I have an early 99 with 408K miles on the clock. I bought it with 402K and it smoked pretty bad and ran rough since I bought it. Doesn't use any oil or coolant and the injectors had unknown mileage on them. I replaced all 8 injectors with rebuilt stockers, found 2 cracked injector cups, so I replaced all 8 cups, replaced the under valve cover harness's, replaced glow plugs.

Now I have it all back together and it runs slightly better, and smokes slightly less. grrr. I did a cylinder contribution test and #5 failed. after ohming out the wiring and finding no problems, I did a compression test and had ZERO compression on that hole. I started it with that injector unpluged and the smoke is 100% was gone. I took it for a drive with the injector un hooked and it runs worse than before, has a miss all the time. With the injector hooked up once I get over 1500RPM when WOT it smooths out and runs on all 8 (acts like a gasser loaded up on gas and you blow it out and it runs perfect) as far as I can tell. After cruising for a little, or letting it idle it smokes again and misses again.

Looking for advice here, what would cause 0 compression but at higher RPM's it has compression again? (I assume based on how it runs)

 

Maybe when the fuel is injected at a higher rate it is helping fill the combustion chamber just enough to fire. I'm just taking a wild guess, I still don't know near as much about these engines as I'd like to!

 

The compression doesn't get better, just the indications are less as the engine at higher RPM's is dependent on that cylinder.

You need to determine why 0 compression. Possible a bad valve or a hole in the piston. If you have a hole, your crankcase pressure would be up there and that would be an indication. Also your oil would be fuel diluted.

 

0 compression and it smokes. Unplug injector and the smoke stops. So, your exhaust valve appears to be working. but your intake valve may not be opening.

If you have a hole in the piston, then you will have a lot of blow by. What happens when you remove the oil fill cap with the engine running?

Did you check and see if any push rods were missing?

 

Rockers move, oil is not diluted and the cap does not blow off the filler neck. However my crankcase vent I have recirculated because it blows out a lot of steam/smoke...

Thanks for the replies

 

Sounds to me like you lost a piston.

 

I agree with Dan. All signs point to something wrong with that piston.

 

But with the injector hooked up it feels like the motor is 100% smooth and the smoke goes away while WOT above ~1500RPM. How could a bad piston act this way? When beating the truck it feels great. As soon as you slow down to a cruise or idle the smoke starts pouring out and it runs rough. Seems like when the combustion chamber temps are really hot it runs like a top. I am going to try to build a leak down tool to see if I can pin point where the problem is.

 

It has to do with the velocity of the piston. High rpm doesn't give the leak enough time to bleed off all the compression, so therefore you get enough compression to heat the combustion chamber enough to get it to fire.
Drop to an idle and the leak is big enough to drop the compression heat down below the ignition thresh hold.
The ONLY cure for you is to rebuild the engine.
And not just a silly little ring job and hope it works.
Bore it out .020 over and get new pistons.
Been there done that explanation too many times to remember with my customers and thier tired out engines.

 

Thanks. Leak down test confirms it. Pressure in the crankcase

Is it possible I can get away with just replacing the piston? Or do these problems usually damage the block also? Where do the pistons usually burn through? I can't afford a motor at this point. I am a mechanic but with very little Diesel knowledge. Given the high mileage though, not sure if a simple overhaul is really going to cut it... Thoughts?

 

I vote you tear it apart, see what your up against,

If it is too bad, start parting it out.

Maybe it's not as bad as you think.

 

There was a guy on here that lost a ring and it made a mess of the inside of that cyclinder. If your going to thear it down do it right. You can buy a long block from Clay or OEM ED. Keep us posted, you don't have that much mileage considering some on here.
Good luck Chet

 

Same symptoms you are describing, I had alot of power when really getting on it, but lugging it around it smoked and chugged along.



FYI here was the post showing the comparison between all the cylinders
https://www.ford-trucks.com/forums/1...l#post10120847

 

Pulled the engine yesterday, and got the engine tore down today. Found a broken ring land and no top ring on the #5 piston. Bottom ring came out in pieces. The cylinder wall has minimal scuffing, no damage to the head. Top of piston looks like new, not sure how. Looks like I need a piston and just a hone to the cylinder walls and it's good to go. Thanks for the help guys, I will post pics.

 

Right on. Glad ya got it figured out anyway and damage sounds minimal. Post up some pics of the carnage!!! and just general engine tear-down stuff - heads (exhaust ports), the other pistons, etc... The more of these we see torn-down the more we have to compare our junk to if it fails!