fan View Post
Question on table labelled 28 above. I have an '89 Carrera that was purchased in Illinois when new. It's now a CA car brought in by previous owner and subsequently sold through CA dealer.

It has the M240 option. I noticed the fuel trim is set at pos. 4 in table 28. I had heard previously that it should always be set to pos. 0 (stock). I reset it from 4 to 0 a while back.

What should it be? Will it even make a difference. I know it reduces advance above 4K rpm. Is that what your really want for a car that runs on premium gas in CA now?
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Old 08-18-2014, 09:30 AM
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How the DME processes the Pin 10 (brown jumper) and the Pin 28 (hi-altitude switch).

Some fuel and/or ign maps within the DME actually have 4 sets of maps and these 2 inputs are used to decide what map (out of the 4 possible maps) should be used. It works like this:

First assume 0 means that pin is NOT grounded and 1 means it is.
So if the brown wires are not connected pin 10 is NOT grounded
Hi altitude switch activates at 1000 meter elevation and grounds pin 28

pin10 : pin28 = map#
0 : 0 = map1 (default map when both 10 and 28 are not grounded)
1: 0 = map2 (if pin 10 is grounded use map2)
0 : 1 = map3 (if pin 28 is grounded use map3)
1 : 1 = map4 (if both pin 10 and pin 28 are grounded use map 4)

This allowed the DME to select different maps for these different conditions. The possibilities for describing all the maps and how they work are beyond discussion on this forum as you have a lot of combinations!
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1984 911 Carrera Cab M491 (Factory Wide Body)
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Old 08-18-2014, 09:48 AM
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To add to the variations Sal mentioned the late '89 8K chip come in two versions. One for U.S. and one for R.O.W.

It's been a long time since I compared maps in these but I seem to recall the R.O.W. version is ever so slightly more aggressive. Porsche had to detune the U.S. version to account for the lesser fuel quality. So you really want the R.O.W. version if you want the most "lively" stock chip.

Now if you ask yourself if this will be an issue in light of the fuel quality here then you obviously will not want to ever consider any aftermarket performance chip.....

Think of it this way. Porsche needed to make sure their engine's longevity would under no circumstances be impacted by poor fuel quality over here. This is why they decided to detune the maps for the U.S.

Nowadays the performance chips go the other direction. They increase timing to much more aggressive levels and try to cover up the onset of knocking with richer mixtures. While that works to some extend it certainly moves the game "closer to the cliff". And unfortunately the 3.2 has no mechanism to catch knocking like the later generation DME. Keep in mind that a performance chip even if custom-tuned on a dyno for a specific setup only reflects the conditions the day it was made. It doesn't account for any changes down the road (engine temp, outside temp, carbon build-up on piston dome, etc.) So while it might not have caused knocking back then it could do so shortly thereafter and thereby dramatically reduce engine life times. But I am sure this has been discussed at length before and everyone is aware of this.

Ingo
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'74 Targa 3.6 (not stock ) - '01 C4 (almost stock) - '00 ML430 (stock)

I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs
Porsche "Hammer" or Porsche PST2 - I can help!!
How about a NoBadDays DualChip for 964 or '95 993
Old 08-18-2014, 01:26 PM
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Don't want to hijack the thread but I assume that I'm safe leaving my stock '89 Carrera with the fuel trim switch set to '0'. Correct.

Also, it sounds like all factory destined US cars had option M240 by default. Correct? If so there are many cars driving around with the fuel trim set to '4" I'd guess. Also correct?

Thanks to both of you guys. "Knowledge is power"....
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Old 08-18-2014, 02:40 PM
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Ingo, well said.

Bottom line is that a tune done on a cold Winter day with no humidity and temps below 30F will not do so good when Summer comes around.

But be aware that the DME has maps that remove ignition if CHTs get to hot and it also has IAT compensation maps as well. However, the factory DME maps don't really use these very much and only have minor compensations. But a tuner that really knows these chips COULD possibly do a tune that would do real well in the Winter months and have the same tune detune it self as IATs and CHTs rise. This is what I do in my custom tunes. The very best approach is to tune at both extremes, Summer and Winter but that type of tuning takes time and money.

