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Old 05-09-2000, 09:52 AM   #1
Tim Prudence
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Have a Nice Day? What is the sound of detonation?

I'm boosting my 99RS to 5 psi with a small turbo, no intercooler. I can hear crackling sounds coming from under the car (it seems). It sounds kind of like a lighter flicking sound only quicker. It usually only happens when I really gas it, though sometimes on deceleration. Is this the sound of detonation?

I only have a paxton rising rate regulator (still at stock pressure base), and a S-AFC. I max out the S-AFC and the sounds keep happening at the same places, doesn't seem to do much. The O2 voltage at WOT was low, about .800 when I was giving +15% with the AFC. Then I gave +30% and it went to .000 at WOT, so I'm kind of lost here...

Any advice would be appreciated.
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Old 05-09-2000, 10:04 AM   #2
Tyrmeltr
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Tim, do you have an EGT or Air/Fuel ratio meter? If you don't, I higly reccomend you do. From the fuel & boost you're running, I doubt you are getting detonation. This may sound dumb, but it could be a very small exhaust leak somewhere. Those can easily make a tick tick tick that speeds up as you accelerate. I had one for about a month that was bitch to find. Check the gaskets and welds with a stethoscope, while the car is lifted and idling, then have some one rev the motor occasionaly as you search for it. Hope that helps! Worst case scenario, take it to Ed at iSR and he'll sort it out.
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Old 05-09-2000, 10:32 AM   #3
edekker
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Tim Prudence,

I'm very familiar with the detonation sounds. I can make them at will. They do not sound like knocking or like marbles in a tin can. Light det make crackling sounds. Serious det sounds like tiny firecrackers going off in rapid succession which gets louder if you don't let off on the throttle. Don't let it continue at this level. The engine's thermal efficiency drops dramatically causing a condition akin to thermal runaway. Left unchecked, the inevitable melting of pistons|valves|sparkplugs will occur guaranteed.

Ed.
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Old 05-09-2000, 10:33 AM   #4
8Complex

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Wihle I'm positive i've heard detonation before, I am not sure... I think it sounds something like hitting some metal together (say a large-ish bolt on a chunk of metal).

BTW, is it possible to get detonation on an RS with just an intake (MY00)? I thought I heard something when taking off a few times but I've never been able to recreate it and it only happened once per take off, maybe 2-3 times total. Maybe bad gas...
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Old 05-09-2000, 10:55 AM   #5
Marius
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Wink

Boom!
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Old 05-09-2000, 11:13 AM   #6
Tim Prudence
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If it were detonation, would my "check engine" light ever go on or start flashing? I thought that the knock sensor would trip the check engine light...

[This message has been edited by Tim Prudence (edited May 09, 2000).]
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Old 05-09-2000, 11:48 AM   #7
ColinL
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No, only misfires FLASHES the CE light. Bad plug wire, coil, ignition, that sort of stuff. CE light does nothing at all while the ECU is pulling back timing under detonation.

EDIT: excuse me, I said "trips" earlier. I meant flashes.

[This message has been edited by ColinL (edited May 09, 2000).]
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Old 05-09-2000, 11:54 AM   #8
rao
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Colin is right, if it is detonation, you won't get a CE light until it is too late.
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Old 05-09-2000, 01:24 PM   #9
edekker
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That's right - I never got a CE light due to detonation.

But after I had the #3 cylinder repaired (I had det damage to #3), I kept getting the 'misfire in #3' code a mystery we couldn't solve at the time. Later, I decided to rebuild the motor a new short block (includes the crank, rods, pistons, etc., pre-assembled), new heads and valves. Since then, the ECU has yet to throw the code.

To save a lot of money, the motor was initially repaired adhoc only the exhaust valve and spark plugs had been replaced. I decided to take a risk and forego some light scoring along the #3 cylinder wall. After the repair we measured the compression on all cylinders. They all measured 190 PSI except #3, which measured 150.

We concluded that the ECU reported the misfire because it sensed #3 wasn't "right".
I thought this was interesting - the only way it can know this, is though the knock sensor and a crank angle sensor or a cam sensor of some sort.

That tells me the ECU uses the knock sensor for more than just deciding if knock occurs.

Ed.
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Old 05-09-2000, 02:25 PM   #10
Tim Prudence
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Hey, I think I figured out the problem. I'm so stupid... after resetting my ECU the other night, I forgot to set the sensor type on the S-AFC. I set the fuel and everything, but I think it was screwing up the signal because it was set on Flap sensor. I think this was the problem, because I'm no longer hearing that crackling sound.

