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Getting rid of PCM in Saturn

40K views 97 replies 18 participants last post by  dladd 
#1 · (Edited)
GO to last pages for new STUFF!!

>>>>>>>>>>>>>>>>>>>>>>>>>


I edited this opening as it contains other things at the end than about the PCM... hope it is helpful!

Tachometer at the end added 11/22/09 ------------ :D

I have been working on getting rid of the PCM in a 1999 Saturn Sl2. Bypassed the Tachometer on atzi's 1998 Saturn... http://www.saturn.offical.net/node/326
So now it is on to the speedometer. I used a Heathkit (yep, I have one!) function generator
to send a pure sine wave to the PCM... I settled on 60 MPH as this is the most important one to use - as it represents 1 mile per min or according to the output in all the manuals I could find the Speedometer = 5000 pulses per mile (thus per min) .. What is strange is all the information I can find says Saturn VSS has 10000 pulses per mile (ppm) so at 60 mph I should have 10000 = 1 min and 10000/60 = 166.66666 HZ... right?
But I get 230 HZ for 60 mph !! that equates to 13800 ppm (VSS sine wave NOT square wave to speedometer) . SO if that is true then there is a strange number to divide by to get the square waves for the speedometer ! 13800 / 5000 = 2.76 .. not the best number to digitally divide by !!


So it does a bit of strange processing NOT the simple divide by 2 that 10000ppm would get me !

The formula I use to get MPH from the sine wave is ---[ MPH x 13800 / 60 /60 = HZ] or 60 x 13800 = 828000 /60 = 13800 /60 = 230 Hz..
Easier to see a different one:
30 (MPH) x 13800 (PPM) = 414000 /60 (min) = 6900 /60 (sec) = 115 HZ (or cycles per sec)
AND YES 115 hz gives me 30 mph!!

I thought I would throw this out to see what others think! Perhaps they phase lock it at some frequency but not sure!

Dave
 

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#2 ·
Great work! I'd like to toss the PCM in mine too, but I really want to be able to keep the OEM tach and speedometer.
 
#4 ·
Used a safety pin into D6 connector Pumped 230 hz sine wave in to the VSS input...

Got 60 MPH MPH OUT AND 84.32 HZ out of PCM!!


SCOPE:
230 HZ SINE (bottom) in .............. 84.32 perfect SQUARE WAVE OUT(top) !!!!!!!! 5000 (ppm that manual says) /84.32 = 59.29 MPH
(close enough)
Figure the meter is off a few HZ and it comes to 5000ppm / 60 sec = 83.33333 my original math for factory!!!

So what the heck is 230 HZ in ? 230 / 84.32 = 2.7277039 aprox ....

Two things still wrong here - the ratio of 2.7 and how the heck are they getting the division ? well I need more work there... Have discovered a pure sine is clean but under noise of EV motor it introduces more pulses -- this opens up a whole new area of RF Noise besides our radios :(


Dave
 

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#6 ·
The VSS puts out a different frequency than the PCM? Why the heck would they do that? Seems to me like it only complicates things.
 
#7 ·
The PCM will compensate for various gear ratios, tire size, maybe models, but why I am getting what I am does not relate to what is in certain manuals.. I have run across 10000 ppm for GM and Saturn FROM VSS - that would be nice as it is 2 to 1 (5000 ppm) - easy to convert the sine to pulse at one half frequency with single flip-flop........

http://ecomodder.com/wiki/index.php/MPGuino

scroll down to chart on various cars......

If anyone has more info on VSS from Saturn - jump in here:)

Dave
 
#8 ·
Well quick thought... using a PLL like a 4046 locked to 4 X 230 HZ (sine for 60 MPH) out of VSS then divided by 11 (non fraction - my 2.7x X 4) gives 83.xxxx square wave that divided into the 5000 ppm will give me 60 MPH - well close enough!! I will make that and post some info.....

