3.4L Cylinder 3 Misfire

[FromTheInside]

Okay, well I would appreciate any input on this issue that has been plaguing me for the past 3 months. I have done many things (checked and replaced) as a part of maintenance or to directly solve the problem. I did not replace anything that I didn't suspect had a problem. I am not fond of "replace 'til it's fixed."

Engine is the 3400 from 2002 with 65,000 on it. I am pulling around 18.5 to 19 in-hg of vacuum with very tiny fluctuation. My rpms are steady and do not bounce.

I had blown a head gasket on cylinder one so I rebuilt everything from the block up fixing the problem and it ran perfectly for a while. Since it ran properly, the pushrods are obviously not mixed up. Everything is sealed and put together exactly as it was taken apart.

A few weeks later I noticed that the thing was running rough but I never got a trouble code, so I thought it could have been a random cylinder misfire: I unbolted the down pipe to see if the catalytic converter was clogged and therefor causing too much back pressure. I ran it (and it sounded like a beast) but the engine shook the very same way.

I had to replace my head gaskets AGAIN for another reason but the problem existed after I rebuilt again. The gaskets are the felpro redesigned metal gaskets. The fact that I replaced all gaskets again confirms that I did not have a LIM vacuum leak.

I have newly rebuilt heads complete with new valves, springs, etc.

All of my vacuum lines are fine. The entire coil pack has been replaced, every injector, the plugs and wires as well. My o-rings are new and have all been pre-lubricated before I set the fuel rail back in.

I have replaced the fuel pressure regulator, harmonic balancer, and fuel filter. My engine was smoked to check for any leaks but it was sealed tight. No leaks at all. If I rev the engine past 2000 rpm, then it looks as if the misfire is almost completely gone. I have no hesitation, backfire, or cutting out.

If I leave the car to idle for a while, I see a pending code on my obdII reader and it stated P0303, Cylinder 3 misfire. I only got a SES light once and that was after a LONG LONG LONG idle with my poking around. I saw the pending code only 3 times. So I decided to put a noid light onto the injector harness and I fired it up. My car ran a lot worse with the injector unplugged and the noid light blinked continuously and sped up as I revved up to about 1500. (Didn't want to rev a 5 cylinder engine too high)

After this failed, I thought that maybe a new part could have been faulty: I took the injector and switched it with number 4, then I switched the 1-4 coil with the 3-6 one as well as the spark plug and I took my old cylinder 4 wire (I replaced all of my wires and kept my old ones) and connected number three. The misfire did not move at all.

I checked my compression and it was perfect. Every cylinder was around 185 without much variance at all. I left the compressed air inside of the cylinder for 5 minutes for each one and did not lose anything.

So then I removed my valve cover for the 1,3, and 5 cylinders and manually rotated the crankshaft with a wrench while watching the valve springs compress the springs. I compared the intake spring compression at the bottom of the stroke of #3 and it compared exactly to that as numbers 1 and 5. I did the same with the exhaust spring. They all compressed the correct amounts. At the top of the stroke, when the valves were closed completely, I checked for play between the rocker arm and the spring but there was none on any of the odd numbered cylinders. I also ran a running compression test. First on #3 and then on #4. They were the same. I hope this gets rid of the possibility of a worn camshaft lobe, worn lifter, etc. My valves are new as previously stated. I cleaned both intake manifolds entirely so no carbon build up is present. I also cleaned the cylinders out as well. My spark plugs are not fouling.

My O2 sensors are new and I swapped out the MAF and MAP sensors with my friend's before I knew the problem was contained in one cylinder to no avail.

The problem occurs at any operating temperature. High rpms seem normal.

My fuel pressure is within specs and I cleaned up the IAC motor. However, the problem exists at 1500 rpm so I doubted that was the problem anyway. I made sure all LIM bolts are torqued properly.

PCV valve is new. The injector on number three IS clicking and as are the others because I bought myself a stethoscope

I also took ground near the air filter box off completely and sanded off the corrosion and made everything perfectly clean and regrounded.

