Help with "strange sound" under hood..

z90sc

Registered User
What sound does the the knock sensor make....does it sound like a "valve rattle"?I've heard a strange noise the last two times I got on the gas hard and I'm trying to figure out what it is.I don't normally "stop light race" but it seems that some of the 5.0 stangs and some of the local ricers think that I'm an easy kill....we're they surprised.Anyway,I need to find the source of this noise.
Thanks ,
z
 
Sounds like your describing Detonation also know as ping, knocking or pre-ignition. Common causes are low octane fuel, too much boost , too much timing or not enough fuel.

David
 
could be more simple

its hard to tell from you post. but could be as simple as a loose plug wire.

what wires are you using, when were they put on, by whom???


describe the sound a little better,
when exactly does it happen. only when past 5,6 psi, or all the time.
does it sound like someone is tapping a piece of metel with a small hammer??

i take it you notice a power loss when when this happens.

anyway, check your wires first, its easy and its cheap. just give the wires a medium tug from the top of the engine bay, about 5-6 inches from where the wire attatches to the plug.

James
Ps. i've been known to have one, just up and pop off.
 
Thanks for the replies..yes it does sound like a small hammer tapping,it only happens when the car is hard on boost [this car will bury the boost guage] with the RPM's between 4- 5k but the sounds stops once OD shifts in.I'm sure it's time for a plug change as the present plugs have about 20k on them,the wires are fairly new and are tight.....is it time to upgrade?I have a set of ported heads,Kooks middies, 36# injectors and 1.73 rollers waiting to go on the car.
z
 
This definately sounds like knock. Also because it is associated with a high RPM while in boost, it also sounds like a fuel delivery problem. This is dangerous if there is in fact a lean condition while in boost at high rpms. Worn plugs could probably also cause this, but I'd think they would present themselves more often. Check your fuel octane, try changing gas stations, check the condition of your fuel pump, change your filter, and look to the injectors for signs that they are dirty. This is were I would start at least..
 
z90sc said:
Thanks for the replies..yes it does sound like a small hammer tapping,it only happens when the car is hard on boost [this car will bury the boost guage] with the RPM's between 4- 5k but the sounds stops once OD shifts in.I'm sure it's time for a plug change as the present plugs have about 20k on them,the wires are fairly new and are tight.....is it time to upgrade?I have a set of ported heads,Kooks middies, 36# injectors and 1.73 rollers waiting to go on the car.
z

Wow. I could think of quite a few things that would cause a sound like that and none of them are good. How many miles do you have? Been driving it hard all it's life? "Penny on a fender" type tap could be a collapsed lifter but you'd hear that at all rpms all the time. A "light hammer on the engine block" could denote a bad rod bearing. That knock would be heard loudest while under load. That's doom for your engine and rebuild time. A "tappa-tappa" could also be a stuck lifter causing the valve to slam shut instead of following the camshaft, but you might pick that up in a miss or backfire first. Sorry to be the bearer of bad news, but all this is highly possible, especially when you say you can "buy the boost gauge". I'd have a professional mechanic check the oil pressure and test the oil pump to help narrow it down.
 
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