ericem Posted October 27, 2007 Share Posted October 27, 2007 Hi I want your opinion on what is wrong. I have replaced the plugs 3 times in 15,000km and they always come out looking the same way with a lot of carbon on the plug. Tried NGK g and v powers with same result. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 27, 2007 Share Posted October 27, 2007 Some carbon is normal. You might have a PCV problem that is sucking oil, or you might have bad valve stem seals, etc. Oil can only get in through the intake, rings, or valves. It's up to you to figure out which it is. GD Link to comment Share on other sites More sharing options...
ericem Posted October 27, 2007 Author Share Posted October 27, 2007 Well a vacuum gauge showed 21 in-hg and the car doesn't burn oil. Just replaced PCV valve, and the plumbing still same thing :-\ Link to comment Share on other sites More sharing options...
Manarius Posted October 27, 2007 Share Posted October 27, 2007 Can you take pictures of the plugs you define as being "carboned" up? Link to comment Share on other sites More sharing options...
ericem Posted October 27, 2007 Author Share Posted October 27, 2007 This is usually how they come out without the rust. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 27, 2007 Share Posted October 27, 2007 Looks normal to me. If, as you claim, you are not using any oil.... well then you have answered your own question. What symptoms are you experienceing that you attribute to this carbon build up? Some carbon is normal and is a normal product of the small amounts of oil natually present in the cylinder, as well as the ignition spark itself. GD Link to comment Share on other sites More sharing options...
ericem Posted October 27, 2007 Author Share Posted October 27, 2007 Lots of hesitation, that I do not beleive was there before. Link to comment Share on other sites More sharing options...
zstalker Posted October 27, 2007 Share Posted October 27, 2007 the only part of the plug that matters for running is the part past the threads that is actually inside the combustion chamber. well, almost...if there's a dark black line running up the ceramic stem of it that's bad, but not really what we're talking about here. go to this page and tell us which one it looks most like. if you're talking about how the threads and hex-portion get darker and the ceramic gets slightly discolored, that's totally normal, just from being so close to extremely high temperatures. ~Erik~ Link to comment Share on other sites More sharing options...
ericem Posted October 28, 2007 Author Share Posted October 28, 2007 Thanks for that link. I would describe my plug as. Dry and Wet Fouling Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 28, 2007 Share Posted October 28, 2007 Those pictures are somewhat misleading. Subaru engines, due to the horizontal nature of the cylinders, are prone to burning slightly more oil than other designs. The plugs usually have a light carbon coating from this. I would still be checking the PCV system - did you use an OEM valve? The aftermarket ones are known to suck oil. GD Link to comment Share on other sites More sharing options...
Cougar Posted October 28, 2007 Share Posted October 28, 2007 There may be a problem with the coolant temperature sensor for the ECU. This is different than the one for the gauge. It may have two leads instead of one. The sensors can go bad and make the ECU think the engine is always running cold and the fuel will be too rich. Link to comment Share on other sites More sharing options...
ericem Posted October 28, 2007 Author Share Posted October 28, 2007 The PCV valve is OEM Just replaced the ECU temp sensor. Same result. Car runs alot better when its cold though. Still thinking about replacing the MAF sensor. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 28, 2007 Share Posted October 28, 2007 Try cleaning the MAF with brake cleaner. Sometimes the elements get dirty. Replacement is not often neccesary, but cleaning often helps a lot. It's pretty easy to test them too. You just look for a resistance drop across the sensor element while blowing air over it. GD Link to comment Share on other sites More sharing options...
ericem Posted October 28, 2007 Author Share Posted October 28, 2007 I have cleaned it before. First time I cleaned it with brake cleaner but was told that isn't a good idea, then redid it with some contact cleaner. Not sure if break cleaner does damage. Going to test it tomorrow thanks. Link to comment Share on other sites More sharing options...
Cougar Posted October 28, 2007 Share Posted October 28, 2007 Maybe the cold start valve has a problem. Link to comment Share on other sites More sharing options...
