For the past couple of weeks my blazer will not start without starting fluid. It has the 4.3 vortec cpi, 4x4.I have replace everything i can think of. Six months ago i replaced the fuel pump, which i just had to replace again this weekend. I have replaced the spider injectors, fuel pump, fuel filter, fuel lines, fuel pump relay, entire exhaust, tps, ignition module, coolant sensor, egr valve, new intake gasket and all new bolts, and cleaned the plenum. I tuned it up with new plugs, wires, cap rotor, pcv valve, air filter, and changed the oil. I have also tried fuel injection cleaner and nothing is helping. There is no pattern to its not starting. It has happened when it is warm and cold. There were no codes when it was scanned this weekend. It also stumbles under acceleration. It falls on its face untill around 3000 rpms, when it seems like it hits a power band and takes off. On the way to work today it started surging and stumbling real bad. It acted like it was slipping, but the truck only has 73,000 miles on it. I was wondering if it could be the computer, or the coil. If there is anything anyone could tell me it would be great. Thanks

Try replacing the coil. I just had mine replaced, along with my ignition module. Random starts and stalls. Only ran at high rpm when warm. Might not hurt to get the ignition module checked, even though it's new. I saw a post here a few days ago where all parts were replaced and the module was weak out of the box.

A stupid question, did you clean the throttle body?

Try checking your tp sensor. Had one that was doing the same thing. Unplug it and see if it will start. If it does you know it is it causing the trouble.

its a cpi there is no throttle body to clean.
have you checked fuel pressure or timing? i dont know much about cpi exept there is alot of problems with them,and i dont like them. tbi is much better and more relieable.

Did not see the cpi in your post. Sorry, cpi is a pain. Lot of trouble with the spyder leaking fuel. Expensive too.

I have tried everything. Over the weekend i put a new MSD coil on, cleanded all the grounds, tested the pickup coil and checked every fuse. Nothing works. The problem is it will start up fine in the morning, when you turn it off it will start right back up, but if you let it sit for about 20 min, it will crank but wont fire. If you spray starting fluid in it, it will run fine. I have given up, i took it to a mechanic who sore he could tell me what is wrong with it. I wrote down a list of everything that i did and gave it to him. This is the first time i havent been able to figure out a car, but once it is fixed i will never forget it. Has anyone heard of the hall effect switch going bad. Thanks for all the help