2001 blazer (4.3 vortec) overheated couple weeks ago when my wife was driving to work, it shut off as she was getting to side of freeway. I towed it home, changed thermostat, flushed cooling system. It now has p0300 code (random cylinder misfire). We have since changed plugs, wires, cap rotor, replaced leaking LIM gasket, new water pump, fan clutch and cleaned all MAF sensors and when it wouldnt start after LIM gasket change, put in new updated MPFI spider. All to no avail. Truck idles rough, but once revs are up to about 1000, smooths out and runs fine.
Im sure it still is misfiring but still have plenty of power when driving and starts fine. Also, I have a ticking (maybe valve?) coming from pass side of motor, which I think is new, as i never really drove truck before overheat. No coolant in oil as i can see. Any ideas/input would be greatly appreciated. Thanks.

 

Did you check the compression? Overheating can blow a head gasket.

 

Compression this weekend, do you know what the compression spec should be or am I just looking to see if one side is higher than the other?

 

Take a good look at all of the plugs when you take them out as well. Water tends to steam clean the plugs it comes in contact with.

As far as compression spec, it varies so much with engine wear & tear. Your cylinders should all be within +/-10% of each other.

 

ok thanks. my buddy/mechanic is bringing compression gauge this weekend, so we'll check it then.

 

did you get anywhere with this i have the same problem i have a 1998 chevy blazer 4x4 4.3 and it was really cold here -50 c it ran perfict for 5 days before my wife brought it to work it died on the road coolant boiled over temp gauge went right to max catalytic converter burnt right up but i have no signs of a head gasket no coolant in the oil no white smoke compression seems to be good when you drive this thing it still heats up but if you rev it it will go back down to normal and heat will come back when you hit 50 kph the check engine light will flash tell you slow back down this problem is really weird and i cant figure it out

could use help with this before i burn the truck lol

 

jrb maybe check your water pump, cause i know sometimes when a car is rev'ed up when the water pump is worn out it will cool it back down, but that would be my first guess

 

thanks man i have a brand new water pump in there, 2 new tstats have been in a new egr valve pcv valve new temp sender new cap and rotor new spark plug wires new fuel filter and still nothing i do know that the o2 sensors can be a real big pain in the *** when it comes to the system so i ordered 2 o2 sensor simulators from the states just wating for them to get here to canada and i have a new ecm sitting here on the table waiting to see if i need to get it re-programmed or not

 

so my codes are now
1 P0300
2 P0340
3P0300 repeat
i have checked almost everything here the wiring seems to all be good i put a new crankshaft sensor and maf sensor in just to be sure it still boils the coolant and runs like a bag of **** all the time when you clear the codes it runs better untell the codes come back in then its back to hell i dont know what else to do

 

so i have an update the blazer is no longer overheating the end of the upper rad hose was cracked and really warn so i fixed it and now it is no long letting coolant out and air in. i ran the truck and the temp stayed right where it should the whole time but i still have the misfire