I am going insane and yes I have brought it to a mechanic who retested everything I have done. Hopefully people don't turn away when they see the length of this thing hahaha

[3100]

injector wires and connectors? check the injector connector that little tongue inside may not have enough pressure and when it heats up it has even less contact on the injector terminal (pull them up some so they fit tighter)
rocker arms torqued to specs?
also injector rail if not adjusted properly will force some of the injectors to not seat right and "O" ring will have little or no effect.
also #3 likes to misfire on this engines it is in the hottest location, according to the GM some misfire counts (up to 6) are normal, however pending code is not good. I can bet that when you disconnect your O2 rough idle will stop, and this will tell you that you have to focus on fuel delivery problem or vacuum leak.

[FromTheInside]

Hey, thanks for your response. Yes I checked with a noid light so the wires are okay. I also jiggled them around and rechecked to see if the wires had any breaks. Furthermore, I did check the connectors inside and scraped them with a screwdriver, bent the little pins upward for a tighter fit and even put a tiny bit of dielectric grease (carefully and making sure that I won't short out both pins with one another) and it is still the same. Also, I have my injectors seated properly because a mechanic I brought this to when I was going crazy inspected my seating.

I also thought about the O2 sensor so I unplugged it and then ran but it did nothing. And finally, as for it being the hottest location - I was reading on a jeep forum that their cars misfire on cylinder 3 because all of the exhaust gases pass over there. The dealerships corrected this problem with a little sleave to put around the injector nozzle or something. However, because I am the only one that is having this bad of a problem and it isn't a widespread thing, I don't see that helping. =[

I appreciate your thoughtful response! Even my mechanic doesn't know what to do. His next thing is swapping out the computer but he has to find me a used one I can test out before I actually pay for one of those.

I forgot to mention another point you brought up: Yes the rocker arms are fine because when I had the 1, 3, 5 valve cover off checking for spring compression, I also checked the rocker arm torquing when the valve was completely closed and it checked out nicely. When I did my head gaskets the second time (the problem started after the first but a couple of weeks after) I rotated the rocker arms around and checked all of the pushrods for flatness and damage. And as a reminder, the cylinder heads were changed completely with rebuilt ones during the second HG job.

[xeroinfinity]

if your ignition system is good then its likey the #3 injector is bad.
Even though the noid light flashes doesnt mean its working the way it should just that its getting a signal and firing. I'd check the ohms resistance for the injectors and exact voltages.

hope that helps

[FromTheInside]

I'm not sure if I posted up there... I could have forgotten...


I replaced all 6 injectors and then it continued. So at that point I swapped the number 3 and 4 injectors, coils, plugs, and I took my number 4 wire and put it on 3 and took an extra long wire and put it on 4 but the misfire did not move.

My entire coil pack has been replaced so it isn't an ignition module. I hate my misfire to death.

[Airjer_]

FYI, Di-electric grease is non-conductive. Which makes it ideal to apply liberally to a socket to seal out the elements. You don't have to worry about the grease touching the two terminals of the injector causing it to "short out both pins with one another".

Sorry if I missed it but have you swapped #3 plug with another cylinder?

[FromTheInside]

Okay lol, I was just being safe. Anyway, all of the plugs are new and gapped to specification. After replacing the injectors, plugs, wires, and the entire coil pack. I took the 3 and 4 plugs, injectors, and coils and swapped them. I also swapped my new #3 wire with my old #4 one. My misfire did not move. My cylinder heads are new and my camshaft lobes, lifters, pushrods, and rockers are okay. My problem started before the installation of the new heads anyway; my valves are fine too. The misfire is worse without the #3 injector plugged in, so I know the cylinder does SOMETHING

=[

[bandit7862]

I know what you mean about a cylinder misfire that you can never find. I had 99 ford e150 van and changed out just about every part possible but all was to no avail. Had to sell it for dirt cheap just to get rid of it. But anyway, I am currently having a problem on my 04 chevy blazer with the #3 cylinder misfire. I know there is definately something wrong with my # 3 injector because after remover the connector to get at the pins, I rang all the injectors out. The specs call for all injectors to be between 11 and 14 ohms with a multimeter. The # 3 is above 19 ohms and the rest are right at 11.5 to 12 ohms. You mention something that peaked my interest when you said something about a coolant issue or the #3 cylinder has exhaust gases going through it. Before I had this #3 injector issue, back this past winter, one day the blazer had a tapping noise only when it was cold. As soon as it warmed up, the noise went away, so I am starting to think that I may have a bad exhaust manifold gasket which may have caused my injector issue, I dont know. Let me know what you think of this.

