2015 Silverado 5.3 Rattle

[Sean007]

2015 Silverado I had a transmission built for my truck as converter went out. When tranny guy put new tranny in I had him turn off AFM/DOD. Since that I have a intermittent rattle doesn't do it right away have to drive for a while and then it doesn't always do it. I have no codes i.e. misfire and trucks runs great oil psi is steady doesn't run hot. Saturday drove it for about a hour and it started so got home and had wife rev motor so i could try and see/hear where rattle was coming from. Upon this I got under truck and it seemed to be louder towards back of motor close to bellhousing. I am old school and these new LS motors are new to me. Master mechanic for railroad but this has me stumped. I would think if lifter it would do it all the time and not sure about injector pump. Is there a easy way of diagnosing the issue. Any help would be appreciated.

[James Dink]

some triple disk converters rattle at idle 

[Sean007]

Billet converter and it doesn't do it at idle. And sometimes it does it and quits all together.

[It's Tim]

On 8/4/2020 at 8:46 AM, Sean007 said:

2015 Silverado I had a transmission built for my truck as converter went out. When tranny guy put new tranny in I had him turn off AFM/DOD. Since that I have a intermittent rattle doesn't do it right away have to drive for a while and then it doesn't always do it. I have no codes i.e. misfire and trucks runs great oil psi is steady doesn't run hot. Saturday drove it for about a hour and it started so got home and had wife rev motor so i could try and see/hear where rattle was coming from. Upon this I got under truck and it seemed to be louder towards back of motor close to bellhousing. I am old school and these new LS motors are new to me. Master mechanic for railroad but this has me stumped. I would think if lifter it would do it all the time and not sure about injector pump. Is there a easy way of diagnosing the issue. Any help would be appreciated.

Cracked flex plate or loose converter bolts.

[Sean007]

Will check that could possibly be either for sure. 

[Sean007]

3 hours ago, It's Tim said:

Cracked flex plate or loose converter bolts.

Just checked converter bolts all right and didn’t see any cracks on flexplate. Really confused on what the rattle is as if it was lifter would think it would do it all the time and have no idea about injection pump. I did look at vacuum pump and didn’t see any signs of leaks or issues with it.

[Snowcamo]

https://www.harborfreight.com/mechanics-stethoscope-63691.html

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[Sean007]

Have tried and that is the problem it doesnt always do it and when it does it sounds like it is on bottom near bellhousing but could just be carrying from somewhere else.

[Snowcamo]

If its only doing it while under load id look at the trans converter. If you have the ability to get the tuner to turn the afm back on id start there as that's when you notice this issue.

Then again it very well could just be a coincidence and your tq converter is defective. How is the power on tap? A defective converter can show issues getting off the line or throught the rpm range.

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[Sean007]

First converter after rebuild came on done so took back and had tranny checked over and upgraded to a billet converter. Not using a tuner tranny guy used his computer to set tire size and tranny perimeters so not to be piggy backing with a speed calibrator. Power is great from start and through all gears. Doesn’t always do it under load some times when slowing down. 

[Snowcamo]

Ok. Have him turn the afm back on and see what happens from there.

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[Sean007]

Will do if he can he thinks because he did it on gm platform that its deleted it in computer but not sure.

[Snowcamo]

Good deal man. I would tell him to set all back to factory minus tire and trans. I wonder if he may of changed the fuel trim. Let us know how it goes.

[Sean007]

Some extra info just drove about 10 miles on freeway no noise at all got off highway and went about 6 blocks and turned and here it is. At idle no noise but rev up to about 2000 rpm there it is.

[Sean007]