Engine misfire ...

[firehawk]

eight-six Wrote:The CEL is on permanently with mine, but it doesn’t seem to affect how the car runs. I think what the guys in Japan did was to remove all sensors the ECU used to control the ignition so it’s pretty much locked out. The Diz has been notched forward 2 teeth and then set to max advance just to get the timing right as the cam timing is very advanced. Maybe that’s the ida the Japanese guys used, throw it onto the base map at 10deg BTDC and then wind in as much advance as possible?

Ok - with the CEL permanently lit, the ECU is not providing any ignition advance and triggers the spark with the base advance only. So by rotating the distributor as you described, you set a lot more base advance, causing the spark to be triggered at a static angle of, for example, 32deg BTDC. This isn't a best possible solution but works reasonably well, especially on race cars which see mostly full-throttle acceleration. I know that several AE86 rally cars in Finland run this way.

When the CEL is not lit, the ECU either uses the normal advance map or the simple overrun map - depending on whether the switch inside the TPS is open or closed. The overrun map is pretty much a static ~30deg advance when above 2000rpm. The normal map is probably the best solution but requires that the ECU can detect all sensors and that the idle switch is always open. The ECU does set error code 11 but doesn't go into limp mode (not a fatal error, so CEL won't get lit) so it'll provide a variable advance throughout the rev range.

JMR_AW11's articles on the 4A-GE ECU secrets were quite helpful in making the ECU play nicely along with carbs but unfortunately it seems that they're no longer online..

Quote:But if the O2 sensor was broken and returning duff readings, or reading a rich condition at higher RPMS (as you expect with carbs) could that not influence the ECU and in turn the timing gets advanced? Are you sure O2 doesn’t have an influence on the running past idle? I only say this as I had a faulty O2 sensor previously on my old SW20 turbo and the car ran like utter crap (driving and idle) – which would imply that the ECU on the SW20 did rely on the O2 sensor to ensure proper running.

Actually, you're right - the idle mixture pot (and thus apparently also the O2 sensor as they use the same ECU pin) has effect when below 3600rpm and partial throttle (light to medium engine load). However, according to JMR's documents, it only has effect on the injector pulse width so the ignition should work normally even if the O2 sensor is outputting nonsense to the ECU.