knock sensor and mech cam
Thread Starter
Racer
Joined: Oct 2001
Posts: 304
Likes: 0
From: sometown new york
knock sensor and mech cam
I've put the LPE 236/244 solid roller cam in my 383cid L98 block in my 91 Vette. The knock sensor is picking up the valve train noise as detonation and killing my horsepower. However, disconnecting the knock sensor puts an error code in the computer. Is it true that this code wiil keep the computer in limp mode? How can I disable the sensor and not throw a code?
Safety Car
Joined: Nov 1999
Posts: 3,891
Likes: 2
From: Houston, TX
Re: knock sensor and mech cam (connellyh)
Well, I would not disable the knock sensor. First, I would try and loosen the knock sensor a little. If it is too tight, it can pick up extra noise. You might even want to try one wrap of teflon tape around the threads to isolate it even more.
This is always dangerous work, so be careful and make sure everything is right.
Good Luck,
This is always dangerous work, so be careful and make sure everything is right.
Good Luck,
Burning Brakes
Joined: Mar 1999
Posts: 876
Likes: 9
From: Mooresville NC
Re: knock sensor and mech cam (connellyh)
I agree with 2FST4U, try to make it less sensitive first. I never have a problem picking up false knock on my LT1, with 2 knock sensors.
If that fails, you can bypass the knock sensor with a resistor. About 2200 ohms if memory servs. Look in the shop manual and see what resistance they expect the knock sensor to test out at.
If that fails, you can bypass the knock sensor with a resistor. About 2200 ohms if memory servs. Look in the shop manual and see what resistance they expect the knock sensor to test out at.
Thread Starter
Racer
Joined: Oct 2001
Posts: 304
Likes: 0
From: sometown new york
Re: knock sensor and mech cam (LT401Vette)
This cam/lifter/rocker setup makes a LOT of noise! At idle, the knock sensor (KS) hears enough noise to cause the rpms to fluctaute. Just a little at first, then after about 30 sec, it goes down enough to kill the engine. The retard at 4000rpm is 8-10`. Talk about killing power. In order for this motor to make peak power, the KS has to be disconnected or ignored. I know detonation can cause minor problems like shattered pistons and bent rods. I am confident that my motor is not suffering from any detonation. Yes, I tried the teflon tape trick. It had no effect. When I disconnect the KS, the computer gets an error code. Will that code force the computer to stay in open loop (limp) mode?
Burning Brakes
Joined: Mar 1999
Posts: 876
Likes: 9
From: Mooresville NC
Re: knock sensor and mech cam (connellyh)
Are you sure they are adjusted correcty? You hear almost no valve train noise at all on my car. Only if you stick your head withing 1 ft or so of the valve cover with the hood over.
At any rate, I have had knock sensors die. If it is disconnected on the 93, the ECM goes to max retard, thats worse than limp mode. That will stall an engine at idle. The resistor works for me, til the new one gets in. No one ever seems to have it in stock :sad:
At any rate, I have had knock sensors die. If it is disconnected on the 93, the ECM goes to max retard, thats worse than limp mode. That will stall an engine at idle. The resistor works for me, til the new one gets in. No one ever seems to have it in stock :sad:
Racer
Joined: Sep 2000
Posts: 402
Likes: 0
From: Beaverton OR
Re: knock sensor and mech cam (connellyh)
think i'm having similar problems. is anyone getting a slight miss or cut out from a weird knock sensor? earlier i discovered the headers burned through the knock wires. after replacing those it's definatly better but with the exhaust i have & a rattly air pump i haven't yarded off yet i have the feeling i'm getting false knock. what exactly would i feel if it was? just a big loss in power? any sputters? spits or misses?
Safety Car
Joined: Nov 1999
Posts: 3,891
Likes: 2
From: Houston, TX
Re: knock sensor and mech cam (LT401Vette)
Well, it is my turn to agree with Phil! :)
Are you sure they are adjusted correctly? How much lash did you give them? You really should not be hearing a lot of noise.
Good Luck,
Are you sure they are adjusted correctly? How much lash did you give them? You really should not be hearing a lot of noise.
Good Luck,
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Racer
Joined: Sep 2000
Posts: 402
Likes: 0
From: Beaverton OR
Re: knock sensor and mech cam (AS84)
sounds like 84 & i are in the same boat, i also have a 1990. also have the oddest feeling the knock sensor might be it. haven't ran diacom yet but should be able to soon. anyway if anyone has had similar issues please post or mail us
Thread Starter
Racer
Joined: Oct 2001
Posts: 304
Likes: 0
From: sometown new york
Re: knock sensor and mech cam (LT401Vette)
LPE recommends 0.020" on int and exh. I have double checked them. I think I've just stumbled on a very noisy combo. The engine runs much better without the KS so, I'm going to run the KS lead thru a resistor to ground.
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: knock sensor and mech cam (connellyh)
Most people have had to disable it with a resistor. I did that with a 4K resistor in place of the knock sensor before, it deos not set a code.
You can try to un-couple the sensor some. Use a 90º pipe fitting to mount the sensor on instead of directly into the block. You can also cut half of it's signal by taking a 2K resistor, putting it in series with the sensor wire connected to the sensor with a 4K resistor connected in parallel to the sensor ( from the sensor contact to chasis ground ).
