what would a bad knock sensor do?
Thread Starter
Safety Car
Joined: Oct 2008
Posts: 4,689
Likes: 4
From: Yucaipa CA
what would a bad knock sensor do?
I am having a horrible detonation issue with this 1990 to where if the est bypass wire is plugged in the car ping extremly bad but when its unplugged it seems to run fine. This car had a very bad head gasket leak and was subjected to sealant put in the cooling system, could this stuff have affected the knock sensor?
Thread Starter
Safety Car
Joined: Oct 2008
Posts: 4,689
Likes: 4
From: Yucaipa CA
I have heard tpi ecm's go to full advance as a pretest during startup to listen for knock and to detect if the knock sensor is working. I also have read the ESC module is internal to the 7727 ecm. My prom is the correct broadcast code so could this ecm be the culprit? It doesn't show any codes related to a faulty ecm but does that mean it couldn't be bad?
I don't want to replace the ecm if it is fine, however another odd thing the car does is the ecm never has been able to turn the cooling fans on. The motor always seems to run good aside from these two things.
does it's cold start elevated idle and once warm idles down, doesn't seem to miss or anything.
Racer
Joined: May 2008
Posts: 312
Likes: 19
On my 91 the KS was not as sensative as another that I had in the garage. You can bench test by tapping the KS with red lead of VOM on the center pin and black lead on KS body, VOM set on low range volts. Also make sure cooling is proper, mine would only ping when warm under load. Hope this helps!
Advanced
Joined: Dec 2002
Posts: 69
Likes: 1
From: Bremen
another odd thing the car does is the ecm never has been able to turn the cooling fans on
The PO may have put in a manual switch for the fans, when the knock sensor failure came up? With a code for the sensor, the fans would have been running all the time.
First you should check the sensor itself using the service manual or try it like written in the previous post.
The knock sensor is controlled by the circuit board on top of the memcal (chip). You might have a wrong or faulty memcal. ECM would be next in line.
A friend had a knock sensor act up on him, but only when closing in or at operating temps. Result was a very strong pulsating idle, about 500 rpm up and down. KS are knowing for strange things to happen, though.
Navigator
Joined: May 2004
Posts: 9
Likes: 1
From: chattanooga tn
Hard Knocking Noise
I too have a 1990 Vet that has an awful knocking noise, when the car warms up. I was told it was the clutch and replaced it. It did not fix it. It knocks so bad the car engine seems to rattle. Its sounds like the engine is going to break up. The oil pressure and such is fine. Its seems to be worse in 5th and 6th gear and has a miss. Would someone please give me and idea of something to look for. It has been looked at with a stethoscope and still cant put a finger on the area that is knocking. Some are saying it may be a lower engine rod, but others say, no, for the oil pressure and such is fine. Its has 75000 miles on it, and I put all but 25000 on it and i baby it. Please help....Could the timing cause this noise. What about the knock sensor? I am not familiar with it and what it does.
Last edited by frisky2002vrod; Jan 15, 2010 at 09:27 PM. Reason: Added and correcting spelling
Racer
Joined: Dec 2009
Posts: 298
Likes: 0
From: Reno NV
My car does the exact same as friskys. Its your flywheel rattling cuz of the miss in the engine. i'm checking the sensors now then the injectors. Fix the miss and the rattle should go away. My coolant sensor should be here tomorrow. Lets see if that works.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Navigator
Joined: May 2004
Posts: 9
Likes: 1
From: chattanooga tn
Please let me know how you fixed yours when finished. I dont want to pay again for something I dont need, like a new clutch I just fixed for nothing. My email is frisky2002vrod@yahoo.com...thanks
Drifting
Joined: May 2006
Posts: 1,428
Likes: 7
From: Chewelah Wa
Sounds to me that you have a problem with the connection to the knock sensor. If it was connected and working properly, the ESC would retard the timing at the first hint of knock. The sealant could have built up in the hole in the block that the sensor screws into, I am not sure how much of a effect this would have. I would check the wire and connector first. The sensor should be installed with bare threads, no sealer or tape.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
[QUOTE=jeffp1167;1571641437]I realize what the wire does, my question is why would the car beI have heard tpi ecm's go to full advance as a pretest during startup to listen for knock and to detect if the knock sensor is working. QUOTE]
I've read the same thing about the pre-test but I can't find the source now.
I posted on this on another Forum when I was trying to help a friend with his question but someone - who shall remain nameless, LOL - wants my source for the pre/self test of the Knock Sensor system and I can't find it.
I didn't find it in the 86 FSM, but I KNOW I read it somewhere. Just don't want guys to think I make up things. LOL
Does anyone know where I can find a source for the self-test that the ECM does on the system when the engine is first started?
Thanks,
Jake
I've read the same thing about the pre-test but I can't find the source now.
I posted on this on another Forum when I was trying to help a friend with his question but someone - who shall remain nameless, LOL - wants my source for the pre/self test of the Knock Sensor system and I can't find it.
I didn't find it in the 86 FSM, but I KNOW I read it somewhere. Just don't want guys to think I make up things. LOL
Does anyone know where I can find a source for the self-test that the ECM does on the system when the engine is first started?
Thanks,
Jake
Last edited by JAKE; Sep 18, 2010 at 09:28 PM.