So since my Saturn only needs the PCM for Speedometer and Tach it looks like a couple of chips can do the job... Now on to interfaceing the temp gauge with pulse width modulation from a thermistor input .... Still no ideas out there?:confused:

Dave
 
#9 ·
Well a PLL of 230 X 100 then divided by 276 will yield the 83.33333 for the 60 MPH on the speedo.... going to make it in components as a pic or Ardunio processor will not output the exact numbers I need... It will be more accurate than the PCM as it will also have a filter system for extreme noise! Both my speedometer and tach will run seperate from all the other things I want to do! I intend to use ALL the idiot lights (of course I will replace them with LEDS! ) out of my own processor and all the temperature sensors, inputs, I can make do other things... OK so we shall see!!!!:D Be it warped - I still have a sense of humor ...

Dave
 
#10 ·
I'm sorry we don't have anyone else here that can contribute much to your thread, but I am following it. Please keep up the good work.

I actually toyed with the idea of putting "idiot lights" at the front of the dash panel where it sweeps upward. The idea being to copy the look of the EV1:eek:.
 
#11 ·
It is ok -- I see a lot have been looking... when I add my own processor, it speaks and shows SOC on the fuel gauge and temps on the temp gauge ( and a small screen ) it may spark a few points to converse with some... I have "lurked" around a bit myself and watched others do some really different things....

Dave
 
#13 ·
Hey, could you please tell me where you located that D6 connector for the speed sensor? I've looked through my Saturn and I can't find it.
What year do you have and where is your PCM located.. I assume you are referring to the pickup for direct tach as on

http://www.saturn.offical.net/?q=node/304

or are you looking to find the speedometer pickup on the transaxle?

Dave
 
#15 ·
I am looking for the speedo pickup. I'm (gradually) making an EV1 inspired dash but I've spent a few hours without luck looking for the speedo sender (found switch 12v power and ground easily). This is a side track from my EV conversion of course.
If you have a saturn it should be on the transaxle case... blue top and a purple and yellow wire to the PCM...
Dave:)
 
#18 ·
Yup, and will do. It'll take a while, especially because the speedometer I got on ebay doesn't display in Kilos which is what I drive in, so I probably won't use it. I found the speed sender cables, thank you :) Do you know of any in the plug that connects to the instrument panel directly? I'm going to tinker with it tomorrow, and if that fails I'll run wires off the sender you showed me.
 
#19 ·
I found the speed sender cables, thank you :) Do you know of any in the plug that connects to the instrument panel directly? I'm going to tinker with it tomorrow, and if that fails I'll run wires off the sender you showed me.
Still not clear on your car and model - year - all that makes a difference....:confused:

Dave
 
#22 ·
I am converting a '94 SC2 and I was planning to pull the PCM and replace the dash gage cluster altogether. For a speedometer I was going to just get an $80 Tomtom GPS unit. More accurate and very simple. As an added benefit I can yank it out and use it for trips when I'm not using the EV.

For a tach I was going to forego the dial indicator and just use a row of LEDs, like race cars do now. I don't need exact RPMs, just a few key points. I would use a simple PIC microcontroller with an optical pickup in the transmission bell housing. It can be programmed for the motor and reprogramed if a different motor is installed. Use green LEDs for the optimal range, yellow for above and below and red for high RPMs approaching max motor speed. Some of the larger PICs have a huge number of digital I/O pins and they can drive LEDs directly. 12-16 LEDs would be more than enough.

If I put in a lot of extra effor I can get motor voltage and current. With an efficiency map of the motor I can calculate the most efficient RPM range on the fly. With tri-color LEDs I can change the green/yellow/red color ranges on the LEDs based on the current motor load. With an additional sensor on the intermediate drive shaft I can get speed as well. Driving a couple of 7-segment displays is trivial with a PIC in case real digital info is needed.

I've considered putting a couple 7-segment LEDs wired for mirrored output and resting on the dash so I could see the reflection in the windshield. Bingo, a heads up display. That would work for the tach LEDs as well.
 
#23 ·
I've considered putting a couple 7-segment LEDs wired for mirrored output and resting on the dash so I could see the reflection in the windshield. Bingo, a heads up display. That would work for the tach LEDs as well.
That would all be nice...
I am keeping all stock gauges (and they will all function on my electronics) and insetting the digital readouts (they will shadow all the analog with much more flash) in the tray above the Radio - they will hide when not in use.... sort of stealth EV :D

There is more in line of voice control but just gotta get the thing rolling ! I work 7 days and sometimes close to 18 hours...........
Dave
 
#24 ·
Just in case any one was trying to figure out what the BLUE wire was on some fans - it is a tach output - and you can use it to sense that the fan is turning - or not!

