Misfire...

I had a misfire on cyl 3 so I replaced all sparks with ngk # 4344 ltr 5ix-11, are they correct? I still have same issue..
I have seen that on the metal contact surface between spark and spark plug there was some kind of white grease, what is it for :uhoh:? Shall I put it back on?
Thanks

clear di-electric grease put on the spark plug boot helps seal out moisture (that can cause shorts to grd) and aids in boot removal so it doesn't get baked on and stuck to the plug.

I had a misfire on cyl 3 so I replaced all sparks with ngk # 4344 ltr 5ix-11, are they correct? I still have same issue..
I have seen that on the metal contact surface between spark and spark plug there was some kind of white grease, what is it for :uhoh:? Shall I put it back on?
Thanks

The Good Book.
AC spark plug book calls for AC plug no. 41-965 at .049 gap.
Most GM engines runs and does better on AC spark plugs

If same problem first check for good spark to that cylinder.
If no spark switch wire or coil with one that is firing good.

Post back what that does.
And if ou are getting good spark to all plugs.

I also switched cyl two and three coils during sparks replacement, I have to reset the car and see what it does but it still bounces at idle for sure..
I'll post back codes as soon as I know. Does this kind of plug work well? I prefer the old hook-on spark plugs at least you can feel it's firmly attacched to spark..

I also switched cyl two and three coils during sparks replacement, I have to reset the car and see what it does but it still bounces at idle for sure..
I'll post back codes as soon as I know. Does this kind of plug work well? I prefer the old hook-on spark plugs at least you can feel it's firmly attacched to spark..

Ac plugs are best.
If miss change cylinder you have a bad coil.

You need to clear codes and recheck.
Also check for good hot spark from coils on missing cylinders.
Let us know what you find.

Code P0303 misfire cyl 3 even if I switch coils and I put on new sparks. What's next? Fuel injectors shouldn't matter this issue, right?

Code P0303 misfire cyl 3 even if I switch coils and I put on new sparks. What's next? Fuel injectors shouldn't matter this issue, right?

A bad/dead fuel injector can give you a miss.

First check for good spark from the no 3 coil.
Does it have good hot blue spark?

Did you check/switch the spark plug or check if it is dry or wet or oil fouled on the end?

Does that cylinder have injector pulse to no 3 injector?

Does no 3 have good compression?

Did you pitch the NGK plugs into the trash can and get some good AC-Delco plugs?

Any large/small vacuum leaks?

How is the fuel pressure?

A bad/dead fuel injector can give you a miss. OK, I DIDN'T KNOW.

First check for good spark from the no 3 coil.
Does it have good hot blue spark? YES

Did you check/switch the spark plug or check if it is dry or wet or oil fouled on the end? ALL CLEAN AND LIGHT BROWN

Does that cylinder have injector pulse to no 3 injector? IF THIS CAN BE SEEN WITH A SCANNER, THERE IS NO OTHER ERROR CODE MORE THAN MISFIRE AT NR. 3

Does no 3 have good compression? IT SHOULD, NO OIL ON SPARK AT ALL. I WILL CHECK IT TO HAVE A FEEDBACK CONCERNING INTAKE/EXAUST VALVES

Did you pitch the NGK plugs into the trash can and get some good AC-Delco plugs?
NOT YET, IT DID THE SAME WITH OLD AC DELCO BY THE WAY.

Any large/small vacuum leaks? WHAT DOES THIS MEAN?

How is the fuel pressure? GOOD

MISFIRE HAPPENS MORE OFTEN AT IDLE RANGE, AS SOON AS YOU GIVE GAS ENGINE WORKS PROPERLY.

THANK YOU

A bad/dead fuel injector can give you a miss. OK, I DIDN'T KNOW.

First check for good spark from the no 3 coil.
Does it have good hot blue spark? YES

Did you check/switch the spark plug or check if it is dry or wet or oil fouled on the end? ALL CLEAN AND LIGHT BROWN

Does that cylinder have injector pulse to no 3 injector? IF THIS CAN BE SEEN WITH A SCANNER, THERE IS NO OTHER ERROR CODE MORE THAN MISFIRE AT NR. 3

Does no 3 have good compression? IT SHOULD, NO OIL ON SPARK AT ALL. I WILL CHECK IT TO HAVE A FEEDBACK CONCERNING INTAKE/EXAUST VALVES

Did you pitch the NGK plugs into the trash can and get some good AC-Delco plugs?
NOT YET, IT DID THE SAME WITH OLD AC DELCO BY THE WAY.

Any large/small vacuum leaks? WHAT DOES THIS MEAN?

How is the fuel pressure? GOOD

MISFIRE HAPPENS MORE OFTEN AT IDLE RANGE, AS SOON AS YOU GIVE GAS ENGINE WORKS PROPERLY.

THANK YOU

If you have good spark and plug and compression and injector pulse and fuel pressure and no vacuumn leaks than you would have no miss.

You are losing something.
What is fuel pressure readings?
You need to check for injector pulse.
Use a injector tester noid light on it.
You have to use a compression tester gauge to check ciompression?
Better do that.
No compression will give a miss.
Low fuel pressure will give a miss.
No injector pulse or bad injector will give a miss.
A bad spark plug new or old or other will give a miss.
Did you switch plug or check gap on it?
A vacuum leak will cause miss.

If that cylinder is missing very bad the plug hould be wet on the end.

A scanner will not tell you everything.
Start doing some proper testing.
Compression and good plug and injector pulse and fuel pressure is valves opening and closing good.

What is fuel pressure readings?

