speed sensor question

Hey all, i have a 77 elcamino, that has been tbi for a number of years, it was running a 90 model ecm, no speed sensor or neutral safety. i recently swapped it out for a 16197427, which i understand "Must" have a speed sensor. i have a cable speedo (which is wrong by about 40 percent) connected to 3rd gen camaro guages. (optical pickup with the little yellow buffer box) my question is can i run the signal from the little yellow buffer box into a drac in order to "tune" pulses so the computer gets the proper info? failing that, i assume the signal coming out of the buffer box can be fed directly to the pcm? any help appreciated, thank you.

I'm not the most knowledgeable about this but I did just swap out a cable set up so I could have a speedo.in all my research for it I saw a lot of cable seizes that had a little box for sending a pulse signal for vss. My set up required Changing the gauge pack to a newer one.it was a bit of a pain to repin the plug as wiring diagrams are hard to find the correct one.if u go to jags that run the site has a lot of info for speedo hook ups.u need a 40 pulse per driveshaft revolution signal to feed a speed buffer and the signal from it goes to ecm.but that still leaves u with no speedo.I think some 3rd Gen camaro firebird came with the cable that has a signal generator on the cable near the end that goes to the speedo gear.ur other option is to find a gauge pack that uses just the pulse signal for speedo.there are also lots of digital speedo set ups but they are not cheap.I got all I needed from scrap yard for cheap and it works fine.alternatively u can get a tail stock that fits your trans that had vss instead of cable and remove speedo gear and install 40 tooth rung. There is lots of info on the Web for this situation.I hope that gives u some useful info.

The 16197427 can use the 2000 (2K) Pulses Per Mile VSS. Maybe a 2K inline speedometer cable VSS from JTR http://www.jagsthatrun.com/SpeedSensors_Order.html

dave w

Sorry.just reread that and saw u said u have 3rd Gen gauges.then u just need the cable with the pulse generator.

thanks guys, i guess i should have been more clear about what im asking, i do have the little yellow speed buffer on the back of the speedometer. What signal (ppm) comes out of this? i have a drac from the truck that supplied the pcm. i guess basically i would like to run it into the drac in order to use jumpers to "correct" the signal going into the pcm, so at least the pcm would see the right speed. (speedo is off by about 40 percent or so(reads 35 or so close to 60 mph) due to my inability to locate the proper drive gears in the tailshaft for the 2.56 gears in the rearend.)

i do have the parts to convert the trans to electric speedo, but i spent a lot of time getting the third gen camaro dash to fit, would like to keep it if possible.

What transmission do u have and do u have cruise control. These pics are off jagsthatrun. Number 3 in the one pic and the one on the right in the other pic is what I think u are needing.the signal from that goes to the speed buffer for the 427.the buffer also feeds the cruise control and has outputs to use electric speedo.Attachment 12375Attachment 12376Attachment 12377

Also not sure what u have for harness.if u had the speedo mounted vss hooked up to the (guessing)7747 ecm then it's just a matter of wiring in the new buffer to some or all of the wires from the speedo sensor drac.if it was not hooked up check if the wires are at the ecm connector.if not u'll have to run a few wires.

That will get u a signal to ecm but it will still be off till u get the correct gear.there is info out there and probably on here about changing the jumpers inside the buffer to get the desired values.

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Originally Posted by skandolis

thanks guys, i guess i should have been more clear about what im asking, i do have the little yellow speed buffer on the back of the speedometer. What signal (ppm) comes out of this? i have a drac from the truck that supplied the pcm. i guess basically i would like to run it into the drac in order to use jumpers to "correct" the signal going into the pcm, so at least the pcm would see the right speed. (speedo is off by about 40 percent or so(reads 35 or so close to 60 mph) due to my inability to locate the proper drive gears in the tailshaft for the 2.56 gears in the rearend.)

i do have the parts to convert the trans to electric speedo, but i spent a lot of time getting the third gen camaro dash to fit, would like to keep it if possible.

