Engine knock... April 13, 2006, 01:57:30 PM I've been experiencing problems with engine knock. Over a year ago it started as a quiet tapping and has developed into a full on loud knock. I've been running around with it like this but I want to try to fix it now that I have a little extra money.When I start the car, it is fine and there is no knock. If I move it in the driveway, it is fine as well.If I rev it or drive it, the knock comes in as the rpms drop usually showing up around 2000-2500 rpm. The knock disappears or at least can't be heard above 2500 rpm.I don't hear any knocking when I'm accelerating or at any point when I'm on the gas for that matter. It is only audible when the car is idling after a drive or coasting through a gas station etc. So under load, it is fine, but I hear the knocking when it's not under load.My question is, what do you guys think it is? I've researched and found possibilities ranging from exhaust to lifters to a rod knock.I doubt it is the exhaust but I'll take another look.The car drives fine and doesn't seem to have any loss in power. It doesn't use much oil and the oil always comes out clean. Oil pressure is fine as well.I was looking at rebuilding the motor but I really don't want to go through that right now. Any ideas? Quote Selected
Engine knock... Reply #1 – April 13, 2006, 05:45:01 PM Hmm mine knocks when the engine is idling at about 800 rpms after a drive. When I first start it up there is no knock. After the drive if I rev the engine to 1,000 rpms the knock goes away and isn't heard all the way to redline. Funny thing is it only knocks in park. If it's idling in drive at 800 rpms no knock . I would think that in both our cases that if we had a rod knock the sound would get worse as the car accelerated or when the rpms went up. Then again yours knocks at a higher rpm than mine does so I couldn't say. Quote Selected
Engine knock... Reply #2 – April 13, 2006, 05:58:12 PM sounds almost like a deisel right? valve train.... Quote Selected
Engine knock... Reply #3 – April 13, 2006, 06:16:51 PM Yeah, its weird. From what I've read, if it was a rod knock, I'd hear it all the time, accellerating or not/ just starting or not.I'd like to think valve train since I won't have to pull the motor and rebuild it. Just the heads.I just couldn't imagine this kind of sound coming from that. It sounds almost like two pieces of particle board slamming into eachother.It's such a PITA to describe. Maybe I can get a sound clip of it. Quote Selected
Engine knock... Reply #4 – April 13, 2006, 06:42:09 PM You can usually tell a bottom end knock from a top end knock by the frequency - a top end knock will be at 1/2 the engine RPM (because the cam only spins at half the engine speed). Generally if the knock is slow enough to actually hear the individual "knocks" at idle it's valvetrain. If it sounds more like a rattle it's bottom end... Quote Selected
Engine knock... Reply #5 – April 13, 2006, 06:49:21 PM Quote from: Thunder ChickenYou can usually tell a bottom end knock from a top end knock by the frequency - a top end knock will be at 1/2 the engine RPM (because the cam only spins at half the engine speed). Generally if the knock is slow enough to actually hear the individual "knocks" at idle it's valvetrain. If it sounds more like a rattle it's bottom end...Bingo, individual knocks I can hear. Okay so it's valvetrain then. That makes me feel a bit better. There's no rattle to it what so ever. I would think any rattling would cause metal shavings in the oil (which I don't have), correct? Anything in particular I should look for or would it just be best to have the heads rebuilt? Maybe it's time to go aftermarket. Quote Selected
Engine knock... Reply #6 – April 13, 2006, 09:16:30 PM get a long screw driver, or a broom stick or something, and poke around your engine with it running to pin point where the knocking is coming from, on my car it turned out to be the alternator... Quote Selected
Engine knock... Reply #7 – April 13, 2006, 11:04:17 PM Quote from: 88cougarxr7get a long screw driver, or a broom stick or something, and poke around your engine with it running to pin point where the knocking is coming from, on my car it turned out to be the alternator...Very good point. Also check the serpentine belt and all pulleys. A chunk out of a belt or pulley can cause a knocking sound. You forgot to mention that you should stick the other end of the screwdriver or broomstick in your ear though (use it as a stethoscope) :D5.0WillGo: The valvetrain knock doesn't necessarily have to be in a head (in fact it's not likely to be there). A worn cam lobe, bent pushrod or sticky lifter is more likely than something in the head. My first guess would be a sticky lifter. Quote Selected
Engine knock... Reply #9 – April 13, 2006, 11:13:44 PM My motor mounts are worn out and the safety keeper thingys make a nocking noise when they bang together. The inside of the thing is all shiny where its been rubbing. Quote Selected
Engine knock... Reply #10 – April 14, 2006, 01:00:21 AM 5.0willgo...I've been trying to figure out the same sort of noise for many months now as well. I replaecd the tensioner pulley with new, replaced the water pump (started leaking shortly after and thought I had found it), new belt, and many long hours of listening with a stethescope. Problem is, I can only duplicate the noise when driving, or when raising the engine RPM's and noone can keep it constant when we do this. As the RPM's drop, the noise goes away. Everything sounds fine through the stethescope. I get the noise when it's cold, or after it's been running for awhile. It has gotten louder, but hasn't changed tone or anything. Also doesn't feel like any lost power. Gas grade idn't change anything, oil looks good with each change, and I have been TOTALLY FRANTIC trying to figure this out. It's driving me crazy. This is my daily driver, and I've felt like I was racing a clock before it leaves me stranded. I SHARE YOUR FRUSTRATION. I've actually started looking for a motor to rebuild as I can't have my car down for long when the time comes to tear it apart. Sounds like the only difference from what you are explaining is your 5.0 and my 3.8. Quote Selected
Engine knock... Reply #11 – April 14, 2006, 01:44:55 AM My '89 Mark is knocking as well.. has to be around 1/2 throttle or higher, and under load. Set timing, didn't go away. Doesn't go away with 89 or 93 octane. I'll change the plugs again in case I gapped the last ones wrong or the SeaFoam REALLY fouled them up, but the one I pulled was pretty clean. Friend of mine rode with me and said he thought it sounded like it came from the exhaust, but I think it sounds like it's coming from the engine.Thinking about trying that Auto-RX stuff to flush the engine, if my problem ends up being similar to what's being discussed here. (lifters, etc.) *shrug* Quote Selected
Engine knock... Reply #12 – April 14, 2006, 04:59:10 AM I'm still debating the pre-cats in the Y-pipe. I had a new cat converter put on about a year ago (wouldn't pass the da?!#$ emissions test), and the mechanic tells me they will rattle when they are bad, but I'm not sure what they would actually sound like. Guess I'm going orward with the plans to pick up a spare 3.8 to rebuild in the garage and drop in. Quote Selected
Engine knock... Reply #14 – April 14, 2006, 05:24:30 PM Ugh, looks like I'll have to tear the motor down regardless.Oh well, it will be a learning experience.Thanks for the input guys.I just better triple check the exhaust to rule that out first. Quote Selected
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