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  #1  
Old 10-03-2009, 12:37 PM
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Default Engine "knocking" or "tapping" noise

Hey guys. This may sound weird, but here it goes. About 4 days ago here at college, I went to start up my truck. It was like 45F, windy and after a heavy rain. It started without a hitch, but then I hear a sequential "knock" or "tap" noise coming from the engine. The oil pressure shoots up to 60-65PSI as usual on startup (running 10W-30 with Lucas Oil Stabilizer). The noise dies away after a couple minutes. I always let it warm up like 5-10 minutes anyway if it hasn't been running for more than a few hours. This noise only happened last winter when it was like 20F and it went away after like 10 seconds. It also has happened 3+ times since it started getting cold, rainy and windy here. The car has 80,350 miles if that matters.

Am I looking at a complex repair, or something simple as another oil additive? Also it is in the 60s today and nice here, so I'll update later when I go out and fire it up.

P.S. Sometimes if I don't let it warm up and I just go after startup, it makes the same faint noise, but it goes away after a couple minutes. It has done it since I got the car at 59,000. No codes are in the computer and the oil, coolant and ATF are normal colors.
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2007 Chevy Trailblazer LT (22,000 Miles)
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1998 GMC Jimmy 4x4 SLT (128,000 Miles)
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  #2  
Old 10-03-2009, 12:42 PM
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sounds to me like maybe your oilpump is taking a crap if your pressure is skyrocketing
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  #3  
Old 10-03-2009, 01:42 PM
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mine does the EXACT same thing. EXACTLY the same. only in cold weather.


knock, knock, knock, knock, knock.... (pause)....knock, knock,knock,knock, knock ....(pause)...knock, knock, knock, knock,knok


just like that right?

i dont know what to tell you, i think (just a wild guess here) it may have something to do with a knock sensor and or maybe worn distributor gears.


also, i wouldnt call 60 psi oil pressure from a cold engine skyrocketing, i get 60 psi daily.
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  #4  
Old 10-03-2009, 01:51 PM
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60 is always normal for mine at startup. Drops to 35-40 when hot and idle, 50-60 at 65 MPH/2000RPM.

Also the noise sound about right, except it is constant for a couple minutes and it isn't that loud, and it dies away until the normal sound and the coolant temp is only a couple bars above 100. I'll have to see what happens when i fire it up in a little while. It is almost 70 here today.
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Mods: PCM of NC Transmission cooler, Interior LEDs

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Mods: Eurotails, Cold Air Intake, B&M transmission cooler, Throttle Body Spacer, Posi-Lok, interior LEDs
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  #5  
Old 10-03-2009, 02:50 PM
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Man, if I worried about all the knocks in my 97 Blazer 4x4 I would be in the "nut ward". Mine knocks at start up it knocks over 3000 RPMs under load, 1800 RPMs no load, etc. The thing about it is it has been doing this for 36,000 miles now. Glad I didn't jump in & try & fix it. Your knock sounds like lifters rattling until they get oil. NORMAL stuff on older used vehicles. Just drive it & enjoy it.
PS. If mine blows with under 150,000 miles I'll replace the motor. If it goes over that I'll buy another Blazer.
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  #6  
Old 10-04-2009, 05:50 AM
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Lightbulb

http://www.blazerforum.com/forum/sho...ld+start+knock








hope the link works.........ive been looking into this too. i have 182,000 on my 97 2 door. knocks on cold startups. i figured it was piston slap, until i started reading everything. i also ran across on onother forum which stated he used stp or whatever flush then changed oil,, his knock was gone. had me curious, not something i like to do on engines with these many miles!!!! but i did, yesterday morning infact.......its been getting colder here upstate ny, so its been getting louder and louder too the point making me nervous.....and embarresed!! i noticed a huge difference straight after the oil flush and change...i just ran outside while typing this and started her up after sitting all night, currently 43 degrees amazed myself i could barely hear the knock at all!!!! could be just a fluke,,, but i think i might run another flush through and see what happens.... but it does make sense gunk and sludge blocking passages until oil warms and thins out enough to bypass it. the only problem doing this is.....as im worried about removing too much sludge and creating oil leaks. i hope this helps, and good luck!!!!



