Ok after doing some research to no avail I've run into an issue with my build. I have a 1991 Camaro RS with a 1987 IROCZ TPI 350 swap. I had a harness made for the 87 engine setup and everything works but the speedo. my issue is that the 87 IROC had a cable style speedo and the 91 RS has an electric sending unit. I was wondering if there was a way to make the 87 PCM capable of running the electric speedometer? the harness has the speedo sending unit wires and they are hooked up and the gear hasn't fallen off inside the tail shaft housing. If anyone has any input I would greatly appreciate it !!!

 

As a suggestion,......

Set up your 91 Speedo system like the 91 TBI cars. 90 -92 TBI cars used a VSS Buffer box to supply the cluster with speed info. 90-91 TPI cars didn't,.... those clusters relied on the ECM for that info. The wiring would be something like:

Factory 90-92 Speedo sending unit
-to-
Factory VSS Buffer
-to-
Factory Speedo Cluster ( and cruise and ECM - if needed )


** Not sure how/if the 87 ECM can handle the 90-92 speedo sending unit signal - do some home-work to be sure about the correct Pulses Per Mile & compatibility !

 

Alright ill do that, I put in a call to the company I had build my harness and their tech guy is gonna call me and he may have an answer too

 

Ok, I have come to the realization that my torque converter isn't locking up due to the lack of a correct speed signal (possibly). so I need a way to give the ECM and the speedometer the correct readings. any suggestions in that area ???

 

This is not a speed signal problem,..... might have missed a few wires when you connected the 2 different wiring harnesses together.

The Brake Signal to the TCC ( purple wire ) runs to C100 @'E7'.
on your 91 dash harness.

87 and earlier cars have the Brake switch to C207 Pin 'P'.


If you didn't resolve this miss-match, the TCC isn't getting power.


The check TCC Operation - once it's properly wired - Connect the positive lead of a test light to PIN 'A" @ the tranny and connect the negative lead of the test light to PIN 'D' @ the tranny. ( Test light needs to be visible INSIDE the car while driving,..... use long wire ! ) Take the car for a ride ( in overdrive ) and verify the light turns ON/OFF during TCC operation. If it never lights up,..... check PIN 'A' for power ( when brake is NOT applied. ) and check ground by wiring a toggle on the ground wire, taking it for a ride, and flipping the switch to see if the light works. ( ECM Bypass ).

I'm pretty sure that's how it works !

 

Well, I actually had a custom harness built for this project, made for an 87 maf tpi setup but its got the input for a speed sensor. And as far as that brake switch goes it wasn't in my car to begin with, so I pulled the one out of my parts car and plugged it in but that still didn't fix anything. I didnt figure it would but at least I have it in now. So does having a custom harness change anything ?

 

The check TCC Operation - once it's properly wired - Connect the positive lead of a test light to PIN 'A" @ the tranny and connect the negative lead of the test light to PIN 'D' @ the tranny. ( Test light needs to be visible INSIDE the car while driving,..... use long wire ! ) Take the car for a ride ( in overdrive ) and verify the light turns ON/OFF during TCC operation. If it never lights up,..... check PIN 'A' for power ( when brake is NOT applied. ) and check ground by wiring a toggle on the ground wire, taking it for a ride, and flipping the switch to see if the light works. ( ECM Bypass ).

 

Alright, by the way I did figure out that the 87 ECM is designed to read an optical signal, and the pulse rate is 2000 PPM and the 91 speedo is supposed to receive a 4000 PPM signal from the vss. But is there a difference in between these 2 signals? Reason I asked, is the company that made my harness told me to get a Dakota digital sgi 5e speed signal converter to correct the problem. But im unsure if it will because all those boxes do is multiply or divide the pulses per mile (please correct me if im wrong)

 

This was really so simple - BUT:

You've got a CUSTOM HARNESS. Since you have a custom harness and you are having some significant wiring problems ( no Brake switch ?? No Speedo ?? ) you need to contact whomever made you this harness to get a map of the circuitry. Obviously things were not "Perfect" and if you don't know how it was made,... how can you - or anyone else - ever be expected to fix it ?

IMO; If the conversion wiring was done "right" then your speedo would work fine by simply installing a 90-92 speedo sending unit and the proper plug for it in the 87 engine harness. ( Your car already had all the parts,..... you just needed them to be included in the "custom" harness ! )

AS THINGS ARE NOW; adding those 2 wires from a 4000PPM sending unit simply splicing / re-pinning to the 2 factory 90-92 speedo wires in your cars dash harness should get your speedo would work normally. ( 90-92 TBI speedo wires are @ C100,.... Yellow wire @ 'D4' and Purple wire @ 'E4'. )


The DD SGI5(e)is a well regarded converter. ( You don't need it - you need a factory 90-92 sending unit, a plug for it and 2 long wires. ) Many have issues @ start-up using the converter, but can get it working after messing with it long enough. I used an older version ( not the 'e' version ) to convert the speedo signal from a T56 to work with a factory 2000PPM stock cluster as well as an adjustable aftermarket speedo head. You can find the PDF installation info for the DD signal converter online,..........

 

Ok Im tracking now, ill go through my diagrams and recheck everything, run through that test you mentioned and hopefully that'll fix the issue. I really appreciate the help!

 

Well I figured out my TCC problem for the most part. I was spliced into the wrong wire and not thinking clearly but I did fix it, except the converter locks up as soon as the trans. shifts to second...... so more homework. Also ill see if I can tap those wires in the VSS and see if that will get my speedometer working. My new harness came with the speed sensor wires so ill look at my ecm connectors and wire it in. Any precautions I should take?