Dave
 

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#25 ·
Dave. I wish you luck trying to save the factory speedo. I initially had the same idea with my Saturn Vue conversion. I decided it was cheaper to just replace the guages with aftermarket ones rather than spend way more in time trying to reverse engineer the system.

I ended up keeping the VSS but using the aftermarket speedo. The "trick" for using the VSS was that it needed a pull up resistor (can't remember if if was 1K or 10K) connected to the send wire and a 12V source. http://justanotherevconversion.blogspot.com/2008_12_01_archive.html

The aftermarket speedo self calibrated to the VSS. All I had to do was get the car to a known speed and push a button. The speedometer did all of the calculations! That was good news for me but bad for you since I never hooked up the oscope to the VSS :-(

The Vue is a 2002 so I don't know how much things changed from your year. The VSS is mounted on the transaxle. It sends an analog signal to the engine control module(ECM). (Not sure if this is the PCM on your vehicle). The ECM then relays the info to the body control module(BCM) via the CAN bus. The BCM drives the speedo.

If I were hell bent on keeping the factory speedo my next step would have been to hook the VSS back to the ECM. Then I would connect the ECM back to the CAN bus and power up the ECM. I tried this with the OEM tach, but it didn't work. The difference is that I was using an aftermarket RPM sensor for the input instead of the OEM sensor. So maybe with the OEM VSS it could work.

Good luck.
Idoco

P.S. I see you are using the Hayne's manual. I would highly recommend the OEM manuals. Way more info, especially on wiring.
 
#29 ·
Good luck.
Idoco

P.S. I see you are using the Hayne's manual. I would highly recommend the OEM manuals. Way more info, especially on wiring.

Never did answer you on that I personally DON't use the useless Hayne's manul I think Sega said that --- you are right on the OEM - I have a few friends with alldata etc

Dave:D
 
#26 ·
On my 99 (or less years ) you can keep the PCM and speedometer will work fine - on those years one can bypass the tachometer and go direct to the white tachometer to a pickup and a 6 lobe cam... yes 6 not 4 and it works fine as I have explained in first input on this thread... Since most of yours is on a bus (CAN) configuration it may be quite different in the head end...

My contention is on the earlier models and other makes one need only know the pulses that come FROM the PCM and throw it out..... ALL the wires to Idiot lights can be cut after the PCM and used with your own circuits i.e. temp light to the high temp switch in most motors... Fuel gauge can be used with an algorithm in a embedded processor to read as a state of charge meter and give a rough idea as to what one has left in the "tank". Likewise temperature gauge shows either/or controller/motor temp....

I have the speedo working with the PCM I just wanted to get rid of it all together - and think I have now - but I work a lot and my EV time is not so easy to secure.....:mad:

Dave
 
#27 · (Edited)
My dialup crashed so I am trying to get out this tidbit on Anderson connectors for all the off subject lurkers out there - I don't know if anyone has shown this but here goes!

1. Note the flat spring locking tabs in the start picture.

2. Now note the little tab on the metal crimp connector and that it is
"tab down".

3. Push in till first "click" - the all the way till second click.

Note: I have not used a wire for ease of showing.

Note: tab is all the way to the front!

4 To extract metal contacts (tabs) use a small screwdriver and push down hard on the spring tab (go to one side of connector) and pull out at same time!

Let me know if this was helpful to those not yet fooling with connectors....

Dave:)
 

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#30 ·
Hmmmmmm I probably should start a build thread But I have 354 pics and I would hog all the site with Trivia! But a few pictures of compactness I will post!

