Heres the situation. 88GT 3.4DOHC 5spd. Dash speedo hooked to the stock VSS. Cannot tap it because the signals are diffrent, so how do I get a speedo signal to the computer?!?
I took apart a VSS from a 3.4dohc car. What do I find? a magnetic pickup pointed at a ribbed wheel. Gets me thinkning, almost all 2 wire electromagnetic pickups work the same. I couldnt find a ABS hub that would bolt in, so I looked elsewhere. Remembered the crank sensor is magnetic. So I started looking for something to aim it at. Settled on the inner tripot of the CV shaft.
Heres my math
the inner tripot has 3 bulges (GO FIGURE! lol)
the ECM expects 4000 ppm. Thats 1.3 pulses per foot
the tires I have are 25.6 " around, 2.13 feet per rev, with 3 pulses per rev, thats .71 ppfoot
thats enough to lower the reading so that I shouldnt have problems with the speed limiter. What is it on this car?? like 120? that means Id have to hit 216 to hit the limit no prob
So it would work out math wise.

I went down to advanced and grabbed every crank sensor off the shelf and started opening them up and looking at em. (they're used to me doing this, so they just laughed) After diggin through 25 or so that they had in stock I suprisingly enough ended up with a CSS7 the stock one for the motor! at 16.99 it was also the best price. I did find a bracket that I liked on CSS127 so I borrowed it (sshhh....) I went back to work and put the bracket on my CSS. Then I found that the drivers side would give the best position. So I took out a tranny case bolt and drilled out the bracket so it would go through. Bolted it back in and tweaked the bracket so the sensor was as close as possible (operating spec is .05") Then wired it into the ECM's VSS. I think the stock plug would actualy fit, but it got caught up in the CV shaft and ripped off a long time back. Took it for a spin:

First thing I noticed NO SES light when engine braking !!! yippy. I also noticed that it idles at about 1400 when the speed is above 20mph and I hit the clutch. The clutch switch still isnt hooked up. When I go below 20, the idle drops down to 800. So now it wont stall anymore when I clutch off high RPMs like it used too. Very cool. Im hoping for better gas mileage now too, cause 19MPG just sucks. Also hoping it might run better under WOT, because previous scanning revealed that the ECM was holding the injectors wide open whenever you put a load on the engine, ie giving gas in 5th at 55mph.

the pic I have kinda sucks, it was dark. I'll get more tomorrow.

what does the stock vss send in ppm ?

oddly enough I think its 4000 ppm also, but i keep hearing its diffrent. I might have been looking at the wrong info. i looked into it for a minute until it dawned on me that it really wasnt relevant to what I was tring to do, so I flipped over to the tdc info.

I had no problem wiring up the speedo in my 88GT. Just hooked up the VSS wires to both the ECM and the speedo and it worked great.

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Chris

3.4 TDC SWAP COMPLETED...this is going to be a fun car

i got that dakota digital speedo calibration module. i think its a sgi-5??? and it will change the pulse and send the correct signal. talk to rodney, he knows which one it is. im sure it is an sgi-5 and its about 70 bucks

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Keith
Topsail Beach,NC
86&87 Fiero GT
86&96 Corvette
04 HD Softail
73 Lotus Europa TC
86 Lotus Turbo Esprit

Very clever installation. I thought about something along those lines when I couldn't get my Beretta transaxle to talk to the Fiero ECM. After many hours with an oscilloscope, I opted to install a TERF speed converter (but still needed a capacitor to remove the transients from the signal.)

When I hooked my ECM in parallell with the speedo, the speedo would not work.

A stock 3.4l TDC, in its factory home, is supposed to dile at 1200+- when it is above 5-10mph, then die down to 800 when less than those, so it sounds as if your's is working correctly.

Just a little fyi, that is perfectly normal.

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You can tap the VSS signal to the dash... just make sure you tap the right wire. I've run my ECM like that for quite some time. In my case I use a FWD PROM that expectes the VSS to connect directly instead of thru the dash. (DIS L4 has a couple valid VSS configurations.)

Depending on the ECM... you may only need to connect one of the two VSS wires. I only have one tapped and connected to the ECM. (I don't remember which one.) The dash and ECM are both happy.

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