In the AC socket on your wall, on side is neutral and one side is hot. The neutral is a return and the voltage on it doesn't change. The voltage on the hot wire fluctuates from -165 to +165. If you hook up a pin that's expecting fluctuating signal relative to a ground reference to the neutral wire, it won't see any signal.
Fierobsessed
MAR 28, 11:14 PM
Started machining the flywheel. For a factory flywheel the machining is pretty bad. My flywheel arbor and the face surface are bang on, but the rest of the machining is pretty bad, even the ring gear seat wobbled. There was a lot of holes drilled for balancing, I'm sure they just make sure the clutch surface is good, then balance it. I'm surprised that the external edge machining was that far off. I have a bit of work ahead of me.
Fierobsessed
MAR 29, 03:35 AM
quote
Originally posted by Will:
In the AC socket on your wall, on side is neutral and one side is hot. The neutral is a return and the voltage on it doesn't change. The voltage on the hot wire fluctuates from -165 to +165. If you hook up a pin that's expecting fluctuating signal relative to a ground reference to the neutral wire, it won't see any signal.
I agree. But... on the VSS circuit, the ground is at the computer, not at the sensor. The sensor is plastic. So if you swap the wires, the old signal wire will be grounded, and the old ground will send back a signal. However, Joseph is correct, the signal would be upside down (mirror imaged) if traced on a scope. Perhaps the ECM cannot interperate the signal if it is upside down, I'd find it a little odd that he found that it can't interperate it, but it's totally possible. It's not exactly like an AC sine wave where everything is symmetrical, its more like a heart beat, with regularly timed pulses and silence between them.
I know the crank sensor can't handle an upside down signal, it relies on an initial "positive"* spike to show when the timing is, It doesn't like it when the initial spike is "negative"* going. *might be backwards, but the point stands.
Seems like this topic is a bit irrelevent to my build though. If Joseph is right and my ECM fails to see the VSS, I will have a fairly informed idea where to look. Either way, I won't know till I have everything together, and I can spin the wheels, or test it in place.
Will
MAR 29, 05:33 AM
Ground and neutral do not have the same function in the circuit.
Fierobsessed
MAR 29, 07:04 PM
I did some machining on the flywheel today. I started with a stock 92 Firebird 3.1L flywheel. I knocked the ring gear off of it since it was absolutely useless with the F40.
So this is what I started with: Firebird 3.1L on the left, G6 GXP on the right
Underside
I could have machined the old ring gear seat down and pressed the Fiero ring gear on, but the seat would have been VERY thin. So I decided to cut off the entire outer ring. I cut a groove in the outer ring of the flywheel, Working this diameter pushes the absolute limit of what my 12X36 lathe can handle, It is a gap bed, but the flywheel just fits wihtin the supports of the saddle by less then 1/16", after a little unnessary diameter is taken down. I cut the groove deep enough to nearly seperate the ring from the flywheel.
Then, I took the flywheel out of the lathe and hit it on the concrete a number of times to crack the ring off. I didn't want to seperate the ring entirely using the lathe, It could have flung off and damaged the bed. With the ring seperated I put it back in the lathe to do some finishing cuts.
My lathe could barely reach around the back of the flywheel for the little bit of a back face cut that I needed to do, but I managed to get it.
The removed ring and the somewhat finished flywheel,
The bolts are flat head M10, I will need to countersink them.
These coupler nuts will hold the ring gear.
I will machine a groove in the coupler nuts, sit the ring gear in them, then weld the coupler nuts and the ring gear together.
The flywheel has 12 holes exactly 30 degrees apart around the edge, I drilled them out to fit the M10 bolts in a tight tolerance, and will countersink them. I'm debaiting on weather or not I will need to use all 12 holes, or just 6. I think 6 will be fine.
Will
MAR 30, 11:28 AM
Can you just stack your modified flywheel on top of a flexplate?
Fierobsessed
MAR 30, 09:10 PM
Great question!
There is little to no centering hub left on the back of the crank with a flexplate mounted, I know I could peel the one ring off to expose a little more hub. The flywheel still has a chamfer on the inside of its ID, so it probably still wouldn't quite make it.
Will
MAR 31, 08:43 AM
I don't know how the dimensions stack up, but if you need a spacer, you could make it locate on the ID of the pilot bore. Maybe you could turn a stepped bushing that would tap into the pilot bore and extend the OD of the locating shoulder.
You don't need the reinforcement washer when you're stacking a flywheel on top of the flex plate.
The circle you showed has 8 bolts... Is that a Northstar?
Fierobsessed
MAR 31, 10:54 AM
3800. It's the only flex plate I had laying around. I know I could have made some sort of adapter or something to get a flex plate sandwiched in there. I just didn't want to. Something about it just doesn't sit right with me. No real reason other then that.
The more I work on this flywheel, the more upset I become with its orignial manufacture. There isn't ANY concentricity amongst ANY of the critical dimensions. It was so bad I started questioning whether or not my 3 Jaw was centering correctly, so I broke out the 4 jaw and did a manual alignment using the pilot bore for center, and the face for straightness. Once I had it dialed in perfectly, I found that the machine work that I did already is still straight and true. My 3 jaw chucking was good.
Then, I began questioning whether the pilot bore was concentric with the pressure plate mounting bolts. Truth is... that it wasn't even close. I measured a total difference in distance from the closest to center, to the farthest from center at .034" So it's safe to say its .017" out of concentric. That's horrible. So for laughs, I tossed the pressure plate on to see how it fared.
Needless to say, It's not looking too good. Mind you, that this is a factory flywheel from GM, and a stock replacement pressureplate for a Getrag Fiero. Worse still, you should see how the internal pressure plate ring wobbles.
I believe that the wobbling, from either poor balance, or poor centering of the pressure plate was the reason that I was experiencing shift "lock out" at high RPM's. Basically what I mean is that the clutch was self engaging at high RPM, and made shifting difficult when ragging on it hard.
So, I'm going to have to finish the ring gear thing. Then, I need to drill and tap new pressure plate bolt holes. Once that's done, the flywheel will need surfacing, and balancing. This turned into a bigger project then I anticipated. Maybe I should have just used the dual mass... It is afterall, designed for the 60 degree engines.
[This message has been edited by Fierobsessed (edited 03-31-2013).]
Joseph Upson
MAR 31, 12:07 PM
Here's an update plus some recent experience and info that might be of use to you.
The computer does not care which terminal is connected to A or B on the Vss plug. After making a new pullup circuit and having the same problem and then correcting the wiring mismatch and having the same problem, it appears either the wiring arrangement for the 727 ecm I switched to is backwards, or I made a mistake that I have yet to see, as with the ECM recognized a signal in both wiring arrangements only with the input signal attached to the purple wire going into the ecm which is the understood ground for the Vss. Whatever the case once I got it working after all the tests I decided there is a pin assignment typo in the diagram.
Be sure to make a good oil catch can/separator, etc. Although many including myself at one point, are opposed to feeding vent pressure back into the engine, the system is actually beneficial to the motor when setup right. I picked up some good ideas from AutoSpeed that you may find helpful as I did. I had never considered what they did and what a fan of the site did to make the system very effective compared to the typical unbaffled container which I was always suspect of. I believe it was Will actually (not tooting his horn just giving him his due recognition (I still believe you're wrong about the flywheel)) that pointed out the need to have those combustion gases actively removed as they will certainly affect the cleanliness of the oil among other things.
You need better flow than the naturally aspirated ports, an easy approach would be a 1/2" fitting on the oil cap to avoid tampering with the valve covers if feasible.
Here are the links on AutoSpeed they have more than one on the subject:
