Someone relieve me of my ignorance, please

I've been playing with my LCD boost control (courtesy of BlackStealth), and it's a nifty as it can be. :)

Been slowly bumping solenoid duty-cycle to push boost - my assumption is I should be able to run comfortably in the 13-14 psi range, given my minor mods (Stillen DP, 13Cs).

I've done a vacuum reduction and tested for boost leaks - I'm good for 15+ psi with acceptable leakdown.

Here's the deal:

From a dead stop, if I let the clutch out and accelerate at what you might call a normally 'brisk' pace, the likelihood is I will get ZERO knock; maybe a count or two at most.

If I hammer it through the gears, shifting at 6K or so, again, the likelihood is ZERO knock.

However-

If I idle off a stop, and roll up through first and second (no/low load, sub-2K rpm), I get knock - 6, 8, 12 counts...last night, immediately after running up through 3rd to about 6K, hitting 13.4psi and 1 count, I basically cruised for another mile to a stop, then pulled away gently, only to record a maxed-out 28 count!

I haven't got the turbo-car/3S experience or intuition to figure this out - I had suspected a sloppy rear mount or some other anomaly as responsible for this, but the low rpm knock counts are increasing as I bump-up the duty-cycle.

In other words, if I backed off to waste-gate boost, I will get, say, up to 8-10 counts under the same circumstances, but having pushed the dutycycle, this off-hand knock can peg a 28, apparently, and this gives lie to my theory about about mechanical vs combustion-type knock.

What in the hell is going on?

When the tank is almost empty dump in a 5 gallon pail of some cheap(ish) race gas. Usually 100-107 can be had for a reasonable price. See if the knock continues. If it does, it is almost certainly false knock from old mounts, loose bolts, etc. also if your car is a 91-92 check that the base timing is set properly.

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Originally Posted by donniekak

When the tank is almost empty dump in a 5 gallon pail of some cheap(ish) race gas. Usually 100-107 can be had for a reasonable price. See if the knock continues. If it does, it is almost certainly false knock from old mounts, loose bolts, etc. also if your car is a 91-92 check that the base timing is set properly.

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That's a brilliant idea.

It'll have to wait a bit though, since the closest race gas is prolly 85 miles away.

I can get booster, but I've never liked using it, particularly with unleaded gas.

Remember, I'm old.

It's still the best idea I've got, though. :D

I would say you probably have phantom knock or a bad knock sensor. Maybe replace the knock sensor? I think OEM is only 40-50 dollars if that.

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Originally Posted by Boost4VR4

I would say you probably have phantom knock or a bad knock sensor. Maybe replace the knock sensor? I think OEM is only 40-50 dollars if that.

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Possibility there, too; I can't afford to be in a big hurry, though, so I guess now I'm wondering what people might have to say about their experiences with functional-yet-defective knock sensors. :)

Well if your knock sensor is "defective" you will read a consistent 7 counts (7 I think it is? Might be 9...) all the time. Again, it will be all the time. From startup on.

Not doubting Greg here, but according to him, our engines are noisy engines and the way the knock sensor is setup, is based off a raw knock voltage. That voltage goes through some filters and is converted into a knock 'count'. That knock count is a calculated number, not a direct amount of times your engine is actually predetinating. Which is why bad mounts can cause you to get 'counts' of knock even if your engine isn't actually detonating in a bad way.

With having said all that, the gas thing isn't going to change anything in all honesty. If your engine is knocking at no load with 93, it will have generally the same result with 116 octane. I'll all buy guarantee your engine always did this, you just couldn't see it on a little screen before. My car does it too, to give you a little stress relief. I'll bet yours goes away with any more or less load too just like mine.

I have been watching threads about this in curiosity and I have talked with Greg about it some too. The correlation between your waste gate duty cycle and the amount of knock is interesting though

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Originally Posted by futurevr4man

Well if your knock sensor is "defective" you will read a consistent 7 counts (7 I think it is? Might be 9...) all the time. Again, it will be all the time. From startup on.

