xt2005bonbon Posted August 10, 2015 Share Posted August 10, 2015 This thread could be really short if the answers to my questions are easily answered... Assumption: injectors, spark plug, coil pack, intake manifold gasket are all just fine. Also, only one cylinder is assumed to be misfiring. scenario 1: misfire only occurs at idle with a cold engine. possible cause: broken ringland. Please add or correct. scenario 2: misfire only occurs at idle with a warm engine. possible cause I can think of: valve clearance issues (I personally experienced this). Please add or correct. scenario 3 (don't know if this is possible): misfire occurs at any rpm range with a cold engine. Causes? scenario 4 (don't know if this is possible either): misfire occurs at any rpm range with a warm engine only. causes? scenario 5: misfire occurs at any rpm range and any operating temps. causes? burnt valve/ very bad ringland Did I miss another scenario? Bonus question: what does the 'roughness count' parameter provided by the ecu really report? I understand it is a count, but a count of a number of misfire per what?, per second or per ---- fill the blank please. Link to comment Share on other sites More sharing options...
xt2005bonbon Posted August 12, 2015 Author Share Posted August 12, 2015 Bump. Surprised no one chimed in. Link to comment Share on other sites More sharing options...
heiche Posted August 12, 2015 Share Posted August 12, 2015 I had "scenario 2" exactly as you described it. Adjusting valve clearances cured it. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
xt2005bonbon Posted August 12, 2015 Author Share Posted August 12, 2015 I had "scenario 2" exactly as you described it. Adjusting valve clearances cured it. As you know, same thing happened to my 05. Adjusting valve clearances also cured it. My 06 is currently suffering from scenario 1... But I have not checked the intake manifold gasket yet. Even though I am not burning oil and the car runs pretty good (no rough idle), I have a feeling it could be rings unfortunately . What else could it be really? Anyway, you're pretty knowledgeable. Would you add any other causes to the other scenarios? Link to comment Share on other sites More sharing options...
heiche Posted August 12, 2015 Share Posted August 12, 2015 Scenario 1 can definitely be IM gaskets too, as you suggested. Especially if they are original (before the taller redesign). Might be a good edit to post #1. This being said, on your 06, I'm sure IM gaskets would be easier to try than #ansb Those can definitely start out leaking, then as the engine begins to warm up, they expand and seal properly until next time. Another thing to consider is whether the misfire is just one cylinder, all cylinders, or somewhere in between. If the misfire is spread out across all cylinders, then it's probably something in common to all cyls, like large vac/boost leak, fuel pressure issue, afr sensor, maf, etc. If it's just one cylinder, then you tend to try swapping everything external to that one cylinder, like coil/plug/injector, and only then start considering internal issues like valve clearance, burnt valve, ringlands, etc. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
xt2005bonbon Posted August 13, 2015 Author Share Posted August 13, 2015 Scenario 1 can definitely be IM gaskets too, as you suggested. Especially if they are original (before the taller redesign). Might be a good edit to post #1. This being said, on your 06, I'm sure IM gaskets would be easier to try than #ansb Those can definitely start out leaking, then as the engine begins to warm up, they expand and seal properly until next time. Another thing to consider is whether the misfire is just one cylinder, all cylinders, or somewhere in between. If the misfire is spread out across all cylinders, then it's probably something in common to all cyls, like large vac/boost leak, fuel pressure issue, afr sensor, maf, etc. If it's just one cylinder, then you tend to try swapping everything external to that one cylinder, like coil/plug/injector, and only then start considering internal issues like valve clearance, burnt valve, ringlands, etc. Actually, I put in the assumptions at the beginning that IM gaskets are supposed to be OK. I will also add in the assumption that only one cylinder is misfiring. Link to comment Share on other sites More sharing options...
jhough77 Posted August 15, 2015 Share Posted August 15, 2015 This being said, on your 06, I'm sure IM gaskets would be easier to try than #ansb Those can definitely start out leaking, then as the engine begins to warm up, they expand and seal properly until next time. Another thing to consider is whether the misfire is just one cylinder, all cylinders, or somewhere in between. If the misfire is spread out across all cylinders, then it's probably something in common to all cyls, like large vac/boost leak, fuel pressure issue, afr sensor, maf, etc. If it's just one cylinder, then you tend to try swapping everything external to that one cylinder, like coil/plug/injector, and only then start considering internal issues like valve clearance, burnt valve, ringlands, etc. I have an 06 with misfires spread out across all cylinders. The shop has ruled out the large vac/boost leak (there was a small one that has been addressed but didn't solve misfires problem), the fuel pressure issue, the MAF sensor wasn't damaged, and afr was also ruled out. Any other culprits you might have heard of? I have posted in a couple different places but you seem to be quite knowledgeable as mentioned above. Link to comment Share on other sites More sharing options...
