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Please help diagnose pinging/detonation

Old 12-15-2015, 01:01 PM
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Ok guys, this is getting weird/frustrating. Took it back to the dealer, and what they are telling me makes no sense at all. First off, they are saying that compression is in the 9s, at 250 rpm, highest values are 9.8 and 9.5. That alone is unbelievable. Second, they are still insisting on the intake manifold, saying its carbon in the runners making that noise... Does the 2nd video I linked above sounds like freaking carbon in the intake??

Apparently a new LIM costs $2772 USD and there is only 1 to be found in the entire country. That and pulling the engine and for that amount of $$ I might as well get it rebuilt. Or they can replace the SSV alone but are not guaranteeing it will fix the problem. But the real issue is they are refusing to acknowledge the pinging/knocking. I think I'm going to go there tomorrow morning and insist the tech goes for a drive with me.
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Old 12-15-2015, 01:04 PM
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Decarb??
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Old 12-15-2015, 01:08 PM
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Already tried that. Didn't make too much of a difference.
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Old 12-15-2015, 01:17 PM
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Please help diagnose pinging/detonation

Boroscope to see how your rotors look?

Double check your plugs are not reversed. And wires are in the correct order.

Sorry I'm in a customs line and can't easily go back to see what's been done. I'm working from memory.
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Old 12-15-2015, 01:27 PM
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That dealer is just making **** up as they go along. Have you verified your pinging VIA a datalog?
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Old 12-15-2015, 01:59 PM
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Would I look for it to pull timing or some other sign? It didn't seem to be pulling timing in the log I posted on the previous page. My only "real" verification is that if I run straight 100 octane race gas it does not do it. Also that it is sensitive to the engine temperature.
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Old 12-15-2015, 02:21 PM
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Is there any may you can just log AFR and RPM? That log is tough to read but based on what I see, it should not be detonating. It could possibly be preignition.

Last edited by 9krpmrx8; 12-15-2015 at 02:24 PM.
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Old 12-15-2015, 02:25 PM
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Have you pulled the plugs and looked at them? Also, have you checked the cat converter?
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Old 12-15-2015, 02:27 PM
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Please help diagnose pinging/detonation

Hence why I asked about decarb ing and 7 heat plugs in the trailing position. Or possibly swapped leading and trailing wires.
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Old 01-24-2016, 09:47 AM
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I've been eyeing this thread from the start. Didn't say anything because I don't know anything about this matter. So, any updates? Did you get it fixed? I'd love to know what caused all this.
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Old 02-11-2016, 03:46 AM
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Hey guys,

I've been really busy but I recently spent some quality time under the car and I owe you an update. First off, here are the compression numbers form the last visit to the dealer:

Rotor 1: 8.6, 8.8, 8.7 (@250 rpm)
Rotor 2: 8.8, 9.0, 9.2 (@250 rpm)

This is a re-man with 12k miles on it. Seems a bit too good to be true, but it does make me feel better. Or maybe those numbers are total BS and I'm just sticking my head in the sand. At least now that the warranty is out on this engine, I feel free and never have to deal with dealer BS again.

During the past several weeks, it has gotten colder and it started misfiring more on cold starts, to the point of setting P0300 and pending P0301 every few drive cycles. However, it did not misfire when warm or when under load. I thought, "aha, maybe I have an ignition problem". I checked that the right plugs are in the leading and trailing positions, and connected to the correct coils. I tested the coils and wires with an HEI ignition tester, and all of them tested good. (Age of coils & wires - 13k miles). I also pulled the plugs. They looked fine to me (layman), but I'd be interested to see what you think. The plugs shown have 4,000 miles on them. It looked like the tech that re-installed the plugs used oil on the threads, some of it got on the tip of the plug when removing. I blasted it off with MAF cleaner before re-installation.

Rotor 1 leading:




Rotor 1 trailing:



Rotor 2 leading:



Rotor 2 trailing:



Incidentally, after re-installing the plugs, the cold start misfire is gone. But now my idle LTFT is up to 16%. Today I checked the torque on the plugs, and all of them were tight.

