Engine knock
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Senior User
Joined: Nov 2008
Posts: 104
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From: Sorrento BC, Canada
Engine knock
My 1991 7.3 idi is making a rod knock sounding noise when cold but goes away once at full temp. I am running 100% wmo in the truck filtered to 10 micron through a huge filter. I can only hear the noise under the truck and near the drivers door. The noise is most noticeable at the drivers rear of the cab. The truck has a smf conversion, with a zf5 manual conversion. The truck has lots of power for an N/A, and reads in the middle for oil pressure on the stock guage at all times. I have also just rebuilt the heads with all new guides, and seals. Could this be an injector? When warm it doesnt smoke but when cold it smokes blue good since its on wmo. What would piston slap or rod knock be like? Thanks.
Post Fiend
Joined: Jan 2005
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Piston slap has a distinctive ring to it, like a bell sound. A rod bearing is like the sound from a marble being shaken in a glass jar. A piston pin bearing is a double knock.
I am surprised you can pick anything out when cold. When my 6.9 starts I can hardly hear myself think until it warms.
I am surprised you can pick anything out when cold. When my 6.9 starts I can hardly hear myself think until it warms.
Post Fiend
Joined: Nov 2004
Posts: 5,638
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From: Manitoba
A weak injector will cause a knock.....since it is dumping fuel ahead of time and compression ignition is before time causing an explosion early...... the rest of the engine is then forced against that out of time compression with a resulting knock....
Thread Starter
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Senior User
Joined: Nov 2008
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From: Sorrento BC, Canada
The WMO makes the engine rattle alot less when cold so I can hear noises that I couldn't when it was on full diesel. The heads have been rebuilt with all new guides, and seals so the valves are good. When I replaced the 2 injectors both of them popped at 1600 is this a low number?
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
What trans do you have....... ZF and a dual mass flywheel.
http://www.zf.com/na/content/en/impo...ing_Guide.html
http://www.standardtransmission.com/dmf.html
http://www.zf.com/na/content/en/impo...ing_Guide.html
http://www.standardtransmission.com/dmf.html
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