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      09-19-2018, 04:58 PM   #23
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Originally Posted by jcolley View Post
Typically the engines I've seen the exhibit this have a fair amount of carbon deposits on the piston crowns and exhaust valve faces. The intake valve faces also to a lesser extent.

The carbon deposits hold heat and can create hot spots, so that on compression of the fuel air charge, it ignites prior to the spark event.

Most often, using a high quality 93 octane or higher (Shell seems to do well at this) will over a few tanks remove some of the deposits and improve things. Sea Foam in the intake may be of use here as well.

Test the theory with a cheap Harbor Freight borescope camera and 90 degree attachment down the spark plug hole and look at the piston crowns and valve faces.

I suspect oils which are noted having lower consumption also reduce the carbon build up as well.
Thank you!!

I will try some different gas and check with a scope.

Running with a tune would just make this a little worse because the tune is a bit more aggressive?

Cheers,
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      09-19-2018, 05:07 PM   #24
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sounds like if a tune is not adjusting to lower quality gas by pulling timing and a stock tune is, wouldn't that mean knock sensitivity is being reduced in the tune? That also makes it less safe, and i'd be very skeptical running that tune if that is the case.
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      09-19-2018, 06:34 PM   #25
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Quote:
Originally Posted by tdott View Post
sounds like if a tune is not adjusting to lower quality gas by pulling timing and a stock tune is, wouldn't that mean knock sensitivity is being reduced in the tune? That also makes it less safe, and i'd be very skeptical running that tune if that is the case.
That depends. Ionic current sensing is only capable of detecting the timing of a combustion event and pressure spike/reverberation (knock) *after* the coil is fired. As soon as the dwell signal is removed, the coil fires, and the mss60 switches the control line over to "monitor" by applying constant voltage to the plug electrode.

So, if the knock is a result of pre-ignition, by definition, the DME can not detect nor correct for it. Additionally, since it's *pre*ignition, pulling timing won't make a difference anyway.

Now, there some other maps than can be adjusted, that can feed into the conditions which set a CC with heavy carbon deposition up for pre-ignition to occur, and those are often modified without much understanding of what they do. There are also differences in some of those maps from one OEM calibration file to another as well as the for fuel quality. Along with knowing what program version (241, etc), it's good to know what OEM calibration your tune is based off of. I suspect a lot of tuners don't actually modify the base file that should be in your car or was read from your car, but copy and send one from a stash of already modified files.
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      09-19-2018, 07:51 PM   #26
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OP, how many miles on the current ignition coils?
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      09-19-2018, 08:05 PM   #27
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Quote:
Originally Posted by Scharbag View Post
I have looked about and have had a bit of a hard time finding info about a noise I am getting at low RPM when I accelerate hard (lug the engine). I think I found a few threads that imply that this can cause some strange noises. Was hoping for some more information.

So my problem is pre-detonation. It is strange because if I run the factory 241 software, the problem goes away. If I try to run the Alpine tune from Alex, I get nasty pre-det at low RPM and some pre-det at higher RPM when accelerating hard.

My plugs all look really good. The only strange thing I have on my car are the Dinan throttle-bodies that the previous owner installed. Intake is a Dinan filter assembly so that really should not change much.

Thanks for the help and I will try to get a video at some point.

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Hi. Have you ruled out an exhaust leak? Might be worth to have a smoke test....coudl be a pinhole leak on the clamps.
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      09-19-2018, 10:10 PM   #28
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Originally Posted by bvrider1 View Post
OP, how many miles on the current ignition coils?
Coils are original, 44,000KM.

Only 94 octane I can get here is Husky. So, I have a full tank of Husky 94, with a can of SeaFoam in there. Hope to have a buddy help me put a can of SeaFoam through the intake in the next couple days. Then I will do some more testing with the tune.

Cheers and thank you for all the help. This forum rocks!!
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      09-20-2018, 06:50 PM   #29
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How about don't lug the engine......... just a thought.

Engines designed to make peak power at 8k+ rpm's are not designed to produce alot of torque low in the rpm range. Try driving around in a lower gear for lower speeds.
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      09-20-2018, 07:00 PM   #30
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I had the same issue and the car was not enjoying driving it. The more you floor and pre-detonation starts and finally it threw a code and went to limp mode. I suspected it to be ignition coil because the code came from cylinder 2. When I removed the spark plugs were bad and especially on cylinder 2 they were touching through carbon build up. New plugs and Liqui Moly fuel system cleaner and RON98 fixed the problem. The cars in now like new - driving experience is like day and night.
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      09-20-2018, 08:20 PM   #31
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Quote:
Originally Posted by Fubar_M3 View Post
How about don't lug the engine......... just a thought.

Engines designed to make peak power at 8k+ rpm's are not designed to produce alot of torque low in the rpm range. Try driving around in a lower gear for lower speeds.
That's the equivalent of saying "Hey Doc, my neck hurts when I turn this way" and being told "Well, don't turn it that way."

