Memcals: Knock sensors and limp home resistor packs

[TO4355]

went to buy some resistors today to give it a go and couldnt buy any...........have to wait a week for them to come with the next order...............DOH

i said to the guy and asked him if he could give me a ring when they come in

guy says ummmm no i cant do that

me........ ummmmmm why not?????

guy......well the phone call will cost more than the profit we make on them id have to charge a dollar for the call

me.........no worries mate 90c for the 8 resistors and $1 for the call ill save up and make sure i have enough by next week

 

[hakhawk]

lol, thats classic, dick smiths or jaycar?

 

[VL400]

awesome topic everyone, some very good info. thought id add my 2c....

As you have probably figured, the main processor inside the ECU is actually blind to what memcal is in there. This is due to the CYL select pin going to the FMD (fuel modeling device, in the schematics link above labeled U12). The main processor and it talk via an SPI bus, there are two bytes that you can request from the FMD - byte 1 is the discrete inputs (ie a/c request, park/neutral etc) and byte 2 contains a few operating flags.

Now byte 2 is the one that is important here, the main processor acually only uses one flag out of the 8bits to confirm that a reference pulse from the dizzy/coil pack occured. Awhile back i thought id have a play and mod the code a little to find out what the other 7 flags do. Found out that two actually tell you what memcal is pluged in, a handy way to check that your memcal cyl select mods have worked

If anyone wants this code (based on $12 code) i can send it to you. The engine will not run with it, have permanently disabled fuel as this is un-tested code intended for educational purposes :whistling It checks the memcal once every second and can get the byte using ALDL mode 1 message 6.

 

[VL400]

i have a 4 cyl memcal converted by holden in very early development days to run a v8, havent run it in a car but its still labelled for a v8 from dyno lab at holden
it has cal 56 jumpered to cal 53
rob

This works as a V8 memcal, not suprising though if it was from holden

For others, basically what you are creating is a voltage divider network. In the link that was posted earlier (http://i4.photobucket.com/albums/y103/gijim/netres.jpg) you can see that for the V6 the 7.5k and 15k in series from ground to Vcc (+5v). At its mid point (where cal 56 is) it is 1.6v (5v*7.5k / 7.5k+15k = 1.6v).

What you are aiming for is this at cal 56...

V8 = ground (7.5k resistor is purely used for current limiting and can be pretty much any value, short to ground can be used but resistor is better)
V6 = 1.6v
4cyl = 3.3v

 

[Chuff]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow:

 

[TO4355]

i bow down to thee also

 

[TO4355]

ok guys
finally got the resistors and did the mod on both a v6 memcal and a 4 banger memcal so tomorrow ill have a play and see if the 4 cyl netres will run the v8 with the cyl select on 8 cyl and if the afrs come back to how they should be

ill try both the 355 and the 5L as the 355 now has a pretty lumpt stick in it

 

[Chuff]

ok guys
finally got the resistors and did the mod on both a v6 memcal and a 4 banger memcal so tomorrow ill have a play and see if the 4 cyl netres will run the v8 with the cyl select on 8 cyl and if the afrs come back to how they should be

ill try both the 355 and the 5L as the 355 now has a pretty lumpt stick in it

Hey TO4355,

Have you had a chance do this this testing yet?