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

Car Knock Sensors and Engine Noises

Question:  2003 Acura NSX miles: 34,000. I ran into your website and couldn't help myself telling you about my ordeal. I'd appreciate anything you can do to shed some light on this. Three weeks ago, I was driving at about 80-mph, when I heard knocking in the engine upon arrival to a toll. Since I've done my share of repairs on cars in the past, from replacing fuel pumps to bearings through the crank, I was almost certain it was a rod that lost either a bearing or something of the sort. I took it to the "experts" at Acura here in PR. They looked at it for about a day and they stated that it was just time for new bearings-all other components had sustained no damage due to my prompt reaction. I found it reasonable, so in went the new bearings - they called the next afternoon and said the car was ready. Arrived the next day, paid the $380 and wait for my car in an outdoor area. The Svc Supervisor went for my car, which was about 50 meters away.

 Immediately after starting the car, I heard the knock for about 1 second and he powered the car off and restarted, obviously, once the oil reached it, the knock quieted down. As he drove on, which in my opinion shouldn't have even happened, him being somewhat knowledgeable in this area, reached me, I mentioned that I heard it still knocking. He made a puzzled face and powered the car off/on again. I commented that it wasn't going to knock at startup again because oil had already lubricated the parts, but had him pop the hood where I pulled the throttle cable a little and the knocking became more louder. He and the Svc Manager insisted that it may be the timing belt at which time I paused to keep myself from falling.

 I asked him to pull the spark plug cable #2 where I heard most of the knocking; with the engine running and they were convinced that indeed the engine needed another look. Next day, I get a call from them stating that the crankshaft although passed all their initial tests the 1st time around with flying colors, now has irreparable damages that may need a replacement. [MSRP$1280; $1400 in my book] Now it's costing me up to $1500 in labor costs alone, plus $700 in parts that I've had to hunt down myself. Is there something I can claim or do about this in your perspective? I understand there's an ethic issue involved here, no. What tells me that in a month's time, my piston head won't warp or bend a valve?

Answer: When someone brings a vehicle to us with the symptoms you described, the first thing we do is tear down the engine to check the crankshaft and the connecting rods. If okay, we replace the rod bearings and reassemble the engine. If the crank and rods do not check to proper specifications, we replace the crankshaft with either a new or re-ground crankshaft. The connecting rods are then replaced with new or re-sized rods. If the crankshaft and rods check okay, the job is relatively inexpensive. Otherwise, the cylinder head has to come off, the pistons removed and the crankshaft replaced which comes close to a complete engine overhaul.

Question: 2004 Toyota Camry mileage: 26,000.  My wife and I just purchased a Toyota Camry.  The car is in fair condition, but here is the problem.  Upon starting the car (cold start only) the motor knocks for four seconds or so.  It sounds like the knock might be coming from the top of the block.  Well, the oil that was in the crankcase when we bought the car was black as tar, might have even been summer weight.  We had it changed to 5W30 Castrol, (along with a transmission flush, coolant flush, power steering flush, PVC and breather, and air filter) hoping that the thick, old oil was not getting to the top of the block, or the passages were just plain blocked with crud and needed to be worked out.  Well, this morning it knocked again.  I thought it was only for two or so seconds this time though.  The new oil, after only having twenty miles on it, already looks like it needs to be changed.  This will be done again shortly.  If the knock does not go away, what could the problem be?  Bad oil pump, etc.  Any ballpark ideas on price?  I hate to say it, but should we look at replacing the motor.  I know it is hard to say without seeing and hearing the car, but I would appreciate any suggestions.  Otherwise than this, the car seems to operate fine.  Thanks

Answer:  Your engine knocks because of extended clearances in the crankshaft area. The engine oil comes up to pressure cushioning the noise. The problem is the noise is telling you there is a deep engine problem.

