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I have been driving with a BPT (GTX) motor in for a little over a year now and have blown up piston 1 twice. the first time it was a minor fracture and I was running again with a few days after replacing the piston. The second time it blew the piston apart. I have replaced the piston again but want to know what could have been causing this? The first time the piston blew the had only been tuned by me with a Super AFC and a wideband O2 gauge. The second time it was tuned on the dyno with a wideband O2 gauge and cross checked with a EGT gauge. I am thinking it is a bad injector since the other 3 pistons were fine this whole time. If it is a bad injector where can I get another one for the same engine?

For fuel management I am using the SOHC ECU and harness since I can't find the stock GTX (BP26)one and using a Super AFC with a 3 to 4 wire TPS mod.

the could be the problem.
why dont you pull your injectors and take them to be cleaned and tested that will tell you for sure if thats your problem.

what size injectors do you need, i think we have a set out of a 323 laying around somewhere. 330s i believe

Sounds to me like your getting detonation on that cyl.. Any pics of it? What about the plug.. how does that look? Check if it is white on the top.. because if it is you are running lean.. Id check that and also check to see what your timing is set at it should be around 13 degrees past top dead center.
I sure hope youre using 91 octane or higher in that car, regular gas is crap and will cause detonation also.
I think that injector could be the culprit though, you said that you were tuning using the egt gauge and a wideband, what was the af ratio at full throttle and the egt temps? The gtx pistons blow up at 900 degrees celsius..
If the injector was leaning out that cyl you would be detonating really bad.. like it should be to the point where youre wondering what that sound is.. (Sounds similar to pennies bouncing around in the engine)

Have you been driving the car hard? Hitting the limiter? The mx limiter is a fuel cut...

I had my setup the same as yours for a little while with the safc on the mx ecu.. but you should be actively looking for the real gtx ecu. I only had to do it because I couldent find the proper ecu in time. Try and get the real ecu from somewhere man. I have a feeling that the mx3 ecu isnt doing your bpt any good. The timing maps are all wrong.. Like your bpt engine is supposed to be probally 18 or 20 degrees or something like that at full throttle and the mx3 might be 30 or 35 or something crazy like that so if you find out that the injector wasent at fault then I would say try and get some better kind of engine management going on. If you cant find the proper bp26 ecu then you can always go with a standalone like a haltech e6x or a megasquirt which is alot cheaper but I have no experience with it so I cant say how good it is.. Alot of people use it though.
Hope it helps. PM me if you have any questions.