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Well...figured out my rough idle issue. Low compression in #4.
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07-09-2023, 12:21 PM | #1 |
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Well...figured out my rough idle issue. Low compression in #4.
Well, I finally got around to doing some more troubleshooting on my rough idle issue that popped up a while back. Did a compression test...all are 160-165psi.....except #4. It's only 55psi 😕 what's the best way to figure out if it's a ring/piston issue...or possibly a valve/spring issue? The plug for #4 looks pretty dark and sooty.
I guess that either way, the head needs to come off first. Right?
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2007 335i, BMS DCI, BMS Chargepipe w/Tial BOV, ARM Catless Downpipes, silicone inlets, Bilstein B12 Prokit Suspension, Whiteline subframe bushings, Front/Rear M3 control arms, G-Plus FMIC, Stage 2 LPFP, Custom E40 tune by Justin (V8Bait), xHP stage 3 transmission flash, RB Two Turbos....10.90 @ 128mph
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07-09-2023, 02:24 PM | #2 |
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Dumped a little oil into the cylinder, psi jumped up to 120. Guess it's definitely broke ring or piston ringland.
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E93Seattle (Racerbruce)806.00 |
07-09-2023, 09:34 PM | #4 | |
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The narrow gap on the rings is what actually breaks the lands, so I'm wondering if the stock pistons might be fine as long as I gap the new rings a little bigger. It's not like I'm running crazy amounts of boost (25psi). I guess I need to get the motor out first and open it up...see what I find. |
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07-10-2023, 03:26 AM | #5 | |
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Do you have to hold the throttle body open when doing a compression test on N54? If so how? Last edited by suspect; 07-10-2023 at 04:33 AM.. |
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07-10-2023, 05:55 AM | #6 | |
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As far as the compression test....nope, just crank it enough times until the needle on the gauge finally stops climbing. It was pretty easy...just make sure you unplug all the connections on the injectors. I have a bore scope....thought about putting it through the spark plug hole to see what I can see in that cylinder. |
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07-10-2023, 07:17 AM | #7 | |
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Looks like compression test is next on the list. Was also thinking of doing walnut blast as I don’t think it’s been done. What adapter do you use for compression tester? |
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07-10-2023, 09:22 AM | #8 | |
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I just felt that odd idle that felt slightly rough...that it. My compressor tester kit came with several difference spark plug thread adapters...I just picked the one that fit
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2007 335i, BMS DCI, BMS Chargepipe w/Tial BOV, ARM Catless Downpipes, silicone inlets, Bilstein B12 Prokit Suspension, Whiteline subframe bushings, Front/Rear M3 control arms, G-Plus FMIC, Stage 2 LPFP, Custom E40 tune by Justin (V8Bait), xHP stage 3 transmission flash, RB Two Turbos....10.90 @ 128mph
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07-10-2023, 12:54 PM | #10 | |
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07-10-2023, 05:05 PM | #12 | |
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I think the thread is M12. |
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07-10-2023, 05:06 PM | #13 |
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From what I've found....broken ringlands is a pretty common issue with these motors. Could have been an injector going bad causing a lean condition, could have been bad luck, could have been too much boost? Could have been just the fact that the OEM cast pistons can't handle much more than 600hp? Hard to tell really........
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07-10-2023, 05:06 PM | #14 |
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07-10-2023, 05:08 PM | #15 | |
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07-11-2023, 06:56 AM | #16 |
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damn, those engine got 99 problems , but internals shouldn't be one.
twins are hard on the engine, more torque at low rpm. Looking for a 6062 gen2 to to begins. I want to prevent any internal failure if possible. Ill recheck all injectors adaptation. I have 3x index 12 and the 3 others are stock. |
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07-11-2023, 07:07 AM | #17 | |
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I think at this point, there are enough people out there I've seen who are making similar power (close to 600) who have had the same issue. I think once you push these motors with the stock cast pistons over 600hp and 25+psi boost, it's just a matter of time. I'm assuming that if I rebuilt it with forged pistons and rods....it should be pretty reliable at the current power it's making?
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2007 335i, BMS DCI, BMS Chargepipe w/Tial BOV, ARM Catless Downpipes, silicone inlets, Bilstein B12 Prokit Suspension, Whiteline subframe bushings, Front/Rear M3 control arms, G-Plus FMIC, Stage 2 LPFP, Custom E40 tune by Justin (V8Bait), xHP stage 3 transmission flash, RB Two Turbos....10.90 @ 128mph
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07-11-2023, 07:10 AM | #18 | |
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07-11-2023, 09:42 AM | #19 |
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A failing injector seems pretty likely to be the culprit to me as going lean under high boost produces an insane amount of heat in the cylinder if that were to ever happen. You already know you had a leaky one on that cylinder so seems quite likely that caused it. The O2 sensors only measure across the whole bank so one could easily go a bit lean without throwing your AFR readings off much in a log, especially if the other cylinders compensated.
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07-11-2023, 10:37 AM | #20 | ||
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If you check audi world, on unitronic webpage, you dont see any doubling power on stock internals. Quote:
is it because it's been tested and has no effect? or nobody tried. very popular on audi/vw engines. something like this (an no this is not for space in that case, but really to avoid O2 get destroyed or check engine code) |
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07-11-2023, 10:51 AM | #21 | |
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07-11-2023, 10:57 AM | #22 |
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Sorry IQ! Keep us posted on what your plans are.
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