mops Posted November 27, 2003 Share Posted November 27, 2003 Hello. I have JDM 94' Twin turbo legacy RS. As the only modification to the engine, it has an pod air filter. problem is that my spark plugs are wearing out pretty fast. last time i bought itidium tip ones, and just after about 8000 kilometers they are black and engine is missing under heavy acceleration at the upper end of the powerband. can worn coilpacks be the cause ??? what else should i check ??? what might be the other reason ??? Quote Link to comment Share on other sites More sharing options...
alias20035 Posted November 27, 2003 Share Posted November 27, 2003 Originally posted by mops Hello. I have JDM 94' Twin turbo legacy RS. As the only modification to the engine, it has an pod air filter. problem is that my spark plugs are wearing out pretty fast. last time i bought itidium tip ones, and just after about 8000 kilometers they are black and engine is missing under heavy acceleration at the upper end of the powerband. can worn coilpacks be the cause ??? what else should i check ??? what might be the other reason ??? I assume that you are gapping the plugs properly, sometimes improper gap can cause problems. Black plugs = oil in cylinder or problem with air/fuel mixture. I would take your used plugs to an expert mechanic and have him confirm whether it is carbon build up or oil build up. Carbon build up = air/fuel mixture problem or misfire from bad coilpack. Oil buildup = oil getting into the intake or bad rings. Are you having to top up the oil from time to time (with no external oil leaks)? Is the throttle body clean or is it coated with oil? If so, perhaps oil is leaking from the turbo and into the intake (and then cylinders). PCV valve? could be bad, change it.... I would scrap the pod air filter, as they tend to confuse or damage the air metering system. If your car has the hot wire mass air flow (MAF) sensor, these types of filters are notorious for contaminating them and making the engine beleive more air is going in than actually is causing an overly rich air/fuel mixture (and carbon buildup). Generally not a problem with the newer Manifold Air Pressure (MAP) sensor system that Subaru now uses. I am fairly certain that your car uses MAF, and you can confirm this if there is a wiring harness connected to the intake immediately after the air filter. Sometimes the MAF sensor becomes coated in the air filter oil, in these cases it is sometimes possible to clean the sensor "hot wires" with brake cleaner (use at low pressure and with a Q-tip). An air/fuel mixture problem should be detected by the oxygen sensor and compensated for and often the "Check engine" light will indicate a problem. Pehaps your oxygen sensors are not functioning correctly. Your coilpack could be gone, they often don't last 10 years, but change it only after you have ruled out the above. Quote Link to comment Share on other sites More sharing options...
mops Posted November 27, 2003 Author Share Posted November 27, 2003 thasnk for reply. Yes, i have MAF sensor I use apexI pod air filter, they do not need any oiling, and they came out as the best cleaning air filter in several independent comparacment test i've seen. The engine does not take any oil, as long as I change it every 5000 kilometers.... but indeed, if i drive more than that it will start to swallow oil (that is once the oil is worn out). i got no idea how to find PCV valve. :-\ gap might be the reason. initially i set the gap to 0.8mm, was ok for first 1000k's then started missing badly, i drove like that another 1000k's, then checked the plugs and they were black already. corrected the gap to 0.7mm and they stopped missing.... after 3000k's they are starting to miss again... I guess my sub is going to get a set of brand sparking new spark plugs for x-mas :santa: Quote Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted November 27, 2003 Share Posted November 27, 2003 IIRC 1mm is about 40 thousandths. I think your plugs may be OK. Do turbos need a smaller gap? If you are experiencing missing maybe the problem is elsewhere? Quote Link to comment Share on other sites More sharing options...