True, peak BSFC won't be found when lugging, but max fuel economy is. If he hadn't, he wouldn't have heard the sound and been warned of a potentially problematic internal condition in the engine. Carbon deposits reduce heat transfer to the piston and valves and create hotspots in the engine as well as reducing air flow on the intake stroke. This last point is problematic as the DME runs open loop fueling on full throttle and relies on the VE map entirely to set fueling properly.

What's interesting is that one DME calibration may allow it to happen and one won't.
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      09-20-2018, 08:58 PM   #32
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Quote:
Originally Posted by jcolley View Post
Quote:
Originally Posted by Fubar_M3 View Post
How about don't lug the engine......... just a thought.

Engines designed to make peak power at 8k+ rpm's are not designed to produce alot of torque low in the rpm range. Try driving around in a lower gear for lower speeds.
That's the equivalent of saying "Hey Doc, my neck hurts when I turn this way" and being told "Well, don't turn it that way."

True, peak BSFC won't be found when lugging, but max fuel economy is. If he hadn't, he wouldn't have heard the sound and been warned of a potentially problematic internal condition in the engine. Carbon deposits reduce heat transfer to the piston and valves and create hotspots in the engine as well as reducing air flow on the intake stroke. This last point is problematic as the DME runs open loop fueling on full throttle and relies on the VE map entirely to set fueling properly.

What's interesting is that one DME calibration may allow it to happen and one won't.
No, it's more like driving the car the way it was engineered.

I agree to the point the preignition is bad and fixable. But lugging the engine is just bad practice.
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      09-20-2018, 09:42 PM   #33
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Quote:
Originally Posted by Fubar_M3 View Post
How about don't lug the engine......... just a thought.

Engines designed to make peak power at 8k+ rpm's are not designed to produce alot of torque low in the rpm range. Try driving around in a lower gear for lower speeds.


I do not choose to lug, but when I make a right hand turn on the city, I typically stay in second gear. The engine may not perform well, but it should not ping...
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      09-21-2018, 09:27 AM   #34
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Quote:
Originally Posted by Scharbag View Post
Filter is pretty clean. The plugs have about 13,000KM on them.

:|

Thanks for the help, keep the ideas rollin

Question: would O2 sensors cause pre-det issues and not throw codes?
Interested in your comment regarding the O2 sensors. I am getting a similar issue, a few months ago I was getting an error code for increased air plausibility, 2B5A I believe. Ended up cleaning the sensor on the air intake attached to the plenum, cleared the code and hasn't come back yet. But like you I am still getting some fluttering/hesitation in the same rev range. I was able to set parameters on carly to check my post cat O2 sensors, but didn't have an option for the pre cat sensors.

I changed my spark plugs recently, no plugs showed excess signs of wear. My next move is O2 sensors, then possibly a fuel system cleaner as I don't trust the NJ gas. I only put 93 in my car.

Keep me posted if you find a resolution.
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      09-21-2018, 09:46 AM   #35
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This happens sometimes on mine, it's pretty inconsistent. Sometimes you can just crank along at low rpm and load it up and it doesn't care, sometimes you get a ping or two, and it doesn't seem to amtter how warm or cold out it is. One thing I've noticed is that as soon as you back out of the pedal from "WFO" or "requesting WFO" or whatever it's actually giving you when you floor it, even just a little, it goes away. When we ask for wide open throttle at low rpm, are we actually getting it or are the throttles partially shut with the stock tune, and open all the way with aftermarket tunes? Would it even matter when the car's still ramping up to peak torque down there in the 2-3k range?

I scoped my pistons last time I did plugs at 104,000 or so, and everything looks pretty good though I didn't look at the valves and couldn't see the piston edges very well, so that's not all that conclusive one way or another. It hasn't gotten appreciably worse over the life of the car though. Evolve Tune, on the car for like 100,000 miles. It's done this for as long as I can remember, again intermittently, regardless of whether I had flashed back to stock etc. I'm almost always filling with BP 93. Fwiw, I can't recall this ever happening in 2nd gear. Usually 3rd 4th 5th at city speeds, rolling up to intersections and leaving in gear as lights change, that kind of thing. Maybe I'm just not noticing it because it's a transient and the car moves through the revs quickly in 2nd, but it seems to pull cleanly from low rpm in 2nd every time

Interesting thread
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      09-21-2018, 09:49 AM   #36
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Quote:
Originally Posted by Richbot View Post
This happens sometimes on mine, it's pretty inconsistent. One thing I've noticed is that as soon as you back out of the pedal from "WFO" or "requesting WFO" or whatever it's actually giving you down there, even by a couple of %, it goes away.

I scoped my pistons last time I did plugs and everything looks pretty good though I didn't look at the valves.

Evolve Tune, on the car for like 100,000 miles
WFO is an unfamiliar acronym to some of us.
What does it stand for?
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      09-21-2018, 10:01 AM   #37
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Wide swear word open
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      09-21-2018, 11:17 AM   #38
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Just ran a can of sea foam through the intake. Pita to hold the car at 1800rpm without help. Thankfully I have some construction clamps that worked!!