Ed, I know that you put in colder plugs after your rebuild (7's I think). How much did that help with your detting?
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Old 05-09-2000, 04:11 PM   #11
edekker
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Tim Prudence,

Since I installed the Rimmer s/c, I've tried three heat ranges with the NGKs.

1) At the time of my #3 mishap, I chucked the Champions for NGKs that were 2 steps colder. I also installed the RR FPR.
2) At the time I had the accident (hit a pole) I had the opportunity to check the plugs they were totally black and sooty. Carbon-like crystals were lodged between the ceramic insulator and the plug's body. My RR FPR could be at least part of the reason (running richer). I replaced them and went down one step hotter (or 1 step colder than stock).
3) At the time I rebuilt the motor (with the new short block, etc.) I saw the plugs again. They were still sooty but had some tan patches. I decided to go back to the stock heat range of 5 (that's NGK 5, not Champion 5 Champion's a different numbering system).

I now realize I had installed the colder spark plugs on the basis of some misguided and false presumptions.

The basis for selecting the heat range of a spark plug should not be on how you want the temperatures affected in the combustion chambers. Neither should it be based on how to compromise non-idyllic conditions that the chamber sees because of poor fuel management or whatever.

The sole and pure reason for selecting the proper heat range is to ensure the spark plug reaches its self-cleaning operating temperature while ensuring its max operating temperature is not exceeded in whatever environment it had been subjected to. The role of the spark plug is not based on what can it do to affect that environment but on how it can accommodate it.

The onus is on the person to make sure the engine's ignition and fuel management is tuned properly and that the conditions in the combustion chamber are right. In a properly tuned engine, the spark plug's heat range accommodates the imposed conditions.

Ed.
---------
'99 Rally Blue 2.5RS - Mods - My Site
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Old 05-09-2000, 04:40 PM   #12
Tim Prudence
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Ed,

I don't know. It's seems like we'd still want to get plugs of a lower heat range because the temperatures in the combustion chamber are going to be much hotter with forced induction.

Corky Bell recommends colder plugs in Maximum Boost, he's pretty much the expert on these matters as far as I'm concerned.

In any case, I'm not getting detonation anymore, but I think that I'm probably running a little lean still. I'm going to try to get things tuned as well as possible, and then maybe add colder plugs. I don't want to foul them immediately.
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Old 05-09-2000, 05:03 PM   #13
rao
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Thew worst thing that will happen with too cold plugs is that they will not get hot enough to clean themselves and will foul prematurely. If you check them regularly there should be no problem.
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Old 05-09-2000, 07:18 PM   #14
edekker
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Tim Prudence,

The purpose for selecting the proper heat range is to allow the plugs to operate in their self cleaning range - not to lower combustion temperatures. If your cumbustion chamber is running hotter, then there's something wrong. Yes, you can select a heat range which will allow the plugs to accomodate the hotter temps, but it doesn't solve the problem - it's a band-aid - the colder plug will be comfortable, but your chambers will still run too hot. When the motor's pulling hard, even running N/A, EGTs can go higher than 1400F. An s/c or t/c properly tuned will not, and should not, push the temps much higher. Go too high with the temps and you're flirting with possible catastrophic engine faiure - detonation needn't occur.

Get your system tuned properly first. Even at moderately high boost levels, a properly tuned setup will keep those EGTs in check - people have done it. Don't rely on too cold a plug to solve a problem.

Good luck,
Ed.
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Old 05-10-2000, 08:34 AM   #15
josh
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Tim,

So how does the smaller turbo feel? Is the car fast? when does the turbo spool? etc., etc.?

josh
 
Old 05-10-2000, 01:25 PM   #16
Tim Prudence
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I still get crackling sounds while I let out the clutch at 4k rpms. The O2 sensor voltage is reading way rich (around .900). Does this sound like detonation? Maybe it is just an exhaust leak which occurs more frequently when I shifting because the engine is moving all around...

But how could I be sure? Pull back timing and add octane booster and see if it still occurs?

[This message has been edited by Tim Prudence (edited May 10, 2000).]
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Old 05-10-2000, 05:19 PM   #17
Tim Prudence
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anyone?
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Old 05-10-2000, 06:19 PM   #18
rao
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When I let off, my a/f meter instantly goes lean.
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