alias20035 Posted November 27, 2003 Share Posted November 27, 2003 Originally posted by 1 Lucky Texan IIRC 1mm is about 40 thousandths. I think your plugs may be OK. Do turbos need a smaller gap? If you are experiencing missing maybe the problem is elsewhere? I think 0.8 mm is the correct gap, or it is close enough. The PCV valve is on the left side (looking from the front) of the intake manifold (above the #3 cylinder if it is in the same location of other Subaru's. A hose of about 3/4 inch diameter comes from it and leads to the crankcase on the left side (from the front) near the flywheel. I don't see the PCV valve causing this, usually they fail and you have no crankcase venting causing very quick oil breakdown. Occasionally the PCV valve will allow engine oil into the intake manifold which is not good. The PCV valve is designed to prevent the crankcase system from flowing air in the wrong direction when the pressure on the manifold side of the throttle body is higher than the pressure on the air intake side (in your case, the intercooler side). The PCV valve costs about $5 and should be replaced every 50,000 km or so (96,000 on 2000+ Subaru's). I would reset the ECU (disconnect negative battery cable for 15+ minutes). The ECU will relearn its sensors (oxygen, TPS, knock, MAF, etc) and may detect something that is wrong. Since you don't have an oil consumption problem you have an air/fuel mixture problem or an ignition problem. I seem to recall that the TT Legacy's had a fuel rail problem that caused low fuel pressure at cylinder 3 or 4 causing lean burn and failure of the cylinder, but that is not your problem.... I would see if the ECU detects misfire with clean plugs. If it does you have a bad coilpack and/or plug wires. Sensors that are involved in setting the air/fuel mixture are: oxygen sensors (1 on your car?, 2 on some newer Subaru's) MAF sensor engine temperature sensor throttle position sensor If more than 50,000 km on them the oxygen sensor(s) are probably not at 100% capability. It might be worth a replacement. I would inspect the MAF and clean it carefully if required, it may require replacement. Engine temperature sensors are a known weak point on Subaru's, it feeds information to the ECU only and not the temperature gauge. It is possible that the ECU beleives the engine is running cold because of a misbehaving temperature sensor and sets the a/f ratio too rich. Throttle position sensors do fail, but this is rare and usually results in a very strange throttle response (jumps and blips in power output). You might need to find a good Subaru mechanic with the tool to plug into the ECU to diagnose the sensors, your car predates the ODB II diagnostic plug requirements. Quote Link to comment Share on other sites More sharing options...
alias20035 Posted November 27, 2003 Share Posted November 27, 2003 I just thought of something. Are you sure that you are using the correct temperature plugs?? If you use a plug that is too cold it will foul in the manner you mentioned, and usually all plugs will foul in a similar manner and rate (which a misfire may not do). If you use a plug that is too hot, it will disintegrate. Hotter plugs expose more of the electrode core so it will heat up more and clean itself off. A cooler plug will have a longer ceramic core to cover more of the electrode which will keep the electrode cool. If your plugs are one temperature range too low, it may be the cause of the problem, I looked through the Japanese NGK and Bosch sites using Altavista's Babelfish Japanese to English translation to see if I could find the temperature rating and gap, but I had no luck. The original manual will quote the exact NGK part number required....... Too bad you don't have the manual. But I would also investigate the sensors I mention in the previous reply. Some information on turbo Volvo spark plug problems According the above link, standed platinum plugs are not used on turbo Volvo's, perhaps the Sube has a similar problem...... Quote Link to comment Share on other sites More sharing options...
mops Posted November 27, 2003 Author Share Posted November 27, 2003 Thanks guiys heaps for very extensive and great input. Now, I do check my ECU often for error codes, and it's clean, i.e no errors (once i had an error when i forgot to plug in one of the pressure sensors almost ****ted myself when engine died in the middle of the highway ) anyways, I noticed strange blips and stuff in power output which would point to the throttle position sensor. I'll get some quotes today... thing is I dont want to spend $1000 for a handfull of new sensors (they do get quite expensive here in New Zealand). plugs are the ones all other JDM subaru use (forgot the exact model number), but they are iridium NGK and all other subbies in NZ use them. where in the engine bay will i find throttle position sensor and oxygene sensor ??? I will check out that PVC valve when i get home. thx in advance. Quote Link to comment Share on other sites More sharing options...
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