Scissors-like abnormal noise from 5.7

[Happygolucky]

Have noticed this noise for some time but been busy trying to find the cause for engine dying when idleing/ low rpm..
AI tells me it could be related to mechanical fuelpump or valves.. Any input from a human would be highly appreciated..

 

[Lou C]

Unless that engine is older than the beginning of the Vortec series (96 and up) it likely does not have a mechanical fuel pump. The sound could be:
An exhaust leak
Related to the drive belt or tensioner of it has one
Valvetrain related (lifter or rocker arm)
You can try starting it with the belt off for a minute to rule out # 2.
#s1&3 it helps to have a mechanics stethoscope….

 

[Happygolucky]

1997 with mechanical fuelpump! (Not vortec)
Will test with belt off tomorrow -

Had exh system replaced last fall by Merc authoriest shop .. elbows risers manifolds ..

 

[Lou C]

The exhaust looks new but try snuggling up the mounting bolts/nuts (like 25-27 ft lbs). Never had a mechanical pump make noise. I’d get a stethoscope and listen at the valve covers and also each belt driven accessory. I had a circulating pump make noise once. PS pumps can make noise as well. Nice that you have closed cooling!

 

[IslandExplorer]

X2 on the stethoscope, really is the only way to figure it out sometimes. Can use a mechanic grade shade tree stick against the ol ear lobe in a pinch too! Doesn't always work but often times you suddenly hear it clear as day in one specific area.

Don't forget to give alt a listen, notorious scissor squeakers they are, when brushes and bearings are old.