sophinity

OK So I have the later FireChicken style two wire speed sensor mounted in te T5 tranny I have. I have the speed buffer to "enhance" the signal. Everything wired as per several sites info, but the best is on chevythunder.
So I have no speed sig getting to me ECM or my speedo.??? How do you test these sensors and possibly the buffer?
Wires on the buffer are as follows from left to right with the wires coming out the bottom..
SS1, SS2, GRND, 4kPPM, 2KPPM, 2kPPM, IGN PWR.
So is there a way to test the buffer? It is a new GM part bought from Gmpartsdirect so I think it should be functionng properly.
The speed sensor is used and came with the trans, is there a way to test? If I put it in a corless drill and spin it what should read at the two terminals? AC voltage if it is working>
Any info helps. Using a VDO aftermarket gauge and a 1226175 ECM,

sophinity

bump...

Vader

Soph,

Are you certain of that ECM part number? I'm suspecting it is a 1227165 (MAF type TPI) ECM, correct?

If you have the later style sensor, it should be an inductive type, generating alternating pulses at varying amplitude and with a frequency relative to the speed it is turned. An AC voltmeter should be able to display some voltage generated by it, but the meter should be a true RMS type to get any kind of useful indication, and even then will only indicate if the VSS is generating any signal at all. The buffer module (and ECM, speedo, and cruise) require frequency signal, not voltage. It would be best if your meter had a frequency scale, or you had a frequency counter to register the VSS output. Turning the VSS at varying rates should indicate a varying output frequncy on the counter. You may also be able to catch it on an oscilloscope, but adjusting the sweep rate of the scope for a variable frequency signal is no easy chore.

All the buffer does is clip teh voltage peaks of teh input signal, monitor the phase reversals of the incoming signal , then uses that reversal to trigger a transistor switch. The switch subsequently alternately fires other switching transistors to either directly output either a positive voltage signal at a fixed level (usually 12VDC ignition power, sometimes 5VDC) and latch it on or turn off the output signal and latch it off, or it counts the pulses through additional switching to effectively half the rate of the input signal.

In other words, the input is an AC signal of varying amplitude and frequency, and the output is a DC square wave at a fixed voltage level. The frequency of the output is either the same as the input, as is the case for the 4,000 PPM output, or half the frequency of the input, as is the case for the 2,000 PPM output. IIRC, the speedometer and ECM on later cars use the 4,000 pulse reference on the later TPI cars (and many others), and the cruise control module uses the 2,000 pulse reference to monitor vehicle speed, thus the two different outputs. HOWEVER, if you in fact are using a 1227165 ECM, you will need to provide a 2,000 PPM input to the ECM instead of 4,000 PPM, another 2,000 PPM to the cruise, and a 4,000 PPM to the speedo. And depending on the speedo hear you're using, it may require 2,000 or 4,000 PPM. If you have a Miata electric speedo head, it may be different yet. A good solution in that case may be the Dakota Digital VSS signal module. It has various outputs which can be tuned/programmed to multiple pulse rates for the various devices.

sophinity

Thank you Vader,
MY setup is,
1226175 ECM 89 $6E
VDO Speedo- Programmable so I am not too worried about PPM for this.
The later Firebird 4000ppm sensor,
Red Drive gear(seems to have different teeth number depending on source so I am not sure?)
Silver Driven 22 tooth.
I do not have access to a osc scope however where can you get a multimeter that reads frequency? I may just get one?
Also my major problem right now is I am not getting any signal to the speedo or the ECM, I am getting an AC signal up to the BUffer. Buffer is new,is there a way to check if it is bad? I checked the wiring, it seems right, checked and am getting +12v ign am getting the AC signal from the VSS, only thing I have not checked is the quality of the ground I'll check that and make sure it is good, but after that I am a bit lost.? I just want to mostly get the ECM to get close to correct speeds (right now any speed would be good). The speedo worst case I can run the raw signal from the sensor to it and it would work just fine, it is capable of reading a good amount of different types of VSS.
The AC I get between the two terminals of the vss is greater the faster you spin it, seems at 800rpm (cordless drill) it reads an output of 4.5~VAC
By hand when I turn it it seems to blip a .5VAC spike several times per rev. Could it still be "bad"
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Yah my bad 1227165 don't know why I mistyped that twice????

Vader

By your description, it seems the VSS signal is good. I'd suspect the buffer module, since you have 12V ignition power to it. Verify the ground, but beyond that it may take a new buffer circuit to prove it good or bad.

sophinity