If you are running a Perf Chip in the 3.2L you really should run 93 octane fuel or whatever hi-octane fuel is available in your area.

Quote:
Originally Posted by ischmitz View Post
To add to the variations Sal mentioned the late '89 8K chip come in two versions. One for U.S. and one for R.O.W.

It's been a long time since I compared maps in these but I seem to recall the R.O.W. version is ever so slightly more aggressive. Porsche had to detune the U.S. version to account for the lesser fuel quality. So you really want the R.O.W. version if you want the most "lively" stock chip.

Now if you ask yourself if this will be an issue in light of the fuel quality here then you obviously will not want to ever consider any aftermarket performance chip.....

Think of it this way. Porsche needed to make sure their engine's longevity would under no circumstances be impacted by poor fuel quality over here. This is why they decided to detune the maps for the U.S.

Nowadays the performance chips go the other direction. They increase timing to much more aggressive levels and try to cover up the onset of knocking with richer mixtures. While that works to some extend it certainly moves the game "closer to the cliff". And unfortunately the 3.2 has no mechanism to catch knocking like the later generation DME. Keep in mind that a performance chip even if custom-tuned on a dyno for a specific setup only reflects the conditions the day it was made. It doesn't account for any changes down the road (engine temp, outside temp, carbon build-up on piston dome, etc.) So while it might not have caused knocking back then it could do so shortly thereafter and thereby dramatically reduce engine life times. But I am sure this has been discussed at length before and everyone is aware of this.

Ingo
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Old 08-19-2014, 06:12 AM
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Correct, run the 89 chip with switch in position '0'

As for the switch settings I'll point you to Steve W site as he sums up the positions nicely
911Chips.com - Fuel Quality Switch
Pos 4 simply removes ignition but only at RPMs greater than 4000RPM. A lot of folks don't know that it's RPM based. The DME has a RPM threshold scalar that it uses and only if above this scalar of 4000RPMs does the ignition reduction kick in.

Pos 4 pulls out about -2.7908 degrees of ignition if RPMs > 4000.

Quote:
Originally Posted by big911fan View Post
Don't want to hijack the thread but I assume that I'm safe leaving my stock '89 Carrera with the fuel trim switch set to '0'. Correct.

Also, it sounds like all factory destined US cars had option M240 by default. Correct? If so there are many cars driving around with the fuel trim set to '4" I'd guess. Also correct?

Thanks to both of you guys. "Knowledge is power"....
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Sal
1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
1964 356SC (SOLD)
1987 Ford Mustang LX 5.0 Convertible
Old 08-19-2014, 06:19 AM
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Quote:
Originally Posted by scarceller View Post
Ingo, well said.

Bottom line is that a tune done on a cold Winter day with no humidity and temps below 30F will not do so good when Summer comes around.

But be aware that the DME has maps that remove ignition if CHTs get to hot and it also has IAT compensation maps as well. However, the factory DME maps don't really use these very much and only have minor compensations. But a tuner that really knows these chips COULD possibly do a tune that would do real well in the Winter months and have the same tune detune it self as IATs and CHTs rise. This is what I do in my custom tunes. The very best approach is to tune at both extremes, Summer and Winter but that type of tuning takes time and money.

If you are running a Perf Chip in the 3.2L you really should run 93 octane fuel or whatever hi-octane fuel is available in your area.

"But be aware that the DME has maps that remove ignition if CHTs get to hot and it also has IAT compensation maps as well."

That statement is partially true in that once the CHT reaches the fully warm mode,
it has no more effect either on the timing or fuel.
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Old 08-19-2014, 07:52 AM
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Correct, CHT once warm has no more compensation but the tables are in place and can be altered and used to compensate fuel and or ignition.

IAT compensation tables also exist and they do alter ignition timing as IAT increases.
The IATignComp table is only used under WOT and looks like this in the 89 chip:

TempC : IgnComp
-----------------------
10c : 0 compensation
45c : -2 degrees
65c : -4 degrees

Simply as IATs increase from 10c-65c the WOT ignition is retarded from 0to-4 degrees.



Quote:
Originally Posted by mysocal911 View Post
"But be aware that the DME has maps that remove ignition if CHTs get to hot and it also has IAT compensation maps as well."

