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Old 10-16-2000, 03:07 PM   #1
omahasubaru
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Question Knock Sensor & Gary's electirc fix. (yes I did a search).

Anyone happen to have pics of how they installed this fix for their Subaru??? I won it on auction at eBay for 6 dollars shipped and just want an idea as to what I'm doing. The instructions although make some sense, there are no pics and it isn't worded to my liking/understanding.

Also opinions as to if installing this is a good idea and especially opinions from those who have it or have had it.

Thanks! omahasubaru@hotmail.com

Information as to what I'm talking about can be found here: http://home.earthlink.net/~hobiegary/hesitation.htm
Also NorthU has taken this apart and has pics, but I can't get to his site... cyber patrol at work has it all blocked. I'm working 4pm to midnight tonight for on-site support.. YUCK! so I'm missing the FIA WRC, I'm taping it, some one please post a link to NorthU's site about the fix and I'll look at it tomorrow before I got back into work at 7:00am.

Thanks again.

[This message has been edited by omahasubaru (edited October 16, 2000).]
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Old 10-16-2000, 03:10 PM   #2
Sean McElderry
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What is this fix you're talking about?

Sean
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Old 10-16-2000, 03:45 PM   #3
Tim Prudence
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It's some kind of resistor or something that you splice into the line from the knock sensor to ECU that makes the sensor less sensitive. It takes more input from the knock sensor before the ECU retards timing.

Could be good, could be bad. Settling down a hyperactive knock sensor will help performance, but fooling the ECU into thinking there is no knock when knock is actually occurring will hurt your engine.
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Old 10-16-2000, 03:46 PM   #4
North Ursalia
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Old 10-16-2000, 04:04 PM   #5
Sean McElderry
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Try it. If you hear ping, take it out. If you still have hesitation, take it out.

My engine has pinged SOOOO many times while tuning. Don't worry...it can take the abuse. With that said, I would recommend driving with the stereo off and the windows closed while you listen, very carefully, for ping. You also have to listen for ping in different weather conditions (hot/cold) and also when you use different gas.

It might not be worth the added stress of knowing that your engine might be pinging and slowly destroying itself

Does the hesitation really bother you?

Sean
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Old 10-16-2000, 04:08 PM   #6
omahasubaru
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Yes it does bother me... as I said I got this deal for 6 bucks so it isn't like a loss. I'm going to just try it out 'cause it is supposed to be easily removable.

Thanks.

Keep the info and opinions coming
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Old 10-17-2000, 05:28 AM   #7
Scooter
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It just blows my mind how many people on this board attempt to solve problems they may not even have or fully understand. I would think one would first verify that their ignition timing is actually being retarded before attempting any mods of the knock sensor.

If you went to your doctor and he or she prescribed high blood pressure medicine without even taking your blood pressure, would you take it?

Also, the signal from the knock sensor is often fed through a narrow bandpass filter. Does anyone know what effect Gary's fix may have on that bandpass filter? I know there are some double Es on this board, any insight?

[This message has been edited by Scooter (edited October 17, 2000).]
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Old 10-17-2000, 08:57 AM   #8
Sean McElderry
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Scooter-

The fix will not affect the filter. The band pass filter takes place immediately, and the hack is after that. It just tones the voltage of the signal down, I believe, which will make big knocks still pass through to the ECU, but small knocks will get filtered down to near nothing.

Sean
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Old 10-17-2000, 09:00 AM   #9
omahasubaru
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Sean!

That is what I was hoping it would do.

Thanks for the info-
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Old 10-17-2000, 09:59 AM   #10
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I have Gary's hesitation fix in my '97 2.5 GT. It has definitely made a big big difference and I have no regrets. The problem is clearly documented in a Subaru TSB and through tons of letters people have written. The TSB shows that dealers actually do read errant signals in the ECU from the knock sensor, so I have no doubt the fix is doing what its supposed to. The hesitation I had drove me nuts. It was right in the early part of the powerband- betw. 2 & 3K which just sucks. I would reset the ECU and it would come back. I never heard/felt knocking/pinging. Whenever I changed the oil it would happen too- and later heard that the air being pumped out of the oil filter can trigger the knock signal. My only observation is that I think I have mild knocking under heavy acceleration, particularly up hill with regular gas. (Sounds like valves are rattling a little bit) Premium gas clears this up right away. Insatall was pretty straightforward, though the knock sensor is pretty deep down- you'll need a good extension to get to it.

hope this helps,
k
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Old 10-17-2000, 11:14 AM   #11
edekker
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Gary's 'Hesitation Fix' is just a simple 2-resistor divider network. It reduces the knock sensor's output signal level while still maintaining a source impedance with which the ECU is happy with (won't throw a CE code).

Here's a diagram, which should help you with the install -
http://members.home.net/edekker/rs/hesfix.jpg

The fix worked well for me. During the time I had the #3 cylinder problem, I had severe hesitation especially immediately following an oil change, which the fix solved. Unfortunately it also exacerbated the detting I'd get on WOT (I've got the Rimmer Sidewinder Eaton s/c). Once the motor had been fixed properly the hesitation disappeared. My fix is bypassed now.

Ed.

