miss and backfire
 

2000 blazer runs great for about 20 miles when first started. After that it misses and backfires under any acceleration. Idles great. Have replaced crank sensor, cam sensor, timing chain, ignition coil, cap, rotor, wires, plugs, fuel pump, fuel filter. Will not start with distributor set on 6 with #1 at tdc. have to back it off 1 tooth and then it throws the P01345 code,but will run.

iowajoe i see you mentioned you replaced the crank and cam sensors, if this is the case you need to get access to a scan tool the can read live data , but more inportantly cam retard/ these vehicles can not be "timed" like most normal vehicles the timing is by the pcm. Anywho the scan tool also needs to be capable of performing a cam and crank relearn procedure so the pcm can do accurate ignition advance and fuel timing.
Please see this link: https://blazerforum.com/forum/tech-a...-timing-24373/

Sorry I forgot to mention that I took it to the dealership and had the relearn done. It will only run at 1 tooth back from 6 on the distributor, and shows 34 degrees advance at that position.

I'm going to put an ignition module in it this weekend see if that works.after that a distributor. If neither help I'll be parting it out

Are you sure #1 piston is on TDC of the compression stroke? Could be TDC of the exhaust stroke;) If that's the case, the distributor is out of phase, (180 degrees off). The distributor makes one revolution for each two revolutions of the crankshaft. If the engine does not run, P1345 will not set. P1345 sets when the distributor is off at least one tooth, (in either direction). If the engine runs, and P1345 is not set, the distributor is meshed correctly with the camshaft. This is the "rough" adjustment for the distributor. You'll need a scan tool capable of accessing live data for camshaft retard, (CMP retard). The adjustment is done by rotating the distributor. Spec is zero degrees, plus or minus 2 degrees. This is part of the job when installing the distributor. Camshaft retard can be off as much as ~26 degrees and NOT turn on the check engine light. However, there will be serious crossfire going on inside the distributor cap, and eventually it will set P0300 to P0306 DTC's which will turn on the check engine light.

There is no doubt if the distributor is installed correctly in my 99. Align crank to the 2 marks on timing cover (TDC), install distributor to a very specific mark on rotor (make sure distributor hold down bolt position is aligned). In my experience (very limited) there is no doubt if distributor and rotor are installed at the correct position. Maybe 2000 is different.

I understand. All I'm saying is when the timing marks on the dampener are aligned like in the image below,
provided the ring on the dampener has not slipped, #1 piston is at TDC. It could be TDC of the compression stroke or TDC of the exhaust stroke. The engine most likely will not start if it's on the exhaust stroke, and without the engine running, the P1345 will not set. Resetting the distributor, as you did, may be enough to make it start & run, and cause the P1345 to set.

Attachment 31441

Found problem and it was a simple fix. Crank sensor was rubbing the actuator. Shimmed it and the Blazer runs great!

Keep in mind that any time the crankshaft position sensor, or timing cover, are moved, removed, replaced, or disturbed in any way, the crankshaft position sensor relearn MUST be performed with a scan tool capable of initiating it. The crankshaft position sensor creates a magnetic field. The tone ring, inside the timing cover, breaks the field 3 times per crankshaft revolution. This is where the pulse is generated for ignition timing and injector timing. The field that the sensor creates is focused in a very small area, the relearn "tells" the PCM exactly where the field is focused. Ignition timing is not adjustable on this engine so the relearn data must be correct if you expect the ignition timing, and injector timing to be correct. If you don't do the relearn, the PCM will use the data from the last relearn, which is incorrect, guaranteed.