Rattle noise from engine at 5000 rpm?????

[fourmustangs]

Have a 87 5.0 Automatic....

It makes a loud rattle noise from engine at approx 5000 rpm in second gear....
It doesnt do it in First gear or third or if it does cant hear it over exhaust...

Is it detonation? Tension/Idler pulley??

Car is set at approx 12 deg and using 89 octane..no real mods...
just 3.55 gears and intake and pulleys and exhaust.....speed density


let me know what ya'll think

 

[PRO50SC]

Drop the timing to 10 and try some premium. If it stops you know it's from detonation. Easiest thing to try first. Won't cost ya nothing but a little time and a tank of premium.

Good luck

 

[luckythirteen13]

could be ping. do what PRO50SC said.

 

[fourmustangs]

Actually I did reset the timing to 10 deg......