I've searched and am more confuzzled than ever!

I'll keep it plain and simple: 1989 700R4 trans in a 5.0 TBI Firebird. What signal output is the trans outputting to the VSS buffer? 2000, 4000, or something else?

The reason I'm asking is I've swapped a 350 TPI from a 91 Z28 into it. I also am using the donor's TPI harness & ECM - spliced at the driver-side dash. I'm not sure where the VSS Buffer would have originally been wired in to the system - as in, has this actually bypassed the buffer, and, should I have done that? I can always re-splice the yellow & purple trans wires back to the block on the firewall, but currently they go to the ECM.

(No speculation, please. I know there are plenty of people with first-hand knowledge on this. Thanks!)

post #5

https://www.thirdgen.org/forums/engi...s-problem.html

So, I've wired in the 700R4 that was originally in my TBI car directly to the ECM via the donor harness. (Car's not running yet, so I can't road test the speed). So, what you're saying is that all 700R4 transmissions output the same signal (which is the reason for the buffer on a TBI)?

(Not trying to beat a dead horse, just trying to grasp the whole concept, not just bits and pieces).

the 1227730 ecm has a buffer in the ecm.The 1227730 ECM it will expect to see a 4k ppm form the vss directly. The tbi used a 2k signal to the buffer. Two was too correct this. One get a new 4k vss and rewire and use the 730 internal buffer or reprogram the tpi Memcal and use the buffer optical signal and use b10 of the ecm.

The output signal you have if it was a tbi car is 2k ppm 1/2 of what it needs tobe. Like I said about and in your other post a few ways too fix it. The Dakota Digital sgi-5 may work as well.

Thanks. That's what I was wondering.

I read the other reply a couple times, but must have misread it. When you say to replace the VSS, you mean the VSS buffer from another GM vehicle? (I did find a list of buffered cars & values)

the vss is the vehicle speed sensor. the tbi uses a 2,000 pulse per mile sensor wire to a vehicle speed buffer and from there it sends a 4,000 optical signal to the speedometer and a 2,000 pulse per mile optical signal to the tbi ecm. The 1227730 ecm has a internal vehicle speed buffer and the signal from the vehicle speed sensor will need to be wired directly to the ecm B9 and B10 but the vehicle speed sensor will need to be for a 90-92 vin F or Vin 8 Tpi car This is expecting to receive a 4,000 pulse per mile magnetic input. Or you can reprogram or have the eprom in the memcal reprogramed to use the optical signal from the tbi vehicle speed buffer and use the 1227730 input pin C6.

acdelco 213-197 or standard motor products sc12. You might want to double check the numbers but it looks like thats the 700r4 4,000 pulse per mile sensor.

http://www.ebay.com/itm/SC12-Speed-S...ce1d31&vxp=mtr

(And the light over my head finally goes ON!!!) Thank you Tuned. That last link really made things much clearer. I know exactly what you're talking about now - I wondered why the plug on the TPI harness was different and had to be spliced. Now, I only wish I had known this earlier. At least it's a fairly easy fix.

(I know how frustrating it can be trying to explain something you're familiar with to someone who has no idea what you're talking about. Thanks for not giving up!)

sent you a pm

Hey 1991_RS, I don't mean to bring up a dead thread but I am in almost exactly the same predicament now that it seems like you were in. I have an 89 camaro that was originally a 5.0 TBI but since then had a 91 350 TPI (actually from a firebird if I remember correctly) swapped in by the PO with the computer and a new wiring harness (a painless one which I would not ever recommend to anyone). So what did you end up needing to do? I know with my painless harness (which came with no connectors) there are a couple wires hanging next to the transmission labeled VSS and I always assumed I would need to swap the sensor or something.

What ended up working for you?

Is there anyone else that can shed some light on this?

I'm still pretty confused as to what I actually need, help would still be appreciated

If your 89 is cable drive speedometer you will need the retrofit vss to send a 4k ppm signal directly to the 730 ecm I assume thats what you are using. Or you can have the memcal remprgramed to accept a optical signal from the speedometer on pin c6 of the 730 ecm
http://tpiparts.net/inc/sdetail/7587

As far as I know, 89s are not cable driven, so what would that mean?

The speedometer is cable driven and there is a device on the speedo that generates a VSS signal to the ecm. You can bypass this by putting a latemodel sensor in the trans and bypassing the speedo or you can modify the signal you send to the ecm in various ways.. The problem being the tpi car signal is twice the TBI car signal. So you have a 2k signal going to a ECM that wants a 4k signal. So you need to modify the signal you have or get another sending unit.

Have the memcal remprgramed to accept a optical signal from the speedometer on pin c6 of the 730 ecm. There is a brown wire coming from the speedometer that went to pin A10 of your 1228746 ecm.
Or the 2k optical signal is coming from a vss buffer.

Alright thanks guys. mmadden55 is that where something like the dakota digital boxes I always hear about would come in to play?

The sgi-5 would take the magnetic pulse 2k ppm and convert it to the 4kppm the ecm needs to see. You can wire it up in place of the vss buffer. The sgi-5 will allow for gear ratio calibration. If you want the other option of reprograming send me a pm I offer tpi/tbi reprograming.

tuned, maybe i am misreading what you are saying. if they have a 90-92 tpi, they shouldn't need an sgi5 for the ecm unless they are running gears bigger than 3.73. all they should have to do with the tpi set-up is bypass their in dash buffer so the ecm can feed direct to the speedometer.

You can do it three different ways, Like you mentioned or have the memcal reprogramed to accept optical vss on c6 of the 730 or off the sgi-5. Im just not sure if a magnetic 2k ppm is sent to the 730 the tcc lockup and divisor output would be half of what is expected.

How would you go about bypassing the in dash buffer? Is that part of the device mounted right behind the speedometer?