351 engine ping or knock
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Junior User
Joined: Feb 2003
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From: Western Mass.
351 engine ping or knock
I have a 97 f250 with a 351w Ihave changed rotor dist.cap wires fuel filter put 2 new exhaust manifolds also new colder plugs,still get an engine knock I guess I know it's more than a ping sounds like rocks rolling around in there.It does it on a hard take off just it hits top rpm at shift point,also on any hill where the engine has to take a load,once it shifts down and you can let up on the gas a little most of the ping will go away. Don't know what else to do hate to hurt the engine only has 44,000 on it. hope someone has some ideas onwhat is wrong.
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Joined: Aug 2001
Posts: 387
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From: MCBH Kaneohe Bay, HI
351 engine ping or knock
Your problem is preignition. The sound your hearin is the valves being slapped back up in the heads when the cylinder fires before the valves shut all the way. Happens when yer goin up a hill or takin off right. Goes away when you give er less gas right. You need to retard the timing a couple degrees or your vacuum advance is not workin right. Same thing happend on my 302. I took the distributor apart and cleaned the vacuum advance arm out. It was rusted and the diaphram couldnt pull the arm out to retard the timing. Give that a try if you cant fix it with retarding the timing.
Semper Fi, PFC McDowell
Semper Fi, PFC McDowell
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Joined: Aug 2003
Posts: 122
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From: kansas
351 engine ping or knock
No vacumn advance on 97 model. Base timing could be too far advanced. ECM controls advance. Base timing should be set after disconnecting ecm control of ign module. Should be able to read sticker under hood for base timing specs. Could be defective knock sensor however. This device tells ecm to retard timing when spark knock occurs.
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