A leak down test 'or' cylinder differential test generally uses a two gauge set, one registers/measures the compressed air being forced into the cylinder, and the other measures the 'percentage' of pressure being lost.. Done with the cylinder at TDC (valves closed) or can[/i] be done at BDC with the rockers pulled ect. to test for a cylinder crack.. A leak down test can help to prove worn or damaged parts like bad exhaust valves,, leaking or bleeding air out the tail pipe, intakes out the intake manifold or plenum.. Compressed air leaking past the rings, valves can be heard sometimes as a ‘hiss’ or howl, and felt at the outlets.. Leaking rings may show up as air escaping from the oil fill/cap.. During a leak down test you can rock the piston up/down slightly to check for worn ring lands, or at times verify unseated rings.. Leak down is also a good way to check for head gasket leaks between cylinders, or as a test for combustion leaks into the cooling system from block/head cracks, or failing head gaskets..

If you were over fueling, I'd think you'd see at least 'some' black smoke as well if enough to wash the cylinder walls..

Going toa 30wt. may result in some 'romping' in cold conditions

 

Thanks a bunch for the info. Sounds as though this test may be just what I need. I do not think it is overfueling either. You can make it blow the black smoke if you stand on it but it is not smoking with just normal driving down the road. It appears to me as though if it were overfueling, especially enough to wash the cylinder walls, it would be blowing black smoke or a least a tinge of it at cruising speeds. What did you mean by "romping"? Again, thanks for your help! I'll let you know what I find out.

 

Romping is somewhat normal for the 7.3.. On a 'cold' start, (more so very cold) lower the temps more the increased chance, what can happen on initial start up is the engine will have series of idle RPM spikes/lows and will make a "romp, romp, romp" for a second or few.. Increasing the viscosity in colder loctions or seasonal lows can make the romp more prominent along with the closed back pressure valve/gate..

Not a big deal, and generally clears after a few seconds... Annoys some folks...

 

Ok I've seen that before and didn't know what was causing it. Found out some good stuff today and will try to get back on tomorrow and elaborate. May be something for others to look for in the future.

 

Also have seen the seals inside the turbo leak oil into the intake side and create this issue as well.

 

I may have stumbled on something yesterday but am not sure yet. I took the truck over to a diesel truck shop yesterday and the tech did the same as everybody else in that he took off the oil filler cap and pulled the dipstick a little. His immediate response was that the blowby was excessive. He asked about the honing of the cylinders and I could not answer his questions so I stopped at my brother in laws place on the way home. The engine builder builds race car motors for him. He also builds NHRA and a lot of other racing motors for every different kind motorsports there is. This is part of the reason I got him to build my motor in the first place and the second was that as a friend he would build it for me for substantially less money. I asked my brother in law about the honing. The general consensus from him was that the engines that the builder is used to building are all very high horsepower gassers and that one of the things that they do different when building these high HP motors is to hone the cylinders very slick/fine. His thought was that if this motor was honed this way and with the extra hardness of the diesel rings that it might be where the problem is. Sounds reasonable to me so I guess this is where I'll start checking next. It is not smoking enough to warrant me to belive that it is a problem with oil leaking into the combustion chamber and I still have the blowby issue which does lead me to believe we are on the right track.

 

I had a 1970 4x4 f250 360 motor new motor 428cj .30 over rv cam 1960 3 duce ran goood uesed oil for 6 mo .. old man tolded me to drive for a hr for motor to get hot in 4th gear go 60 or 70 mph let off to 25 or 30 mph putt foot in it go to 60 or 70 mph and keep doing it till it pu up speed you will feal it start to pu up speed and will seat the rings the old way ITS WORKS per ratlermike.. old man now oldddd!!!! good luck