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Discussion Starter #1
So my wife and I have a 2004 Nissan Frontier V6 Auto with 68,000 miles on it. (already posted similar question, but this one is now a little different and updated)

We are to the point where some preventative maintenance needs to be done, but there is also a problem that I can't figure out.



While driving slowly and lightly accelerating (I notice this in parking lots) around 4-5 mph, the motor is knocking. I figured it was probably running lean, so I put 93 octane in it. That solved the problem for a while so I have run 93 octane for the last 6 months, but now the knocking is back. There are also symptoms that the truck is running rich (conflicting). For instance, we average about 14.5 mpg around town. And even after the motor warms up, the exhaust fumes are still visible, even on a warm humid day.



So I am thinking of a few possibilities.



1. Carbon build up in the fuel system. Ran a top cleaner and some fuel and oil additive. Spitted and spewed like crazy and cleaned a lot of nasty crap out. Truck runs noticeably better now (better throttle response), but still knocks. I was thinking this was the most likely since it would cause the truck to run lean, spew crap out the exhaust, and get lower mpg. No dice. Unless it will just take some miles to take effect.



2. Spark plugs? My wife had new plugs put in before we were married (14,000 miles ago) so I am thinking this is not the problem.



3. Timing issue cause the knock sensor to pre-detonate?



I kind of want to sell/trade the truck anyways, but my wife is really attached to this particular truck (it was her first truck so I know how she feels. I almost cried the day I sold my first truck). I am just trying to decide if it is worth it to chase this problem around (the computer isn't throwing any codes) to potentially either not fix it, or reveal a very expensive problem.

I am not able to work on the truck myself right now since being injured in an accident last month, so that is another concern. The truck needs new belts (not super urgent as they are just starting to crack a little on the outside), new wheel cylinders, and exchange of all fluids (neglected to do this at 60k.). Also, one of the bearings in a pulley is making some noise, so I am thinking that a pulley will need to be replaced as well (when belts done obviously). Other than that, everything is solid. Suspension, transmission, drive line, etc...



Any thoughts as to what the problem might be? What would you do? If we sold or traded the truck, whatever we got for it (probably $9k or so) would be our shopping budget as we are not interested in acquiring a car payment. Also, we don't technically need a truck, as we only use it for fishing, and any other truck/car with a roof rack will suit this need just fine. We just both like this truck as it has served us well, and are hesitant to get rid of it.

I just can't justify 14.5 mpg when we don't have to. Also can't justify $1500-2000 in repairs and maintenance. Seeing how I could do it all (except timing, I don't want to screw with that myself) for $500 or less if I were feeling better.

Thanks for any advice in advance.
 

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1st thing I would do is knock the timing back a couple of degrees. Buy a timing light and instruct you're wife on its use. Or, take it to a mechanic and get it done. Shouldn't cost much. As to the rich problem, well, others will be along.
 

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If you sell the truck, you will likely net a higher price if you can eliminate the knock.

Personally, I wouldn't adjust timing just yet. There are some simple things you can check first.

If you hear the knock at idle, then pulling plug wires and listening to the engine might help you determine which cylinder is acting up. Also, pulling the spark plugs and examining buildup on the electrodes might help you diagnose problems with fuel mixture.

Does the knock persist at constant speeds?
 

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Discussion Starter #5
It doesn't knock at idle. Only when accelerator is applied. I can't tell if the knock persists. It does speed up (the frequency of the knock) as the rpms do, but the sound of the motor drowns it out above 5 mp or so.

This is what makes me think it has to do with timing. I might have another place try to read the codes today. I am wondering if I don't just have a bad knock sensor?
 

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Discussion Starter #6
OK, not the knock sensor or the timing. No codes and we looked at it with a timing light and we're OK there. I did just realize that I would have to remove the intake manifold to get to it (more work that I can do right now).

Guy that read the codes said it might be bad gas (no, since it has been doing it) or a fuel filter/fuel pump issue. I suppose this might make some sense. Fuel filter is $10 and not too difficult to put in (I could probably do this myself). I don't think it's a fuel line as I didn't see any leaks when I looked. The filter should also be replaced every 30k miles and it has been about 30k since we did that. Will probably just do this anyways. $10 and may help with the problem.

Fuel pump is $100 for the part and you have to remove gas tank, and is fairly labor intensive, so I can't do this right now in my shape. Probably costs an arm and a leg to have someone else do it too.

Well, I feel like I am chasing a leprechaun here, but I will figure this thing out.

Will try the fuel filter tonight and see what that does. If that doesn't fix it I am not sure what I will do.


There is some minor body work I am going to do to the truck in the mean time as well. Get it up to snuff in case this doesn't work. Even if it does work, at least she'll be a little prettier while we have her. HAHAHA


Anyways, does the fuel filter make sense to you guys? I suppose it kind of does, but this seems like wishful thinking as I would bet on the pump before I would the filter. But the thing that makes me doubt both of these is that the truck is pretty responsive to the throttle. Especially after cleaning it out yesterday.
 

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new plugs at 50k? thats way to early. Pull a plug and look at the condition of the tips. They will tell you lean or rich. Cylinders 1-5 are easy to get too. If you can use a timing light you can pull a plug. do an italian tune up, also suck in some seafoam. These are all things I would do on a truck with 168k miles on it...seems rather early for you.

check the plug temperature as well....I wonder if the new plugs are the wrong temp

14.5 isnt abnormal for a 1st gen if your a little hard on the gas.
 

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Discussion Starter #8
I didn't use the timing light. I had someone else do it...

Plugs are something I could do normally, and probably could now. But I don't think that's what is going on. The mechanic yesterday looked at them and I am sure he would have been happy to sell me some plugs and labor if he thought I needed it.

Thanks for the suggestion though.

If the fuel filter doesn't fix the problem, I will try replacing the spark plugs. I could probably get my brother to do it if I walked him through it and gave him a case of beer.

If that doesn't work, I think I am done chasing the cause. Will probably trade it in at that point.
 

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so you've said you've changed the plugs right? but have you ever changed the plug wires or distributor cap and rotor (if it had a distributor)
 

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Discussion Starter #10
I don't think the wires and cap were changed. My wife had someone do it before we were married so I can't be certain.

I am now second guessing myself as to the type of knocking. Since I have checked anything that could cause spark knock (I think), I am windering if it isn't valve knock.

However, I have only heard this once before, and it doesn't sound the same to me. But maybe this is a different sound because the vehicle I heard it on before was a Jeep?
 

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these trucks run rich when the engine is cold, my truck actually really stinks when i first start it up but it goes back to normal after normal operating temps. the knocking sound i have no clue, mine made a knocking sound when it was new but its better now. these trucks are good trucks, hate for you to sell it due to a problem, take it to a professional if you cannot figure out the problem, take it to the dealer (yeah i said dealer) due to you can have a nissan master tech look at it and see what he finds.
 

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Discussion Starter #12
I will consider that at this point.

however, this would not be the only reason we would get rid of the truck. We really don't have a need for a truck right now, so we have been toying with the idea of getting rid of it for a few months. This is kind of just a little nudge in that direction we were already thinking about heading.

Neither one of us wants to get rid of it, but there are worse things for sure.

I will call our Nissan dealership. I figure at least for the peace of mind of knowing what the heck is wrong with it might be worth it. And if it's an easy fix, we'll fix her.
 
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