heiche Posted August 15, 2015 Share Posted August 15, 2015 Misfires spread out across all cylinders can happen for a lot of different reasons. Sounds like your shop definitely has made a good effort so far. When they say the MAF sensor wasn't damaged, did they actually swap it with another known good unit as a test? If they really did rule everything else out (boost leak, fuel pressure, etc) then possibly as you mentioned in a different post, a clogged cat can definitely cause these types of issues. Does your car still have a catted UP? If it does, it should be replaced with a straight pipe (even subaru did in later models). That cat can break apart and kill the turbo with chunks of itself. The main cat in the DP could be suspect too, so you might consider swapping that out with another. Sometimes with a bad cat you can hear a rattling/clinking noise coming from it when the engine is idling. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
jhough77 Posted August 19, 2015 Share Posted August 19, 2015 Misfires spread out across all cylinders can happen for a lot of different reasons. Sounds like your shop definitely has made a good effort so far. When they say the MAF sensor wasn't damaged, did they actually swap it with another known good unit as a test? If they really did rule everything else out (boost leak, fuel pressure, etc) then possibly as you mentioned in a different post, a clogged cat can definitely cause these types of issues. Does your car still have a catted UP? If it does, it should be replaced with a straight pipe (even subaru did in later models). That cat can break apart and kill the turbo with chunks of itself. The main cat in the DP could be suspect too, so you might consider swapping that out with another. Sometimes with a bad cat you can hear a rattling/clinking noise coming from it when the engine is idling. They did not swap the MAF sensor. But yes it is bone stock so I believe it should still have the catted UP. However I'm saving up some $$ now so that I can start doing some light mods and I think the exhaust could be a good place to start. I'm getting a diag from a 3rd shop Monday and if it is in fact the CC, would I be better off going with an aftermarket system that has no CC OR just replacing the CC? p.s Sorry if i'm threadjacking, not my intention I just need a solution at this point. Link to comment Share on other sites More sharing options...
heiche Posted August 19, 2015 Share Posted August 19, 2015 The UP (uppipe) should be replaced with a catless straight-through design, whether this is your cars issue or not. The DP (downpipe) can be replaced with a new performance catted piece, either for more power, or if your cat has internal damage. MAF could also be a culprit. Front AFR sensor could also be a culprit. Other stuff too. Hopefully your 3rd shop can identify the issue. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
xt2005bonbon Posted May 22, 2016 Author Share Posted May 22, 2016 Reviving this thread... Is it possible that a 'bad' valve causes misfires in a given cylinder only when cold and while idling? In my head, I don't see how this can be possible. But maybe somebody can answer this question? heiche? Link to comment Share on other sites More sharing options...
heiche Posted May 22, 2016 Share Posted May 22, 2016 It's been my experience that a bad valve (defined in this case as slightly distorted as to cause too tight of a clearance) has caused a misfire only when hot. Then that misfire usually is most obvious at idle - it gets rough, and misfire counts start to rise. Start it up the next morning and it idles fine when cold. Buuut I'm just one guy with one experience. ymmv. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
bigBADbenny Posted May 22, 2016 Share Posted May 22, 2016 ^I recently refurbed a set of '08 heads (for my spare engine) and sure enough 1 valve was a coupla thou too tight. My rebuilder took a little from the rear of the valve and all good. I had misfire on the cylinder nearest the turbo, tuned for vf46, 3"tbe, 3port, dw65c. The car bucked and stumbled... Misfire logged via BtSsm at 10psi and up in S# 15psi mode, 3rd gear pull, 6mt, 180mi. Replaced that coilpack (which looked fine) with a low mi s/h item and applied the twist pin trick (w/pliers, 5-10') to promote continuity on all coilpack plugs. Finally, check and reco or upgrade the ground straps from the heads to the chassis rails. Log, diagnose, refurb or upgrade, repeat Link to comment Share on other sites More sharing options...
xt2005bonbon Posted May 23, 2016 Author Share Posted May 23, 2016 so do you guys also believe that is impossible for a valve to throw a misfire only at cold idle, provided everything else is in good working order? Link to comment Share on other sites More sharing options...
Wagonation Posted May 23, 2016 Share Posted May 23, 2016 I had a warm idle misfire code 302 that turned out to be a vacuum leak. No problems since. Link to comment Share on other sites More sharing options...
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