I have a 92 f150 351 and I here a soft knock at idle which goes away if the engine is above idle. I took the belt of and knock is still herd. The truck has about 130k and has been making the noise since about 70k. I always thought it was a bad pully but now I know better. I started listening to other pre 97 ford trucks and many of them have this knock. I was wondering why this is?

 

More than likely you have worn out rod bearing. at idle there is less oil presure and this seepage allows for the rod knock. With this many miles this is proably the problem

Dave

http://a2ztowing.homestead.com/a2ztowing.html

 

I posted this topic on some other boards and others hear the same noise, some with V8 and some with staight 6's. Some discribe as rattle/knock at idle even with lower miles? I think your right and at idle the oil pump is not puting out the oil pressure required to support the bearings.

 

my dads 92 flareside, 4.9 six, has a little over 125,000k and when first started up the bearings raise hell for abouut two seconds, then the knock clears ups, and thats the last of it until, next cold start up.

 

When I first start it there is no noise at all since the idle is higher. When the idle goes down the light knock is heard.If the idle is at 1000rpm no noise is heard. That's why I think it is a problem with oil pressure. My freind's 93 Ford Truck has a 302 and his is making the exact same noise?

 

My '89 w/ EFI 302 did the same thing. It turned out to be the heat shield on the Cat. I removed it ( the cat, not just the heat shield) and have not heard the noise since then. Just something els to look at.

Roger Lane
Test Analyst
Sr. Automated Test Engineer
IBP, Inc.