VSS adaptation

From the files of the 2012 Challenge V8 Fiero.

Ok, I'm using the complete TBI system (computer, dist, etc) from a '95 Chevy truck to replace the carb etc. Main issue seems to be the VSS. The '88 Fiero has a gear drive that produces a 2 pulse signal, while the truck used a magnetic pick up at ( i believe) 4 pulses... How do I get these to work?

Do you actually need it?

Four magnets tapped to the axle with a hall effect sensor?

Depends on where the pickup is in the original setup.

pick-up is in the trans for both applications. Yes I need it to run the speedo and keep the fuel injection happy.

I dont think you need it, unless you know something I don't. Never seen an early OEM fuel injection system that needed vehicle speed to work.

It'll work without it, but it will work better with it. Idle control is part of the deal. Still need it for the speedometer.

Do you just need to be able to differentiate between stopped and moving? If I read correctly you're using the fiero transaxle so the speedometer works fine

The Fiero computer runs the speedo, but is being replaced by the truck computer. I possibly could have the Fiero computer run the speedometer and do nothing else, but still have an issue with getting a proper VSS signal to the truck ECU.

To be clear, you don't NEED the VSS on the TBI ECM, it just runs a little bit better if you do in terms of driveability stuff (not power, fuel economy, etc.). Look at the service manual for the make/model/year that your engine controller is for and see what it wants in terms of pulses per mile (ppm) and type of signal (square or sine). The Fiero has a pretty unique way of modifying the VSS due to the available parts bin stuff at the time, so you can get 2000 ppm from the cluster or 4000 ppm from the transmission. One of those should get you close enough to get the coast down idle and such working properly, but without knowing more about the specific ECM you are using it's hard to say.

If you're using this for racing only, it's probably not even worth the hassle. If you're driving it daily, then it's a little extra splicing but probably worth it.

Bryce

Oh, to clarify, most (NOT ALL! '87-88 4 cylinder cars were different IIRC) Fieros are wired so the VSS is sent to the instrument cluster first (4000 ppm sine), then that signal is modified and sent to the ECM (2000 ppm square) and cruise control. If you just want to be sure the speedo works, you shouldn't need to do anything after you remove the original ECM if your car started as a V6. If it started as 4 cylinder, different story.

Bryce

Car started life as a 4 cyl, 5-speed w/o cruise. So my different story is written how again?

IIRC, an '88 4 cylinder without cruise would have had wiring for the VSS to the ECM, then from the ECM out to the speedo (unlike the rest, which went from VSS to instrument cluster, then cluster to ECM/cruise). It'll take some googling and asking on the Fiero forums for help to confirm. These are the best places to ask:

fieroforum.com realfierotech.com

Before posting there to clarify, you should look up the donor truck and see what the ECM wanted for a VSS in that application.

Bryce

Already posted this on Pennocks, will try the others too. Thanks.

Well then I'll leave this here for the next schmuck trolling through the internet trying to find the same thing:

http://www.fiero.nl/forum/Forum2/HTML/119840.html

Bryce

ok, I'm confused beyond belief..........