My 05 Trailblazer with 96,000 miles is doing the same thing. After having the 100,000 miles service and smog check done at the local dealer it came back with an occasional miss at idle. You can feel the miss behind the wheel and sometimes see the rpm drop then its back to normal. Not real noticable, but you can really hear it at the tail pipe. Probably about 2 misses every 10 seconds. It's not enough to set a code right away, but after about 30 mile in traffic it finally will. Code P0300 and P0305. = Missfire on #5

Dealer said they swiched Coils around, but doesn't clear up misfire. Then told me to put some miles on it and see if it clears up and/or sets more codes. 150 miles later still have the idle misfire. They did a compression test and it was fine, but a running Compression test shows the lower compression. Now they are saying "valve seat it loose in #5" and need to pull the head off for a valve job. They say ths is common with this 4.2 engine.

No miss before they changed the spark plugs in the 100,000 service. Now have a miss and they say it will be at least $1,500 to fix, if the head is still good. :chair:

I've found a lot of idle misfire issues on the net and most of them occured after a spark plug change. I find a alot of the misfire are on #5. Is there some type of design problem here or is it something simple?

My 05 Trailblazer with 96,000 miles is doing the same thing. After having the 100,000 miles service and smog check done at the local dealer it came back with an occasional miss at idle. You can feel the miss behind the wheel and sometimes see the rpm drop then its back to normal. Not real noticable, but you can really hear it at the tail pipe. Probably about 2 misses every 10 seconds. It's not enough to set a code right away, but after about 30 mile in traffic it finally will. Code P0300 and P0305. = Missfire on #5

Dealer said they swiched Coils around, but doesn't clear up misfire. Then told me to put some miles on it and see if it clears up and/or sets more codes. 150 miles later still have the idle misfire. They did a compression test and it was fine, but a running Compression test shows the lower compression. Now they are saying "valve seat it loose in #5" and need to pull the head off for a valve job. They say ths is common with this 4.2 engine.

No miss before they changed the spark plugs in the 100,000 service. Now have a miss and they say it will be at least $1,500 to fix, if the head is still good. :chair:

I've found a lot of idle misfire issues on the net and most of them occured after a spark plug change. I find a alot of the misfire are on #5. Is there some type of design problem here or is it something simple?

Best to start a new tread on your problem.

If no miss before dealer serviced it or replaced plugs than you should no have a miss after service.
A valve seat does not come loose right after a service.

If just plugs were changed I would be checking them first thing.
Even new cold be bad or damaged on install.
But.

You need some proper testing by a trained tech to find the problem.

As your dealer if or to put a factory trained engine running tech on it.
If he refuses ask for your money back and find another dealer that will.

Let us know how it goes.

Think I got mine. In Italy, as in many other european countries, we use to put on propane or natural gas systems on gasoline cars 'cause this is so expensive. Latest systems are really sophisticated and high tech with one gas injector each cylinder. If I drive engine by gasoline, everything is fine, but if I use it by propane it starts to have this misfire. Propane burns very well but not as well as gasoline, I probably need to work on injection timing and fuel mixture again.
I thought misfire was just an electric problem related to sparks or coils, I didn't know that also fuel or compression may effect it.
Thanks to everybody for support, talk to you next time!

Think I got mine. In Italy, as in many other european countries, we use to put on propane or natural gas systems on gasoline cars 'cause this is so expensive. Latest systems are really sophisticated and high tech with one gas injector each cylinder. If I drive engine by gasoline, everything is fine, but if I use it by propane it starts to have this misfire. Propane burns very well but not as well as gasoline, I probably need to work on injection timing and fuel mixture again.
I thought misfire was just an electric problem related to sparks or coils, I didn't know that also fuel or compression may effect it.
Thanks to everybody for support, talk to you next time!

You forget to tell us about you running propane/butane.
Next time tell us about things like that.
They do make a big difference.

the post troll has done it again!!!

I did not forget about the propane system at all, I didn't talk about it on purpouse:
1- I thought that "misfire" was an error code just related to an electric problem, not to fuel or mechanic issues
2- I don't believe you have much experience in the states reguarding these systems, I don't even know if anybody started to install them. It may be a good business for you...
Thanks to everybody by the way, I don't feel to be a troll!

I did not forget about the propane system at all, I didn't talk about it on purpouse:
1- I thought that "misfire" was an error code just related to an electric problem, not to fuel or mechanic issues
2- I don't believe you have much experience in the states reguarding these systems, I don't even know if anybody started to install them. It may be a good business for you...
Thanks to everybody by the way, I don't feel to be a troll!

You are welcome.
But for us to help you need to give all info and any add on about what you have.

As you have found out a fuel issue/problem can also give missfire code.
You have got to have good spark and fuel and compression to each cylinder or the computer will find and show a miss fire.

Here in the states they were using propane burners when and before I was in Diapers.

I have had over 50 years of experiance running/driving and working on propane/butan systems on trucks and cars and farm equipment.

Nothing new to me.
If the propane system is the problem find someone in your area that is up on the system to help you.

Ps.
I am not in the troll post deal.

But I do need all info to be able to help.

Good Luck

The Good Book.
AC spark plug book calls for AC plug no. 41-965 at .049 gap.
Interesting. I just pulled the plugs out of my '03 4.2L today.

Just looked at my AC catalog (old edition--2003) and the print catalog at the local NAPA (newer, but I don't know what year--forgot to look. Probably '07) and my old catalog calls for different part number plugs for '02 vs. '03. The '02 uses 41-965 but lists 41-981 for '03, and those 981s are the plugs that were in my '03. The newer catalog at the local NAPA says all 4.2 inline 6 from '02 to '07 use 41-103 plugs.

My '03 catalog called for a .043 gap for both '02 and '03, also.