I have an 03 blazer xtreme that i had to change engines in and i bought an engine out of an 05 1500 pickup with a 4.3L. After everything was changed and running im now getting a random misfire on deceleration around 75mph and flashes for about a minute and stops and will start again shortly after until i get off the highway and slow down. Now driving around town its fine, ive basically replaced everything but i started doing alil research and the knock sensor off the engine i got is different then the one off my original engine. I put my old sensor on the new engine but im wondering if i should put the sensor that fits the new engine on mine because i think its sending the PCM incorrect readings and tripping the computer. Please any help is much appreciated, ive been fighting this issue for months now.

 

The PCM is programmed to the vin of the vehicle. That may be some of your problem. Also, when I received a tuned pcm, I had to have a crankcase relearn done to it as well. The tuner reprogrammed the pcm to match my vin but you have to have the right scan tool to do the crankcase relearn.

 

Well i had the case relearn procedure done as well after the engine replacement.

 

I would try the correct knock sensor. How do the plugs,wires, cap and rotor look?

 

get the correct knock sensor for the newer motor? the cap rotor plugs wires and distributor are all new

 

Yes, for the new motor. Did you check the retard on the distributor?

 

I dont know how to check it. I have a matco scan tool that i can read some of my parameters and i saw one called "ign advance". I noticed when the light starts flashing the ign adv starts retarding and advancing like crazy and then when its running normal it always stays in a certain range.

 

I know the gm tech 2 can read the camshaft retard. It should be steady on 0 degrees. The "ign advance" is probably the same thing. Check out your hold down screws and clamps.

 

When the ignition is off it should say "0" right? If so then yes its correct. when its idling its at about 19 degrees.

 

Edit: there are a lot of variables to consider the advance at idle. Anywhere from 15 to 30 is not uncommon.

https://blazerforum.com/forum/tech-articles-diy-29/edi-engine-timing-24373/

This link should help you out on it. But yes ignition off should be 0, I will have to check what is the acceptable range for idol.