You can try to un-couple the sensor some. Use a 90º pipe fitting to mount the sensor on instead of directly into the block. You can also cut half of it's signal by taking a 2K resistor, putting it in series with the sensor wire connected to the sensor with a 4K resistor connected in parallel to the sensor ( from the sensor contact to chasis ground ).
Racer
Joined: Sep 2000
Posts: 402
Likes: 0
From: Beaverton OR
Re: knock sensor and mech cam (BBA)
just spoke with chirs at TPIS about this today. from everything i trouble shot & told him on the phone it basically came out to be the knock sensor. sometimes a really loud exhaust can do it, vibration from engine mounts or just a faulty sensor. his advice if the teflon tape didn't work was to move the sensor up to the head & see if that takes care of the problem. looks rather simple to do as all a person needs is a drill & tap. the other thing to do is the resistor bypass to see if it cures the problem. it could just be a faulty knock sensor he's mentioned a few going bad that did exactly what our problems are. :chevy
Instructor
Joined: Dec 2000
Posts: 161
Likes: 0
From: Columbus, Indiana
Re: knock sensor and mech cam (importeater)
Just an idea here, but the knock sensors are specifically designed to pick up a certain frequency. If you switch the kind of cam that you are using then you also need to get a Knock sensor that is calibrated for that style of vave train. You also need to get a new ESC module. I got a new ZZ4 in my 84 and it went into limp mode, then I got the correct Knock sensor and ESC module and it kicks butt.
Let me know what you find out.
:flag :flag
Let me know what you find out.
:flag :flag
Thread Starter
Racer
Joined: Oct 2001
Posts: 304
Likes: 0
From: sometown new york
Re: knock sensor and mech cam (slvr84)
there is no KS that is specifically tuned for a specific cam. some sensors are less sensitive than others, i.e. the lt4 og 85/86 g-body units. my valve train is making so much noise that neither of those will do the trick. the main problem is that solid roller cams make noise in the same frequency range as minor to mild detonation. after all the answers i've received on this issue, here and elsewhere, i've come to the conclusion that the pcm needs to be programmed to ignore the knock sensor. as a precaution, i am going to have the spark curve pulled back some and the a/f ratio on the rich side.
Safety Car
Joined: Nov 1999
Posts: 3,891
Likes: 2
From: Houston, TX
Re: knock sensor and mech cam (connellyh)
LPE recommends 0.020" on int and exh.
I still say that you should NOT have to disable the knock sensor to get this to work.
What kind of lifters are you using?
Drifting
Joined: Jan 2001
Posts: 1,669
Likes: 1
Re: knock sensor and mech cam (connellyh)
YES you have to disconnect the knock sensor. Fellas he has solid lifters and they are very noisy. It is not the same that came in the LT-1's or any other of the new Corvettes. You can disconnect the sensor either by eliminating it in you program or testing with resistors until it no longer throws a code. I had to eliminate mine also due to the fact I had a solid roller cam.
Thread Starter
Racer
Joined: Oct 2001
Posts: 304
Likes: 0
From: sometown new york
Re: knock sensor and mech cam (2FST4U)
LPE recommends 0.020" cold. The engine builder recommended 0.018". The cam card recommended 0.020" int and 0.022" exh as starting points. I am using Crane light weight pop-up style roller lifters, 4130 pushrods (5/16), CompCams Pacaloy springs (240#/582#), and CompCams 1.6 roller rockers. Apparently, this is a very noisy combo. With the hood closed, you can hear the valve train.
Burning Brakes
Joined: Mar 1999
Posts: 876
Likes: 9
From: Mooresville NC
Re: knock sensor and mech cam (connellyh)
OK, now we might be on to something.. It doesn't seem likely that LPE is giving cold lash recommendations. I could be wrong, but I would recheck that. Solid cam lash figures are almost always given in hot lash form. An iron block with alum heads will loosen up by about .005"-.006" further when it warms up. I feel much more comfortable keeping the lash tight on a setup that is driven regularly. The cam card that Cam motion supplied me recommended hot .022" lash. I have found .016-.018 to work better for me. That means my cold lash is generally only .012-.013". I have a quite valve train too.
[Modified by LT401Vette, 9:50 AM 10/26/2001]
[Modified by LT401Vette, 9:50 AM 10/26/2001]
Safety Car
Joined: Nov 1999
Posts: 3,891
Likes: 2
From: Houston, TX
Re: knock sensor and mech cam (connellyh)
LPE recommends 0.020" cold. The engine builder recommended 0.018". The cam card recommended 0.020" int and 0.022" exh as starting points. I am using Crane light weight pop-up style roller lifters, 4130 pushrods (5/16), CompCams Pacaloy springs (240#/582#), and CompCams 1.6 roller rockers. Apparently, this is a very noisy combo. With the hood closed, you can hear the valve train.
It looks like you are using the 943 Springs. Those are great springs! Are you using the 720 Titanium retainer? I hope you are not using steel retainers.
Send an Email to Tech@SpeedDemonMotorsports . He has set up a few solids and even come across these problems.