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Discussion Starter · #1 ·
Firstly I apologize for the long post, however I am going to try and make it as clear as possible as to what I have done so far and what is going on with my truck.

The truck is a 2002 XE Crew cab 4x4 with a 3.3l V6 non supercharged engine. The parts I have replaced so far include the following:
Air Filter
Spark plugs
Spark plug wires
Distributor cap
Rotor button
Fuel filter
Fuel injector cleaner in the tank

Now for the problem, I have a recurring misfire on cylinder #6, that will set the engine check light. I have a diagnostic scan tool so I am able to clear the code, however it takes less than 1 day to re-occur. After a night of standing usually the first start of the morning the truck idles really rough, at this point no engine check light is flashing or set. The engine continues to warm up and will set the light solid after about 1 minute of idle. If I clear the code with a scan tool I can drive the truck the whole day with stops and starts and it will not set the light. I do however feel the engine running rough when I stop at a traffic light, but it will not set the engine check light nor do I get the light flashing as others report in the forum.

I am at a total loss at this stage apart from tearing the intake plenum apart to check for air leaks or maybe a faulty injector. However I have unplugged other injectors and they do not set a misfire code. Any help at this stage would seriously be appreciated from fellow owners. I am very experienced at rebuilding motors and working on cars and trucks, this one has me fooled.
 

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its probably either a bad injector or coil
 

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Discussion Starter · #4 ·
More updates:

Just pulled #6 plug for the millionth time I am becoming a real pro at it only takes a few minutes. Hooked up my compression gauge and turned the motor over, good news the head gasket is not to blame the compression is perfectly within service manual spec.

I replaced the spark plug which I might add is still in perfect shape and proceeded to inject Sea Foam into the intake, I am waiting a few minutes before starting her up again to let the Sea Foam work. Iam going to check the timing again.

If it was the coil I think the misfire would be more random, it is always on #6 unfortunately.

I agree it is starting to look like the injector is the problem here, might not be spraying a full pattern and causing a lean misfire.
 

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hi, only ignition related problems will cause your ses light to flash.

If you think an injector is at fault, litsten to all of them using a stethoscope(sp), you should be able to hear them click.

Also if you think you have an air leak, spray brake cleaner or whatever around the IM. You should be able to tell if there's a leak if the engine stumbles when you hit a certain spot.
 

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Discussion Starter · #6 ·
Thanks 1fstmax, I thought of the stethoscope but unfortunately injector #6 is just unreachable without removing the air intake plenum. So no go on checking it while the engine is running.

I will have to do more research on the vacuum leak, again if there was a vacuum in the air intake would the misfire not be more random and not isolated to always being on cylinder #6?

Thanks for all the advice so far guys keep it coming.
 

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Discussion Starter · #7 ·
Just another quick update, dumped a bottle of Gumout Fuel injector cleaner in the tank today in the hopes that the injector might just be dirty. I will give that a few days while I start to price the parts to replace the injector.

As a side note at least this gives me an excuse to finally fix my knock sensor that went out about a year ago, still not looking forward to the loads of work in taking the intake out. Specially not with the 90+ tempretures here in NC at the moment, man I wish I had AC in the garage. :(
 

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Make sure you reseal your goose neck coolant pipe. This is the pipe that houses the thermostat. I've not seen the back of it personally but from what I here this is a part that leaks and you cannot get to it unless you take off the upper and lower intake. just a thought.
 

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a few years ago a friend of mine had a problem with his maxima. He was getting random miss fire codes, also his engine was running rough. He replaced coil packs, spark plugs, tried various fuel treatsments to no avail. On a whim i suggested to check his fuel pressure. Turns out he was only getting 31 psi outta 51 psi. Turned out to be a clogged fuel filter. once we replaced the filter, car ran like a rapped ape.

anywhoo, it's worth a try see what your fp is.
 

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Discussion Starter · #10 ·
Frustrated and annoyed I spent more time last night diagnosing my problem. I did manage to get a stethoscope up on injector #6 and what would you know the injector is ticking like a time bomb. So I guess I ruled out another problem area it does not appear to be the injector.
I then noticed a small 5mm vacuum line at the back of the intake manifold that was ported into the runner tube for cylinder #6 and immediately thought this could be my problem all along. An air leak unique to cylinder #6 I promptly pulled the hose and plugged the port. My excitement was short lived no change.

After all the diagnostics I have performed I sat down and tried to record the exact moments the issue occurs, I noticed a pattern if anyone can shed more light I would appreciate it.

1) The rough idle and stumbling only appears to happen after a long period of sitting with the engine off, for example over night in my garage. When I first start the truck up in the morning and allow it to idle the engine stumbles and runs rough and then throws the misfire code, engine check light is on. However if I clear the light and start the engine cold and then pop the gas 2 or 3 times racing the engine to 3000rpm and then letting it idle again the engine does not stumble and does not throw the code.
2) Second it appears that the code is only thrown when at cold start if I drive the truck stop start though the day on and off, only stopping for an hour or so I don’t get the code.

Something appears to be happening while it is standing for long periods, fuel pressure and drain down does come to mind. Either pump or fuel pressure regulator, however I would expect a more random misfire and again its always on #6.

The investigation continues.
 

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Or swap plug wires with another cylinder of the same length and see if the misfire moves.
 

