Sunday Night Analysis

At the time of this writing, the engine idles pretty much flawlessly and tweaking some cells in the VE Table improved reving somewhat before I fumbled. Don’t ask me how, but I loaded and burned a previously saved msq file when I was switching back and forth between MegaTune and TunerStudioMS. I had done that a few times earlier, but I must have clicked ‘Yes’ to the question. At least it’s not like starting COMPLETELY over.

There are a couple of things going on that do not seem right. Most troubling is very flakey signals from the O2 sensor. It mostly stays pegged at 5 volts (or AFR 21.9, depending on which gauge you’re looking at), but will occasionally scatter like a crazy monkey. It was working well earlier in the day, at least returning believable numbers. Wiring looks good. I will try to locate or replace the programming cable and verify that the LC-1 is programmed correctly.

With essentially no O2 sensor, I’m tuning kinda blind and my nose says it’s rich at idle and my ears say that it leans out around 4000 RPM. Right before I shut down for the evening, I made a log file of a short run.

The first thing that was less obvious in MegaTune is a pulsing 5 KPa swing in Map at idle. This pulse occurs 6 or 7 times in most logged seconds, which corresponds with the expected vacuum pulses at idle. My vacuum signal is from one TB, which feeds two cylinders. (850 rpm / 2 cylinders) / 60 seconds per minute = 7 pulses per second. I recall a mention of such pulsing making tuning difficult and a damper made by restricting the vacuum signal slightly and following the restriction with some kind of accumulator, such as a clean, dry fuel filter. I will implement such an accumulator.

In the mean time, I will continue analysing the log file.

In a more entertaining note, it’s interesting to see single isolated MAP readings of 159 or so, which I presume correspond to backfires. Early in the first start process, when it was beginning to have a useful amount of fuel but was still too lean to run, I had a few spectacular backfires. One of them actually popped one side of the throttle body out of its rubber boot!

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