Both the Fiero and 4.9 seem to use the same type of 4000 pulse per mile sine wave generator VSS. On the fiero this goes to a buffer on the I/P which then passes a 4000 ppm signal to the speedometer. The buffer also produces a 2000 ppm signal which goes the Fiero ECM.

On the Caddy the VSS is wired to the PCM which then in turn sends a 4000 ppm square wave to the speedometer.

In lieu of building the converter shown on fieroaddiction.com, has anyone just wired the 4.9 PCM and Fiero speedometer buffer in parallel to the VSS?

I am not sure exactly what you are asking, but if I am thinking what I thought said. Then the answer is yes.

My 4.9 with Fiero VSS runs from the VSS into a Y split one pair of wires goes to the ECM and the other goes to the speedometer.


------------------
85GT 5spd ,93 Eldorado 4.9 Dual O2 Custom Chip, Archie Clutch. Custom Exhaust. MSD Everything 245/50/16's Not Your Average 4.9 Capt Fiero Com --- My Over View Cadero Pics Yellow 88GT 5spd Stock.

[This message has been edited by Capt Fiero (edited 08-26-2006).]

quote Originally posted by Capt Fiero: My 4.9 with Fiero VSS runs from the VSS into a Y split one pair of wires goes to the ECM and the other goes to the speedometer.

That's the answer I was looking for

Are you running the Caddy automatic that is putting out 24,000 PPM (I think that is right) or are you using a manual 4 or 5 speed that puts out 4,000 PPM? With the manual, yes I ran a split vss signal (see my web site). But if you are using the auto, you have to send it to the PCM first and then take the 4,000 pulse out of the PCM and drive the speedo. Hope that helps.

Jack

------------------
If you can not run with the big dogs, stay on the porch!

quote Originally posted by J Gunsett: Are you running the Caddy automatic that is putting out 24,000 PPM (I think that is right) or are you using a manual 4 or 5 speed that puts out 4,000 PPM? With the manual, yes I ran a split vss signal (see my web site). But if you are using the auto, you have to send it to the PCM first and then take the 4,000 pulse out of the PCM and drive the speedo. Hope that helps. Jack

The 1992 Caddy manual says the VSS for the automatic is a permanent magnet generator type that produces a sine wave. This is identical to how the Fiero manual describes the fiero VSS. The high frequency VSS that came with my Quad 4 transaxle is not a generator type - there's a reluctor wheel.

The Caddy manual also says this about the VSS:

"The PCM takes the sensor/voltage pulses from the VSS, through the PPL and YEL wires and uses them to close solid state output switches. The output terminals are switched to ground at a rate that is proportional to vehicle speed. The speedometer, CCR controller, and passive restraint timer module are switches at the same frequency that the PCM produces: 4000 pulses per mile."

I'm interpreting the above to mean that the Caddy PCM simply takes in a 4000 pulse per mile sine wave and outputs a 4000 pulse per mile square wave.

My 91 Seville/ Eldorado manual shows that the speed sensor output is 40,000 pulses per mile, these pulses input the ecm at terminals B9 and B10, outputs from the ecm at terminals B11 and B12 is 4,000 pulses per mile. The signal still needs to be altered to run the speedo. I use the method that Rockcrawl shows on his site, my speedo works fine.

Guns kill people, like spoons made Rosie O'donnel fat. Joe

If using the Cadillac automatic
The Caddy automatic transmisson is not compatiable with the Fiero speedo:

1) you have to run it to the ECM first
2) the output of the ECM 'has' to run it through the filter on Rockcrawls page

The speedo will not work without the filter as the voltage level is too low

If using the stock Fiero tranmisson (auto or standard)
You can use the 'y' method as explained above


NOTE: you have to run the speedo signal to the ECM regardless, the engine stalls when downshifting if it not when you are using a standard tranny - not sure if anything happens when using the Fiero's stock 3 speed auto (not sure why you would use this tranny in the first place).

My prefered method: VSS to ECM, ECM to filter to speedo, cruise controlled by the ECM (Fiero cruise module thrown out). But that's just me

[This message has been edited by Mickey_Moose (edited 08-27-2006).]

Thanks everyone. I'll do the Rockcrawl circuit - just trying to save a little time.

In lieu of starting a new thread, how has the A/C wiring been done?

The Fiero has a 12V "A/C on" input to the ECM. This causes the ECM to ground the coil for the A/C relay.

On the Caddy the "A/C on" is coming from the BCM over a data line.

...one thing I forgot to meantion, you may have to have the chip reprogrammed when using the Fiero tranny. The ECM probably expects to see the 26000 ppm (or whatever it is)...

I can't say for sure, all the cars I have worked on have had Rockcrawl's chips for them, so I never compared the ECM readings with a stock chip and a Fiero tranny - I do know that the ECM does monitor the speed (maybe only for cruise), and the 4000 ppm output might also be wrong (ie: speedo no workey unless you use the 'y' method).


As for the a/c, sorry can't help you, haven't worked on a car that has the a/c hooked up. There is this thread however (may help): https://www.fiero.nl/forum/Forum2/HTML/076307.html

[This message has been edited by Mickey_Moose (edited 08-27-2006).]

quote Originally posted by Mickey_Moose: ...one thing I forgot to meantion, you may have to have the chip reprogrammed when using the Fiero tranny. The ECM probably expects to see the 26000 ppm (or whatever it is)... I can't say for sure, all the cars I have worked on have had Rockcrawl's chips for them, so I never compared the ECM readings with a stock chip and a Fiero tranny - I do know that the ECM does monitor the speed (maybe only for cruise), and the 4000 ppm output might also be wrong (ie: speedo no workey unless you use the 'y' method). As for the a/c, sorry can't help you, haven't worked on a car that has the a/c hooked up. There is this thread however (may help): https://www.fiero.nl/forum/Forum2/HTML/076307.html

I'm using the Caddy 4T60E that came with the engine. I did find in the 1994 FSM that it says 40,000 ppm for the VSS. I didn't find that in the 1992 manual - very curious.

quote Originally posted by sanderson: Thanks everyone. I'll do the Rockcrawl circuit - just trying to save a little time.

If you ever swap to a "modern" cluster like the 93-96 Firebird or anything from the 90s you will have to take out the Rockcrawal circuit and put the 4000 ppm directly into the cluster. Or else you will get a crazy harmonic of half or double the real speed.

quote Originally posted by jscott1: If you ever swap to a "modern" cluster like the 93-96 Firebird or anything from the 90s you will have to take out the Rockcrawal circuit and put the 4000 ppm directly into the cluster. Or else you will get a crazy harmonic of half or double the real speed.

Makes sense. All the Caddy stuff is looking for the square wave direct from the PCM.

Jon, on your 4.9 chop top that was done by PBJ is the A/C functional?

[This message has been edited by sanderson (edited 08-28-2006).]

quote Originally posted by jscott1: If you ever swap to a "modern" cluster like the 93-96 Firebird or anything from the 90s you will have to take out the Rockcrawal circuit and put the 4000 ppm directly into the cluster. Or else you will get a crazy harmonic of half or double the real speed.

...tell me about it

Just don't know what is up with the tach - the FB tach does not like the HEI system at all...