btw i run castrol high mileage 10-30 and a bottle of lucas
cai, 31x10.5 bfgoodrich tires with a 2" body lift
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  #7  
Old 10-30-2009, 09:05 PM
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Quote:
Originally Posted by cedarjunki View Post
http://www.blazerforum.com/forum/sho...ld+start+knock








hope the link works.........ive been looking into this too. i have 182,000 on my 97 2 door. knocks on cold startups. i figured it was piston slap, until i started reading everything. i also ran across on onother forum which stated he used stp or whatever flush then changed oil,, his knock was gone. had me curious, not something i like to do on engines with these many miles!!!! but i did, yesterday morning infact.......its been getting colder here upstate ny, so its been getting louder and louder too the point making me nervous.....and embarresed!! i noticed a huge difference straight after the oil flush and change...i just ran outside while typing this and started her up after sitting all night, currently 43 degrees amazed myself i could barely hear the knock at all!!!! could be just a fluke,,, but i think i might run another flush through and see what happens.... but it does make sense gunk and sludge blocking passages until oil warms and thins out enough to bypass it. the only problem doing this is.....as im worried about removing too much sludge and creating oil leaks. i hope this helps, and good luck!!!!



btw i run castrol high mileage 10-30 and a bottle of lucas
cai, 31x10.5 bfgoodrich tires with a 2" body lift
I know this is an old tread, but I switched to Mobil1 5W-30 High Mileage (from the oil change place near my house), same oil pressure and everything (also with the Lucas) and the engine runs quieter at times. Sometimes I don't even realize it is running if I am stopped in a parking lot. I have to look at my gauges to tell it is running. Sometimes a little tick at startup if it is below 40 or if it was raining hard, but it runs quieter. Just giving a tip. Thanks.

BD
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  #8  
Old 02-10-2010, 09:04 PM
 
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My 98' knocks terrible below 40 degrees. The colder it is, the harder and longer it knocks. Goes away as it warms. Quiet all summer. I've tried all kinds of additives which slow the front main seal leak but does nothing for the knock. It blew the intake so I put a set of lifters in it and flushed the crap out of it. Same thing. The good news is it has done it for years and doesn't seem to get any worse. I also have a 1990 boat with a lot of hours, that 4.3 is plain worn out. I have to run 20-50 with stp in it or the oil flies right out the exhaust pipe. It knocks 2-3 minutes at startup to but has never flown apart and still makes good power. The compression is pretty decent but the oil control rings just aren't doing it anymore. I figure it must be piston slap or these engines would have failed ages ago. Just tell your neighbor you converted to diesel.
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  #9  
Old 02-11-2010, 05:19 AM
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My 2000 LT 4x4 has had a "Lifter" rattle every since I bought it in 2002 It had 42K on it, now 100K. It would do it only at starting off from a dead stop then go away. I put some sea foam in the oil and it stop it for awhile (but also started other leaks) and now its back at it. I figure what the hay, its runs great, so don't fix or attemp to fix something that isn't really broke yet. After 58K that I put on it since I have own it, It runs just great (now watch something go wrong, hahahahahaha). Just had that happen, was giving advise about volt meter jumping around when the turn signal was on and a few other problems. I suggested to retighten the battery cables. Had the problem myself and the old whine through the radio, and I'll be damn if I didn't go out and get into the truck and bam, there it was again..When I got home, retighen the battery cables and its gone once again.

Now should I dare to start the truck again? hahahahahahaha....
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  #10  
Old 02-11-2010, 11:51 AM
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If the knock goes away after it warms up a little it is no big deal. The engine is cold, tolerances are tight, Oil is thicker and it just takes a little bit for everything to expand and for the oil to get where it is needed. I have had many cars that knocked a little when it is cold out. If it continued to knock when it was warm out, the valve lash could need adjusting, you could have weak valve spring or a collapsed lifter could be the cause. If it goes away, no worries mate. The simplist fix and least expensiver is adjusting the valve lash. Everything else starts to get expensive. Removing and rebuilding heads and replacing lifters or even bent pushrods. Any item that is out of spec. in the valve train could cause tappet noise.
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Old 02-11-2010, 11:51 AM
 
 
 
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1998, 84, blazer, chevrolet, chevy, dies, engine, enigne, knock, knocking, noise, slight, startup, tapping, till, warm, warmed


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