Help-Name that horrible sound!

[surffj62]

Truck sounds terrible- This is the set up. Cold engine, normal start up and I let it idle for 30 seconds or so before I start driving. Within a few minutes at low RPMs- 1800 to 2100 and low speed 20-35 mph I get this horrible rattle/ grind. Almost like a machine gun but not as smooth. This happens only when I am on the gas, not when I am coasting, no loss of power noted- never has any anyway. Upon accelerating to 35+ it goes away and then sometimes it comes back when I slow down- not on decelerating but when driving under 35 and on the gas. This only happens sometimes- seems not to do it if the engine is warm, but did it when the outside temp dropped and it was raining.

I crawled under the truck and tried to tighten all the exhaust bolts and the bolts around the exhaust/ intake manifold. All seemed OK. It sounds like it is on the front left side. Fan shroud and fan are fine.

I do not think it is anything on the axel, the transmission or anything on the drive train because it only happens under load or on the gas. If I pop the hood and start it and leave it in park and run it up it can go to 3500 Rpm and sound just fine. Truck idles fine- Just had Randy- Ianitscareed do a minor tune up last month and he said it was running great. Oil /Tranny fluid level is good.

Any ideas?

 

[brian]

exhaust leak.

 

[cfdlighthouse]

you may have bad lifters. lifters are the piece between the cam shaft and the push rod that actuate the valves as the camshaft turns and the different lobes raise the lifter-pushrod-openig the valve. Hydraulic lifters are charged(if you will with oil) and on a cool engine with leaky(uncharged lifters) it can sound like a rattle trap until the lifters have filled with oil giving you the machine gun noise that goes away when the engine warms up.

how many miles on the engine?

 

[RockDoc]

Maybe the fan hitting the shroud with a broken motor mount?

 

[surffj62]

Fan shroud looks good- I replaced the motor mounts with the engine swap 3 years 15k ago. Motor has about 86K on it. I have given the valve lifters a thought but Randy did a valve adj on them last month and said that it was looking good. It does sound more of a leak though.

Any ideas on how to trace an ehaust leak? I guess start on the front and go backwards and check every bolt and torque to spec. Had one leak last year and fixed it.

Could it possibly be a specific gear in the tranny ie 2nd?

Thanks

 

[REKCUT]

Does it only do it in a certain gear? Can you manually shift it and get it to happen in more than one gear?

 

[cfdlighthouse]

if you think its a leak just look for the carbon trails, ie black soot eminating from the exhaust manifold, egr setup, flange gaskets etc.
i would start with the manifold gasket though.

 

[brian]

it's a gasket gone south. tightening will do nothing.
find and replace is it.
you mentioned it does it only till it warms up? that's a classic early sign, give it another few weeks and it will be easily found.

 

[surffj62]

I think that it has been found. For just a second it sounded like the rattle on my 100 series cats heat shield........ so went under and I found a weld that was broken. I drilled one of the tabs and put a bolt and lock washer into it- tabs only not the cat.. I was so happy- I thought that it was fixed. Until I drove it #^#$!$!

I put it back in the garage and took my BFH out and beat the exhaust with the rubber mallet and found that one cat had a rattle in it like it had a loose golf ball inside.
I think that I am on to something here. So I am going to get it replaced or cut out all together. I am going to start a new thread for my next question

Thanks for the replies!

 

[vipergrhd]

sounds like

chitty chitty bang bang chity chity bangbang,just joking couldn't help it.hope you find the cause.

 

[surffj62]

It was the a cat that had gone out. The honeycomb on the inside had split in half and turned 90 degrees and was blocking out that exit to the muffler and the rattle and banging was when it would go from 90 to inline and back and forth.

New high flow cats put in. So far it runs and idles better. Not a significant power increase. More importantly, hopefully the mpgs will go up some.

 

[Fharfignugen]

im still curious about the noise...did it also sound like the car was gonna hock a loogie, cause my fj60 does that at around 2300 rpm in gears 1-3...