i have a 99 blazer that runs rough, it seems to have multipul miss fires on all cylinders, i've set the timing multipul times and im 99% sure its on, but i cant seem to get the motor to striaghten out, its got a miss ,so i tried to pull plug wires off and it seems to not change anything unless i pull 2 off at the same time????? i changed the crank senor also, put new plugs , cap, rotor and wires on it and it still has a miss. i have had people tell me o2 senors, tps senor, bad gas, check compression or even unplug the sercurity sytem it has from factory, idk if anybody has had this problem or knows where i should turn to next, please reply so i can get this thing working right again, not sure what to try next, what do i do????, thanks

 

Considering that you cannot set the timing on these motors (96+)...

I would start with a fuel pressure test as described in the Tech Article (DIY) section and follow that up with a compression test of all cylinders. Let us know the specific pressure readings found.

 

What exactly did you do to "set" the timing? Do you have a check engine light? Does this miss go away at higher rpm's when you drive it or does it get worse under load?

 

There is no timing adjustment other than what is controlled by the PCM unless you modify either the distributor housing itself or the distributor hold down clamp. If you did not do either of those two modifications, you cannot manually modify the timing.

 

i ran a compression test on the cylinders and #1 is 75 # 3 is 0 and the rest are around 90??? shouldnt they be around 125?? wat would cause #3 to be 0, we bought the truck with a cracked head, and both were cracked, put head gaskets in it, and new intake, i'm guessing that the previous owner overheated it, so wat would cause this the rings bad??? or valves, the heads were used i inspected them for cracks before installing them, seemed to be fine. short of trying to buy a lower half or put new rings in wat else can i do?, thanks for the help on the last post

 

They all seem quite low, but #3 is disturbingly low.

Check it again, but this time, squirt some motor oil in through the spark plug hole prior to putting the compression tester on and turning the motor over.

Aside from using a bore scope, you will likely have to pull the heads to assess their condition. If it were me, I would be looking at a complete rebuild.