Repair Topics / Knock Sensor-1 / Knock Sensor-2

Car Knock Sensors and Engine Noises

Question: 2002 Mitsubishi Eclipse mileage: 53,200. I hear a knocking noise coming from the engine. I can hear it sometimes at idle but mostly when the engine is revved to 2-3k RPM. The sound seems to go away if I unplug the spark plug to the #4 cylinder. Any suggestions on what it could be?

Answer: It could indicate a possible broken piston or broken ring, or a failing wrist pin or rod bearing or a possible blown head gasket between cylinders on the #3 and #4 cylinders.

Question: 2001 Dodge Dakota mileage: 70,200. I have loud knocking sound when the throttle is pressed down halfway or more, and the knocking gets louder the further I press the pedal. However, the engine idles fine and accelerates smoothly at low throttle. The car also uses more gas than usual. Using high-octane gas or additives doesn't make the problem go away. I hooked up a code scanner, and the EEC-IV computer shows the following trouble codes: CODE 31: "EGR sensor voltage too low". I changed the sensor and cleared the codes, but it's still showing this code. CODE 41: "Oxygen sensor readings constantly show a lean condition". I also used a sensor tester, and it also shows the oxygen sensors are reading a constant lean condition. I replaced both oxygen sensors, but the engine is still running lean and giving this trouble code. In the past 5000 miles I have: 1) Changed the spark plugs, spark plug wires, air filter, fuel filter, and battery. 2) Checked the ignition timing and timing advance. 3) Checked for any vacuum leaks. I don't think there are any, because a vacuum leak would make the engine idle too fast, but the engine idles fine. 4) Checked and cleaned the fuel injectors. I used a fuel injector and harness tester, and they open and close properly with no obstructions to the fuel flow. 5) Checked the fuel pressure. It reads 35 PSI, which is within the normal range. 6) ** Hooked up a vacuum gauge. It shows a steady 15 when idling in drive, which seems too low. 7) Checked the Rpms with a tachometer, and it idles correctly at 550 Rpms. 8) Checked the charging system, which reads a constant 13.8 volts. In the past 20,000 miles, I have: Changed the EGR valve, timing chain, gears, camshaft, hydraulic lifters, and alternator. Other observations: I believe the main crankshaft bearings are slightly worn, as indicated by low oil pressure and a knocking sound when engine is first started. Also a slight ticking sound coming from a hydraulic lifter on cylinder #3. I would very much appreciate any opinions, guesses, or even blind hunches from you gentlemen before I take this car to a repair shop.

Answer: You are having internal engine problems. You possible have a broken piston or broken rings, Blown head gasket between cylinders can also cause this condition.

Question: 2001 Chevrolet Impala mileage: 84,000. I've got a knocking problem with my car that is driving me nuts. The knocking occurs when about 1/3 to 1/2 of the throttle is engaged. I've tried different brands of fuel, different grades of fuel, replaced the EGR, and run 2 bottles of complete fuel system cleaner with little results. The fuel system cleaner helped some, but the knock is still exists. When I mash the throttle and downshift, the knock ceases. Under almost no engine load, there is no knock. Under high Rpms and engine load, the knock ceases to exist, probably because my ECU doesn't look for EGR at wide-open throttle. I do not suspect a fuel delivery problem because I plenty of power at high load/RPM. I do not suspect an ignition problem either because I've been told that if my opti-spark is bad, I'd have lots of problems at high Rpms, which I don't. I'm frustrated at this point because when my engine knocks. The check engine light is not on. I'm afraid that eventually I'm going to damage something. Can you shed some light on this mystery knock problem?

Answer: Change the knock sensor. What happens is the sensor as far as the PCM is ok but in reality the knock sensor has lost its ability to detect minor knocks and only sees the larger one therefore not triggering the" Check Engine" lamp.

Question: 2004 Jeep Grand Cherokee mileage: 25,000. I read about the "knock sensor" that you have alluded to in answers to other questions. Does my model have one of these? I am experiencing extreme knocking when I use anything but premium gas! This has been going on for a long time now, but has really only hit home recently with the rise in gas prices. Would the knock sensor be the only thing that could explain this problem, because I have asked my mechanic before about it and they didn't mention this?

Answer: Your car may not be equipped with a knock sensor. Check the EGR valve. If it is not functioning properly, it can cause engine pinging.

Question: 2004 Cadillac Deville mileage: 33,500. The Deville began sounding as though it had a rod knock that would develop during normal driving. But as soon as the check engine light would come on the knock would disappear. Then it began on start-up, with the same result as the check engine light came on. Upon pulling the engine down and checking the bearings and the crank with a micrometer, we found the bearings and the crank to be perfect to specs. We replace all the bearings, buttoned up the engine, and began again. With the knock still present, we removed the air cleaner and found the knock to be coming from a backfire through the TBI. We checked for vacuum leaks and found none, then we went step by step through the ignition system till all components were replaced, still the same result. Earlier this year I gave up on finding the problem in the engine after checks in the valve train, timing gear, and all hard parts had been checked, cleared of fault or replaced. I then changed the ECM, no change. So I bought a replacement engine and upon fire up no knock. But within one week, the knock\backfire was back. Can you give me any help here before I take 5 gallons of gas and a stick match to this car?

Answer: Change the knock sensor. What happens is the sensor as far as the PCM is ok but in reality the knock sensor has lost its ability to detect minor knocks and only sees the larger one therefore not triggering the" Check Engine" lamp.

Question: 2003 Dodge 1500 Ram mileage: 34,000. We were on a trip when the valves started knocking really loud. We pulled over immediately and shut it down, and added some oil, when I tried to restart it; it ran for about 5 seconds then died. After a LONG tow, I am trying to find the problem. I removed the valve cover, rocker arms and timing belt, camshaft turns smoothly. The crankshaft will turn easily about 3/4 turn then locks tight. The car has never burned or leaked oil, but the oil light stays on. I checked the oil regularly and used synthetic thinking it would prolong the car's life. I am thinking a broken connecting rod, but I'm a carpenter not a mechanic. Any advice?

Answer:   First check the oil pump, if the the spring breaks inside the oil pump the oil pressure drops to almost zero. If you caught it soon enough replace the oil pump to repair the problem.

Question: 2002 Toyota Avalon mileage: 45,000.  When accelerating, a cluttering noise can be heard from engine, especially if accelerating up a hill.  Have tried different types of gasoline.  Nothing helps.  Any suggestions as to what it could be and what I can do about it?  Thanks in advance.

Answer:   Your engine is equipped with a knock sensor, which adjusts the ignition timing to the computer.  Yours may not be functioning properly.

Repair Topics / Knock Sensor-1 / Knock Sensor-2

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