can you diagnose this? she's a smoker

[ritathebus]

woo-hoo! first legit post

so. rita is my bus. 1970 GMC suburban charter bus. 40ft with a detroit diesel 8v71 in the back. auto trans, she runs, brakes work, etc...

i will try to provide as much information as possible, so ask away, if you think it's going to help.

I recently got the bus and it had been basically unmoved for over a decade, and life before that owner is unknown. when i started her cold, she'd smoke while idling, but once the air pressure was high enough foe the air brakes to release and i could give her the pedal to the metal, she'd clear right up. as soon ass we could get somewhere where we could jam on the pedal there'd be no smoke, and minimal smoke while idling (stopped).

because it'd been so long, i decided to change the transmission oil, transmission oil filter, oil, oil filter, and the 2 fuel filters- one cartridge and one sock. i took all the filters off and put them in a bag so i could make sure the new ones were the correct size. all replacements fit except the sock, so i cleaned the minimal amount of oil out of the filthy old sock filter and put it in with the new ones so i could at least start her up. ran her for less than 10 minutes like this.

later i fixed the new sock filter bu banging one side down so it would fit in the casing. it still fit in really snug and i took out the old/oily/crappy sock, disccarded the fuel in the casing, and put in/on the new sock with fresh diesel in the casing.

at first she smoked a lot while in idle, then not so much. it wasn't until we were going fast, and shifted into gear (this trans has only 1 gear with hydraulics used to get up to speed to shift in) that she started kickin out dark smoke. drove her about 20 mi and everytime she got fuel from a dead stop, or when we shifted into gear (about 30-40mph) she kicks out smoke. dark grey smoke.

what is going on? before idle was smoke and driving was fine. change the filters and give her new fluids and and she's fine idling, and smokes while driving.

please help me cuz i love rita but i don't love her smoking like a chimney. it's gross. she needs to kick that bad habit. if you need more info or have questions or whatev ask em, i'll do my best to help you out

thanks

[DmaxMaverick]

Welcome aboard!

Your experience sounds absolutely normal.....for a Detroit that's been sitting for a decade. Probably nothing more than sticky rings (expect above normal oil consumption for a while), and injectors. Did you replace the fuel? Or just run what was left in the tank for 10 years? Diesel fuel doesn't "go away" over time like gas, but it can become contaminated, and actually start to grow stuff in it (algae), and collect water. If the filters/sock were real dark and gooey, that's probably a biological. It will take several tanks (and filter changes) to get that completely purged, if you treat it correctly. You'll need to change out as much fuel as possible (tank flush if you can), and treat your fresh fuel with a biocide, as well as regular fuel additive/injector cleaner treatments (very heavy, at first). I won't go into name brands, but your local bulk oil/fuel distributor can help you best with that. Your rings should loosen up over time, or you can help them a bit with an engine flush solvent (or just some MMO - Marvel Mystery Oil).

Sounds like a fun project. Have fun with it.

I'll move this thread down to the "General Diesel" forum.

[Yukon6.2]

Hi
I would check the air filter and related piping.In a decade their could be a few critter condos built in the nice dry shelter of intake piping.If you don't care for the old style fuelfilters,you can go to a truck wrecker and get some newer style bases to use spin on filters.Easy swap and makes changing filters easyer.
Have Fun Thomas

[Robyn]

I owned a GMC TDH 4519 transit coach that I bought from the city of Portland Oregon back in the mid 80's

My bus had the little transverse mounted detroit too as well as the VH tranny.

I replaced the VH trans with a VS2 that had an overdrive along with hydraulic and direct. This gave the beast about a 70 mph top speed instead of 55 with the little detroit screaming.

Now as was mentioned the air intake could be inhabited by little creatures that found it a cozy spot.

Nornally these rigs were set up with small injectors and made very little smoke.
This said there is no way to tell what may have been changed by the previous owners.

Someone with a lust for power may have screwed in some huge injectors with HP in mind.

Now the detroit two strokes will smoke a bunch right off the line when the pedal is mashed especially if someone installed large injectors.

The detroit uses a roots type blower to provide combustion air and at low engine speed and heavy throttle the air supply is low as compared to the fuel.

Once running at speed the stack should clear out (No black smoke)
If your tranny is in direct and the road speed is fairly low,but not down to the shift point where it will reengage hydraulic the engine speed will be low. Hard throttle at this point will bring about a lot of smoke.

I would do as Maverick suggests and get some clean fresh fuel in the beast and see what happens. I would also pop the outside valve cover and look at the injectors. Each injector will have a little tag inset into the barrel assembly.

This tag has a number, see what that is, the larger the number the bigger the injector and the more fuel (smoke) it will make.

While inder the cover, dont mess with the "rack" unless you are well versed on a 2 stroke detroit.

I would also make sure that the emergency shut down switch on the dash will actually trip the air hat flap on the engine.

The air hat flap will have a solenoid close to the front of the blower (usually) with a latch. Under normal conditions this flap is open and the latch is set.
When tripped by the switch the flap closes and will shut down the engine.

This is only used during a runaway situation such as a stuck fuel rack :eek:

Many times these will not work due to lack of maintenance or someone has wired the mechanism open.

Just be sure it will trip when the switch/button is operated "Very important" to have working.

After you have checked the air intake system for critters and changed the fuel I would do an oil change on the engine.

Delo 400 30wt or Rotella T 30wt should be great for this creature.

Detroits are notorious for low oil pressure so dont use 15-40

Once you get this done, running the engine under load for some time should clean out all the oil residue in the airbox and see the stack clean out.

Now the airbox is the chamber under the blower where the cylinders breathe from.

Detroits left sitting at idle will tend to "slobber" oil into the air box and if the drains that allow this to run out on the ground are plugged (little hoses from the side of the block) the oil can build up.

This oily crap will get sucked into the engine and burned making once big blueish gray cloud.

The smoke screen can take time and miles to clean out especially on a rig that has not been run in many years,

The exhaust system has likely been oiled up too from short running of the engine, and it too will take time and some heat to clean out.

I have a lot of intimate experience with these busses so if you have any other questions, I may be able to help.

Best

Robyn