ok, i did all the wiring to the quad4 fiero 5 speed getrag that i have, the speedo is NOT working, i already tried another speedo on it and that did not correct the problem.

im 99% sure that the speedo signal on the the car goes from the speedo, to the ecm, then from the ECM out to the dash, i just want someone to tell me im right

its too late for me to go work on the car right now, but i want to know exactly what i need to track down,

matthew

I haven't looked into the diagram in detail yet since I still have to complete that part of my swap, but in building my wiring harness I got the impression that the ECM gets a feed off the speedo rather than actually controlling it through a brown wire going through the C203 connector. You should be able to follow the stock Fiero diagram up to the odometer and only need be sure of the pin ID for the ecm. Make sure there is no break in your wires from the transmission and that the sending unit from your transmission is working as well as compatible since at some point the signal method was changed requiring a circuit modification or splitting the case to swap in the sender gear from the Fiero trannies.

quote Originally posted by Joseph Upson: I haven't looked into the diagram in detail yet since I still have to complete that part of my swap, but in building my wiring harness I got the impression that the ECM gets a feed off the speedo rather than actually controlling it through a brown wire going through the C203 connector. You should be able to follow the stock Fiero diagram up to the odometer and only need be sure of the pin ID for the ecm. Make sure there is no break in your wires from the transmission and that the sending unit from your transmission is working as well as compatible since at some point the signal method was changed requiring a circuit modification or splitting the case to swap in the sender gear from the Fiero trannies.

the wiring from the speedo to the quad4 ecm is good, already verified that, im not sure of the speedo output from the ECM to the actual speedo on the dash, ive got to find some quad4 wiring diagrams, also, i have not got a spare speedo sensor to test, so ill have to get one of those.

matthew

Matthew,
On my swap, I had to redo the speedo wiring as well. The wro wires coming off the VSS (purple and yellow I think) Have to have a split in them for the 3.4 DOHC. So you end up with two purple and two yellow wires. One yellow and one purple feed the ECM, The other two wired go to the C203 - Yellow to Pin G and Purple to Pin R.
I am not sure how the wiring works on your motor, but the speedo wiring should remain the same?
Nick

the quad4 speedo is magnetic, the ECM takes that magnetic signal, and converts it so the fiero's speedo can get the correct electronic pulse.

matthew

I believe what Nick is getting at is that the Fiero speedomter sensor output is used to feed the ECM but it is also fed directly into the speedometer to dirve it. As long as your speedomter is receiving the Fiero speedomter sensor outputs it should work.

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87GT - 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
87GT - 3.4L Turbocharged engine, modified TH125H
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