How do I get a 4000 pulse signal to the ECM from a 2000 pulse VSS on a 1988 5sp GM NV3500 transmission? thanks

Its not possible to directly get a 4000 ppm signal from a 2000 ppm. You can get a 2000 ppm signal from a 4000 ppm but you can create pulses. You would need to replace the speed sensor or at least get some king of adapter if it even exsists. Seeing as how im not too familiar with that trans i cant recommend anything specific but maybe someone else can.

Been informed that the NV3500 actually has a 40 pulse per revolution VSS. Without a tailshaft cover, the entire tranny must be disassembled to get at the reluctor ring area. Was hoping someone out there did a NV3500 SD TPI swap and could help.

If you dont have a wireharness yet, you can do the OBD2 setup mentioned in the sticky. Then you can wire the trans direct and calibrate your speedo in the pcm to whatever you want.

Dale

Thanks for responding, guess I'm a little slow..not following you. In any event the sticky above outling TBI to TPI has me all fired up. (BTW: Outstanding sticky)

The question about a 5sp tranny (VSS signal) was brought up in the sticky..but not answered. I prefer an active VSS feeding the ECM and not by-passing it.

Can't understand why I can't tap into an "input buffer" AKA: DRAC and use the 4000 pulse signal intended for cruise control (no cruise anyway)?

Just checked my 88 truck again (305, 5sp, no A/C, no cruise) and could not locate anything that looks like a 4 out buffer or DRAC. My wiring schematic shows a "ratio adapter" and "input buffer" apparently built into the instrument cluster? If so, it does show both 2000 and 4000 pulse outputs. I'd like to tap into the latter.

(Also) Wondering why I couldn't just power an external DRAC and feed it from the VSS then use the 4000 pulse output intended for the cruise control to feed the ecm.

Not the sticky about TBI to TPI. But the one about running TPI with an OBD2 pcm.

My 2000-4000 buffer was under the right side of the dash, not to far from the ecm(91 model). It was white plastic.

Thanks..l also learned that my truck buffer is integrated in the instrument cluster.

Are you putting this in a truck, or fbody?

Going in my truck.

oh, so my location info didnt help any.

I would really look at that OBD2 setup then. Might cost a little more, but it would be worth it IMO.

Dale

I'd rather stick with the OBD1 setup. I already have 100% of the hardware, complete TPI, harness, ECM, MEMCAL, Fuel Pump, etc...the only thing holding me up is a source for the 4000 pulse VSS signal. The TBI to TPI swap is right up my alley...get to use my trucks TBI harness.

I'm sure that between, the NV3500 40 pulse VSS, a DRAC or (4 Out Buffer) and the Speed Density ECM..there must be 4000 pulse source already there that I can tap into....there must be a forum somewhere on the Internet that can give me an answer?

I'm not the only one with the dilemma...I'm sure someone "Que puede hablar sine & square wave" can help?

Thanks for the help