280ZX ECU in '78 BMW

[Josh Karnes]

> * Why doesn't the closed loop system compensate for any mismatch in
> the EFI system?
> 
> There are two problems. 
[snippo] 
> 2. the other problem is that the closed loop is only operational
> when the
>    car is cruising and hot.

Makes sense :)
 
> * MW is 180, Z car is 135-150
> 
> Using all the Z stuff in the BMW may cause you to run lean at max
> power. This is because the air meter 'might' run out of range at
> about 160hp. 

Now, the AFM in the BMW is considerably bigger.  I'd say about twice 
as big.

> This is important if you use the all the matched
> components from one car. You can of course use larger injectors, or
> a different air meter.  The problem is which ones?

Well, howabout the ones that came stock in the BMW?  Here's my case:  
the 280ZX digital injection was just about like the earlier analog 
L-Jets that the Datsuns were using.  The only big differences are the 
ECU, harness and O2 sensor.  So, they basically replaced those parts 
and had a similar, better? running car.

In theory, then, can I just do the same with my car?  The ECUs are 
similar between my BMW and the Nissan unit found in the good old 
analog 280Z, right (I'm asking, because I don't know for sure)?

>   You can
> calculate the injectors, but you will still need to trim the result.
> 
> 
> * The existing system is open-loop and runs rich
> 
> See first item above.  Very few systems run closed loop when burning
> valves etc is a concern.  I don't know of any system that truly runs
> closed loop when under max power. Some digital systems calculate the
> mixture during cruise closed loop running, and then apply enrichment
> for max power. 

Makes sense.

> 
> I think your best bet is to back off the enrichment (change the tune
> on you existing car),

Alright, so how do I do this?  I know, monkey around with the AFM, 
and it will run leaner up until the AFM is no longer a part of the 
equation, maybe 3000 rpm or so.  But what about the rest of the 
range?  Does someone know exactly which part does what on the Analog 
ECU?  Like, which part do I change if I want the car to run richer 
over the entire band?  Is there a schematic for this ECU bouncing 
around somewhere?  Or for the 280ZX ECU?

> run a custom system like the TechII, or get a
> system from a car witht the same injectors and engine size. 
> Otherwise it is too difficult unless you have lots of equipment.

Well, all I can say is that right now, the car runs so bad, and is so 
inefficient, that anything would be better.  It gets MAYBE 9 mpg in 
the city.  For a 3300 lb car with a 3.0L six, that's about half of 
what I would call minimum acceptable gas mileage.

So, I need to do something.  My options are to try to monkey with the 
L-Jet that is in there and see if I can improve things, trial and 
error, or to start over and replace the entire ECU and harness.  
Nobody says I have to run this thing in a closed loop if I put the 
Nissan ECU in there.  My bet is that the ECU from the 280ZX is tuned 
to run the car maybe a hair rich based upon the input from the AFM, 
TPS and O2 sennsor.  So, seems like if I tune the AFM and perhaps the 
fuel pressure with the Nissan computer then I should be in good 
shape, eh?  Maybe just an adjustable pressure regulator is what I 
need.  This must be better to make broad-band changes in the fuel 
curve than AFM mucking.

Later-
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Josh Karnes                                                 joshk at tanisys.com
Renaissance Man                        http://www.tanisys.com/~joshk/home.htm
Tanisys Technology                                     http://www.tanisys.com
Austin, Texas                      '78 BMW 530i | '72 Datsun 240Z | IZCC #308
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           *** opinions expressed herein are MINE, ALL MINE!! ***