Question: 2002 Mazda Prot�g� mileage: 38,000.  I just had a service done on this car (a little early because I didn't know it's previous maintenance history).  I had plugs, fuel filter, timing belt, and all fluids changed.  When I got my car back, it had terrible engine knock under acceleration or load.  It had a small knock before, but this is much worse than it ever was before.  I am wondering what I should do?  Could the timing belt have been put on wrong or I am just hearing an old problem better now that everything has been replaced?  Any help would be great thanks.

Answer:   There is a very good chance that the timing belt may be off.  This would change the ignition timing and cause the ignition knock or pinging.

Question: 2002 Mazda MPV mileage: 34,000.  It has a 3.0L V6 engine with 34,000 miles.  When I start it up cold, the engine makes a tapping noise for about one to two minutes.  As the engine warms up, the noise goes away.  When you raise the hood and listen, the noise seems to be loudest near the valve cover on the passenger side.  The engine does not use any oil between changes (3000 miles), and is very quiet when warmed up.  Is this noise anything to be concerned about?  What can be done to remedy this problem?

Answer:  From what you describe, you have a hydraulic lifter that is failing.  Replacing it should fix your problem.

Question: 2004 Ford Crown Victoria mileage: 62,000.  Hello, I am a deputy sheriff with a local sheriff's dept.  I drive the above listed car.  My problem along with several hundred other deputies is pre-ignition spark knock.   We can use several different kinds of gasoline but we must use 87 octane.  I don't of any way lower the timing on a D.I.S. Our county service techs don't seem to know what to do.   I was a service tech for 10 years before getting into law enforcement.  Any help will be greatly appreciated.

Answer:  The ignition timing is adjustable.  You have a octane adjustment bar that needs to be removed. It will retard the timing 4 degrees to stop the engine noise.

Question: 2002 Nissan Frontier mileage: 43,000.  After 10 minutes of running knock which I only hear at idle goes away.  How long can engines last with this problem?

Answer: Your engine knocks because of extended clearances in the crankshaft area. The engine oil comes up to pressure cushioning the noise. The problem is the noise is telling you there is a deep engine problem.

Question: 2001 Toyota Truck mileage: 58,000.  Hello, I have a question concerning the knock in my engine.  I was driving down the road this weekend when I had a sudden drop in oil pressure and my engine had this awful knock.   I think it might be a flat cam or I threw a bearing what do you think?  It still starts up but it sounds awful.  I am going to buy a master rebuild kit today and I am gonna start as soon as possible.  I am just gonna pull the engine; any pointers on what I will need to rebuild the engine.

Answer:  You probably “spun” a rod bearing.  A total rebuild would be best rather than just a crank kit.  When a rod bearing fails, it spreads metal pieces throughout the rest of the engine.  You may be money ahead to replace your engine with a rebuilt one.

Question: 1996 Ford Ranger mileage: 178,000. The engine has a loud knock when I first start it like the lifters are not getting any oil to them, the dipstick says I'm full on oil yet the pressure gauge never registers above zero even at highway speed, yet the truck seems to run OK after it warms up, not great, just OK. It seems to rattle when I accelerate. I haven't seen any sign of an oil leak, just a small leak from the transmission. I usually use a 10/40 grade of oil. Any help would be appreciated.

Answer: You may have low oil pressure. With engine the stopped, remove the oil pressure-sending unit. Replace with a temporary mechanical oil pressure gauge. Start the engine and note pressure at idle and at 2000 RPM. At 2000 RPM, the pressure should be approximately 40 to 50 pounds and about � that at idle. If you do not get these results, you may have internal engine problems. One possibility is a stuck oil pressure relief valve. Another possibility is an engine bearing (rod or crank) has failed. That may be the source of your knock.

Question: 1989 Ford F-150 5.0 mileage: 300,000. My engine spark knocks on hills and during acceleration, but only when the engine is warmed up. Switched to 89 octane from 87 but it did not help. Engine has new plugs. Any ideas?

Answer: Check ignition timing and the knock sensor; it may be failing. It is located behind the intake manifold in the block.

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