So in summary, I seem to have established that I have good compression and my ignition is healthy. Today the temperature was 80 F outside, and the detonation was back in full force when climbing uphill. In my mind there are 3 things left to check, before starting on the road to pulling the engine: mystery vacuum leak (but it is not showing lean when the detonation happens), incorrect fuel pressure and clogging of the cat (though I fail to see how it would cause detonation, but not obvious bogging/power loss). As always, I appreciate your feedback!

Last edited by Jastreb; 02-11-2016 at 04:00 AM.
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Old 02-23-2016, 08:14 PM
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Today's update:

Took a look inside the catalytic converter. I was surprised how good it looked for having 100k miles on it. It looked almost new, with no carbon that I could see readily. The matrix looked perfect. So I think together with my prior ignition inspection, this rules out a faulty ignition.

Also had the fuel pressure tested. The fuel pressure at idle was 59 psi (a bit low but within 54.4-65.2 psi specification) , and the fuel hold pressure was 29 psi (per specification). So the fuel pump isn't obviously the problem... but could it be not delivering the required pressure at higher load/ after extended operation? The mechanic seems to think my fuel trim behavior is consistent with a failing pump, but if the detonation is caused by a fuel delivery problem, I would expect it to be running lean when it happens, and it's not running lean. The only time I see it running lean is at idle once warmed up.

So the only other possibilities remaining seem to be weird vacuum leak that only affects one of the rotors, as previously mentioned, or carbon buildup that can only be cured by a re-build I am willing to try a new fuel pump before pulling the engine, but I am not hopeful it will help.

Last edited by Jastreb; 02-23-2016 at 08:36 PM.
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Old 05-05-2016, 06:49 PM
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May 5th Update

Time for another update. Took it to Neptune Speed in Huntington Beach. The master mechanic believes there is a leak at the LIM gasket. He took off the upper manifold and pressure tested it, and there were no leaks there, which leaves only the LIM. I think this is the diagnosis most consistent with my low MAF reading at idle, the fluctuating idle under electrical load, the idle fuel trims that will sometimes go up to 14-16% when engine bay is heat soaked, but then go back down a day later... Kudos to Brettus for putting forth the theory months ago.

EDITED after picking up car

Unfortunately, this is the most expensive fix short of an engine rebuild, as it does require dropping the engine. I was ready to set up to do this and fork over the money, but Yoshi-san does not believe that light detonation is harmful to the engine, based on reports of similar problems in JDM Series II RX-8s, and that Mazda basically said there is no fix for it. I might have been freaking out too much over this. Can I justify the $1200 cost of dropping the engine to replace the LIM gasket if there's no significant harm being done in the current condition? Probably not right now, as long as it doesn't get worse... A more economical approach may be to improve my detonation margin by making sure my water and oil temps are well managed, maybe throw a new front O2 sensor at it (still on the original @ 118k), maybe BHR ignition would help?

Last edited by Jastreb; 05-06-2016 at 11:33 PM.
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Old 06-16-2016, 06:26 PM
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So on the way to work today, was getting MIAC sound, except this time it was between 5500-6500 rpm and sounded different. Like a metallic flutter, where the can with the marbles is shaken with a regular interval. Seemed very much rpm dependent, and would stop by 6500 rpm. I could accelerate through it in 2nd, 3rd and 4th gear. In 5th gear it bogged, and I noticed flashing CEL (misfire). Have pending codes P0302, P2004, P2005. (Yes I checked what they mean, both APVs stuck open.) Next drive cycle P2004 & P2005 cleared, and I could not get the problem to re-occur in 2nd -4th gears.

Not entirely sure what to make of this: if this is an unrelated problem, another consequence of LIM/LIM gasket leak, or actually points to root cause. 8k miles ago, coils & wires tested good, plugs and cat looked good as well, but I think I have noticed noise of this nature before and just thought it was more detonation.

Last edited by Jastreb; 06-16-2016 at 09:34 PM.
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