Not sure if this is in the right spot but hopefully I can get some advise. Last August I purchased a 408 long block from Texas speed. Another technician and I installed it in my ws6 at our auto repair shop. I took the car to a very reputable tuner who i've had tune my car multiple times. For the past year now i've had an issue with the vehicle that has intermittently been causing the car to back fire at 6k rpm and then shut off. I usually get a p0335 code out of it and once in a while i've gotten a p0336 crank relearn code. I have put multiple crank sensors in it, from stock ones, to a sensor that I had machined down at the shoulder by 10 thousanths to sit further in. Now, in April of this year we put a new pcm in the car and re wired the 3 crank sensor wires. The 3 wires were re pinned in the pcm and i installed a new connector to a new sensor. At this point, after all this was done with a new stock crank sensor (not modifyed) installed as well, i didn't have an issue. The car ran great, for approx. 1900 miles. Now about a month ago, it randomly started acting up again at around 6k rpm. It'll ramp up and bounce off the rev limiter but then immediately back fires and shuts off. The weird thing is tho, that it won't do it right off the bat when the motors a bit cooler. But once its at full operating temp it'll do it. I've considered replacing the entire harness, but again, the crank wires have been replace and are running seperate from the rest of the wiring harness, going directly to the crank sensor. The pcm has been replaced and so have crank sensors, multiple times. We have also checked the reluctor wheel (callies forged crank) for any kind of chips or noticable defects ( just what we could see by turning the motor over by hand and shining a flash light scope in the cranks sensor bore). I don't have any crank shaft end play whatsoever. Multiple people have told me that it could be a possible defective tooth on the reluctor wheel, but i don't understand how it could run fine for almost 2k miles and then randomely act up again. Any advise or insight on this issue would be greatly appreciated, this has been driving me nuts. I'm hoping it's not a crank shaft issue, especially with the kind of money i have wrapped up in it with purchasing it as a complete long block. But it is what it is at this point, i just need some advise what to do at this point now.

thanks in advance,
Mike

 

good thing tsp has been a huge help through all of this (insert sarcasam here)

 

Another thing that i forgot to mention, when it backfires the rpm gauge drops to 0 (obviously loosing crank signal). And yes, when i first put the motor in and started experiencing these issues during the tuning process, i did contact TSP. They gave me some advice on where i could start to look for the issue. Since then I feel as tho i have done everything...besides pull the motor apart