it started out just being hard to start when it rained or was humid.its progressivly gotten worse over about a year.last week it rained and it wouldnt start at all.turns over great,but wont fire.has 55lbs fuel pressure,has strong spark.replaced plugs,checked wires.the distributor didnt have any cracks,the posts did have a little white buildup where the spark hits,i assumed that its all right.anybody have any ideas as to what it could be before i take it to a shop?

it was throwing a random multiple cylinder misfire code

 

When did you last change the cap and rotor?

 

at 100,000,replaced the cap last year when it started acting up.it didnt help.the rotor looks great.my blazer acts like its out of time when it doesnt start.

 

Worked through all these steps? 98+ No-Start - Engine Cranks OK

 

Needs an AC Delco cap and rotor, don't forget to put a dab of silicone dielectric grease on each terminal, inside and out, of the cap. When the current passes from the rotor to the cap, the grease crystalizes and that's the "white buildup" you found, it's supposed to be there.

Fuel pressure at 55psi is too low. Must be 60psi to 66psi, this thread will help diagnose the problem: https://blazerforum.com/forum/showthread.php?t=45941

 

the fuel pressure is fine.its not a fuel issue.its gotta be timing or something.the white buildup wasnt on the front of the electrodes,they were all in different spots on the electrode some front some side,not really an order to it

 

Sure sounds like crossfire in the cap. Looking at it, you won't see anything out of the ordinary. The grease spots in different places could just be the way they put the stuff on when the cap was replaced, or it could be an indication of a worn distributor gear. Gotta do more checking.

Here are a couple of possibilities:
There might be a problem with camshaft retard being off too far. It will not set a DTC if it's off, unless the distributor gear is off a tooth or more. It CAN cause crossfire inside the cap though. Cam retard is checked/adjusted with a high end scan tool. Spec is zero degrees + or - 2 degrees.

The distributor gear itself might be worn which could set any one or more P0300 series DTC's caused by crossfire in the cap. You can visually check the gear by removing the distributor.

 

when i pulled the cap off i checked the rotor for slop and it did have about 1/8 in back and forth slop.would all these things youre recomending me checking out cause my blazer to only act up when its wet or humid?i drove it yesterday.it has a slight random mis at idle that gets stronger from idle until about 3000 rpm,or if i bury my foot into it seems to clear up

 

I just had this happen over New Years eve/day. Had a brake line problem that needed attention. Took care of that, then tried to start it to bleed the caliper. It wouldn't start at all, when the day before it ran fine.
The cap and rotor were replaced when I bought the Blazer, because of the same problem. That's been a little less than two years ago. On both occasions, it was cold (40°) and humid. When I removed the cap, I found some rust and the white deposits which is aluminum oxide. Al2O3 is a insulator, and a enemy of current path.
The cure is getting a rotor and cap with brass conductors. Also, a little dielectric grease on the posts won't hurt. I've also heard that WD-40 can be used to help prevent problems under the cap.
You will pay a little more for a premium cap and rotor, but it's worth the peace of mind.

 

The distributor must be removed to check the gear and bushings for wear. Turning it while it's still installed doesn't tell you much.

Crossfire in the cap can happen at any time: hot, cold, acellerating, decelerating, at idle, or while cruising at a steady speed. Humidity and moisture make it more noticeable, as water conducts electricity. Make sure the vents in the distributor housing are clear. They keep the distributor ventillated so condensation doesn't build up on the under side of the cap. Incorrect cam retard, worn distributor gear or bushings and a cheapie aftermarket cap: all of these things contribute to short cap and rotor life. If everything is in order, an AC Delco cap will last 100K miles, you'll never get that out of an aftermarket cap, maybe 40K.