How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask JCTech Your Own Question
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
Type Your Heavy Equipment Question Here...
JCTech is online now
A new question is answered every 9 seconds

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: 4 years ago.
Category: Heavy Equipment
Expert:  JCTech replied 4 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 4 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 4 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 4 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 4 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 4 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 4 years ago.
Glad you got it figured out

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
< Previous | Next >
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
  • used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will recommend you and use you in the future. David L. Richmond, TX
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil Marysville, CA
  • Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible. Charles Walnut Creek, CA
  • As a single woman, I really appreciate an excellent and affordable opinion.
    Thank you Geordie, I will not hesitate to contact justanswer in the future!
    Sue Charleston, WV
  • Another great insight to what may be the problem. I will have my mechanic take a look at it tomorrow. Thanks again, do indeed know your stuff. Jim Castleberry, FL
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK

Meet The Experts:

  • Chris (aka - Moose)

    Chris (aka - Moose)


    Satisfied Customers:

    16 years of experience
< Last | Next >
  • Chris (aka - Moose)'s Avatar

    Chris (aka - Moose)


    Satisfied Customers:

    16 years of experience
  • Tim's Avatar



    Satisfied Customers:

    23 Years Heavy Equipment and Truck Repairs Shop and Field in the Minning and Construction Industry
  • J.R.'s Avatar



    Satisfied Customers:

    13 years as warranty technician for Detroit Diesel
  • Cat Man's Avatar

    Cat Man

    Caterpillar Engine Expert

    Satisfied Customers:

    23 Years Caterpillar Engine experience.
  • Wayne's Avatar



    Satisfied Customers:

    34 years experiance as engine rebuild and problems.Thermo-King repair and trouble shooting.
  • DR.Cummins's Avatar



    Satisfied Customers:

    16 Years working on Cummins Diesel engines,
  • Curtis B.'s Avatar

    Curtis B.

    service manager

    Satisfied Customers:

    30 years exp. with diesel engines, heavy equipment and forklifts, including lp forklifts