Not doubting Greg here, but according to him, our engines are noisy engines and the way the knock sensor is setup, is based off a raw knock voltage. That voltage goes through some filters and is converted into a knock 'count'. That knock count is a calculated number, not a direct amount of times your engine is actually predetinating. Which is why bad mounts can cause you to get 'counts' of knock even if your engine isn't actually detonating in a bad way.

With having said all that, the gas thing isn't going to change anything in all honesty. If your engine is knocking at no load with 93, it will have generally the same result with 116 octane. I'll all buy guarantee your engine always did this, you just couldn't see it on a little screen before. My car does it too, to give you a little stress relief. I'll bet yours goes away with any more or less load too just like mine.

I have been watching threads about this in curiosity and I have talked with Greg about it some too. The correlation between your waste gate duty cycle and the amount of knock is interesting though

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I can easily buy all that as well, Nate, and also equate that to a reluctance on anyone's part, generally-speaking, to belittle knock, as to do so with these cars can be fatal.

My assumption all along has been that my sensor is functional, but what you've imparted about how the ECU interprets what it's told makes a buttload of sense, especially given how it reads, then reports, knock.

The limit at 28 counts toward a conclusion of phantom/anomaly reporting.

My limited experience can't reconcile the low-rpm/load counts with the high/highest loads and their lack of knock.

Then again, this is the squirreliest car I've ever tried to get a handle on...:rolleyes:

Hey, thanks for responding, guys - been wondering all day. :)

Kevin mine did the same thing as well. Sometimes when coming off cruise load. I was freaked at first, but somewhere in some thread on here I asked, and it was concluded phantom knock I believe. This as bpu status on 9b's.

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Originally Posted by CoopKill

Kevin mine did the same thing as well. Sometimes when coming off cruise load. I was freaked at first, but somewhere in some thread on here I asked, and it was concluded phantom knock I believe. This as bpu status on 9b's.

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Then I have to assume my 13Cs would be at least as touchy, yes?

Just today my CEL flashed (CEL flash on knock with the Chrome ECU) for a second and then right back off while cruising at about 1500rpm. its done this a few times before, and i even managed to log it once but didnt see anything out of the ordinary in the log to induce knock. I figure its from the solid lower mounts and poly mounts allowing the knock sensor to pick up on noises it normally wouldnt hear.

Mine has quite a bit of knock frequently when pulling away from stop lights. If an engine has slightly loose tolerances (like mine... Most race engines are built like that) then they tend to be a bit 'noisier' as far as the knock sensor is concerned and will show some knock. It's annoying, but nothing that should be worried about. I may play with the filter on my knock sensor a bit but it will be in the future after I feel like I know tuning inside and backwards.

And Kevin, like I said, it's interesting there is a coorelation between your duty cycle and the phantom knock you get... I wonder if it is repeatably more with more duty, or if you just happened to notice it once.

My first post was mainly to explain how the knock sensor works. Once you understand what is going on mechanically and electronically, the rest is fairly common sense :)

I'm going to be the dissenting opinion here, and theorize that it is in fact showing that much knock...

Under very light load is where the timing is at it's max, and the mixture is lean... Those are the conditions that will light off pre-ignition. Take any old V8 and start feeding it enough timing to make it start pinging, and check under what driving conditions it pings...

You can check if it's real knock or not without chasing down race fuel by just yanking some timing out of it and see if it goes away....

Are you getting a flashing alert on your LCDBC? or is that just the max recorded?

What spark plugs are you running?

I second the idea of verifying base timing.

Hey Kevin, My '93 TT was having the symptoms prior to rebuilding it(9b's)- 28 count after going into 2nd, no load-granny driving.

A few things I attributed to it once the motor was apart-

The knock sensor was leaking & was replaced-
The knock sensor bracket>block had shitty contact patch area-

The main bearings were dangerously at the end of their life-

Never did it again with my 13c's after rebuild.

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Originally Posted by RealMcCoy

I'm going to be the dissenting opinion here, and theorize that it is in fact showing that much knock...

