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JCTech, Diesel Mechanic
Category: Heavy Equipment
Satisfied Customers: 387
Experience:  31 years experience as a Diesel Mechanic, 14 years at Cummins, good with electronic control systems
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Hi i just overhauled my 1991 cummins 350 big cam cpl..cylinders..turbo

Customer Question

hi i just overhauled my 1991 cummins 350 big cam cpl 840 it has a pt fuel pump i started the unit it ran fine for about an hour then began pouring white smoke filling the entire shop i did a compression test on all cylinders low was 410 psi high 500 i am not sure what the normal opperating pressure is but i found that running engine on five cylinders the unit did not smoke but i found raw fuel at exhaust manifold and exhaust side of turbo so i know it is a major fuel issue but i dont know if i need to recheck the timing at the cam lift [cam follower gaskets] or if i need to take the accessory drive back down and recheck timing there but i was sure it was correct either way i need cummins help before i wash out my cylinders
Submitted: 5 years ago.
Category: Heavy Equipment
Expert:  JCTech replied 5 years ago.
I do not think your problem is a base timing issue, you would have had white smoke from startup and also when running on five cylinders. Your issue is with the cylinder that causes the smoke to disappear when cut-out.
Go over your valve and injector adjustment again, try swapping the injector from the suspect cylinder with its neighbour and see if the smoke follows the injector.
White smoke is caused by incomplete combustion, either low compression in that cylinder, (piston, piston rings or a valve issue) or an injector issue causing poor atomization of the fuel or retarded timing.

Hope this helps
Customer: replied 5 years ago.

i removed each injector and rreplaced it with the compression tester and on each cylinder it would smoke heavy just for a few 30-45 seconds and then clear up but i think that was due to removing the injector and the raw fuel draining on to the piston i tried this on all 6 cylinders and the end result was the same but when i install the 6th injector it starts bellowing white smoke i am afraid to do to many more start ups for fear of washing out my cylinders the puzzler to it is that fuel was coming out the #4 exhaust port at manifold when doing each cut out and the compression on the #4 cylinder was 460 psi the cut out test eliminates the issue on all cylinders but i dont think icould have 6 bad cylinders when i have good compression


Expert:  JCTech replied 5 years ago.
If you remove the injectors you will get fuel draining into the combustion chamber, as you state. this will cause a small amount of white smoke and rattle.
If you did not have white smoke after the compression test until you fitted number 6 injector, then there is a good chance that the smoke is being generated in number 6 cylinder. The fuel you see at number 4 may be "wet stacking" (where unburnt fuel is generated due to cold and low load conditions. There is a chance that your white smoke may be due to wet stacking if you have not driven the truck/engine after rebuild yet.
It may be that you need to get heat into the engine to get rid of all the unburnt fuel in the piston bowl, head and exhaust system, this will help narrow down a culprit cylinder.

Customer: replied 5 years ago.

ok i will rerun the overhead in the morning and run engine to temp and and try to burn the excess fuel off of the piston . thanks will contact tomorrow for now lets rest

Expert:  JCTech replied 5 years ago.
Hi, To get all the fuel out of the cylinders, you need combustion temperature rather than coolant temperature, to clear up a small amount of white smoke the engine needs load on it. If you are certain that you do not have a missfire, everything sounds good - take it out on a road test.

Customer: replied 5 years ago.
hi i figured out the problem this is a big cam 4 there is a fuel line coming from the back side of the fuel pump going to the bottom of the air cooler inside the pump there are two sides with a seal between i belive the bellows are bad in the pump i disconected the line and started it had almost completley stoped smoking besides the build up in the bore so once i get it running hot i think that will solve all my problems the bellows going out would explain the sudden problem i just had the pump tested and they said it was good to go but iguess not good togo very far thanks for trying to help
Expert:  JCTech replied 5 years ago.
Glad you got it figured out