Detonation or Rod Knock....

Mike Manzo

Registered User
I have a possibly dumb question...

My 1994SC has been experiencing what I consider to be "rod knock" for quite some time now. It has not gotten any louder and is not apparent at cold start, at idle or even when revving. Under load and in drive, however, this knock, which reminds me of when I actually HAD rod knock in a previous engine, comes shining through...

Now, my buddy claims that the sounds of detonation sound eerily similar to rod knock, but never experiencing this first hand, I have no clue. There is no oil pressure drop at high-rpm and, in his theory's defense, this only really started after the MPII system (with 85mm TB) had been installed. I have 42lb Bosch Ford Racing injectors and a 255lph forced induction fuel pump (WalBro). The EEC tuner, to the best of my limited knowledge, is setup fine for this application and these are the only engine mods.

Just curious if anyone could add to his theory or tell me how to confirm mine. I am contemplating replacing the engine and ressurecting the 94 with a warrantied Ford reman'd and keeping all these bolt ons.

Any thoughts???
 
Detonation does not sound like rod knock. Detonation has a distinctive "ting" to it and generally is only heard on WOT unless your tuning file is just way too aggressive.

A rod knock is usually not heard under load but is very loud on higher rpm (above 2500) closed/light throttle. What do you consider to be "fine" oil pressure?
 
See, thats what I thought....

Back in the day I had some issues with a croaking engine and it would lose oil pressure up around 5000+ rpms and had a real good knock.

I have heard that a cracked header can sound rod-kockish, but not detonation and it had always been described as you had said. More like a "ting, ting ting" sound...

I know this engine was beat within an inch of it's life as a reman'd itself. I do have to say that if the head gaskets dont blow, these engines deal with a lot of stress....

Thanks...
 
Why dont you pull the octane plug and see if it makes the same noise.That should pull 2 degrees of timing out. If is still doing the same thing than it may be rod knock.
 
My 94 has the same problem, has done it since I got the car. I was told it was indeed a rod knok. But my engine builder said this (rattle like sound) was either a bad rod bearing, compliments of a HG failure, or maybe a wrist pin or piston ring had seized to the piston. I've had no problems from the car until the past week. I drive it tough, I top at 17psi, have great oil pressure, and a rattle that shines through on the downfall of acceleration, or when rpms are above 1500 and vacuum is present. Can't figure it out, have tried a few things. My engine builder said just drive it til it blows up, then you'll know it was.
 
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