PO300 ! The devil does exsist!

[Blazer SS]

PO300 the all encompensing code that can mean anything. Two months ago I got this code. It took a few days to diagnose the problem.

First of all I had a backfire problem. Engine was shaking so bad, side to side that the headers were hitting my engine mounts. So I figured that it was a spark plug wire so I checked them with a meter. They were fine but the #1 Spark plug boot was toast , it had been grounding out against the header. I replaced it with another boot . Next I started it , same problem. Figured I would check out the #1 spark plug, WET! And fouled!! Cleaned it and put it back in. Same problem! Next I thought I would look at the cap and rotor. Cleaned and reinstalled them. SAME PROBLEM!! So I went ahead and replaced the cap and rotor , It was time. Again same problem! When started.

Now I figured that I might as well replace my poppets with the MFI for the winter, I kind of do this swap alot. Poppets for performance and the MFI for driving on the street there is a difference. two of my poppet seals were blown and the electrical connector was in 1 inch of gas!! Surely this was my problem. Put in the MFI and put the poppet to the side to rebuild it later. Started the truck , SAME PROBLEM!! What the @#$#@!!

Now would be a good time to check the fuel pressure. I started by pulling the fuse on the inline pump to check the rear pump pressure. IT WAS DEAD!!
I HAD BEEN RUNNING ON THE INLINE PUMP !! For who knows how long. I replaced the rear in tank pump, surely this is the end. NO SAME @#$#@ Problem!! I had found several things that needed to be fixed and fixed them. Picked up more fuel pressure, wich added to more HP!!

The Blazer kept running through all of them. What IS IT!!??

Well after a day of just running every possible thing over and over in my head I figured it must be a loss of cylander pressure . Maybe I blew my head gasket? Maybe when I lifted at full boost I put a hole in my piston. No not possible. Forged. What else? Wait thats it Pressure!! fouled plugs, burnt number one piston boot, missing on #1 Piston . PULL THE VALVE COVER!! There it was My rocker arm was laying to the side , and the problem (drum roll please) The push rod was broken in half, the bottom part was laying on the lifter cover and the top part was still in the hole bent into a figure s.

The misfire had caused the sparkplug to fire at the wrong time and under full boost When I lifted , there was a whole lot of fuel and pressure in there the valve was forced closed the pushrod had no where to go so it bent and broke!!

End result. The Blazer runs a whole lot better. Cost me $ 89 for the new fuel pump, $21 for the new cap and rotor. And some time.

PO300 the ungodly code from hell !!

[BlazerLT]

interesting read.

Thanks for sharing.

[DelCoch]

Very interesting!! Good post.

[laxman21]

What year truck. And what's a poppet?

[Blazer SS]

The poppet valves are spring loaded fuel injectors that GM used in the late model suv's , they now use true solenoid based injectors (MFI). The Poppet valves have a problem with sticking. So GM replaced them With MFI . OF coarse as always near the end of the run.

And my Blazer is a 98 v6, these are old pitures, but you can get an idea of what it looks like. It now has a 4.5 due to stroking of the crank and other engine mods

http://photobucket.com/albums/c391/Blazer111/