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weird misfire at idle and low load

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Hello,

I had a question regarding to my current build. I had an mk3 supra with 2jz-ge nat setup. The engine has bc 276 cam, 10:1 CP, FIC 2150 cc injector, denso audi coil, G42-1450 turbo. The engine is running on emu black, and I fabricate the wiring harness. car has been put down about 5000 mile since the build. I'm not sure if the injector is too big or not, but sometimes at low-load cruising, it has a misfire. But that is when I barely tap the gas(< 1% TPS reading,MAP: 50 - 58 Kpa). Keep in mind it idle around 52-57 Kpa. Sometime when the car warms up it has a slight misfire as well. If I turn it off and start it back up, it might went away. Other than the problem I mentioned above, the car drives fine. car made 650 WHP(16 psi) on 93 pump gas.

You might need to adjust your accel enrich settings and see if it improves the situation.

Sounds an awful lot like a lancer evo I had that had massive injectors. Solenoids arent very stable at under 10%ish Duty cycles. I had to run it at a higher idle speed and just had to deal with the car running slightly rich at lower loads.

As has been said, with larger injectors it can be very difficult to control them accurately at very short duty cycles where the opening and closing period is a significant percentage of the open.

What does the lambda log show when it's not quite in the misfire range? If it's trending to rich it would suggest a rich misfire - NOTE, when it does misfire it will register as a "lean" condition, because the lambda is reading the unused oxygen in the exhaust gas from the mis-fire - if it's trending to lean it's probably a lean misfire.

As a general rule, if you can hear it, a lean condition will be sharp like a "crack" and a rich one more muffled like a bang.

Spark plugs can tell you a lot about what's happening in the engine, I'd fit a fresh set of spark plugs - what heat range and gap are you using, btw? - and run the car in the misfire range for a few minutes, then cut the ignition and come to a stop. Pull the spark plugs and have a look at them - are there any marked ly different from the others, as that will suggest a single problem.

Are they a dry white, a shiny white, dry sooty, or wet and sooty? The first would suggest a lean misfire, the second may be the fuel not being ignited, the third would be a rich mixture that's being ignited consistently, and the last a possibl3e rich mixture that isn't being consistently ignited.

You don't mention it, but I assume you're using a manifold reference for the fuel pressure? If not it may help, with retuning, as it will reduce the affect of the large injectors at low load.

If it's an option, you 'might' see some improvement with moving the lower rpm/load injection point around a little?

Oh, on that, you are using rpm and load timing advance - light load can use a LOT more timing than under heavy load.

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