westslope Posted July 3, 2009 Share Posted July 3, 2009 Recently had a bit of work done on the vehicle (02 sensor, catalytic converter replacement; RHS exhaust manifold removed, machined, replaced with new gasket, studs, nuts and washers, valve cover tightened). The vehicle was running a little rough during acceleration at lower speeds so I replaced the distributor and decided to haul the NGK V-Power spark plugs (BKR6EY) for an inspection, cleaning and gap adjustment. The plugs were of good colour, not at all fouled up. The plugs should be gapped 0.032 inches. The plugs I took out had gaps that were between 0.042 and 0.044 inches. The plugs were put in about 80,000km ago and in theory should be good for another 20,000km. I cleaned the plugs with white gas and a wire brush. I also wiped down the wires and cleaned the plug clips. The vehicle still runs a little rough sometimes when accelerating from lower speeds. Something else is amiss.... In the meantime, how critical is the spark plug gap? I get the impression that some garages, gap them, install them and then don't bother looking at the plugs until 100,000km later. Link to comment Share on other sites More sharing options...
Simon Posted July 3, 2009 Share Posted July 3, 2009 It's fairly critical. Gap them to spec, and she should run better. Link to comment Share on other sites More sharing options...
westslope Posted July 3, 2009 Author Share Posted July 3, 2009 Simon, That is what I would have thought. Mind you I just read through the wiki page on spark plugs and now I'm not so sure. Pasted: The gap adjustment can be fairly critical, and if it is maladjusted the engine may run badly, or not at all. A narrow gap may give too small and weak a spark to effectively ignite the fuel-air mixture, while a gap that is too wide might prevent a spark from firing at all. Either way, a spark which only intermittently fails to ignite the fuel-air mixture may not be noticeable directly, but will show up as a reduction in the engine's power and fuel efficiency. The main issues with spark plug gaps are: +narrow-gap risk: spark might be too weak/small to ignite fuel; +arrow-gap benefit: plug always fires on each cycle; +wide-gap risk: plug might not fire, or miss at high speeds; +wide-gap benefit: spark is strong for a clean burn. A properly gapped plug will be wide enough to burn hot, but not so wide that it skips or misses at high speeds, causing that cylinder to drag, or the engine to begin to rattle. Spark plug eroded: note the center electrode (dark bump) had been a cylindrical rod, and the top ground electrode (like a claw) formerly had square edges. As a plug ages, and the metal of both the tip and hook erode, the gap will tend to widen; therefore experienced mechanics often set the gap on new plugs at the engine manufacturer's minimum recommended gap, rather than in the center of the specified acceptable range, to ensure longer life between plug changes. On the other hand, since a larger gap gives a "hotter" or "fatter" spark and more reliable ignition of the fuel-air mixture, and since a new plug with sharp edges on the center electrode will spark more reliably than an older, eroded plug, experienced mechanics also realize that the maximum gap specified by the engine manufacturer is the largest which will spark reliably even with old plugs and will in fact be a bit narrower than necessary to ensure sparking with new plugs; therefore, it is possible to set the plugs to an extremely wide gap for more reliable ignition in high performance applications, at the cost of having to replace or re-gap the plugs much more frequently, as soon as the tip begins to erode. Link to comment Share on other sites More sharing options...
BowTied Posted July 3, 2009 Share Posted July 3, 2009 The larger teh plug gap, the higher the voltage required to junp the gap meaning your coil is working harder/hotter. Follow the FSM, if still running rough, the problem could be old wires, or a host of other things. Link to comment Share on other sites More sharing options...
westslope Posted July 3, 2009 Author Share Posted July 3, 2009 FSM= ? Link to comment Share on other sites More sharing options...
