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i have a weird problem on a customer's EF which keep on melting number 3 cylinder piston. it have a built b20 making 238whp running pump gas. i change 3 sets of injectors from h22 330cc to evo 510cc to ID1000s with or without resistors box.

people keep telling me it is detonation but im the one tuning it and i have confident in my tune it is not detonating. other cylinder piston is perfect without a scratch. if it was detonating it would have melted all of them.

number 3 cylinder is at individual fuel trim is at 6% when it happen. AFR was at 13.3 first time it blow, put in new piston and run it conservative at 12.8 and added 6% at 3rd cylinder, still melted a big hole..this time it crack the sleeve too.

what is the possible cause of this?

Check continuity on the injector wiring from the injector to the ECU. The ECU also may be at fault if it's not pulsing injector 3 properly.

injector wiring have been check from ecu to injectors first time the engine blow. i even send out injector to be cleaned and balanced.

how to check the ecu fault?

Moates engine SIM:

http://www.moates.net/honda-b-series-en ... l?cPath=69

Injector firing is shown on LEDs

Have you made sure its not the build itself? I had a buddy who built his motor with high comp pistons and #4 was slamming against the head and eventually crapped out the motor.

Start checking plugs before it gets that far damaged if you are aware of an issue. Try pulling some timing from the cylinder and get better fuel and work your way back if you'd like.

If you want to get real thorough, individual EGT or WB, or at least get one on cylinder 3 to check, and some det can wouldn't hurt.

B series is commonly leaner in #3 cyl. Your final output may show 13.3:1 AFR, but that could be 12.5:1 on 1/2/4 and 14.1 on 3, which is a 12% variance, not 6%.
Individual EGT/O2 is the only way to check for sure, but that cylinder may just have a sharp edge or carbon buildup that's heating up and causing preignition.
*edit - I also had a tune that was knocking hard on 3, but it turned out to be a bad distributor cap was igniting that one plug too soon. Food for thought.