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I think it depends on what year thirdgen...IIRC the '85-'89 put out 2000k whereas the '90-'92 went to 4000k. I'm sure what you're trying to accomplish will work as long as you can get the signal from the DRAC to the PCM. From there, you can use your datalogging software to display your actual speed. I'm sure you're familiar with the DRAC jumper mods.

If u go on rockauto and look up the speed sensor for a 92 camaro there is one listed that is like what's on jagsthatrun site.it says it's out of stock and does not say what the output signal is.but at least u know a factory part can work.I don't know the year of the gauges u have but if a cableless gauges of the same style was available then cableless is doable.

Quote:

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Originally Posted by skandolis

thanks guys, i guess i should have been more clear about what im asking, i do have the little yellow speed buffer on the back of the speedometer. What signal (ppm) comes out of this? i have a drac from the truck that supplied the pcm. i guess basically i would like to run it into the drac in order to use jumpers to "correct" the signal going into the pcm, so at least the pcm would see the right speed. (speedo is off by about 40 percent or so(reads 35 or so close to 60 mph) due to my inability to locate the proper drive gears in the tailshaft for the 2.56 gears in the rearend.)

i do have the parts to convert the trans to electric speedo, but i spent a lot of time getting the third gen camaro dash to fit, would like to keep it if possible.

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A 2K Pulses Per Mile (PPM) VSS signal can be sent directly to the 16197427. Typically 1993 - 1995 vehicles with a 16197427 using either a 4L60E / 4L80E transmission Do Not have a speedometer cable. Typically the DRAC converts the 40 Pulses Per Driveshaft Revolution (40 PPDR) signal coming from either a 4L60E / 4L80E into a 2K PPM for the 16197427. The DRAC is used to supply other outputs for the , Electronic Speedometer, PCM, and Rear Wheel Antil-Lock (RWAL) brakes. Here is a link to Calibrate a DRAC http://tbichips.com/?page_id=504

Perhaps this link will help with understanding the options available to successfully use the Third Gen Camaro speedometer: http://www.jagsthatrun.com/V8-chapte...ed-Sensors.pdf

dave w

dave w thanx for explaining that...I recant what said above...totally misunderstood where the DRAC gets it's input from. I'm still curious as to what transmission is being used as it appears you can get about any gear from flea bay. Or perhaps the real issue is...gotta drop the trans, pull tail shaft off, change drive gear, etc, etc...easier to fool something with a keystroke!!!

Dave w thanks for clearing that up.I read so many different things trying to figure how I'd make my set up work.I had opposite were I could no longer run the speedo cable due to trans having a pulse ring and sensor.I didn't know the 427 would and accept 2k pulse.that's interesting because in my plan to go back to auto trans I thought about converting the cable drive on the auto to electronic so I didn't have to mess with the speedo issue again.but at least now I know I could go back to cable if I had to and get the signal to the ecm.good info.thanks

thanks guys! think im on the right track now. trans is a 700r4, i have actually bought gears twice now, the aftermarket color/number of teeth don't seem to match gm stuff, may try again later to get the speedo working.

If I am hearing correctly: in my situation, installing a muncie m-21 behind an '86 TPI with factory wiring and computer, I can find and use the OE 86 yellow box, and cable from tranny to yellow box, plug the harness from yellow box into computer, and cable out of yellow box to my aftermarket mechanical gauge, and I should be okay. Obviously, I need (and have) the correct cable drive gear that matches the rear end gear ratio.
Is that correct?
Obviously, I will need to reprogram the computer for the manual tranny, and I have the code for that ('89).
I tried ordering the JTR generator, but they were out of stock and refunded my $$ after I waited several months.

Upon additional research and seeing the yellow box...the answer is, "if installing the OE Camaro speedo, yes use the yellow box. The speedo is mechanical, but has atached the pulse generator, which the yellow VSS buffer then plugs into. if installing aftermarket mechanical speedo, source the 2PRS unit from JTR. If installing an aftermarket electronic speedo, probably ok to use the OE tranny mounted VSS."