Drivability is now much better, though one loose end is when slowly transitioning from no gas to slowly accelerating. The “handoff” from essentially idling to accelerating still needs some work, as the transition still has a bit of a hiccup.
Anyway, my brother and I did a car show at our old high school. It was a typical hot rod show where few people do the work on their own cars and everyone walks around looking at 50’s-60’s muscle cars that after a while, all start looking the same. Worse, about the only people there were car owners, with virtually no crowd of onlookers. There was one notable exception to the cookie-cutter muscle car: the guy started with a USPS Postal truck, removed the body, then added his own frame and paneling, and calling it a “33 Riley”. The engine’s from a Nissan 280Z and fits the car’s character perfectly. He made everything himself, cut, bent, and riveted the paneling, added big drum brakes, complete with real wire wheels. He “wins” in our book, though we didn’t stick around for the expected win of no doubt some $150K muscle car that’s hardly ever driven. The Rikey builder said he’s put about 70K miles on it since finishing it.
While maintaining a constant low speed at zero boost, lambda (air/fuel ratio) swings back and forth quite a bit between about 0.80 and 1.2. A side effect is feeling an oscillation in the car, like someone’s pushing and letting off the gas about once a second.
The fact that it was oscillating reminded me that closed-loop lambda control has its own PID loop. Comparing the values with an old tune showed that the tuner had set the (P)roportional constant about 4X what I had and the (I)ntegral constant at about double. I suspect he just set it to something in order to get on with the main tuning. Well… that’s fine, but it leaves the car with yet another drivability quirk. It’s harmless, but it’s stuff like startup, idle, and partial-throttle performance that gets noticed far more often because 99% of the time that’s where the car operates. If I’d taken the car for a test drive, we’d have easily been tuning the rest of the afternoon, but since he doesn’t fit on the passenger side(!), I don’t think sticking around would have helped.
I’ve talked to other tuners and they said this is where all the time goes – drivability issues. Customers get all excited about loud pulls that produce dyno curves for bragging rights, but it’s the little, nuanced variables that complete the tune and make the car act, what, like a real car?
The little fire turned into a beast which is still completely uncontained; a couple coworkers are waiting to see if their homes are still standing. Last night our pond skimmer worked overtime collecting tree debris. Imagine that as burning embers driven by 30-80mph winds.
In car news, it’s fairly straightforward tuning a fuel and ignition map, what’s not is cold-start and idle. It takes a lot more time because it’s so subjective, plus cold-start can only be worked on for a few minutes before the car has to cool off.
AEM’s ECU versatility allows changing many parameters, some by a lot. For example, the idle PID control loop terms appear as “X.XXX”. Annoyingly, they don’t give a rough idea where to start, instead sticking with “every engine will be different.” Well, yes, and no. For example, is a good starting point 9.000, 1.000, 0.456, 0.045, or 0.005? If you start with 0.005 when the majority of engines need 1.000, it wastes time. It’s like being asked to guess a number between 1 and 10,000 without even a ballpark starting point, or even the state where the ballpark is located…
I bring this up because idle is currently running an “I” term of 0.010. Today I found a post where someone got AEM to reluctantly cough up a starting point. The response was “… cars with aggressive setups and big injectors may need a ‘P’ term of zero and an ‘I’ gain of 0.1-0.2 at idle to prevent oscillation.” So, maybe what I thought was okay could stand further improvement. Increasing “I” to 0.05 didn’t show a marked improvement, but it needs to be driven, but now it’s time to pick up the wife at LAX. Told the neighbors that if things get insane around here before we’re back, to rescue our dog.