Cat 320B fuel problem

[Big Iron]

my 320 has developed a fuel problem i can't seem to figure out. when i start it it will smoke dark grey to blk smoke. this will continue even when the machine is up to operating temps. if i start working it the smoke clears up and it looks normal as long as i continue working it. once i let it return to an idle it will slowly return to a dark grey to black smoke. doesn't seem to be any lose of power it runs smoothly with no missing or out of the ordinary engine noise. i can't find any obvious fuel or air leaks anywhere. its a 5BR008xx sn
any ideas!!

 

[WhyWhyZed]

anything else in your fleet running on the same batch of fuel?

 

[Nige]

How much engine oil do you need to add and how often..?
Does the engine start up OK from cold..?

 

[Big Iron]

first off thanks for the reply,s. to answer your questions

i have a 400 BC in the dump truck and several smaller tractors (JD) and they all seem to run fine on the same fuel.

this machine has never burned any oil and i have seen no signs that it it. starts right up and idle's smoothly, just smokes like a chimney and there is no doubt that it is fuel smoke, dark grey to almost blk and smells like you stuck you head in a drum of diesel.

to date if have pulled/replaced the air cleaners will do the same to the fuel filter.
all fuel lines are tight and show no signs of leakage.
the manual pump knob is screwed in tight
pulled the air intake off the turbo (it has some rough feel to the impellers and i am going to rebuild it, although it seems to spin freely when running)

I'm kind of at the end of my knowledge so any ideas would be helpfull

 

[WhyWhyZed]

unburned fuel at idle isn't a turbo issue.

I'd try to do a leak down test or compression test first (how's the blowby out the breather?) then maybe a set of nozzles if the engine checks out. I don't know a lot about those Zexel pumps but I suppose delivery valves hanging open might cause a ton of fuel to be dumped in at idle.

just going to go look at what sort of timing advance might be on that pump if any too.

 

[WhyWhyZed]

no advance unit that I can see. I would however check that the inj pump is tight - not removed and installed by someone who didn't understand the timing is affected in the process of mounting of it.

Did this issue start suddenly? or get gradually worse?

 

[Nige]

Sounds to me like over-fuelling either from injection pump or injectors. I can't see that the turbo would cause your symptoms, especially if you get a smell of unburned diesel at first startup when the turbo is hardly spinning at all. Did you happen to try the turbo for play or could you see any indication the wheel had been rubbing the housing when you had the intake line off..?

Any history of overhaul work or repairs to the injectors or injection pump in the recent past (say last 12 months)..?

 

[Big Iron]

compression is fine. this issue started overnight, ran fine all day started it the next morning and wow lots of smoke.
after checking the turbo it feels like the bearings are about at the end of their life, little rough when rotated by hand.
it has not had any injection system work since new (8100 hrs) regular maintenance for filters, additive ect.
it is definitely over fueling at idle, the puzzling part us when i work it it clears up and is normal, let it idle for a while and it goes back to smoking. bout ready to drive me nuts!!!

 

[Nige]

Overhaul the turbo if you want - it's probably ready for it by now. But for my money the first thing I'd do is pull the injectors and have them tested.

 

[Big Iron]

well turbo's off injectors are out. back half of the exhaust man (last 3 cyl) was soaked with raw diesel, front 3 are fine. thanks for the advice i'll let you know how the injectors test out when i get the results, but just looking at them they been in a long time probably since new.

 

[Big Iron]

just to let you know the outcome. all 6 injectors were badly out of spec including 1 that was stuck open (my smoke problem) reman cost about 80/90 per injector. the turbo exhaust wheel was just starting to touch the housing still waiting for a cost estimate on that. ran a compression check and all was good there. got the injector holes cleaned up and just waiting on parts now. thanks again for the comments guys.

 

[Nige]

just to let you know the outcome. all 6 injectors were badly out of spec including 1 that was stuck open (my smoke problem)

......and also where the smell of raw diesel was coming from when you fired 'er up ............

 

[Big Iron]

well i got the injectors and turbo back and in several months. still smoked so i drained the fuel tank and cleaned, refilled with new fuel and Howes fuel additive. replaced the fuel filters and fired again and still smokes at idle cleans right up under full throttle. let it return to idle within 4 0r 5 minutes it will be smoking again. so i removed the injectors and returned to the shop and watched while he tested each one they all popped of within 2 or 3% of spec. i am going to redo the compression test just to make sure and then pull the pump, unless someone has a better idea or a way to test the pump on the machine.:Banghead

 

[Bob/Ont]

Is the smoke at idle coming out in puffs? Might be a cyl damaged by the bad injector washing down the wall.
Later Bob

 

[Big Iron]

no puffs steady smoke runs great no miss,s no smoke when working it