Knocking sound at first cold start up

[afsmith]

Hi all hoping, to enlist some help from the vast pool of knowledge here. I have a 93 D-250 that just recently developed a significant,consistent knock after first,cold start up in the morning. Once things come up to temperature the knock disappears. I regularly plug the truck in over night but knock is still there ,just not as noticable. I notice the belt tensioner moves a bit with each knock. I have been living with it for a few months like this, but I dont want to let it go on if it is a sign of bigger problems to come down the road. The truck has 275,000 miles on it and is basically stock. New IP and injectors at 210,000. New water pump and fan pulley bearing about 5,000 miles ago as my fan decided to shed some blades during a road trip and had to drive it a ways to get home with the out of balance fan. Which ultimately led to the failure of the fan bearing. Almost made it home before it shedded one more blade and took out the radiator. Seemed like a good time for some E-fans anyway. Back to the knock, if you all have thoughts it would be of great help. Thanks a bunch

 

[Philip]

Check crankshaft end play. Some people have had the crank thrust bearing come apart.

Have you ever cut open one of your old oil filters and checked for debris?

 

[DVolk]

Take loose the belt and fire it up see if you have the noise . you might have a bad A/C compressor they will rattel and knock if there going south it also could be a injector knock

 

[NIsaacs]

It might be the pump timing is a little fast. With the added advance of the KSB on cold start, might be the cause. Next time you cold start it, unplug it and see what happens.

Nick

 

[afsmith]

Thanks for the response everyone. I'll have time this weekend to dig into it and try your suggestions. Thanks a bunch for the help. Keep ya posted on the results.

 

[afsmith]

just to fllow up.I removed the serp belt on first cold start and fired it up. no knocking was heard. Determined it was the a/c compressor. Changed it out, problem fixed. Thanks all for the help, saved me alot of time and money trying to diagnose myself

 

[DVolk]

Your welcome ,that's what I thought it was