piston slap
 

ok 08 Ford F250 6.4 has developed a knocking noise in it on the driver side. Took to the dealer they are calling it a piston slap they are going strictly off sound i feel its being mis-diagnosed. Truck has 40,000 miles 1955 engine hours my question is if i have what they say a piston slap wouldn't i see a loss of some power? or some white smoke? something to support this... Truck runs EXCELLENT and at 40mph you cannot hear it. It sounds to me as a rod knocking maybe a cam problem.. Any ideas here would be greatly helpful.

Does it use any oil ?
You will need to do a compression check to see if you
have a bad cyl.

Thanks AHolt i did a compression check on it and #4 cylinder is bad its at 4% compression. Tech says i will for sure need a new short block. AHolt do you feel i will need a new short block? The reason i ask is i have lost NO POWER NONE!! I have a offer from a guy to buy it for $20,000 as is and he will replace motor. I just don't want to sell it and its a minimum cost to fix it. Right now as is dealer wants $17,000

What do you mean 4% compression? Compression is usually measured in PSI. Cylinder leak-down is measured in percent. You have to do the leak-down test with the piston at TDC of the compression stroke so that the valves are closed. If you have low compression or if it has a lot of leak-down it means something mechanical is wrong, in which case the engine will have to be torn apart.

i took it the shop the tech did a compression test on it thru the OBDll port and it showed the # 4 cylinder down on the graph in the yellow i seen a 4 it might be at 4 psi i am not sure. The thing is the truck runs awesome it does not miss a beat. My question is will i need a short block for it or just replace the broken parts. If i do a short block i get a 1yr/unlimited miles warranty.

I hope you are not driving it anymore, if a piston slapped a valve, you are going to have to at least replace the psitons, as long as the bore is ok (dought it)you head will have to be re-done, more than likely decked and vavle job, you will have to deck both side can just deck one side.(2 heads)
most shops do not have all the equipment to do a rebuild, so they order longblocks from people like me, jasper, REM, ECT.

what will be needed if you did have a piston slap
boring bar, with bits or hone, depending on how bad it is, you might get away with just a hone or deglazer
guide and seat machine
surfacing machine
good luck