95 p0306, changed plug&wire, still misfire

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?

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.

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?

How old is the cap & rotor?

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

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?

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?

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

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?

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

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?

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.

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?

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?

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.

There is and will be argument over "good or bad" as far as oil choices go, but the good thing is that you change it. :) You will be surprised how many do not, and wonder why they have problems. I would say to try switching your fuel brand and see if it helps the problem. They might have gotten a bad tank-truck full of stuff - they being your regular gas station. If your plugs are still glazing up, try swapping over to Castrol GTX - there are plenty of people that seem happy with that stuff if you are not willing to go to a synthetic oil. I personally swear by synthetics myself, and in my opinion, hasn't been much else better for our engines. Though changing oil at 3000 is a tad wasteful. Even the most God awful oil can go 5000 on a decent filter. GM/AC Delco filters are good. Never had any troubles with them. Be sure they get swapped @5k miles with your oil and you're good. Others may prefer a Purolator Pure One, or a Fram Extended Guard - go with what flows and your pocket can afford to part with. However stay away from Penzoil, and regular Fram filters, in particular Double Guard filters. The teflon they lace those filters with turns into white lumps of rock in your oil pan and engine galleries. (DuPont also says that they never intended Teflon for crankase use - so keep that in mind) Other than that though, I would definitely switch to a different brand of fuel immediately to see if your glazing/ashing problem at least slows - then on your next oil change try some Castrol 5w-30 and see if it cleans the problem up comletely.

However, there is a simple test to figure out in your valve guides/seals are leaking. Let the truck sit overnight. The first time you crank it over in the morning after it sits, stone cold for at least 6 hours - observe your exhaust. Are you seeing blue-white clouds of smoke? Your truck will seem (and smell) like it is burning oil for just a minute, but then it goes away. This is a classic, tell-tale sign.

Good luck.

if i let my car idle for about 7 mins, it will start to smoke. it smokes for the first 5 seconds of acceleration. other than that, it doesnt smoke. the smoke color is a light blue. smells like raw fuel out of the exhaust.

You may benefit then from switching to a different brand of oil, but if indeed the truck is smoking like you describe, you now know why your plugs are glazing and ashing up. Sad to say it friend, but you are going to have to bring the truck in for a valve job. I am sure someone here can give you a better idea of what it would cost you, as I never had to have this done on any vehicle I owned. Good luck, man!

if i let my car idle for about 7 mins, it will start to smoke. it smokes for the first 5 seconds of acceleration. other than that, it doesnt smoke. the smoke color is a light blue. smells like raw fuel out of the exhaust.

Sounds like your valve seals are gone.

Light blue smoke is oil for sure.

yea it has been smoking for about 2 months, lightly. i only burn like a 1/2-3/4 every oil change. i add a little every now and then. thought that my engine might need some major work so i have been contiplating getting this one fixed or perhaps buying a new engine. or just a new car. who knows. how much is the valve job going to cost?

If you were smart, you could go and yank the heads off a junker blazer and swap them on.

You can replace the valve seals without removing the heads.

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?

Sounds like the 'old' tried and proven tricks are the best.

Pop off the plug wire from #6, and connect it to a spare sparkplug. Ground out the side of the sparkplug to ground. Give the engine a few cranks and see if you got spark. Shutdown the engine.

No spark, It's Cap and Rotor or new plugwire time! - Done

If you do have spark, shutdown the engine, re-connect the #6 wire.

Start it up again. Turn wheels hard left. You'll find a flap on the inside of the wheelwell. Lift it up, and peer into the spark plug. Do you see a coowel electrical light show happening in there? If yes, you'll have to fix the plug wire. You might try poking it with a stick to see if the engine all of a sudden changes.

If no, then we have to look at fuel injectors, valves, compression, etc.

Regards,
------- Robb -------

You can replace the valve seals without removing the heads.

Coowel - How?

Regards,
---- Robb -----

Coowel - How?

Regards,
---- Robb -----


Work on one cylinder at a time:
Remove the sparkplug, bring the piston to top dead center and thread an adapter in to the sparkplug hole so you can connect an air compressor to it. The air compressor will hold the valves in place while you work from the top.

The haynes manual has a walkthrough. I have not done this personally, but my father-in-law, who was a mechanic for over 50 years, told me about this several years ago, so it isn't just some BS that haynes came up with.

Or you could replace the #6 injector if the engine is 1996 or newer.

1995 blazer. i have no idea what im doing when it comes to swapping heads out of another blazer. how much do you think that valve seal job will cost me??

If you do some reaerch, you can probably do it yourself.

I'd hate taking a risk by swapping something like that with a junkyard. Who knows the history of that engine and what may or may not be wrong with what you're getting. Something like that, I'd be very careful of.

If it was in a wreck, chances are the heads will be fine.

Good word, it is a chance. You aren't willing to chance a CPI unit which is much simpler bolt on device, but you're willing to chance heads?

They have their places, but in this case, this is not something I would do. But that is my opinion.

comparing a factory flawed CPI injector swap to a good head from a body wrecked low mileage 1995 engine is ridiculous and you are now nit-picking my answering in other threads to back your point?

Comon now.......

I'm not nitpicking. You acknowledge it is a chance, yet you are against it for something much more simpler, less time involved, and reveling.

Have you done any deep work like that?

Sure, you should/could have the heads checked.

Low mileage does not always or automatically mean good. That would be an assumption.

I'm not nitpicking. You acknowledge it is a chance, yet you are against it for something much more simpler, less time involved, and reveling.

Have you done any deep work like that?

Sure, you should/could have the heads checked.

Low mileage does not always or automatically mean good. That would be an assumption.

It is an option, I am not arguing that the valve seal swap is a bad idea, I am giving the guy other options to look into.

So please understand that.

i just noticed this today. when accelerating the RPMs twitch. like 300 at a time. they go up and down like 150 each way. while misfiring that is.

it is almost like the gas is pulsating. like it sends gas in then cuts off for a split second, then gives gas again. it isnt getting any better with a new tank of gas from a different gas station. whats next for me to do?

it is almost like the gas is pulsating. like it sends gas in then cuts off for a split second, then gives gas again. it isnt getting any better with a new tank of gas from a different gas station. whats next for me to do?


Have you pulled your plenum to check for washing? Again, one of your poppets may be stuck open. Your fuel pulsator may also be going out. Have you run a pressure test at the shrader valve?

where is the shrader valve? 95 W 4X4 4.3

where is the shrader valve? 95 W 4X4 4.3

Back of the plenum on the inbound fuel line, looks like a fat tire valve (may have a black plastic cap on it)

i also noticed today that my car is running a little colder than normal. not too much but 2 notches. you make anything of that? im bringing my blazer into the shop tomorrow. to a known mechanic of the family for about 20 years. but id like to try something else before i put it in there. so anything?

I'm not nitpicking. You acknowledge it is a chance, yet you are against it for something much more simpler, less time involved, and reveling.

Have you done any deep work like that?

Sure, you should/could have the heads checked.

Low mileage does not always or automatically mean good. That would be an assumption.


40000 mile 4.3 vortek, blue smoke first start up in the morning, valve seals leaking.