Nope, does not work. Main reason: the output of the Caddy ECM is too small to drive the Fiero speedo. The 'conversion' circuit a bias voltage so that the Fiero speedo can 'see' the correct signal.
Programming the ECM only changes how many pulses per mile is outputted - compensation for different tire sizes and different VSS senders (the stock Caddy VSS sender output 26000 ppm vs the Fieros VSS sender at 4000 ppm (if you are using a standard tranny)). Joe's write up (above) explains it
I guess I'm not understanding.
I'm using a fiero manual..
If the fiero VSS can run the fiero speedo and the caddy ECM can be programed to compensate for different VSS's. Then why cant you just run the VSS wires to both the ECM and speedo? This would not compensate for tire size of course. That would be determined by the VSS gear. You wouldn't even be using the caddy speed output yet everything would get the signal it needs. Maybe I'm just twisted.
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12:09 AM
stickpony Member
Posts: 1187 From: Pompano Beach, FL Registered: Jan 2008
Nope, does not work. Main reason: the output of the Caddy ECM is too small to drive the Fiero speedo. The 'conversion' circuit a bias voltage so that the Fiero speedo can 'see' the correct signal.
Programming the ECM only changes how many pulses per mile is outputted - compensation for different tire sizes and different VSS senders (the stock Caddy VSS sender output 26000 ppm vs the Fieros VSS sender at 4000 ppm (if you are using a standard tranny)). Joe's write up (above) explains it
works just fine from what all my customers tell me and works in my car...i can change the road speed constant and the ip divisor... problem solved, no need for any "modules"
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02:28 AM
stickpony Member
Posts: 1187 From: Pompano Beach, FL Registered: Jan 2008
If the fiero VSS can run the fiero speedo and the caddy ECM can be programed to compensate for different VSS's. Then why cant you just run the VSS wires to both the ECM and speedo? This would not compensate for tire size of course. That would be determined by the VSS gear. You wouldn't even be using the caddy speed output yet everything would get the signal it needs. Maybe I'm just twisted.
in your situation bro, it is best to have the ecm altered properly, and use the speedo output from the caddy ecm to drive your speedo, because the computer still needs to see the signal from the VSS, even if it is only a 4000 ppm signal. that can be compensated for with reprogramming..
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02:37 AM
Fieroseverywhere Member
Posts: 4242 From: Gresham, Oregon USA Registered: Mar 2006
in your situation bro, it is best to have the ecm altered properly, and use the speedo output from the caddy ecm to drive your speedo, because the computer still needs to see the signal from the VSS, even if it is only a 4000 ppm signal. that can be compensated for with reprogramming..
I'm doing it like that temporarily. The reason being that I don't have the new wheel and tires yet. I was going to run the wires from the VSS to the speedo then jumper them to the PCM. The PCM will still get the signal it needs aswell as the speedo. This should temporarily have my speedo running off of the VSS. Once the new wheels/tires are on I can change the wiring and use the caddy outpu to re-correct the speedo for new tire sizes. You've already done the chip and right now I can see no other way to have the speedo run correctly until I have the new shoes on. I don't know for sure yet if the VSS is capable of driving both the ECM and speedo but I'm hoping it will.
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11:50 AM
Fiero redux Member
Posts: 135 From: Asheboro, NC Registered: Dec 2007
Originally posted by stickpony: works just fine from what all my customers tell me and works in my car...i can change the road speed constant and the ip divisor... problem solved, no need for any "modules"
OK, I messed up thinking everyone wires the car the same way.
So to clarify my statement...
1) if you are driving the Fiero speedo directly from the VSS then NO conversion circuit is needed. 2) if you are driving the Fiero speedo from the ECM's output, then yes, you need the conversion circuit.
Do do need to feed the VSS signal into the ECM at some point as it causes problems. Of note, you do not have to reprogram the ECM if you drive the speedo directly, the ECM does not care what the signal is so as long as it gets one. You will need to program the ECM VSS 'if' you use the Caddy cruise system - not, if you use the stock Fiero system.
Also don't forget to ground the 2 tranny inputs to the ECM with a manual car (the car stalls each time you come to a stop).
There are people that are running thier 4.9 with the stock chip (not programmed at all). I heard that Ed Parks does/did it this way.
My preference is that I feed the VSS to the ECM and then the ECM output to the speedo - I also use built in the ECM cruise system. But that is just me
quote
Originally posted by Fiero redux: All this concern over the speedo makes me think a GPS speedo is the way to go! Hook vss to ecm, hook +12v to GPS gauge, and go.
Heh...until you drive into an area where you can't receive the satellite signal...
[This message has been edited by Mickey_Moose (edited 04-27-2008).]
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02:25 PM
Fieroseverywhere Member
Posts: 4242 From: Gresham, Oregon USA Registered: Mar 2006
Also don't forget to ground the 2 tranny inputs to the ECM with a manual car (the car stalls each time you come to a stop).
I didn't do this. I haven't had a stalling problem yet. Course I've only driven the car around the building and never even got it out of first. I had a bad ground for the ECM at the time also.
Just to clarify... your talking about A2 and C10 of the caddy PCM connectors right (trans input A & B)? Or do you mean pins F4 and F10 (shift A & B)? I believe Aaron programed the chip to stay above 1500 rpm until the speed gets below 5 mph. This would solve that problem also, correct? I believe its about the same effect as grounding the two wires. Aaron please correct me if I misunderstood your explaination. It wouldn't be the first time.
[This message has been edited by Fieroseverywhere (edited 04-27-2008).]
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04:31 PM
Apr 28th, 2008
Mickey_Moose Member
Posts: 7543 From: Edmonton, AB, Canada Registered: May 2001
Originally posted by Fieroseverywhere: Just to clarify... your talking about A2 and C10 of the caddy PCM connectors right (trans input A & B)? Or do you mean pins F4 and F10 (shift A & B)? I believe Aaron programed the chip to stay above 1500 rpm until the speed gets below 5 mph. This would solve that problem also, correct? I believe its about the same effect as grounding the two wires. Aaron please correct me if I misunderstood your explaination. It wouldn't be the first time.
C10 and F7
...unless of course this is now taken care of in the software - most of my info is now at least 4 years old...
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12:07 PM
jscott1 Member
Posts: 21676 From: Houston, TX , USA Registered: Dec 2001
I bailed on my 4.9 project a couple of years ago, now. I've forgotten most of what I learned, so I am not a good source of info on anything to do with 4.9 building, wiring, installation, painting, or maintenance.
A friendly reminder here. Don't waste your time asking me--as Sgt. Schultz used to say, "I know NOTHING!"
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02:38 PM
Mickey_Moose Member
Posts: 7543 From: Edmonton, AB, Canada Registered: May 2001
how much more info do you need? The 4.9 wires to the ECM ExaCTLy as shown the the diagrams on rockcrawls site (or see the Caddy FSM) - the C203 and C500 wiring diagrams are in the Fiero FSM (ie: C203 power for the injectors - well, hmmm, I think it MIGHT go for power to the injectors on the 4.9) - sorry being sarcastic.
Here are all my notes that I use (I posted these before, but here they are again), there is no special magic diagram or cheat paper that I use. I have given these same pages to a couple of other people locally that have completed thier 4.9's using only this and the info in my post linked to above.
Thanks to Rockcrawl for the "original" diagrams.
[This message has been edited by Mickey_Moose (edited 01-21-2009).]
