Hi guys. Sorry to be gone so long. It has been a crazy pre-christmas season, being in retail and all, plus the weather was not ideal for car play. Now it has gotten warm again, and things are slowing down. I was wrong that the switchover from heated to cold air was causing the problems. They are caused by something else that I have not identified yet. I built an outside air pickup, and installed that yesterday while watching the Redskins finally win a game. Today I fired it up, and when the ECT(engine coolant temp) hit 160, it went crazy again. I probably could have left the heated air door in place.

I tried dialing in extra temp/VE table coeficient to richen it up at 160 degrees, but it did not help much. There are several other modifiers that are temperature related, but I don't understand them yet. I think I will buy the book for their Gen VI system, which, although obsolete by the new version, likely has helpful tuning tips.

Once the ECT got up to 190 or so, it smoothed out and ran OK, but is now too lean, since the intake air is now coming from outside the engine bay. I will spend some time tuning the VE table again. In the mean time, I just bumped up the ECT/VE table coeficient modifier to compensate so that it runs about 10% richer than the VE table says.

What the heck happens at 160 degrees? I don;t know. Timing looks OK, but O2 voltage does drop, so something is happening that leans it out, and the heated air box switching over can no longer be considered the culprit. It was a good theory. Time for a new theory. Any ideas?

One of the values that can be tuned is a compensation for how much of the fuel puddles on the sides of the manifold or around the intake valve, that then gets sucked in when the valve opens again. This is controled by a table that has MAP values along one axis, and ECT along the other. It is called TAU. I don;t know if this a standard EFI term, or if it is just Accel's term. I suspect this table might be of help here, but don;t know how to tune it. In the mean time, the car is still pretty, but more of a project than a car.

Sam

_________________

I believe that's X-Tau acceleration enrichment. It's shown up in a few OEM systems, and Megasquirt-II (but not the original Megasquirt) can use it, too. It's not particularly useful for steady-state tuning, but helps with acceleration enrichment.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Thanks for the feed back Matt. I think I understand what is being calculated, and why, but I do not understand how a change in the table value effects the fueling. I don;t know if the number should be made bigger or smaller if the mixture seems to me getting too lean when opening the throttle. The table has vriious MAP readings, and various ECT temperatures values so it can be tuned for variious warm u0p states. Do you think maybe the accelration, or attempt to open the throttle from idle at 160 degrees could introduce a troublesome change that tuning on the x-tau could help compensate for?

There are also tables that consider the difference in manifold temp and coolant temp to try and calculate the intake valve temp. I wonder if the intake manifold surface temp on a slant stays cooler than the default on a V-8 would relative to the ECT? Or maybe it is just the other way around. What I need here is a practical description of how changing these things effects the drivability, and how changing things affects it. Then, what is needed is a sequence of tunings. Which ones are the dependent variables. Everything depends upon the VE table to correct at full operating temperature, but then which things do you change first after that? Does anybody know of a web site, or manual that has a good general procedure for t his. I know it is the same question I have been asking all along.
Sam

_________________