tvsubaru Posted December 4, 2015 Share Posted December 4, 2015 So I have been dealing with some detonation issues at idle with my car for a little while now. When the car is still warming up and i cum to a stop the first or second time after leaving my house, ill get a mild/rough shake at idle below 900 or so rpm. Once the engine is warmed up it runs fine. I went through the top end of my engine when I did head gaskets on the car over the summer. I finally did a compression check on the engine a few weeks ago; which I was afraid to do b/c of what I may find out. Despite my fears compression on all cylinders was good. All four were reading between 175 and 180 psig. I have no MILS on the dash either. Putting premium in helps a little with the issue. Talking to my instructor and a friend who builds performance engines I believe that I have narrowed it down to two things. Number 1 is I believe that it is a little to rich at a cold idle. To help address this, when I'm off for Christmas break I'm going to get it into the dealer for the ECM to be reprogrammed in accordance with Recall #WVU31. Secondly which brings me to the main purpose of this post is spark plug heat range. Currently I have a new Subaru ignition coil installed, NGK wires, and NGK 5464 (bkr5eix-11) plugs installed (and yes I gaped them to spec). The heat range on these plugs is a 5, and the wires are stupid low resistance compared to the stock ones. I'm going to try replacing the plugs with a lower heat range plug like a BKR6EIX-11 # 3764 plug. In NGK's system the higher the number the colder the plug is. The colder plug should help keep cylinder temperature down by pulling more heat from the cylinder, and the result should be a reduction in detonation. I'm thinking that one step colder should be enough unless anyone else thinks otherwise. And i did check the thread and reach on these plugs are the same, the heat range is the only difference. Link to comment Share on other sites More sharing options...
apexi Posted December 4, 2015 Share Posted December 4, 2015 I wouldn't do it. If you want to try a different plug, I'd try the stock fr5ap-11's. I wouldn't run a different heat range though. You shouldn't have had to adjust the gap on the 5464's, did it need to be adjusted? Sounds like something else is going on, the question is what. *One more thing I forgot to mention. Definitely have the dealer do any ecu updates before going to far with this, in my opinion. That'd be the first thing I would do. Link to comment Share on other sites More sharing options...
apexi Posted December 4, 2015 Share Posted December 4, 2015 I just looked over the "Software update for your transmission" thread and saw you were having some transmission issues as well. These issues you describe in this thread could be related to your transmission as well, as odd as that might sound. Your ATF level and condition might be playing a role in this issue, as well as any other transmission issues you're having. Another part of your transmission could be contributing as well, but I don't know enough about AT's to say which specifically. I'd check your ATF level sometime if you haven't already. Link to comment Share on other sites More sharing options...
tvsubaru Posted December 4, 2015 Author Share Posted December 4, 2015 I'll keep that in mind. But the stock plugs are going to be the same heat range. And I'm not going to have that much invested in trying those plugs. I don't remember the exact values on the gap for the spark plugs but they were off. In the Subaru service manual it lists a range for the gap and I put it right in the middle of that range. What makes this all weirder is that my gas mileage has actually gone up all the while that this has been going on. My commute now consists of more freeway driving but the average mpg on the dash display used to be fixed on 23.4 mpg and now it is usually reading more around 24.9 and i have seen it as high as 25.5 mpg for a brief moment. Link to comment Share on other sites More sharing options...
tvsubaru Posted December 4, 2015 Author Share Posted December 4, 2015 Oh, transmission fluid level is fine. First thing that i did when i purchased the car about a year and a half ago was a full fluid change. I changed the transmission fluid and the spin on filter. I have an occasional hard shift when I take a turn real hard. Although I have checked the fluid level recently (and it was fine) that could be more of a fluid shifting away from the sump in the pan kind of thing. Other than that I don't have any problems with the transmission. Now it will skip 2nd gear in manual transmission mode occasionally;but i'm far from the only person on this forum that has that problem. Link to comment Share on other sites More sharing options...
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