SilverPath Posted July 3, 2009 Share Posted July 3, 2009 Factory Service Manual Link to comment Share on other sites More sharing options...
alexrex20 Posted July 3, 2009 Share Posted July 3, 2009 Simon, That is what I would have thought. Mind you I just read through the wiki page on spark plugs and now I'm not so sure. Pasted: The gap adjustment can be fairly critical, and if it is maladjusted the engine may run badly, or not at all. A narrow gap may give too small and weak a spark to effectively ignite the fuel-air mixture, while a gap that is too wide might prevent a spark from firing at all. Either way, a spark which only intermittently fails to ignite the fuel-air mixture may not be noticeable directly, but will show up as a reduction in the engine's power and fuel efficiency. The main issues with spark plug gaps are: +narrow-gap risk: spark might be too weak/small to ignite fuel; +arrow-gap benefit: plug always fires on each cycle; +wide-gap risk: plug might not fire, or miss at high speeds; +wide-gap benefit: spark is strong for a clean burn. A properly gapped plug will be wide enough to burn hot, but not so wide that it skips or misses at high speeds, causing that cylinder to drag, or the engine to begin to rattle. Spark plug eroded: note the center electrode (dark bump) had been a cylindrical rod, and the top ground electrode (like a claw) formerly had square edges. As a plug ages, and the metal of both the tip and hook erode, the gap will tend to widen; therefore experienced mechanics often set the gap on new plugs at the engine manufacturer's minimum recommended gap, rather than in the center of the specified acceptable range, to ensure longer life between plug changes. On the other hand, since a larger gap gives a "hotter" or "fatter" spark and more reliable ignition of the fuel-air mixture, and since a new plug with sharp edges on the center electrode will spark more reliably than an older, eroded plug, experienced mechanics also realize that the maximum gap specified by the engine manufacturer is the largest which will spark reliably even with old plugs and will in fact be a bit narrower than necessary to ensure sparking with new plugs; therefore, it is possible to set the plugs to an extremely wide gap for more reliable ignition in high performance applications, at the cost of having to replace or re-gap the plugs much more frequently, as soon as the tip begins to erode. why ask the question, if you're going to answer it yourself? regardless, the article you quoted says that "experienced mechanics" set their plug gap at the minimum or maximum recommended specification. they're setting it within the factory allowed specification, so what makes you think it's not important? Link to comment Share on other sites More sharing options...
westslope Posted July 3, 2009 Author Share Posted July 3, 2009 why ask the question, if you're going to answer it yourself? regardless, the article you quoted says that "experienced mechanics" set their plug gap at the minimum or maximum recommended specification. they're setting it within the factory allowed specification, so what makes you think it's not important? I dunno Alex, would you have answered the question for me? The plugs were de facto gapped at 0.042 to 0.044. I reset the gaps to 0.032. I noticed no difference in vehicle performance. None. Link to comment Share on other sites More sharing options...
alexrex20 Posted July 3, 2009 Share Posted July 3, 2009 I dunno Alex, would you have answered the question for me? The plugs were de facto gapped at 0.042 to 0.044. I reset the gaps to 0.032. I noticed no difference in vehicle performance. None. looks like another one of those questions that you're going to answer yourself... Link to comment Share on other sites More sharing options...
tekazgtr1984 Posted July 3, 2009 Share Posted July 3, 2009 Sorry to thread-jack but how often should spark plugs be checked? I replaced my plugs and wires back in February and have only put on maybe 4,000km since then. Link to comment Share on other sites More sharing options...
Precise1 Posted July 4, 2009 Share Posted July 4, 2009 Sorry to thread-jack but how often should spark plugs be checked? I replaced my plugs and wires back in February and have only put on maybe 4,000km since then. The Haynes manual says every 30k miles or 2 years for a WD21 although time based seems silly unless it has been sitting most of the time? Like I told an in-law who was out checking/regapping his plugs again... Leave them the F alone!! They are good for 20-40k, all you are doing is wasting time and stressing the threads!! As long as the gap is within range (they will burn larger) and your engine runs properly (good air/fuel mixture, no oil blow by, etc) they require no attention for quite a while. Here in NorCal with 2 year smog intervals, I'd check and maybe clean/replace the plugs, dizzy cap and rotor then. Good spark plugs are important and last a long time... B Link to comment Share on other sites More sharing options...
tekazgtr1984 Posted July 4, 2009 Share Posted July 4, 2009 Thanks, B! My VG33E runs wonderfully at the moment so I'll leave those spark plugs alone. Link to comment Share on other sites More sharing options...