[FromTheInside]

The tapping noise that goes away when the car warms up are your lifters ticking. It is very common so don't worry about it. As long as it goes away when you're warmed up.

[bandit7862]

Is there anything I can do about the tapping noise from my lifters ticking? It was very weird how this problem first happened. I had got home from work one winter day and left the truck running for about 10 minutes just idling. The next morning is when I noticed the very loud tapping noise until it warmed up. So do you think I may have blown the exhaust gasket or something to do with the cooling system? Any info would help greatly.

[bandit7862]

By the way, with your 3.4 #3 cylinder misfire, have you tried ohming out all 6 injectors to see if any are above the specs. Normally they should read around 12 ohms. A bad injector will read higher resistance. Hope this will help.

[FromTheInside]

Well, try using Lucas oil stablizer to see if the ticking calms down. I was told to do that but it didn't work. You will not be able to quiet them unless you tear 1/3 of your engine off from the top and replace the lifters. If you ever change your LIM gasket, you will be right there so go for it. Anyway I am not near your car so I do not know anything about your cooling system. Of course anything is possible, but your symptoms do not necessarily mean it at all. Lifter tick with this engine is very common and isn't a big deal. As I stated before you do not necessarily have a bad exhaust manifold gasket. That is not the ticking you are hearing. I always warm up for 10 minutes and do not rev my engine while it is ticking. Don't worry about it. And whenever you change the gaskets just replace your lifters and it should fix the problem. For now, while it IS annoying, it isn't a big deal at all. Only worry if noises don't go away when warmed up

As with my misfire, I changed out all of my injectors and also tested their resistances so that isn't the problem. I had swapped my brand new #3 and #4 injectors to see if the misfire moved (in case my new ones were defective) but it did not.

[3100]

Hey try this sometimes helps, since our ignition system is a waste spark this will not hurt but sometimes it helps. swap 3 and 6 ignition wires so coil tower #3 connect to #6 cylinder and tower#6 to cylinder #3 it will work fine it will just reverse ground if the problem switches to #6 cylinder then you know you have ignition problem not engine mechanical.

[xeroinfinity]

Originally Posted by FromTheInside

The tapping noise that goes away when the car warms up are your lifters ticking. It is very common so don't worry about it. As long as it goes away when you're warmed up.

Originally Posted by bandit7862

Is there anything I can do about the tapping noise from my lifters ticking? It was very weird how this problem first happened. I had got home from work one winter day and left the truck running for about 10 minutes just idling. The next morning is when I noticed the very loud tapping noise until it warmed up. So do you think I may have blown the exhaust gasket or something to do with the cooling system? Any info would help greatly.

Lifter tick should quit rather quickly, 1-2 mins, unless its below 30 deg.

Another tick/knock sound is a problem with most newer GM engines is piston slap. Hear these all the time.

Also FromTheInside, check your fuel pressure with just the key "on" and then while its running. Fuel pressure should be between 41-47 PSI , could be a weak pump.

Btw have you taken it out and just run the P&^* out of it ?? Might do wonders

I realy wouldnt worry about the misfires unless its causing the engine to constantly jump and shake around irraticly.

[FromTheInside]

My fuel pressure is fine sorry I did not post that. Also, I swapped coils and replaced the entire coil pack.

Yes, I did drive it hard when I got pissed as hell that replacing all of the injectors did not solve the problem. I was pissed off.

My engine shakes and I can feel it through the car when I'm at a stop light and it puts me in a bad mood. This is the second engine inside of this car. I also replaced the transmission. Many of you may be thinking I drive it hard hearing that - I do not at all. I never go above 2300 rpm ever unless I need to merge into a lane quickly or something. Never ever above 3k though.

So, after spending SO MUCH money on this car, it DAMN WELL BETTER RUN PROPERLY. lol, sorry I just spent 4 hours tearing into it. I suspect that my intake port on the lower intake manifold for cylinder 3 may have a crack in it near the head. That is my next mission. I will smoke the thing with the firewall valve cover off to see how everything looks.