Effect of absent VSS sugnal?

[89S10_Project]

Folks-

I've been troubleshooting problems with my 5.7 V8 swap into my 89 S10 Blazer. It's out of a 89 C21500, in front of a 700R4, I have the proper ECU (1227747) out of a similar application.

I recently extended my harness to reattach the VSS as the swap and some harness rerouting required it. I'm not getting VSS data in my log, and I'm thinking that has to figure into the air/fuel tables.

Logs are attached- took a trip to the grocery store 10 minutes away. It's a cold start to the grocery store, then a warm start back. I think my idle is a bit low (it registered 525 at times) and it does appear to vary (I figure this is IAC at work). Otherwise I think my data looks pretty good overall.

My (quite possibly very wrong) take from this:

-Vacuum looks great. It ranges between 15-24"
-TPSvolt appears high at idle, but linear. I need to adjust the sensor.
-INT, BLM, MAP- I need to learn about them.
-Truck is rich on accel, I'm thinking that may be as designed.
-BPW MS.... err, what?!!
-O2 sensor volt is crazy high. 872v? I'm thinking no.
-IAC appears fine.
-knock count is 81 in a 10 minute drive. Is this excessive? I know it's more important to see when they occur, but if it's not excessive why worry?.

[damanx]

It's been a month or so since I've done any tuning because I've had other things to do and the fact that I've not had time to drive out of the way to try to tune the areas of the tables that aren't normal has not helped either.

In any case, I've asked before about knock counts and the value but would have to dig through my posts to find what the consensus was. If I recall correctly, the question was whether the knock count reported by the ECM to the data stream was a total of individual counts or, how many cycles of 256 counts had occurred.

Regarding the VSS, I believe that will affect deceleration cutoff, but don't quote me on that. I do also believe it affects when the ECM goes into "open loop idle" when you come to a stop. I don't recall what else it could affect, but I know I've read that people have just hard wired the VSS input to either gnd or +12v to try to fool the ECM.

Personally, I have no idea why anyone would go through the hassle of installing TBI and then shortcut the VSS signal when it's easy to deal with as all you would need is a DRAC and a VSS from a '91 time period gm car. It looks like image at the end of this post. This VSS will work with your 700r4 because you should have a cable drive if you are using the analog speedo. The drive gear you have on the output shaft will mesh with the driven gear on the VSS. Adjusting the offset for the correct speed gets a little more technical when using this VSS/DRAC, but that is done in the DRAC.

"Rich on acceleration" would not be by design because the VE tables control the fuel delivery based on MAP and RPM values. If you aren't using the ECM with the matching BIN file for that specific engine, TBI and tranny for which the engine came from, those values will be different. If you look in the GM BIN subforum under any ECM part number, you will see different BIN files for simply nothing more different than the rear gear ratio.

BPW refers to the flow rate of the injectors and the size of your engine. That number really needs to be correct before you do any tuning to the VE tables.

BLM, INT, and MAP correlation, plenty of pages on the net to explain that stuff. If you are going to get into fine tuning, you might want to look at getting a wideband O2 sensor. I went with the AEM 30-4110 sensor/gauge. Well worth the cost because you have to remember, the data you see on the computer is at least one second behind what is actually happening and with the wideband, you can see actual ratio on acceleration in real time across a broader mixture range than with the narrow band factory sensor.

[89S10_Project]

Thanks for the input-

Vehicle originally had and still has a 700R4 trans. To the best of my knowledge the speedo is not cable-driven. There's a VSS sensor on the tailshaft, with three wires going to it. Other than the TCC clutch solenoid connector and TV connector, there's nothing else attached to trans or transfer case.

I'm using an ECM that matches the application, thought I said that. The difference is I've moved the application to another vehicle in a non-factory installation. I was able to use the existing wiring harness, and in fact could have used the existing ECU apparently, as folks have done so.