That statement is partially true in that once the CHT reaches the fully warm mode,
it has no more effect either on the timing or fuel.
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Old 08-19-2014, 08:02 AM
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Quote:
Originally Posted by ischmitz View Post
And here is the ECU with the O2 sensor components in place. Note the two raised calibration resistors. This is what you'd find in all U.S. versions and most later R.O.W. versions as well. My guess is Bosch later just made this to reduce variants.

Ingo, thank you very much. I haven't opened the ECU as yet but your photos are invaluable.

Do you know if there is any issue running a RoW 1989 DME ECU with a 9.5:1 compression engine with no catalyst?

I see no evidence of a RoW DME (so for the 10.3:1 engine) being compatible with an O2 sensor, has anyone tried it?

(I have assumed as you suggested that the later 1989 DME has the 02 circuit already installed)
Old 08-23-2014, 11:27 PM
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Quote:
Originally Posted by big911fan View Post
Don't want to hijack the thread but I assume that I'm safe leaving my stock '89 Carrera with the fuel trim switch set to '0'. Correct.

Also, it sounds like all factory destined US cars had option M240 by default. Correct? If so there are many cars driving around with the fuel trim set to '4" I'd guess. Also correct?

Thanks to both of you guys. "Knowledge is power"....

Note: Positions 1 + 2 enrich the mixture whilst keeping the same ignition curve (Compared to position 0)
Old 08-23-2014, 11:33 PM
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Quote:
Originally Posted by mysocal911 View Post
"But be aware that the DME has maps that remove ignition if CHTs get to hot and it also has IAT compensation maps as well."

That statement is partially true in that once the CHT reaches the fully warm mode,
it has no more effect either on the timing or fuel.
Yes, but doesn't the IAT sensor remain operational however?
Old 08-23-2014, 11:37 PM
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Quote:
Originally Posted by scarceller View Post
Correct, CHT once warm has no more compensation but the tables are in place and can be altered and used to compensate fuel and or ignition.

IAT compensation tables also exist and they do alter ignition timing as IAT increases.
The IATignComp table is only used under WOT and looks like this in the 89 chip:

TempC : IgnComp
-----------------------
10c : 0 compensation
45c : -2 degrees
65c : -4 degrees

Simply as IATs increase from 10c-65c the WOT ignition is retarded from 0to-4 degrees.

Whooops, thanks, I just read this now, ignore the previous post! So the IAT sensor ONLY works at full throttle. Hmmm

Last edited by Carl Jones; 08-23-2014 at 11:46 PM..
Old 08-23-2014, 11:39 PM
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It seems a lot of you guys have to put up with a max of 93RON pump gas, is this correct?

One of the reasons I'm going to play around with this is because our 1986 onwards 3.2 cars were able to run on 91RON. Now we have 98RON readily available, it makes sense, to me at least, to have a bit of a tweak.

(No annual emissions test helps too)

Last edited by Carl Jones; 08-23-2014 at 11:48 PM..
Old 08-23-2014, 11:45 PM
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Quote:
Originally Posted by Carl Jones View Post
It seems a lot of you guys have to put up with a max of 93RON pump gas, is this correct?

One of the reasons I'm going to play around with this is because our 1986 onwards 3.2 cars were able to run on 91RON. Now we have 98RON readily available, it makes sense, to me at least, to have a bit of a tweak.

(No annual emissions test helps too)
Call me a skeptic, but I seriously doubt you will notice a significant difference other than what a placebo would provide.




Cheers,

Joe
Old 08-25-2014, 03:18 PM
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IAT ignition comp only is for WOT.
But IAT Fuel comp is always in play, the AirFlowMeter measures air flow (not mass) so the DME is always compensating fuel from the given IAT. Hot air is less dense so fuel is removed, while cold air is more dense and fuel is added.

In summary: the IAT sensor is used to compensate IGN at WOT and Fuel at all times.

Quote:
Originally Posted by Carl Jones View Post
Whooops, thanks, I just read this now, ignore the previous post! So the IAT sensor ONLY works at full throttle. Hmmm
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Old 08-26-2014, 05:04 AM
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