I'm almost done putting a TPI conversion (speed density) onto a 1993 TBI in a Caprice wagon. The 93 used a buffer between the VSS (vehicle speed sensor) to split the original signal in 2K & 4K pulses for the ECM, speedo and Cruise .

I'm using a "730" ecm. When I look at the pin outs, it appears the ECM takes the VSS wires directly anddoes the splitting internally as I see 2K & 4K pins out on the Schematic.

Can anyone verify that this is the case and I must now bypass the Buffer?

The second question is the connections for the A/C hookup The two schematics, old 93 FSM and "new" 730 seem to have different terms used from the Caprice compared to the 730. I'm not sure id the term "A/C request" is the same as A/C power. If I'm running through the Caprice relay, 4 wires total, two light blue wires, dark green and dark green with white strip. Can anyone verify how to hook it up.

The "Painless" manual says: The Dk.Grn/Wht wire labeled A/C POWER should be spliced into the A/C compressor power wire, in a location close to the compressor itself. I don't know which is which as the 93 FSM doesn't make refernce that way.

 

I'm not sure about the buffer bypass but the 4K pulses per mile should go into the ECM at B10 (high volts) with 0 reference of B9.
Thats where it needs to read into. Depending on the type of VSS signal, there is a bit in the bin for Magnetic or optical signal type.
Using the buffer signal "may" be the optical setting, running directly in "may" be the magnetic.
either way the connections are the same. Hopefully someone will clarify that bin setting for you.

The Grn w/ Wht stripe is the A/C clutch (should be) and will indicate to the ECM when the A/C is requiring additional idle RPM, etc.
It should go into "C9". I've seen that its called "A/C request" and it never made much sense to me either. In any case you want the power wire from the compressor clutch. The wire going to the ECM should be from the Clutch side of the wire so that if the high pressure switch opens the ECM can see the compressor is not running and won't compensate.

 

Although I don't have the 730 pinout diagram in front of me, but there were four pins envolved on the ECM. not only for the signal in on B9 & 10, but also pins labeled 4k & 2k pulses OUT. They were earmarked as for instument cluster (speedo) and cruise.

These last two were different from the B9& 10 INPUT of the yellow and purple wires from the tranny. That fact lead me to beleive the conversion of the signal is internal of the ECM, therefore not needing the buffer that my TBI system had. Can't see any reason to buffer the signal twice IF that's the case, which is what confuses me on the issue.

My gut feeling is take the Tranny signal direct to the ECM then take the ECM OUTPUTS to the dash as required.

Additionally I throwing in a Nordskog digital cluster, which is programmable to any range of pulses per mile. So I figure give the cuise whatever it requires and give the second signal out to the Nordskog, then find a measured mile to get it dialed in..

I'll play with the A/C tomorrow. I "think" I follow you. Thanks in any case. Still not to too sure about that other Green wire on the opposite corner of the relay.

 

The '90 and later TPI ecms used an internal buffer and the gear driven, electric output VSS. Therefore, you should not have a separate unit for the VSS buffer. The 2K PPM output is supposed to go to the speedo.

 

The "other" green wire could be from a power steering switch.
The A/C clutch on mine had a "loop" through the high pressure switch on the A/C system and also went through a closed contact on the power steering. If PS pressure got too high the clutch would be released so not to bog down the motor with both loads.

Check out my drawing of my 86 Monte.
It won't be exact to yours but may help you see how it might be wired.
http://www.wideopenwest.com/~Johnand...T/favorite.htm

The draing is the PDF file.

 

Thanks guy. Sounds like "case closed" for the VSS and buffer.
Good to Know I was an the right track.

BY the way, my car has an external Knock Sensor buffer as well. on a brackey in the engine bay. Does the 730 process this signal internally as well, therefore allowing me to bypass it too?. And would that require a specific sensor on the block to do that?



THe old ECM did have a power steering pressure switch pin out. Per Painless that has been pliced into the a/c unit. Some how though I 've come up with an extra wire that I obviously didn't mark well. ON the A/C relay There are four wires, 2 light blue, the dark green with a white strip that) and the final plain green wire. So i'm still a little shakey on those four wires.

 

The 7730 also incorporates the knock sensor buffer in the ecm, so the external knock sensor buffer is not needed.

Not sure what knock sensor is used in the '93 Caprice, but the safest way would be to use a knock sensor for a '90 - '92 IROC TPI Camaro for either a 305 or 350, depending on the engine size in your Caprice wagon. This would ensure that the knock sensor signal matchs what the 7730 is looking for.

David

 

Thanks for the Info Dave. That makes good sense. to be on the safe side. A little money money on the sensor , would cure a lot of hassles

 

The memcal & KS should match the engine size.
The KS processing is done on the memcal and then sent to the 7730.