[This message has been edited by edekker (edited October 17, 2000).]
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Old 10-17-2000, 11:19 AM   #12
omahasubaru
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All this information is good, now how about some more detailed install instructions other than the crappy ones that came with the fix.

Thanks again everyone!
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Old 10-18-2000, 05:58 AM   #13
Scooter
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Sean wrote, "The fix will not affect the filter. The band pass filter takes place immediately, and the hack is after that."

Sean, are you saying the band pass filter is in the knock sensor itself? If so, how do you know this? Have you seen schematics for the sensor or taken one apart? I thought all processing of the knock signal takes place within the ECU. If so, how could the "hack" be after that? Do you have or ever seen schematics for the ECU?
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Old 10-18-2000, 06:27 AM   #14
omahasubaru
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Anyone have a pic of where the Knock Sensor is?

Thanks-
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Old 10-18-2000, 02:44 PM   #15
Sean McElderry
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Ed-

Thanks for that explanation. Assuming the filtering is done within the ECU, Gary's hack will still work. It doesn't change the frequency of the signal, just the level. So all the frequencies will still pass through to the filter, just at a different level.

Either way, the hack will work, IMO.

Sean
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Old 10-18-2000, 03:35 PM   #16
Italiano
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here is my .o2 cents on this issue:

I had a nasty hesitation problem after every oil change...would last about a week...drove me crazy:
(i own a 97 Impreza)

What did i do about?

I hate the idea of "rigging" anything on my car so i:
Replaced the knock sensor with a MY00 knock sensor
Havn't had hesitation since-

like i said, just my .02 cents, every car has it's own personality-

Domenic
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Old 10-19-2000, 12:02 AM   #17
Sean McElderry
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Scooter-

You could be correct. I just assumed that the filter was in the sensor itself. I do not have a schematic available. My understanding was that the microphone picked up noise in the engine. A filter narrowed it down to only allow the high pitched, knock like sounds through. Those sounds triggered a voltage on the line depending on their volume. That voltage gets passed to the ECU.

Does anyone know if the filtering is done in the ECU or the sensor?

Sean
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Old 10-19-2000, 12:49 AM   #18
edekker
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The knock sensor is a simple, passive (non-powered) piezoelectric, audio microphone. There are no additional electronics in the unit that I am aware of, which would alter its output. Its output impedance is very high (at least 50K Ohms) and the audio level is in the range of 1 to 2Vpp with the motor pulling hard. I've had the unit removed and I've played with it in the lab. It's capable of outputting signals across most of the audio range.

This signal is sent directly to the ECU. There is no filtering network, or any other device for that matter, between the sensor and the ECU. I couldn't tell you exactly what happens to the signal once it's in the ECU. There could very well be an audio filter of some sort, centered on a group of frequencies with which knock or ping is made up. The ECU might use simple level detection incorporating a sample-and-hold in conjunction with crank angle. It could also use a more complicated technique such as A/D conversion and run some complicated algorithm. Who knows?

Ed.
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Old 10-19-2000, 05:05 AM   #19
omahasubaru
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MY01's don't have the same hesitation problem as our cars?? I thought all (most) Subaru's have this problem I didn't know they fixed it by changing the sensor.
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Old 10-19-2000, 06:38 AM   #20
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omaha - Gary's fix was inspired by the hesitation in 97/98 5-speed Subaru's. I haven't experienced the hesitation in newer cars, but the hesitation he is referring to can be *very* severe. The car stalls and jerks like mad and you have to constantly keep the revs above 3500 rpm's to lessen it. I've had the hesitation since my first oil change in the fall of '97. I keep wanting to take it to the dealer while it's happening, but end up losing patience and re-setting the ECU myself instead.
Dennis
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Old 10-19-2000, 08:14 AM   #21
skidplatez
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Thumbs up

The problem is in late model cars here is the subjest of the TSB:
Subaru Service Bulletin Number 11-53-98 Date: 1/5/99
Applicability: 97~98 Legacy, Impreza, and Forester Manual Transmission vehicles with 2.5L & 2.2L engines.
Subject: Hesitation On acceleration

Note the Applicability this is the TSB where they finally admitted there was a problem later models should be unaffected.
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Old 10-19-2000, 08:44 AM   #22
Sean McElderry
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Mild hesitation still exists on a MY00 around 4k.

Sean
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Old 10-19-2000, 01:39 PM   #23
skidplatez
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true enuff Sean but the Gary's "fix" was for the listed models.
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Old 06-05-2006, 10:00 AM   #24
Patrick Olsen
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Quote:
Originally Posted by North Ursalia
Just bumping this one back to the top. (If this isn't a record for "Oldest Thread Revival", I don't know what it takes!)

Maybe you were just being nice on your website and didn't want to say, but is the part you "dissected" what this guy is selling for $89? If so, that guy's making a killing on these!

Interestingly enough, I never had a hesitation issue on my '97 2.5GT when it was stock. It wasn't until I did the Cobb heads and cams and big stuff like that that the hesitation began.

Pat Olsen
'97 Legacy 2.5GT sedan
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Old 02-05-2008, 07:22 PM   #25
ChayesFSS
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anyone have that paperclip.html page still? Need to see this in the worst way?!?!?
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