Erratic Tach only on Laptop

[NorthState]

Morning! I will try to keep it short. 1997 ECSB with slightly spicy 5.7. (Details upon request if necessary) Successful 411PCM swap thanks to @Lextech! (He’s the man!) Successful base tune load thanks to @Carolina_'99Hoe! (also the man) Only slight adjustments to HPtuners to get it to run, but fires right off. The problem me and @Carolina_'99Hoe seem to be seeing is that the truck tach and the efi tach seem to agree, but the tach on the laptop is very erratic. It would be great if it was only a setting in HPtuners to calm the laptop gauge down so we could set shift RPM parameters.

Anyone ever ran into this or could help?

 

[NorthState]

Ok heres the theory. Since my motor wan built and ran in a 70s nova show car for about 2 years, it doesn’t have a lot of the sensors namely cam position and crank position. It has a Skip White HEI distributor that is sending a tach signal to the dash and the efi system. I guess that since the signal that the ECM wants, which would normally have come from either crank or cam position sensors, is not coming off the distributor and could be either just a dirty signal or picking up interference from something in the harness. Regardless, I think I’m to the point that I know I have a great engine, that runs stron. It just isn’t set up to be compatible with the electronics of the truck. That being said, I wanted to LS swap it to begin with and I think I’m going to go that route again. I’m going to try to sell the 355 that I have now locally here in eastern North Carolina maybe to someone who is building a pre 95 truck or classic car. When my credentials get upgraded, I may be able to list in classifieds.

 

[NorthState]

Just an update:
Since this went cold immediately after posting, I wanted to report findings for the archive so that if anyone had this question in the future they could reference my unfortunate conclusion. The 5.7 that my truck had from stock used the crank position sensor and or the cam position sensor to send the signal to the ECM, which would generate a computerized tach gauge reading. Since my engine didn’t have crank or cam sensors, the thought was to run tach signal off the distributor. This is totally acceptable in most applications. In fact it’s where the signal would have had to come from, I believe, in early engines. Anyway, either the signal was too “dirty” and or we needed to “fake” a low reference to also send to the ECU. We tried running a dedicated shielded grounded tach wire to the ECM, and even considered running tach off the alternator like some of the diesels do, but apparently, you have to buy another signal converter to make that work. At the end of the day, I could maybe have changed trannys to a non electric, but by then, I was just ready to go back to the LS swap plan I had in the beginning. The whole thing turns out to be a compatibility or integration issue. Great motor, great tranny, the ECU just didn’t understand what to tell the tranny to do.

Onward…

You must be registered for see images attach

You must be registered for see images attach