alright i got a 1996 4wd 4.3 blazer. It drives fine, but it just shakes pretty bad while idle. I know something is definantly wrong because it didnt run like this in the past. I took it to autozone and they read the code PO305 or whatever... and said its a misfire on #5. My dad used to be a mechanic, so he fixed what he could. We've replaced the plug, the wire, the cap, and the rotor, and it still is misfiring. What is the problem?!

 

could be weak fuel pressure try doing a fuel pressure test

https://blazerforum.com/forum/tech-a...agnosis-23038/

 

I doubt that fuel pressure is causing a single cylinder misfire, but weirder things have happened. *IF* it is a fuel issue and *IF* #5 is the only cylinder misfiring, it could be a plugged or gummed up poppet nozzle at #5.

How did the old plug look?

Have you monitored each cylinder's misfire counts with a capable scan tool to see if it is dedicated to #5 or if that was just the first cylinder to meet the P030x misfire count requirement?

Have you checked the compression on that cylinder & compared with the rest of the cylinders? Cylinder leak-down? Possibly an LIM gasket leak either allowing outside air into that cylinder or possibly coolant?

Some 'lite' reading for you....

 

thats true it would be more then one sorry kyle and welcome back

 

The old plug looked like it definantly needed a replacement. it was a dirty, and looked a little burnt up.
the wire looked... pretty much the same as the plug.
the old cap was also covered with green stuff.

i havent monitered them individually but i can do that tomorrow. i just had the computer scan it and just PO305 popped up. It only feels like it misfires until 2000 rpm-ish. then it drives fine. but at 2000 rpm the SES flashes.


Sorry about my little knowledge. dont know much about engines

 

If it is flashing, thats a serious issue. VERY serious. It signifies that the misfire is engine destroying. It is only signifying cylinder 5 on the scans? green stuff.. was it coolant? Moss? did you stick your finger in it and take a whiff? The green stuff could be from your heater core hose, spewing coolant on the cap/rotor. Some could of seeped down into it and caused the misfire.

When you replaced the plug, did you also replace all the other plugs, cap and rotor with delco?

Also, does it feel sluggish to drive like you are pulling something? Are you running in 2wd or 4wd? Might be irrelevant, might not be. Before I fixed my 4wd actuator, i was locked in 4wd, it was sluggish to drive, at around 2000-2500 rpm range it would hesitate, cel light would pop on and flash a couple times. Long story short, I fixed the actuator (re-hooked the vacuum hose) drives better, not sluggish, no more hesitation at that rpm range.

In the blazer owners manual it says somewhere that driving on dry roads in 4wd can cause some problems to the drive/power train. If your locked in 4wd (which you might be without realizing it) you could experience those problems as well.

 

yeah i only got cyclinder 5. and i wouldnt be surprised if the heater core spewed coolant on the cap/rotor. but i just replaced all that at the beginning of the summer.

i only replaced the cap and rotor with delco. i dont remember what i bought the plugs as.

im running in 2wd and it doesnt feel to sluggish. i have a slight hesitation when i really hit the gas, but other than that it only runs rough idle.