dave morris

Bob,
I like that picture. How do you get the front left wheel to lift up like that? Hee hee.

dave morris

Sorry, meant to say right front. Maybe I'm dyslexic (sp?).

Lorenfb

"The early 90 ECU's have and adjustable pot. on the left side to adjust fuel +/-. Position 2(to the right) add's 6% more fuel and 10 rwhp. greater than later 964 ECU"s"

1. Switch not pot.
2. 6% more fuel & 10 rwhp - Dream on!

rodders

what does the switch do and why was it put there ?

Lorenfb

"what does the switch do and why was it put there ?"

1. It leans the mixture where a CO emissions standard
may be a problem, e.g. USA & Japan.
2. It richens the mixture where a NOx emissions standard
may be a problem, e.g. USA & Japan.
3. It retards the ignition timing where a NOx emissions standard
may be a problem or where a very poor octane level may exist.

So, based on this switch, it should be obvious that the 911/964/993
Porsches were NOT setup (mapped/programmed) for the worst case
conditions as some performance chip hyperbole indicates, thus allowing
for tweaking.

Bottom line: It gave Porsche the ability to tweak the DME ECM for
some markets without changing the EPROM in the field.

KirkF

Loren,

I was under the impression that although the function of the DMEs remained the same, the actual circuitry changed slightly after 1990. I thought they upped the clock speed the unit was running at?

Do you know what change bosche made that porsche decided to re number the DMEs from 911 to 964?

Do you happen to have an 89 vs 91+ to compare? I wouldn't mind seeing a couple pics of the boards from each. (Not sure how many Porsche DMEs you have come around. They rarely break)

If you check through the posts on the stalling topic (And there is a million of them) I was noticing it seemed like the earlier cars were having more stalling problems than the older ones. Although the ISV was also updated, I dont know in what year. So maybe that has more to do with it.

I work on industrial control systems, so when I watch my car trying to stabilize its idle, it looks like a PID loop with too much gain, struggling to meet setpoint. I have been wondering what causes the problem for a while now.
In some ways it seems like the DME is struggling to keep up with the changing signal from the flywheel ref sensor, and then overshooting on its response.


Kirk

rodders

Even tho there there are some diametrically opposed views, the knowledge displayed by Lorenfb Redrooster Adrian et al is remarkable.
I know they have been doing it for some time but I for one am grateful for the advice and passion - its just great.
some things - like chips - curiosity drives the uninitiated forward despite good advice.
I am so mechanically challenged I would go out and try to by a left handed screw driver - so stay with us - we need you
and thanks

kris

Rodders, are you telling the audience that flying a Lear through a military exercise area as a target for electronic warfare is easier than understanding the ECU mysteries of a 15 year old car You must be kidding

fstockcarrera

1. Switch not pot.
2. 6% more fuel & 10 rwhp - Dream on

Yep your right switch it is. And it is +6.3% fuel zero timing change @ position 2, since I'm getting graded. Not dreaming just reporting my dyno results. If you have not done the dyno pulls, your just guessing. I have spent many hours on the dyno and building m64/01 motors. Just trying to help

rodders

Hi Kris - i just pressed things, pulled things, and worried about birds, lightening, and other peoples finger trouble - i got seriously lost inn the company of OLD CROWS - not an arena to bull**** - much easier to claim the need for a left handed screwdriver - every body left you alone !!
So shush - i know nothing !!

Lorenfb

"I was under the impression that although the function of the DMEs remained the same, the actual circuitry changed slightly after 1990. I thought they upped the clock speed the unit was running at?"

The circuitry is identical. The clock has always been 10MHZ.
Early Porsche DMEs ran at 6MHZ.

"Do you know what change bosche made that porsche decided to re number the DMEs from 911 to 964?"

Totally different for 964, e.g. sequential injection, DSP type knock control, fault codes & CEL, and
parameter learning/memory (volatile).

"Do you happen to have an 89 vs 91+ to compare? I wouldn't mind seeing a couple pics of the boards from each. (Not sure how many Porsche DMEs you have come around. They rarely break)"

They're identical. The 911 DME was only changed for the '95 993.

"I work on industrial control systems, so when I watch my car trying to stabilize its idle, it looks like a PID loop with too much gain, struggling to meet setpoint."

All 911 Porsches have a small closed-loop instability as one might expect given
a feedback type of control system, e.g. the O2 loop. The loop gain of the idle
circuit is such that it's fairly stable. The major problem occurs when a "step"
input occurs when the RPM drops at too great a rate, e.g. LWF, and the system
undershoots causing stalling or oscillations. The DMF helps dampen the oscillations
and reduces the rate of change of the RPMs.

C H

Isn't that switch called the high altitude switch? Used for people who dirve in the mountains (Colorado, Alps ect)