My '88 Fiero - The Never-Ending Saga

[GTRS Fiero]

LOL!  They don't want you going 255MPH?

Let me make sure I have this.  First of all, it  can run normally with the VSS unplugged?  If it does run normally unplugged the problem is the signal, or the program?

[f85gtron]

Assuming you've swapped the transmission too, then the vss will probably be different. More than likely, it will send a 24000ppm signal. If Ryan programmed the ecm for a normal fiero trans, then he set the signal for only 4000ppm.  He could have set the mph limiter at whatever value, but usually programmers set it at maximum value of 255mph.  Another symptom would be your Speedo jumping all over the place, spazzing out (80's terminology, out of respect for the fiero). 

To answer your question:
Yes, the ecm and car will run without the vss plugged in. The ecm will throw a code (because no speed input) and should default to programmed shift points and fueling from other inputs, such as map (load) and cts (engine temp), along with rpm for calc'n.
If runs smoothly unplugged, the problem is the program.

[GTRS Fiero]

Ok.  So the ECM would need to be programmed for a 24000ppm signal?

[f85gtron]

Yes, assuming that's what the vss is putting out.

[GTRS Fiero]

Well, hopefully, the problem has been found.  When doing a fuel pressure test, the fuel pressure fell from 42 PSI to 18 PSI almost immediately.  The injectors are leaking.  The plugs were all wet.  These were new injectors.  Another set of new injectors has been ordered.  Another wait.

[GTRS Fiero]

Before you look at these pics, the old one had sat for a months outside (not happy about that), but it is what it is.  It was a lot cleaner when I dropped it off.  Anyway, no excuses.  The newer one isn't completely assembled to the point that the old one was, but I was doing a comparison, myself, and thought I'd share.

[GTRS Fiero]

It's been a while.

The original new injectors were bad.  New injectors arrived and were installed...and the battery is dead.  I have a portable jumpstarter, but it's here, and the car is not.  More waiting.  Sigh....

My battery is only about a year old, but when it's just left to sit, I guess it dies.  Not sure how it died in 1 week, though.

[GTRS Fiero]

Running again, but the gears are all off.  It drives great--in reverse only.  Need to check if still running rich.

[GTRS Fiero]

The fuel gauge reads zero.  Nada.  Zip.

Like it isn't connected.  If the fuel sending unit is bad, that'll be another bad new part.  I hope it's just wiring.

There's 8 gallons in the tank.

[GTRS Fiero]

My transmission has to come back out.  Something isn't right, apparently.  So, the cradle will drop, and down will fall...the transmission.

Anyway, this had better not cause more delay.

[GTRS Fiero]

I'm curious.  What would happen, if you used an ECU that was expecting 24000ppm from the VSS, but the VSS only put out a 4000ppm signal?

Originally, the ECU was going to use the VSS that came with the 440T4 transmission, but is now using the VSS that came stock with my TH125.  What VSS came with the 440T4?

[GTRS Fiero]

Small problem with the TV cable.  Another wait for the part.

Patentease?  What?  I'm not familiar with this word.

[Raydar]

I'm curious.  What would happen, if you used an ECU that was expecting 24000ppm from the VSS, but the VSS only put out a 4000ppm signal?

Originally, the ECU was going to use the VSS that came with the 440T4 transmission, but is now using the VSS that came stock with my TH125.  What VSS came with the 440T4?

Is it a 7730? I *think* the 7730 can be programmed for whatever ppm is required.
One problem is the wave shape that is output by the VSS. One of them outputs a square wave signal. The other outputs a sine wave signal. There is a cheap filter network that I have seen in several places, that converts (I think) the square wave to sine wave.
The 440T4 probably has the later VSS, since it's a newer trans, although it's still kind of "borderline".
I'm wondering why they changed it back to the 125 type VSS. Of course, if you still have the original ECM (7170?) that would explain it.
But still... the pickup methods are different. (Reluctor wheel vs pinion gear on the output shaft.) Seems like a real PITA to change.   

This may be a little bit of information overload, but it mentions the different VSS types and programming.
http://www.fiero.nl/forum/Archives/Archive-000001/HTML/20120111-2-091336.html

[GTRS Fiero]

Ah.  So the 24000 is digital, and the 4000 is analog.  As it turns out, mine is using the 4000ppm VSS, with the 7730 ECU, and the 7730 ECU is programmed for a 4000ppm VSS, supposedly.

I was first told that the engine is purring.  The VSS was changed to the one from my THM125C.  It drove about 2 blocks, round trip, but had no power, then I was told that it was terrible above 1500 RPM and had no power.  After the injectors were replaced again, and the spark plug wires were replaced again, I was told that the engine was purring again, but wouldn't go forward.  Now that the TV has issues, I'm told that the engine is running terribly.  Of course, the engine hasn't run since is was pulled to remove the transmission to find that the TV cable was bad.

I'm tempted to fly down there, and see what's going on myself.  Of course, I'd have to fly back, because it can't possibly be ready.

That reminds me.  I can't understand why the calipers can't be replaced while the cradle is out.  I've never tried, but it would seem to be much easier that while the cradle was in the car.  Less stuff in the way, and all that.  Maybe the cradle moves when you put some torque on the bolts.  I can understand the difficulty in replacing the brake booster while the back of the car is raised.

[GTRS Fiero]

I'm ignorant of a lot of stuff, and in many cases, happily so.  I have no wish to have personal experience of volcanos, space vacuum, asphyxiation, etc.  I'm fine with the existence of high pressures at extreme ocean depths, and high gravity on Jupiter, but again, no desire to personally experience them.

I've lately decided that I wish to remain blissfully ignorant of the inner workings of automatic transmissions.  Apparently, issues with the TV cable can destroy the valve body.  I bet you wish you didn't know now, too.