Hi, I'm new to the forum, although i read posts here before. I have a 2000 blazer 4wd, auto trans, 4.3 V6. Thursday night, the check engine light began flashing. I checked with my scanner, and it was a cylinder 3 misfire. Pulled #3spark plug and it was good. Found 4 bad plug wires. Replaced them and it changed to a random misfire code. Made sure the plugwires were connected good and got a cylinder 4 misfire code and a crank to cam sensor code (P1345). Replaced the crank sensor and itcranked, but would not start up and got a crank sensor input signal code. Put the old sensorback in andthe enginestarted up and ran and got a cyl 3 code again. Replaced the crank sensor pigtail, left the old sensor in and it ranbut with a miss, with thenew sensor inno start, old sensor back in,engine run with miss and a cyl 3 misfire code. Used a timing light to rule out fire problem on #3 cylinder. Pulled plenum and ohmed injectors ( all were 11.6). Hooked up injection unit (no noid light) and had a friend crank the engine. All injectors workas avertised. Put it all back together and now we're back to the cyl 4 misfire. I'm about ready to pour gas on it and collect the insurance. I'll ride my harley for now, but i need my blazer as I'm a volunteer firefighter/first responder. Any help would be greatly appreciated as I'm at my wits end with this thing.

 

You cannot just replace the CMP or CKP sensors without performing a CASE relearn (aka crankshaft variation learn procedure).

Check out the P0300 threads (THIS ONE & THIS ONE) which runs through pretty much all of the possibilities. Also, here is the P1345 Explained thread.

Have you had the ICM tested? How about the coil? I assume you have done a complete tune up...?

 

I haven't had the ICM tested nor tested the coil and am looking at doing that this week. I did a tune up sans the wires a few months ago when i had to replace the driver side intake gasket(i know, shoulda replaced the wires then)and replaced the wires friday. The engine has had a slight surge in it since i bought it earlier this year, but only on the pedal, not on cruise. I still have the new crank sensor and will hold on to it for now. About that conversion to MFI, is it a direct swap or are there modifications involved? Thanks for the info...I'll peruse through it and keep you posted.

 

For my old 2000 Bravada, the MFI spider was a direct swap for the SCFI spider it was originally equiped with.

 

I ended up taking it to a garage this past wednesday. They found the problem which turned out to be a burn hole in the distributor cap on the #3 & 4 connectionswhich was causing crossfiring. I called myself checking the cap, but did not fully remove the cap for inspection, only rotated it enough to look at the contacts. The burn hole was only visible when the cap was completely removed. A new Delco cap and some change later, she runs like a champ. Lesson learned here...don't buy the cheap stuff ( I did ) and perform a thorough inspection. Thanks for the help!!!
Harry