I got problems, 01 Blazer 4 dr 4x4 4.3 auto
 

It all started going to work one morning. I dropped a valve and had the engine replace at a shop with a used engine. I got it back about a month and a half ago. The service engine soon light has been on ever since and not just on but flashing at me. It has a po400 code, random miss fire, most times it is cyl #1 & #4 with #4 showing more misses. At the same time as the engine I also had the MAF sensor and fuel pump replaced per the shops recommendation. I have had it back numerous times for the same code. They have replace the plugs 2X and the wires 2X the MAF sensor 2X and distributor, cap and rotor. Still the same code. Today they cleaned the injectors and added sea foam cleaner to the tank plus other tests. I took it for a drive and the service light came back on. All the come back parts and labor is on there dime and they now think it's the computer module.

Now the last week it has also started making a buzzing noise, it sounds like the back of the engine on the drivers side. I tried the carb cleaner trick because it kind of sounds like a vacuum leak and it didnt seam to change the RPM's at all. the best part is its getting louder with the more miles I drive. It seems to be running good I have put 2200 mi on it and getting about 15 to 17 mpg which isnt that bad.

There was other codes that did show up, but have gone away.

What is wrong, what to look at next, anybody have any thoughts
PLEASE HELP!!!!

If it has not yet been done, different engine would require a crank sensor relearn. Any pro shop doing such work should know this.

Thanks for the reply Les
I hope they did the relearn but I will ask them when I call them Monday. When I picked up the truck on Friday they were talking about taking it to a GM dealership for the diagnosis because they cant seem to figure it out

Taking it to GM would be fair as long as they do it and are paying for it. If it runs good, then I'm betting the crank sensor relearn has not been done. It is specifically for misfire detection and needs done any time the crank sensor is disturbed. Switching engines they should know this. Did they provide the used engine or did you? If they provided it, then they should be on the hook to make it right. If they didn't provide then their liability gets questionable as other things have potential to cause a P0300.

Yes they are paying and they got the used motor. The repair shop hasn't charged me anything for any of the added work related to the engine swap.

Sounds like they are making big efforts to take care of you. Good deal. Be nice to them!!

Hello Les
Well I got a call the other day and the problem the GM dealer found was a few burnt valves and the repair shop has sent the heads out to be rebuilt. I should have the old Blazer back tomorrow.

Finally!!! Problem solved.
 

Hello lesmyer.
Well after all the headaches I think the local shop found the problem. After 5 months of BS and the blazer running like **** I have no service engine soon light. It ends up being a oring wasn't seated just right between the intake and the spider injector unit. The local shop has spent close to $5000 total out of there pocket to make things right.

I will be buying the guys lunch real soon as a thank you for sticking with it.

glad to hear your problem is solved.