OB99W Posted October 28, 2007 Share Posted October 28, 2007 [...]Dry and Wet FoulingAlthough there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon. NGK may know how to make spark plugs, but either there are typos or the author of the web page the above came from is "confused". A plug that measures 10 ohms from center electrode to shell will be very unlikely to fire; the spark energy will typically be dissipated in the usually much higher resistance of the ignition cable and/or built-in plug resistance, etc. Using an ohmmeter, a new plug will measure infinite resistance from center electrode to shell (ground electrode). Even a plug which measures hundreds of thousands of ohms is somewhat fouled, although it may fire. One measuring tens of thousands of ohms and lower could be significantly impaired. (The ratio between the resistance of the fouling material and the ignition cable or a resistor-plug's internal resistance affects the final result.) Not all dark deposits on a plug are conductive, and therefore wouldn't necessarily be considered fouling. Measure the resistance from center electrode to shell on a suspected plug, and see what it is. However, also be aware that a typical ohmmeter applies very low voltage (typically under 3 volts, although some use slightly more for a high-resistance range) in comparison to the tens of thousands of spark volts; that can mean that a plug which an ohmmeter test indicates not to be fouled may still have a problem under actual use. Link to comment Share on other sites More sharing options...
ericem Posted October 28, 2007 Author Share Posted October 28, 2007 My wires look to have some corrosion on the plug side. Should I clean them up or just replace them? Link to comment Share on other sites More sharing options...
OB99W Posted October 29, 2007 Share Posted October 29, 2007 My wires look to have some corrosion on the plug side. Should I clean them up or just replace them?If the ignition wires are otherwise okay (insulation good, resistance not excessive), the ends can be cleaned of corrosion. Use a small wire brush, a knife blade or other metal tool, steel wool (remove any remnants), etc. However, I'd suggest not using "sandpaper" of any kind; the abrasive is usually a semiconductor, and if it remains can cause arcing/pitting of the contact area. Clean the ends of any residue when you're done. Afterwards, before reattaching to the plugs in the engine, take a spare plug and verify that a snug connection can be made at each wire. Link to comment Share on other sites More sharing options...
uniberp Posted October 29, 2007 Share Posted October 29, 2007 If the ignition wires are otherwise okay (insulation good, resistance not excessive), the ends can be cleaned of corrosion. Use a small wire brush, a knife blade or other metal tool, steel wool (remove any remnants), etc. However, I'd suggest not using "sandpaper" of any kind; the abrasive is usually a semiconductor, and if it remains can cause arcing/pitting of the contact area. Clean the ends of any residue when you're done. Afterwards, before reattaching to the plugs in the engine, take a spare plug and verify that a snug connection can be made at each wire. If your wires are even somewhat corroded, they are probably quite old and that could easily be the source of the hesitation. The wires are subject to engine and resistance heat and lose conductance over time. Buy new good quality wires, OEM or higher grade silicon FITTED wires. Watch for the correct coil end hoods and angle connectors. Link to comment Share on other sites More sharing options...
FiremanBob Posted October 29, 2007 Share Posted October 29, 2007 Are you using the correct plugs as spec'd in the owner's manual? If you run too cold a plug you'll get carbon crust on the plugs and everything else in the combustion chamber. Link to comment Share on other sites More sharing options...
Cougar Posted October 29, 2007 Share Posted October 29, 2007 Are you using the correct plugs as spec'd in the owner's manual? If you run too cold a plug you'll get carbon crust on the plugs and everything else in the combustion chamber. Good point, FiremanBob. Link to comment Share on other sites More sharing options...
OB99W Posted October 29, 2007 Share Posted October 29, 2007 If your wires are even somewhat corroded, they are probably quite old and that could easily be the source of the hesitation.Not necessarily; I've seen corrosion on wires that were only a couple of years old, and fine in other respects. The wires are subject to engine and resistance heat and lose conductance over time.The wires can suffer both conductance problems and insulation damage, which is why I said "If the ignition wires are otherwise okay (insulation good, resistance not excessive)". Buy new good quality wires, OEM or higher grade silicon FITTED wires. Watch for the correct coil end hoods and angle connectors.Most of us here generally recommend getting OEM, rather than trying to find a particular brand that's as reliable. Link to comment Share on other sites More sharing options...
ericem Posted October 29, 2007 Author Share Posted October 29, 2007 Yes I am using plugs specified in the manual(same NGK partnumber) the wires are a little over a year old I believe, rubber looked good. Got a wire dremel bit and cleaned it up then blew it out. I believe it coroded because of me. Last time I cleaned the motor, water got past the wire somehow and the water was in there for a bit and I got misfiring but ignored it. Then I sprayed contact cleaner while the motor was hot. SO 2 possibilities where I damaged the wires. XD Link to comment Share on other sites More sharing options...
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now