Engine knock or false knock?
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 855
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Engine knock or false knock?
I have an AutoXray and it is showing recorded knocks at WOT. I thought this was false knock and replaced the knock sensor and ESC (knock module). I torqued the KS to 14 ft LBs. I checked the timing and its at 6 deg. I'm running 89 octane. I don't have an overheating problem. I checked the O2 sensor and its fine. I replaced the fuel pump (w/AC Delco) about 10 months ago. I don't have a fuel pressure gage yet. Is there anything else I can check before I get the FPG? The O2 is reading low 800's. Is that considered lean? TIA
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Engine knock or false knock? (Rick86)
That is indeed lean; between high 800s and low 900s is good.
Maybe an AFPR would help; before you pull the stock fuel pressure regulator measure the pressure at idle with the vacuum hose disconnected. This is the baseline for the AFPR startup.
Maybe an AFPR would help; before you pull the stock fuel pressure regulator measure the pressure at idle with the vacuum hose disconnected. This is the baseline for the AFPR startup.
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 855
Likes: 0
Re: Engine knock or false knock? (GusBustamanteJr)
Why would you attempt to run this car at 89 octane???????
Of course its going to knock!
Of course its going to knock!
This car is mostly stock and owner's manual only calls for 87 octane, plus when I run 91 octane I still get the knock. :confused:
Drifting
Joined: Jul 2001
Posts: 1,751
Likes: 1
From: Miami, FL, USA
Re: Engine knock or false knock? (Rick86)
I would change the plugs\wires\cap\rotor, set base to 6 degrees and run 93 only. Should go away, otherwise check the knock sensor, motor mounts, etc.
I think everyone will agree these cars need all the octane you can throw at them!!!
I think everyone will agree these cars need all the octane you can throw at them!!!
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Engine knock or false knock? (Rick86)
Rick, you have done several mods to increase air flow yet are running stock fuel pressure; so I suggested to install an AFPR to match fuel flow to increased air flow.
Also, when you changed the ESC module, did you install the stock part of use the upgrade listed on my site? Gordon Killebrew suggested this upgrade when I too was having a false knock problem and it fixed the problem.
Also, when you changed the ESC module, did you install the stock part of use the upgrade listed on my site? Gordon Killebrew suggested this upgrade when I too was having a false knock problem and it fixed the problem.
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 855
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Re: Engine knock or false knock? (65Z01)
Thanks for the advise, and the new ECM was the updated model. I ordered a fuel pressure gauge and AFPR. I post what I findout after I check the fuel pressure.
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 855
Likes: 0
Re: Engine knock or false knock? (Rick86)
Well I checked the fuel pressure with my new gauge and here are the results:
key on=44psi
car running @ idle=38psi
vacum disconnected =46psi
30 minutes after shutdown gauge still reading 38psi
I guess I'll check for vacum leaks next, I also think I be hearing some loose rockers. Can loose rockers tricker the knock the sensor?
key on=44psi
car running @ idle=38psi
vacum disconnected =46psi
30 minutes after shutdown gauge still reading 38psi
I guess I'll check for vacum leaks next, I also think I be hearing some loose rockers. Can loose rockers tricker the knock the sensor?
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Team Owner
Joined: Apr 2001
Posts: 22,267
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From: Dallas TX
Re: Engine knock or false knock? (Rick86)
Why would you attempt to run this car at 89 octane???????
Of course its going to knock!
With a comment like that I feel like I must be the only person running 89 octane?
This car is mostly stock and owner's manual only calls for 87 octane, plus when I run 91 octane I still get the knock. :confused:
Of course its going to knock!
With a comment like that I feel like I must be the only person running 89 octane?
This car is mostly stock and owner's manual only calls for 87 octane, plus when I run 91 octane I still get the knock. :confused:
And why the hell does it say it only requires 87 octane :eek: :confused:
[Modified by GlockLT4, 2:23 PM 4/22/2003]
Former Vendor
Joined: Jun 2001
Posts: 7,204
Likes: 6
From: St Marys PA
Re: Engine knock or false knock? (GlockLT4)
First don't run 89 octane. Second of all, you can test it pretty easy to see if its false knock.
Loosen the distributer holddown so you can barely move the cap. Retard the timing about 2* then take it for a ride. See if the knock decreases. Then do it again, record the log.
The base chip has TONS too much timing in it for emmission reasons, they want you burning every last molecule of gas, then some. This leads to knock problems that are addressed by the knock sensor. Don't let anyone kid you, they installed these knock sensors for more emmision reasons, than to help save engines. On top all that they make us pump hot air (EGR) back into the cylinders that make the problem/potential for detonation even greater.
Do the little test I explained above, you should see the counts decrease each time, till there are few or none. If they remain, then you have false knock.
Hope this helps.
:cheers:
Loosen the distributer holddown so you can barely move the cap. Retard the timing about 2* then take it for a ride. See if the knock decreases. Then do it again, record the log.
The base chip has TONS too much timing in it for emmission reasons, they want you burning every last molecule of gas, then some. This leads to knock problems that are addressed by the knock sensor. Don't let anyone kid you, they installed these knock sensors for more emmision reasons, than to help save engines. On top all that they make us pump hot air (EGR) back into the cylinders that make the problem/potential for detonation even greater.
Do the little test I explained above, you should see the counts decrease each time, till there are few or none. If they remain, then you have false knock.
Hope this helps.
:cheers:
Thread Starter
Burning Brakes
Joined: Nov 2000
Posts: 855
Likes: 0
Re: Engine knock or false knock? (ski_dwn_it)
Thanks for the help, and I think I'll try the timing test. I'm leaning towards the fact that my AutoXray might be sending bogus info. About two years ago I had the car scanned at a reputable corvette shop and they said they tested the car and their equipment didn't show any knock. On the way home I plugged the AutoXray back in and it showed knock counts. What my AutoXray will not show is if timing is being pulled. I have a forum member that is going to scan my car with his EASE software and laptop.
Thanks for the support and help. I just want to make sure my baby isn't sick before I go and do any more mods.
Thanks for the support and help. I just want to make sure my baby isn't sick before I go and do any more mods.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Engine knock or false knock? (Rick86)
Your fuel pressure sounds about right, at least at idle.ad
Route the gauge out from under the hood onto the windshield and hold it in place with the wiper. Then go out and hammer it into 2nd gear and observe if the pressure maintains or drops off as more fuel is drawn.
I still think that O2 value 800mV at WOT is way low; try upping fuel pressure till it rises to around 900mV and check for knock retard.
Route the gauge out from under the hood onto the windshield and hold it in place with the wiper. Then go out and hammer it into 2nd gear and observe if the pressure maintains or drops off as more fuel is drawn.
I still think that O2 value 800mV at WOT is way low; try upping fuel pressure till it rises to around 900mV and check for knock retard.
Melting Slicks
Joined: May 1999
Posts: 2,037
Likes: 0
From: Sarasota FL
Re: Engine knock or false knock? (65Z01)
Run premium. Also, run a can of GM top engine cleaner through it. The carbon buildup really gets the knocks started. If the AutoXray is seeing it, so is the knock sensor.