BowTied Posted July 4, 2009 Share Posted July 4, 2009 Sorry to thread-jack but how often should spark plugs be checked? I replaced my plugs and wires back in February and have only put on maybe 4,000km since then. You are fine. 99% of the time the plugs are gapped correctly from the factory assuming you are using the correct plug. It is good practice to verify the gap before install. Once in leave till the next change interval. Link to comment Share on other sites More sharing options...
tekazgtr1984 Posted July 4, 2009 Share Posted July 4, 2009 You are fine. 99% of the time the plugs are gapped correctly from the factory assuming you are using the correct plug. It is good practice to verify the gap before install. Once in leave till the next change interval. Thanks for the info. I checked them before installation (NGK Iridium IX plugs w/ NGK wire set) and everything was as it should be (even though they were brand new plugs it's still just proper diligence to check). I'll let them be until I change 'em. Link to comment Share on other sites More sharing options...
westslope Posted July 4, 2009 Author Share Posted July 4, 2009 (edited) .....Once in leave till the next change interval. Change interval? Oil change or spark plug change? teka: no hijack; the question is absolutely relevant given that the gap will likely spread larger than specification during that time period, and I thank Precise1 for his answer. Edited July 4, 2009 by westslope Link to comment Share on other sites More sharing options...
alexrex20 Posted July 4, 2009 Share Posted July 4, 2009 Change interval? Oil change or spark plug change? he meant oil change, because that's obviously what this thread is discussing. Link to comment Share on other sites More sharing options...
tekazgtr1984 Posted July 4, 2009 Share Posted July 4, 2009 he meant oil change, because that's obviously what this thread is discussing. Dood, you're such a sarcastic ass. Link to comment Share on other sites More sharing options...
BowTied Posted July 5, 2009 Share Posted July 5, 2009 I thought the thread was about spark plugs. In either case, I meant leave the plugs alone until the next scheduled change interval. Link to comment Share on other sites More sharing options...
94extreme Posted July 5, 2009 Share Posted July 5, 2009 yes, the gapping makes difference and you need to have them within specs.. Link to comment Share on other sites More sharing options...
westslope Posted July 8, 2009 Author Share Posted July 8, 2009 94extreme: Well, that's the conventional wisdom and what I have believed for years. BowTied wrote: "Once in leave till the next change interval." westslope continues: That's what I'm hearing from some mechanics. However, if that spark plug interval is let's 100,000km as some of them claim, then the gap will likely spread over the change interval to a much larger gap than the spec range. Am about to put in a new NGK wire set and NGK G-Power Platinum spark plugs (to replace the existing NGK V-Power spark plugs). ------------------------------------------------------------------------------------------------------- For the curious, this is what the NGK Canada web-site says: Q: How often should I replace my spark plugs? A: Unfortunately,there is no single answer to this question. As spark plugs grow older, they lose their sharp edges as material from the center and ground electrodes is slowly eroded away. As the gap between these two points grows, the voltage required to bridge the gap increases proportionately. Even the best ignition systems will be strained to supply enough voltage to completely burn the fuel. It is at this point, when fuel is being left unburned, that the time has come to change spark plugs. Replacing worn out spark plugs with new ones (with sharp new edges) effectively restores the ignition system's efficiency. Misfires are reduced, power is restored, economy of operation is enhanced and emissions are reduced. The best guide is the manufacturer's recommendation for your vehicle, as this particular service varies from brand to brand and model to model. In the absence of this information or in conjunction with it, you can rely on the advice of a mechanic who is familiar with your type of vehicle. In the best of all worlds, this would be a mechanic who is also familiar with the vehicle you own. If you find a good mechanic, whether dealer or independent, stick with him. The better he knows your personal vehicle, the better he will be able to diagnose and service it. The end result is very much like a doctor-patient relationship and, in the long run, you will have a healthier vehicle. The Nissan Pathfinder 1995 owner's manual stipulates replacing the plugs every 48,000km (30,000 miles). Link to comment Share on other sites More sharing options...
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