I just had my 420A rebuilt with everything done to spec. I put it back in the car and now it will not start, After a couple of seconds of cranking it will backfire out of the intake? but thats all it will do.it has fuel/air/ & spark/ plus ive gone over the wiring over & over and everything is right, Theres a couple of things im not sure if there causing the problem or not? 1 the ECM is making a a low buzzing noise, is this normal? or is mine bad? 2 it also looks like the sensor all the way to the left, if your sitting in the car, on the back of the block has a little crack in it, can anyone tell me what this sensor is called so i can replace it? Someone told me the timing could have jumped, does anyone know if theres a way i can go about checking this if the cars not running? anyone that has any info, Thanks

 

re set the timing that is what i wound try

 

Check the timing marks... i have a feeling thats where your issue is

 

Is the sensor that your refering to the knock sensor look something like this?

 

i say cams are out of time. there are marks on both sides of the gears, its not hard to put one 180* out

 

check timing marks, i have a friend that did the same thing, with the rebuild and all. and his timing sliped, and was doing the same stuff your is doing. good luck.

 

Ok thanks to everyone that replyed! my problem now is that when he put it together, i had him in install crower stage3 cams & unorthodox cam gears,
so with that being said, the plastic piece with the timing marks is gone, so my next question would be how should i go about checking it without those timing marks? someone told me about a something called a dial gauge? does anyone know where i can buy one, and if so will that work?
Thanks Again

 

I swear that the timing markes are on the gears themselves?

 

there are but, isint there sopose to be one one the bottom to?

 

You mean the crank? Yeah.. its on the sprocket.. or it should be.