Engine misfire ...

[eight-six]

Hey Jani,

Thanks for the reply.

Well I am not holding my breath but I took the car out last night with the new igniter installed and also with the O2 sensor unplugged; and on the few pulls I did do I didn’t hit the invisible rev limiter. Car seems to pull cleaner and my butt dyno says the car is quicker as a result. Whereas before the power would feel quite linear to the redline – it now seems to have a surge once it reaches 4k, and the cams come into play. Engine note sounds keener as well.

Quote:Hmm, I have a similar setup with 44mm Mikunis and the standard ECU for ignition. Do you have the TPS and MAP plugged into the wiring loom but not connected to the throttle shaft/vacuum?

Both are disconnected. When I got the car originally the MAP wasn’t connected and the TPS module was connected to the loom but not doing anything.

Quote:I had problems with misfiring at first when I had the MAP connected electrically but not into manifold vacuum. The ECU didn't provide enough advance at above 3500rpm and I had fire spitting out both from the carbs and from the exhaust. The hotter the engine got, the worse the misfiring became. Providing vacuum, albeit only from cylinders 1 and 4, to the MAP sensor fixed the problem.

The engine seems to pull pretty cleanly. Discounting the magic redline the engine is a bit boggy lower down as to be expected with big carbs, and lumpy cams but once it clears (circa 2k) it just takes off and runs perfectly. Even better now I pulled the O2 sensor and changed the igniter. I am going to have a go at hooking up the Map and the TPS to see what it does to the running. I will customise a old fuel rail for an inlet plenum to take my vac reading from and see what I can do for the TPS.

Quote:The same problem also occurred when the CEL is lit due to missing sensors and the ECU falls back to base advance (~10deg BTDC as standard) only.

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?

Quote:Off idle, the ECU only considers RPM and MAP when it determines the ignition advance so static readings from the other sensors doesn't really matter. The ECU is happy as long as the sensors return a sensible voltage/resistance

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.

Even if its only minimal adjustments in the timing its enough to throw the timing out completely?

Cheers

James