ECU AND SPEED SENSOR

[frotosride]

Ok so almost every OEM ECU receives a drive signal from the transmission via some type of speed sensor. All GM late model vehicles have some form of VSS to give that signal to the ECM in order for the computer to adjust fuel and IAC opening for low load idle conditions. Not using this feature will cause your engine to suffer from per milage and stalling. The question is where dies the TBI speed sensor in pin A 10 get its signal from when in a 4th truck? Is there a sensor driven off the back of the speedometer or does it receive the signal another way? I have yet to pull my glove box and verify if there is actually a pin in this location but either way how did GM get around this in the prep Electronic transmission models for 4th that only have a sped drive cable

[frotosride]

OK I figured it out! My only question is what is it? And can I convert it to work with my modern PCM?

[frotosride]

Oh and while I was in there I fixed another problem. If you recall when I was relocating to Maine I had an episode with a knock sensor and while trying to pull codes I couldn't even get the code12. Well my sokets were wore and slightly raised so the bulb wouldn't seat. So I chances the soldering tip to a plastic weld blade and fixed the problem. Also I found this...

[LTZ C20]

Oh and while I was in there I fixed another problem. If you recall when I was relocating to Maine I had an episode with a knock sensor and while trying to pull codes I couldn't even get the code12. Well my sokets were wore and slightly raised so the bulb wouldn't seat. So I chances the soldering tip to a plastic weld blade and fixed the problem. Also I found this...

LMFAO.

[mcintyrederek]

The speedo has a magnet and a reed switch that creates a momentary closure each time the speedo cable turns a round.  If it's like mine, there are two wires that hook to that little green box (which is a pulse buffer - I have one if you need it) before it goes to the ECM. 

I'd bet that nearly any aftermarket ECM would have various inputs for speed control.  The pulse counter method is the most common.

[frotosride]

This one I isn't magnetic. But same function. Either way I am curiouser if it's malfunctioning and causing the stumbling. The engine only stalls when changing gears. I'm going to get me a cheap tach and check the IAC. Do you know tyebactual name of the green box or the light pickups...speed sensor? That's me guess and I'm going to try to find one today as well. If it doesn't change anything I will just return it.

[Captkaos]

The Green box is called the Vehicle Speed Sensor Buffer - VSSB

[mcintyrederek]

If you need one, I have one and will be glad to get it to you.  I removed all my electronic stuff and kept all the parts just in case..  If it looks like the one in the photo, that is..

Mack.

[frotosride]

Well thanks for the help but I figured out the issue and it's simply having to adjust the idle and reset the IAC properly. The ECM wasn't picking up the load and opening the IAC circuit like it should have. My idle speed was at 650ish and that's why it was stalling especially in reverse and also while the engine seemed to stumble at idle because of the electrical load on the alternator. Rpms were low so power output was low and even lower when my fans kicked on or when the power steering switch would tell the ECM to Rev up under load and stall. I haven't had an issue since I adjusted the idle properly. But does anyone know the pulse of the VSS for the TBI. Is it at least 4k. I'm only asking to see if I can keep it and use it for the 6.0l swap?