GeneralDisorder Posted July 19, 2012 Share Posted July 19, 2012 EJ22E, '97 Legacy, #4 cylinder has burned a valve.... again. This car had a burned #4 exhaust valve about 2 years ago at 199k. I actually mentioned it in this thread: http://www.ultimatesubaru.org/forum/showthread.php?t=116101&highlight=burned+valve The valves were done by a reputable head shop, the injectors were replaced along with the fuel filter, and the valve clearances were set by yours truely. The going theory being that the valve clearances were not checked at 105k and this contributed to a burned valve at 199k The car now has 218k on it and suddenly burned a valve again on the same cylinder. 30 psi on the #4. So now I'm considering checking the injector driver circuits on the ECU and possibly just replacing the ECU entirely after I fix the valve for the second time. Has anyone seen this and found a definite solution? I've got a neighbor a few streets over with a '92 sedan that's been through 3 cylinder heads.... I've heard of this happening on hydro lifter engines so it's got to be something to do with the fuel system or the intake leaning out a specific cylinder. Valve clearances are not the problem on the hydro lifter engines and clearly not the problem with this '97 either. ~19k miles for the problem to return..... that's not something I want to happen again so I need to find the problem once and for all this time around. GD Quote Link to comment Share on other sites More sharing options...
Crazyeights Posted July 19, 2012 Share Posted July 19, 2012 140k on my '93 EJ22 with hydro lifters and it had 5 exhaust valves burnt beyond being able to be ground. I had the heads done and it runs great. I never did find a cause though Hmm....... Quote Link to comment Share on other sites More sharing options...
Ricearu Posted July 19, 2012 Share Posted July 19, 2012 (edited) Perhaps, one of the lifters is hanging up and holding one of the exhaust valves open slightly during combustion, eroding the valve seat until compression is gone? Stupid chinese scooters I work on do this all the time as they require 1500 mile valve adjustments and people run them until there is no compression left. Edited July 19, 2012 by Ricearu Quote Link to comment Share on other sites More sharing options...
ivans imports Posted July 19, 2012 Share Posted July 19, 2012 rings its burning oil on #4 the burnt oil builds up and creates carbon on valve that gets hot and overheats the valve most burnt valve engines i see have been burning oil on that hole for a while change rings and problem will go away Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted July 19, 2012 Author Share Posted July 19, 2012 Intersting theory Ivan. I think you are probably right that it's the short block that's causing these failures. It's the only thing that is consistent with all the stories of repeat burned exhaust valves that I've heard. In almost all cases changing the entire engine fixes the problem. I should also mention that this car endures a very short 10 minute commute 5 days a week - it spent about 60k miles before the first valve job doing this commute and other driving. As well as the 19k before the second burnt valve. It doesn't get fully warmed up when doing this and I feel like that is a contributing factor.... They change the oil every 2500 with synthetic. They had noticed increased consumption due to the short drive cycles but consumption was not bad on longer trips. Also - I've been told by my tuner that the #4 runs the hottest due to differences in the timing and fuel for that cylinder. He said it has to do with it's proximity to the knock sensor and Subaru trying to adjust out noise in the signal from the sensor by adjusting the #4 to quiet down background noise. GD Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted July 19, 2012 Share Posted July 19, 2012 I lost a couple exhaust valves on a 92 EJ22 to oil burning. Both valves looked like they had a cutting torch taken to them, and they both happened on the same cylinder. I chucked a used 95 head on it and that lasted 6 months before it's valve burned. Oil consumption would go through the roof running it with the burnt valve. I'd unplug the injector, but it was using a quart every 400 miles. There was oil residue all over the back of the car. I drove it like that for about a month each time, the second time I chucked in a used engine out of a postal wagon and it didn't have any issues. It could be an injector issue, I put the postal engine in fully dressed. Same computer and firewall harness though. I beat the hell out of that engine and it never flinched. Quote Link to comment Share on other sites More sharing options...
nipper Posted July 19, 2012 Share Posted July 19, 2012 rings its burning oil on #4 the burnt oil builds up and creates carbon on valve that gets hot and overheats the valve most burnt valve engines i see have been burning oil on that hole for a while change rings and problem will go away What he said Quote Link to comment Share on other sites More sharing options...
bstone Posted July 20, 2012 Share Posted July 20, 2012 You should ask GeneralDisorder, he's the exper......aaahhhhhh crap....nevermind. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted July 20, 2012 Author Share Posted July 20, 2012 The owner has decided to replace the engine. At 212k with the abuse it's taken on her commute and the oil consumption.... we agreed that it's probably best to just find a lower mileage replacement engine and swap it out - along with a block heater, oil pan heater, and remote start. This way it can be warmed up for 15 minutes prior to her drive and hopefully negate the effects of her short commute. GD Quote Link to comment Share on other sites More sharing options...
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