odd knock

[kb3jhp]

i have a 96 bravada with 90000miles on it and use mobil1 and a pure one filter. in the morning or when it has cold off i will start it and pull out and at 2800rpm it makes this knocking sound it makes no noise until 2800rpm and stops when it warms up is this a rod bearing or what it is driving me nuts also i tryed useing a higher octane no change

[rlith]

Is it coming from the top or bottom of the engine?

[kb3jhp]

cant tell it only does it when driving it doesent do it if i rev it up to 2800 parked

[rlith]

Originally Posted by kb3jhp

cant tell it only does it when driving it doesent do it if i rev it up to 2800 parked

Use a wooden dowl while the motor is running. Touch both valve covers then touch the oil pan (with you ear on the other end of course) and you will figure out where it's coming from.

[BlazerLT]

Is their any vibration with this knock?

[534BC]

My bet is pin/piston

[blazes9395]

Like 534BC mentioned, it could be piston slap as a result of a loose/worn pin, or just the piston itself, until it warms up. You have to take a good look and take a listen to the engine when its cold, something like rilth mentioned.

[BlazerLT]

I am almost leaning towards a torque convertor going bad seeing it happens only at a certian rpm.

[kb3jhp]

ther is no vibration with it

[Rick Norwood]

O.K. this is a long, long, lonnng shot, but I have a friend that had a similar issue with a Brand-X (Ford) truck. To cut to the chase, a couple of the Bolts/studs on the exhaust manifold had broken off causing the manifold to clatter until the truck warmed up enough to expand the metal and stop the clattering. I won't cost you anything to look for broken bolts/studs. I suggest you get a small inspection mirror from your favorite parts house. after he replaced the broken studs, the problem went away.

[kb3jhp]

yep i checked the exhaust dident fix it

[kb3jhp]

this is driving me crazy

[534BC]

How long has it been doing it (in miles? ) If you were to take it to an engine shop an experienced ear can tell you what it is.

A rod or main may not last very long, but a piston or pin can knock for a very long time. An oil sample test can also be helpful for telling what it is .

[muddog321]

Is this really a knocking or a lifter noise - you should be able to tell and if upper end/lifter check your lower intake manifold gasket for a leak (look at the reservior for dropping fluid level) - as water sprays in the valley it gets on the lifters, cam, and balance shaft and usually evaps so you will not see it in the oil.