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Old 07-22-2004, 07:17 PM   #1
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GM engine knock on startup

Ok, I know we've talked about this before. However, I was under the impression that GM fixed this issue for the 2004 models. The one where for the first 20-30 seconds of startup, the engine has a slight knock to it.

I found a new 2004 3/4 ton Suburban today with the 4L80E and 8.1 and sure as all hell, the thing did the piston slap (knocking sound) for about 20 seconds after it was started.

Anyone else have an 2004 8.1L? Does it too have the knocking sound from what sounds like the piston slap?

Also, just to verify, those of you that do have the 8.1L are you getting about 10mpg all around (towing, city, hwy, etc)?

Thanks.

Eric
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Old 07-22-2004, 07:51 PM   #2
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new new or slightly used?

what kind of oil filter is in it? was it sitting for an extended period before starting it?

john
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Old 07-22-2004, 08:00 PM   #3
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19 miles like new new.

Not sure how long it sat, but I ran it for about 5 minutes got warm, not hot in the 85 degree amb outdoor temps. Turned the key off, let it sit for about 5-10 minutes and she did it again.

It had whatever the standard PF GM oil filter came installed from the factory.
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Old 07-22-2004, 08:46 PM   #4
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2001 8.1 in a 2500hd with no knock. I get 14.9-15.1 on highway, no A/C and 68 mph. In town with A/C I get either side of 10 mpg. Towing at 65 mph I get 11 with A/C and 12 without. I also have the 3.73 rear end.
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Old 07-22-2004, 08:49 PM   #5
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David,

You burnin any oil?

Thanks for the info you shared.

Eric
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Old 07-22-2004, 09:17 PM   #6
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have the dealer let you take it "on approval" for a couple of days and see if the noise quits or gets worse. or the deal's off!

otherwise, walk away!

btw, is a mexico truck?

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Old 07-22-2004, 09:24 PM   #7
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I have the 8.1 in my 2002 Avalanche and love it. A really sweet running machine. Yes it uses as a quart of oil between oil changes - have to remember those pistons are about the size of milk jugs - oil use is expected. Get up to 16-17 miles to the gallon on the highway, 10 mpg towing 25 Tradewind and 12 mpg towing my old 59 Traveler.

Had the front end aligned the other day, had a hard time getting it back from my mechanic after he drove it

I don't get any knock at startup, its been a little chattery until everything gets going. Again, don't forget its a BIG motor.

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Old 07-22-2004, 10:19 PM   #8
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That's a good queston John. Not sure where it is assmb, but I seem to recall some place in the US.

Ken, thanks for the info....you know, we owned a 454 7.4L in 1985. It towed most of it's life a 24' SOB. The truck in 1998 had 135k on it and it too was a big engine. It never burned any oil between changes-- never, not once. The 8.1L is a 496. To me I agree it's a great engine, but I think a quart between oil changes is a bit much considering what I've seen out there first hand.

I think I am just gonna walk. It is a nice truck though.
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Old 07-22-2004, 11:01 PM   #9
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I think if it is already making noise it is best to steer clear. Doubtful it will get better. I can't believe that GM hasn't completely fixed it yet. They said it was fixed in '03, then '04, and yet at the same time they also claim it won't hurt longevity. Uh-huh. I recently heard a new one start up from 10 ft away and it clattered pretty bad. Noises like that worry me too much. When I had to get a new truck this Spring I seriously looked at the new 2500hd, since my last truck was a K2500, but I just knew how bummed I would be if I got a bad one, so I decided not to chance it. Its a shame because the GM trucks drive really well and the 6.0 is an awesome motor if you get a good one, which I'm sure most are. My luck though, would be to get one with a problem.

The old 5.7 was so incredibly reliable. What happened?

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Old 07-23-2004, 12:55 AM   #10
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My 2004 4x4 2500 8.1 with 4.1 axle Avalanche is a little chattery on startup like Ken's and then quiets down, but no knocking. I hear the chatter probably more since I park in my garage with the echo on the walls. Gets about 12mpg city/hwy, 14 highway, 10 pulling my 22' CCD. Great tow vehicle!
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Old 07-23-2004, 05:50 AM   #11
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eric

one other point, ask the dealer to change the oil then start the truck up again.

they may have 0w30 in it from the factory!

i'd still walk on this one! good thing you didn't order one to hear it clatter on startup!

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Old 07-23-2004, 07:08 AM   #12
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Yea, I also reviewed the www.pistonslap.com website. It appears that the new pistons that were discussed for the 02 model year may not have appeared as once thought. I could live with a bit of knock at startup as it was slight, but as indicated, it might get worse if it is already doing it at 19 miles on the odo. Plus some of the oil consumption comments also have me perplexed. I mean an engine that is still fairly new (IMHO) not be chewing up a quart of oil between oil changes. Maybe I'm just out if touch. None of the cars my fam or I have ever owned 305s, 307s, 350s, 400s (a few 60s 400+s), 454s have ever chewed any oil in their life, or at least that was noticeable on the dipstick.

I suppose if I wanted the piston slap sound, I'd get a Duramax, which frankly, I still might do since the same gassers that are placed in the 3/4 Burban, go into the Silverados as well.

Anyone own a Duramax that drinks oil?
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Old 07-23-2004, 08:21 AM   #13
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Put a A/C filter on it.

Most start up knock is due to crap anti drain back valve in the filters. Amoung the worst are FRAM and anything you get a oil change place. Stick with a A/C filter and you will be ok. Bosch filters are made by the same manufacture as A/C and I have had good luck with them as well.

My 88 Burb was doing this when I bought it. Change the oil and got rid of the fram that was on it and it has to sit for several days now before it will do it at all.

A good read.
http://minimopar.knizefamily.net/oilfilterstudy.html
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Old 07-23-2004, 09:32 AM   #14
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THe PF-XX filter I was talking about was the AC Delco brand, I was just calling it the model number PF-??

Anyway, all trucks that I heard the rattle on startup had AC Delco filters.
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