i have a 1997 chevy truck. what dose the knock sensor really do and could it cause a fantom miss?

Answer 1

Engine Knock is another term for predetonation or early detonation of the air fuel mixture in the engine cylinder as it is in its final stages of the compression stroke. Early detonation of the air fuel mixture can cause knock as the cumbustion takes place before the piston is within the correct range for detonation at near top dead center of stroke. During predetonation the piston not only is still trying to compress the air fuel mixture but now the air fuel mixture is in detonation and is expanding as it burns. The added impact on top of the piston will actually ping or make a knock sound that resonates throught the engine casting. The bad part, as if this sin't bad enough for satisfactory performance, is that this compressed detonating fuel is actually pushing cylinder pressure beyond what it is designed for and results in piston burn and other valave train problems and if it is allowed to continue will result in engine failure. Many a drag strip evening was cut short due to burnt pistons or worse for those that didn't understand how to detect knock and adjust to prevent it. This probaly isn't the stress you are subjecting your truck to but in time an uncorrected knock will stop knocking just about the time the engine fails. Three of the more popular culprets that cause knock are 1) low grade or too low of an octane rated fuel for which the motor was designed to operate, 2) improper engine timing, and 3) high carbon build up in the combustion chamber. The Knock sensor detects the Knock resonating through the engine casting and the computer tries to adjust fuel delivery and engine timing to prevent damage and try to dial into the conditions that combustion is occurring. Yes a knock sensor could cause a phantom miss but it is due to something else causing a knock and the sensor and control module is trying to tune back the engine to prevent it. If engine maintenance and tuning is in good shape and there are no other component failures causing knock one of the easiest ways to determine if it's the fuel you are using is to go to a reputable gas station and bight the bullet and put in a good dose of premium grade fuel. If perfromance improves and the phantom miss goes away then the decision is what do you want to pay for, higher priced gas or a new set of pistons. If it doesn't clear up its time to hook up a scope and address some tuning issues or locate another failing component that is causing the problem. I have a 95 K-2500 with a 454 CID TBI engine with 220K miles. It demands premium fuel and I too recently tried the cheaper stuff and a recent trip home with a loaded car trailer behind it was almost embarrassing. I went back to premium and on the next loaded trip I was experiencing the typical power house I have been used to for more than 12 years. The truck busted me being cheap at the pump.

Answer 2

I own a shop, and without getting too technical here, lets just say the knock sensor retards the ignition timing up to as much as 10 degrees, and would play no role in a miss. A phantom, or intermittent miss shouldn't be caused by the decrease in ignition timing by the knock sensor. Try this: Use a long extension or pipe, and bang on the engine block near the sensor. As you do this it will lower the timing, and it should cause a noticeable change in the engine rpm's. This means the knock control system is working properly. Any problem with the circuit will set a code, and a check engine light should come on. A miss as you are talking about is usually caused by a sticking injector. Purchase a bottle of STP (black bottle only) fuel injector cleaner, and add to 3/4 of a tank of fuel, and this should resolve the issue. This miss can also be caused by fire jumping from a plug wire, but from my experience, a fuel injector sticking momentarily is the culprit 90% of the time.
Glad to help out, Good Luck!!!

Answer 3

Chevy Truck 1997

Answer 4

I would guess that as the knock sensor changes the timing it is possible it could. But more likely an injector or a spark plug or plug wire. If it is detectable it will set a code and turn on the check engine lite.

Answer 5

A knock sensor consists of a small piezoelectric microphone, on the engine block, connected to the engine's ECU. Spectral analysis is used to detect the trademark frequency produced by detonation at various RPM. When detonation is detected the ignition timing is retarded, reducing the knocking and protecting the engine. you may have to replace your plugs and use a higher grade of gasoline .

Answer 6

if the engine pings/detonates/knocks then the sensor will retard the timing somewhat to stop the knock...