95 p0306, changed plug&wire, still misfire

[cubanlorenzo]

95 4.3 W auto 4X4. about a week ago my SES light came on. scanned the computer, came back with a p0306, cylinder 6 misfire detechted. so i changed out number 6 plug and wire. i pulled the neg battery cable for 20 mins to reset computer. I started the car and right away the SES light came back on. took it for a test drive and that last about 2 seconds before the car was sputting again. scanned the code, SAME code again. suggestions?

[TonyMazz]

Originally Posted by cubanlorenzo

95 4.3 W auto 4X4. about a week ago my SES light came on. scanned the computer, came back with a p0306, cylinder 6 misfire detechted. so i changed out number 6 plug and wire. i pulled the neg battery cable for 20 mins to reset computer. I started the car and right away the SES light came back on. took it for a test drive and that last about 2 seconds before the car was sputting again. scanned the code, SAME code again. suggestions?

I'd pull the plug on the number 6 and look at it....carbon stuck on it, or damaged ...might need to be replaced.

Could also be related to an injector too...

Many different condition could cause an intermittent misfire.
Check for the following conditions:


Check the IC control circuit for a intermittent short to ground.
Check the spark plug wires and the coil wire for the following conditions:
Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.
Check the wire routing in order to ensure that cross-firing is not occurring.
If the misfire occurs when the weather is damp, the problem could be due to worn plug wires.
Check for contaminated fuel or a low fuel level and the following conditions:
Check the fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition.
If the fuel level is low, the fuel pump may draw air into the fuel rail, causing a stumble and possible misfire condition. Check the fuel trim numbers in the freeze frame to determine if this has occurred. It would be likely if the short term fuel number was above + 20.
Check HO2S for abnormal voltage readings.
Check for a vacuum leak as a possible cause of the engine misfire.
Sticking intake or exhaust valves can cause a misfire when the engine is cold.
An intermittent may be caused by any of the following conditions:


A poor connection
Rubbed through wire insulation
A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. See: Diagnosis By Symptom

Test Description
The numbers below refer to the step numbers on the diagnostic table.


The misfire is considered random on all cylinders if, while viewing the misfire counters in the misfire data list, the misfire seems to move to different cylinders.
The misfire is considered consistent if the misfire is occurring on the same cylinder(s) consistently.
When checking the spark at the spark plug wires, the spark should be consistent. A few sparks then nothing is no spark.

[cubanlorenzo]

the misfire is always happening in cylinder 6. i have just recently (3-40000 miles ago) done a full tune-up. i just pulled the spark plug and it is perfectly clean and gapped correctly. the wire leading to it is in the correct spot on the distributor so they arent mix matched. as for most of the other things you said, im not sure how to do it. i have some mechanical knowlege but im not a professional. the gas level is fine, i never let it go below a 1/4 tank because i read on here that the pump will pick up anything dirt or other substance on teh bottom of the tank if it is too low. thanks for you input. any others?

[BlazerLT]

How old is the cap & rotor?

[blazee]

More than likely it is a clogged poppet. I'd try running a bottle of techron through.

[cubanlorenzo]

i just went out and checked all of the other spark plugs. every single one of them are corroded with a hard white substance, i had to chip it off and scrub it with a wire brush to get the pieces off. is that from running too rich?? antifreeze maybe? should i be expecting to have my head gasket changed soon?

[BlazerLT]

Originally Posted by cubanlorenzo

i just went out and checked all of the other spark plugs. every single one of them are corroded with a hard white substance, i had to chip it off and scrub it with a wire brush to get the pieces off. is that from running too rich?? antifreeze maybe? should i be expecting to have my head gasket changed soon?

Are you using any fuel additives?

[cubanlorenzo]

i have never used gas additives. that white stuff a sign of running too rich? could it possibly be a stuck poppet?

[BlazerLT]

If it is running too rich, the plug wil be fouled black and really dark.

Are you saying all them had white crusty stuff all over them?

[Turbocpe]

White ash can be fuel/oil additives that are being burned. Also, leaky valve guide seals can lead to this.

[BlazerLT]

Originally Posted by cubanlorenzo

i have never used gas additives. that white stuff a sign of running too rich? could it possibly be a stuck poppet?

Where are you buying your fuel from?

[cubanlorenzo]

hess and Mobil stations. they were crusty hard white on the plugs. the two plugs (1,2) had the most. then 3,4 had a little less, and 5,6 had the least. i have never used fuel additives. i think that i might just drop a new engine in there. between the valve tap, and slowly leaking/burning oil. i feel this engine is doomed for failure.

[cubanlorenzo]

i cleaned all the plugs and reinstalled them. car drove smooth for a day. today i started to go up a steep hill and i felt a little putting going on. later on i felt more and more. not nearly as much as it was before i cleaned the plugs but noticable. think it is one of my poppets?

[wolfox]

Fuel additives, rotten fuel, or worn valve guide seals will ash and glaze up a plug like you are describing. Switching gasoline brands, changing the oil for another brannd (5w-30) *may* solve the problem. How often do you keep up with your oil changes anyway?

[cubanlorenzo]

i do an oil change every 3000 miles. i already use 5W-30. quakerstate 4X4 high mileage. good or bad? with a ac delco filter. I heard those are the best. I will switch fuel too. lets see what happens.