John in KC - Roadster Build Thread

[JMD]

Big milestone this week: I think my tune is pretty much dialed in. I've been working on it for weeks now, starting with the ignition timing, deciding on a final AFR target table, dialing in my hot idle and hot & cold startups, then once my learn table was only showing 1-3% values I started fine tuning them manually and working on my acceleration enrichment tables. Actually swapped out my air cleaner because I could see the kpa drop in the manifold during a power pull. Lots of datalogging, some experimenting, and just a few days ago ran the car in the first open loop tune to see where the fuel table really was without the closed loop affecting it. It actually ran great. I took a bunch of datalogs, did a few more rounds of fine tuning the AE & base fuel table manually and think it's about done. (Well, tuning is never 'done', but good enough that no significant changes are needed.) It really is amazing how an engine can seem to run pretty well when 'in the ballpark', but paying attention to the details and sensor data and making changes based on that data will certainly give you a sharper, crisper and stronger feeling engine. My father thought I was crazy to keep messing with it. He thought it ran fine and it did...until I made a change and you could feel it improve. He kept thinking 'that must be as good as it gets, why do you keep messing with it?'. But at this point I do think I'm finally about there. Some in depth dyno tuning might pick up something here and there, but I'm pretty sure it's about where it needs to be. You've got to be willing to experiment and find what the engine likes. Totally worth it!

The Sniper wizard setup and learning will get your engine running decently well, but there are a lot of parameters that need to be custom set for each engine. There are multiple parameters that dictate how the IAC works, which affect your hot and cold starts and how the car idles and comes back to idle after throttle. Not to mention the 6 different AE tables that tell you when and how much accel enrichment there is and where, temperature offsets for startup and fueling, cranking fuel tables, startup enrichment tables, how your closed loop and base fuel tables learn...so much. You're never going to get a great starting and running engine with a 'box tune' that simply adapts the fuel table to an overly simple AFR table. So yes, the Sniper is great, it will usually do a good job of getting your engine running safely, but you will need to get it tuned or learn to tune yourself if you really want it to perform properly. (Lots of Joe Simpson videos on this topic on youtube.) Ok, stepping down from my soapbox...

I've really enjoyed learning the Sniper EFI system and so glad I did. If you can't tell, I do tend to geek out about this kind of thing quite a lot. Definitely one of my favorite parts of the build.