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Discussion Starter · #13 ·
Checked the resistance of the old wire was running at 7.8k ohm, the service manual specifies 11k ohm. The new wire is running at 10.8k ohm, which is far better than the old wire but did not cure my misfire problem unfortunately.
 

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Frustrated and annoyed I spent more time last night diagnosing my problem. I did manage to get a stethoscope up on injector #6 and what would you know the injector is ticking like a time bomb. So I guess I ruled out another problem area it does not appear to be the injector.
I then noticed a small 5mm vacuum line at the back of the intake manifold that was ported into the runner tube for cylinder #6 and immediately thought this could be my problem all along. An air leak unique to cylinder #6 I promptly pulled the hose and plugged the port. My excitement was short lived no change.

After all the diagnostics I have performed I sat down and tried to record the exact moments the issue occurs, I noticed a pattern if anyone can shed more light I would appreciate it.

1) The rough idle and stumbling only appears to happen after a long period of sitting with the engine off, for example over night in my garage. When I first start the truck up in the morning and allow it to idle the engine stumbles and runs rough and then throws the misfire code, engine check light is on. However if I clear the light and start the engine cold and then pop the gas 2 or 3 times racing the engine to 3000rpm and then letting it idle again the engine does not stumble and does not throw the code.
2) Second it appears that the code is only thrown when at cold start if I drive the truck stop start though the day on and off, only stopping for an hour or so I don’t get the code.

Something appears to be happening while it is standing for long periods, fuel pressure and drain down does come to mind. Either pump or fuel pressure regulator, however I would expect a more random misfire and again its always on #6.

The investigation continues.
how many miles does the truck have on it? cylinder # 6 may not be getting oiled properly... causing the piston stroke to act slightly different. might be a good idea to check your oil journals and/or oil level.
 

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Discussion Starter · #16 ·
Finally solved the mystery, after weeks of diagnosis which I am glad I did instead of throwing money at the problem.

I ended up loaning a Radiator leak test kit from a parts store and performed a leak test on the cooling system. Well no immediate visual leaks and the pressure remained pretty constant. I left it to sit for about 30 minutes and noticed the pressure had dropped slightly, the longer I left it the more it dropped. I had found a small leak in the cooling system, the question was where?
No visual leaks at all on the outside of the engine, and the fact that the engine idled rough meant it was leaking into the cylinder. This would mean either the head gasket or the intake plenum gasket had failed. The fact that I had consistent cylinder #6 misfire and nothing else would say it could be the intake intake plenum. A quick compression test between cylinder #6 and the adjacent cylinder I think #4 confirmed no leaks between the two cylinders. The compression test also showed as before that the pressure was within manufacturing specifications. This meant the intake plenum was definitely the culprit here.
Also check the codes again and I picked up a new misfire on cylinder #5 which is on the opposite bank to cylinder #6 which definitely confirms unless I have both head gaskets blown the coolant passage between #5 and #6 is leaking in the intake plenum. This is causing the misfire code and the rough idling as the engine tries to burn the coolant, this also explains why it was rough at start but disappeared after a few seconds. Once the coolant that has pooled in the cylinder from standing has been burned up the engine performs normally.

Good excuse to fix my knock sensor while i am down there, well I will update all on the progress once I have replaced the gaskets. Thanks to everyone for input on the topic and again it pays to diagnose the hell of a problem before throwing money at it. I am planning on documenting the repair with detailed pictures, as I have noticed many people on the forum requesting information on knock sensor replacement.
 

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Finally solved the mystery, after weeks of diagnosis which I am glad I did instead of throwing money at the problem.

I ended up loaning a Radiator leak test kit from a parts store and performed a leak test on the cooling system. Well no immediate visual leaks and the pressure remained pretty constant. I left it to sit for about 30 minutes and noticed the pressure had dropped slightly, the longer I left it the more it dropped. I had found a small leak in the cooling system, the question was where?
No visual leaks at all on the outside of the engine, and the fact that the engine idled rough meant it was leaking into the cylinder. This would mean either the head gasket or the intake plenum gasket had failed. The fact that I had consistent cylinder #6 misfire and nothing else would say it could be the intake intake plenum. A quick compression test between cylinder #6 and the adjacent cylinder I think #4 confirmed no leaks between the two cylinders. The compression test also showed as before that the pressure was within manufacturing specifications. This meant the intake plenum was definitely the culprit here.
Also check the codes again and I picked up a new misfire on cylinder #5 which is on the opposite bank to cylinder #6 which definitely confirms unless I have both head gaskets blown the coolant passage between #5 and #6 is leaking in the intake plenum. This is causing the misfire code and the rough idling as the engine tries to burn the coolant, this also explains why it was rough at start but disappeared after a few seconds. Once the coolant that has pooled in the cylinder from standing has been burned up the engine performs normally.

Good excuse to fix my knock sensor while i am down there, well I will update all on the progress once I have replaced the gaskets. Thanks to everyone for input on the topic and again it pays to diagnose the hell of a problem before throwing money at it. I am planning on documenting the repair with detailed pictures, as I have noticed many people on the forum requesting information on knock sensor replacement.
Did replacing the gaskets solve the problem? I'm having the exact same problem and don't want to start blind.
 
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