Under very light load is where the timing is at it's max, and the mixture is lean... Those are the conditions that will light off pre-ignition. Take any old V8 and start feeding it enough timing to make it start pinging, and check under what driving conditions it pings...

You can check if it's real knock or not without chasing down race fuel by just yanking some timing out of it and see if it goes away....

Are you getting a flashing alert on your LCDBC? or is that just the max recorded?

What spark plugs are you running?

I second the idea of verifying base timing.

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Been looking for my timing light for three days...:D

I forgot to mention about the alarm - I have yet to get the flashing display, but I get the tone real early - maybe passing 4K at 7psi - I had my audible alarm settings at 10 for knock and 235 for temp, so I'm pretty sure something is wonky, there - the numbers just don't correlate, and frankly, I'm not paying attention to it at the moment.

Plugs are whatever stockers should be, platinum-specie - got 'em from 3SX, but can't remember the number.

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Originally Posted by Primus101

Hey Kevin, My '93 TT was having the symptoms prior to rebuilding it(9b's)- 28 count after going into 2nd, no load-granny driving.

A few things I attributed to it once the motor was apart-

The knock sensor was leaking & was replaced-
The knock sensor bracket>block had shitty contact patch area-

The main bearings were dangerously at the end of their life-

Never did it again with my 13c's after rebuild.

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Waiting on my Blackstone results, too, so that may shed some light.

There's a good chance I should, just for the exercise, pull the plenum and check/replace the sensor and peek at the plugs, but I'm betting, absent some sort of breakthrough, I won't do that until I park it for winter.

You know how that goes...:p

You said it knocks bad with basically no load? My car has always knocked with moderate load/low RPM (climbing a hill without dropping a gear). I have come to the conclusion this is normal although I do try to avoid it (back off the throttle or downshift). When the engine is under low load knock isn't as damaging from what I have gathered. Low/no load with knock is strange though!

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Originally Posted by HLxDrummer

You said it knocks bad with basically no load? My car has always knocked with moderate load/low RPM (climbing a hill without dropping a gear). I have come to the conclusion this is normal although I do try to avoid it (back off the throttle or downshift). When the engine is under low load knock isn't as damaging from what I have gathered. Low/no load with knock is strange though!

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That's my take on it, too, for the most part.

My dealing with knock, historically, is knock I could hear, going back to my V8 days, and always with pure mechanical compression, not power-adders.

This is still very new to me, and added to the paranoia these cars breed owing to their normal fragility, I'm gonna find out everything I can. :)

I think perhaps this is one reason why I am thinking of not using a knock sensor with my build... My spare engine doesn't have a knock sensor currently, so maybe run without one?!

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Originally Posted by Boost4VR4

I think perhaps this is one reason why I am thinking of not using a knock sensor with my build... My spare engine doesn't have a knock sensor currently, so maybe run without one?!

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I don't think I'd run a pressurized motor without a sensor of some type, Kev.

Be nice to find one compatible with our controls that was more foolproof and reliable.

I'm gonna put it on a hoist tonite or tomorrow to check for knock-gremlins and I'll take a peek at the timing while I'm at it.

Okay, took a look: the front carrier bearing is definitely sloppy and sagging, and the second one is not too far behind.

Could be my culprits knock-wise, for sure.

What are they worth, and is Cherry Hill my best bet?

Also: timing was spot-on.

Order a boot/lube kit for the lobro too as it has to come apart for one of the carriers-

Suggest comparing price of parts & labor of lobro overhaul vs a nice 2 piece DS :D

Revel in your time

I was quoted $50 cheaper than an alumi-steel 2 piece, just saying...

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Originally Posted by CoopKill

I was quoted $50 cheaper than an alumi-steel 2 piece, just saying...

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'Splain, Bill?

Probably quoted for repairing the stock one vs a new 2 pc alum.

Quoted to rebuild the stock one with serviceable u-joints for $50 under the price of the alumi 2 piece.

I'd love to go light, but I don't have the cash until I get busy dumping some stuff on Ebay, guys.