Dave :D
 

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#32 ·
I tried to get a new horn for the Saturn - 100 bucks! ( They have a built in relay ).. SO I thought I would look for one at the junk yard -- lol - they were all rusted - SO I bought a cheap 12 volt horn from Autozone and added a relay.. I redid the harness, filled it with hot glue, shrink tubed the thing, cleaned the bracket and put it back on! Works great - till I put the electronic horn on... :D
 

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#33 ·
hi guys, i need serously help about electronic spidometer ant tachometer, i making my ending project of scool... so who can help me?? i need schemes and programs to do electrical spidometer, i thinx to do it wits lcd... so i`m waiting for help from you guys
 
#34 ·
Ive been told by my certifier that the battery box extractor fan needs to run on 3 minutes after charging is finished. However I cant figure out how to wire the turbo timer that I bought so it does this. Ive attached the red lead to positive feed, black and brown(handbrake switch) to earth, blue to the fan positive The fan is earthed. Yellow to on-off switch. When I switch off yellow the timer counts down but nothing seems to happen. How does the positive current get through to keep running the fan?
 
#37 ·
This is what I did on the Saturn ADC motor - cost of pickup is around 20 bucks - very immune to noise - might need a pullup on some inputs - gear can be handmade (without mill machine ) -- In the Saturn 60 degree equal 6 lobes for the 6X to direct feed to the Tach (AROUND the PCM)... I'm sure you have seen me post it before BUT on another Saturn... :D

P.S. It"s a Cherry speed sensor buy at Allied Electronics or for a bit more Digi-Key... Brown to key 12 volt - Blue to ground - Black wire output to white wire (cut off after PCM) to dash tach -- there is an internal pullup of about 10k on the tach BUT I found putting in another 10k (makes 5k lol) clips any noise - but noise is not much of a problem....
 

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#79 ·
This is what I did on the Saturn ADC motor - cost of pickup is around 20 bucks - very immune to noise - might need a pullup on some inputs - gear can be handmade (without mill machine ) -- In the Saturn 60 degree equal 6 lobes for the 6X to direct feed to the Tach (AROUND the PCM)... I'm sure you have seen me post it before BUT on another Saturn... :D

P.S. It"s a Cherry speed sensor buy at Allied Electronics or for a bit more Digi-Key... Brown to key 12 volt - Blue to ground - Black wire output to white wire (cut off after PCM) to dash tach -- there is an internal pullup of about 10k on the tach BUT I found putting in another 10k (makes 5k lol) clips any noise - but noise is not much of a problem....
Great stuff. Any idea how big of an air gap differential (hall tall do the gear teeth have to be?) is needed to trigger the sensor? I did not see it in the spec sheets.

I'm pulling together parts to make the tach sensor for my car and this sensor looks like it should do the trick. Thinking of adding a couple of bolts radially into my motor adapter to trigger the sensor or cutting some slots.
 
#38 ·
Sorry for even asking this, but does that have to be a magnetic metal, or can it be non magnetic. I know some magnetic fields can affect materials like brass and aluminum.
 
#39 ·
Magnetic, David - I have not really tried to set up an aluminum one to see if it would trigger eddies ... The reason for painting (powder coating ) it was the condensation I am noticing in this crazy warmer weather... we usually have tons of snow by now!! My garage - in - a - box seems to trap moisture :mad:...
 
#40 ·
While I am not planning on getting rid of my gas engine at the moment (the inefficencies translate to a nice and toasty cab in the winter time :) ) I have started a project of figuring out what makes the Saturn ECM work. I am fairly sure that somewhere around the web I have seen things like formula for converting the VSS signal into speed, but I dont remember where at the moment.
One thing I can add though is for schematics if you go to Autozone you can sign up for their free diagnostic service and one of the options afterward is for wireing diagrams. They are not the best, but they are free.
If you want I can try to keep you up to date with my project to figure out the Saturn ECM (and other modules)
 
#41 ·
I have kinda thrown it out :D - going to use (err AM using) my own software on embedded processor..( will post more of that later) Have seen the Autozone wire diagrams - don't blow up too well but it is a start... If you waded thru my thread here you will see the only reason to keep the PCM is for the speedometer .. UNLESS you have more things tied to it - my 99 SL2 has no ABS and air bags are NOT hooked to PCM - everything can be bypassed and fed to the idiot lights on the dash - which, by the way will all be replaced with led equivilents :cool:...

http://ecomodder.com/wiki/index.php/MPGuino

has specs WRONG for my Saturn - so what year are you talking about?

:confused:
 
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