I will re-flash to 91 octane stage 1 soon. Going to run a full tank of 94 with sea foam to give it a good chance to clean the tops of the chambers. Here is hoping.

Cheers,
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      09-21-2018, 06:10 PM   #39
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And then this happens. FFS.
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      09-21-2018, 06:47 PM   #40
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Good grief And there goes summer!
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      09-21-2018, 07:57 PM   #41
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Quote:
Originally Posted by Scharbag View Post
Just ran a can of sea foam through the intake. Pita to hold the car at 1800rpm without help. Thankfully I have some construction clamps that worked!!

I will re-flash to 91 octane stage 1 soon. Going to run a full tank of 94 with sea foam to give it a good chance to clean the tops of the chambers. Here is hoping.

Cheers,
I can relate to this, as ever since this started showing on my S65 50k-ish miles ago I have been trouble shooting on and off to no real success. new spark plugs, new coils (individual cylinder and all 8), low fuel pressure sensor, upgraded OE software, aftermarket software, injector/fuel system cleaner, thought I tried them all. What I felt is these things provide temporary "relief" to the issue, but never fully "solve" the problem at root. The car would run smoother with each of these parts change/software flash, but eventually the knocking or low rpm pre-det returns. I actually get the knocking at high rpm as well sometimes, during certain throttle angles

I will say tho, putting in brand new coil packs all around and running Chevron Techron Concentrate Plus (in separate instances, not done at the same time) made the most dramatic improvement, especially the former as it instantly restored the urge/eagerness to rev on my aging S65, it was to the point where I could dial back my throttle input a little to achieve the same, or if not stronger, pace of acceleration as before. And the latter allowed the engine to run notably smoother and quieted down the (old) injectors. But nothing lasted, the det always slowly creeps back.

Like some of the guys here have mentioned, my main tech firmly believes it's octane induced given the lowly 91 premium fuel we get in CA. The one thing I never did remember to try was to run octane booster or mix in some race fuel to bring up the octane and run that for an extended period of time.

My latest attempt to address this seemed to have worked well so far - I replaced all of the injectors. And the past couple months have truly been knock free, especially in low rpm instances where sometimes I was caught being in one gear higher than where I needed to be in. Was supposed to send my old injectors out to get flow tested, just to see what kind of shape they were in, but i think the shop lost them...

Maybe with the crappy 91 gas being the only option available my injectors will eventually wear and develop the pre-det again, but just wanted to share my experience as the car has been a blast to drive the last 3 months without me ever thinking/worrying about triggering this noise
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      09-21-2018, 08:18 PM   #42
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Originally Posted by Icecreamfoo View Post
I can relate to this, as ever since this started showing on my S65 50k-ish miles ago I have been trouble shooting on and off to no real success. new spark plugs, new coils (individual cylinder and all 8), low fuel pressure sensor, upgraded OE software, aftermarket software, injector/fuel system cleaner, thought I tried them all. What I felt is these things provide temporary "relief" to the issue, but never fully "solve" the problem at root. The car would run smoother with each of these parts change/software flash, but eventually the knocking or low rpm pre-det returns. I actually get the knocking at high rpm as well sometimes, during certain throttle angles

I will say tho, putting in brand new coil packs all around and running Chevron Techron Concentrate Plus (in separate instances, not done at the same time) made the most dramatic improvement, especially the former as it instantly restored the urge/eagerness to rev on my aging S65, it was to the point where I could dial back my throttle input a little to achieve the same, or if not stronger, pace of acceleration as before. And the latter allowed the engine to run notably smoother and quieted down the (old) injectors. But nothing lasted, the det always slowly creeps back.

Like some of the guys here have mentioned, my main tech firmly believes it's octane induced given the lowly 91 premium fuel we get in CA. The one thing I never did remember to try was to run octane booster or mix in some race fuel to bring up the octane and run that for an extended period of time.

My latest attempt to address this seemed to have worked well so far - I replaced all of the injectors. And the past couple months have truly been knock free, especially in low rpm instances where sometimes I was caught being in one gear higher than where I needed to be in. Was supposed to send my old injectors out to get flow tested, just to see what kind of shape they were in, but i think the shop lost them...

Maybe with the crappy 91 gas being the only option available my injectors will eventually wear and develop the pre-det again, but just wanted to share my experience as the car has been a blast to drive the last 3 months without me ever thinking/worrying about triggering this noise
Than you for the information. I sure hope I do not need new injectors... Here is hoping that a little sea foam and 94 octane will do the trick..

Cheers,
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      09-22-2018, 09:47 AM   #43
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Injectors are on my PM preemptive send off to somebody to get checked list next time I have the manifold off. Too many stuck injector horror stories
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      09-22-2018, 10:58 AM   #44
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Injectors are on my PM preemptive send off to somebody to get checked list next time I have the manifold off. Too many stuck injector horror stories
That is a good plan. I garage the car for winter. I should just pull the injectors and test them this winter. Can also fix my seeping valve cover gaskets.

Cheers,
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