Strange noise from plenum
Thread Starter
Racer
Joined: Sep 2001
Posts: 266
Likes: 7
From: Sumner WA
Strange noise from plenum
My 88 with recently rebuilt L98 developed a new problem driving home from work last night. (rebuilt last month to factory specs +.030 over) I hear and feel a metallic snapping like sound from the plenum. I've never heard anything like it before. It doesn't set any codes and at first I suspected that maybe a rocker had come loose. I used a stethoscope on the valve covers but the noise appears to be coming from the plenum. I can even feel the pulse through the gas pedal. maybe it's a weird sounding backfire in the intake? I'm going to check if maybe the fuel regulator diaphragm broke tonight although I don't smell gas. The sound isn't rhythmic but definitely increases with engine RPM.
Any thoughts where I should look?
Ron
Any thoughts where I should look?
Ron
Thread Starter
Racer
Joined: Sep 2001
Posts: 266
Likes: 7
From: Sumner WA
Thanks. not the diaphragm. Definitely missing. Any easy ways to check lifters / springs without removing valve covers or intake? I guess the good news is that it sounds like the problem should be covered by the rebuild warranty.
Burning Brakes
Joined: Sep 2005
Posts: 993
Likes: 3
From: Iowa
Not easy but you could get a little information on the problem with a compression check; Depending upon what's going on you will see some strange stuff on the gauge. Outside of that I would pull the covers and check it out before something goes out the exhaust....
Safety Car
Joined: Jan 2008
Posts: 3,939
Likes: 1
From: Vero Beach Florida
Take it back to the builder, if you mess with it yourself it could void your warranty. You spent money to have it right get them to fix the trouble. Don't drive it, if something has come loose in the bottom end you could do more damage
Last edited by floridamale; Sep 25, 2013 at 06:37 AM.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Could be a loose rocker? Have friend that just went through this putting new heads on his '67 Mustang. Realized they gave him the wrong locking nuts and his rockers kept working themselves loose.
Though, I agree, take it back to the builder if indeed there is a warranty.
Though, I agree, take it back to the builder if indeed there is a warranty.
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Thread Starter
Racer
Joined: Sep 2001
Posts: 266
Likes: 7
From: Sumner WA
Problem Solved
I received my car back from the builder today. Turns out a rocker stud snapped off at the threads (rocker end). The studs were not replaced during the rebuild. So he replaced the stud and rocker and now it runs like normal. No charge.
Thought you might want to know the cause in case you experience similar symptoms.
Ron
Thought you might want to know the cause in case you experience similar symptoms.
Ron
