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Author Topic: my6v92 Is a Dog  (Read 3077 times)
onemule
onemule
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« on: April 08, 2006, 11:39:35 PM »

Can anyone give me a few pointers as to what i can do to help increase power or (torque) on inclines. I have read some of the other articles , and one alternative that was given to me was to increase thef boost in the turbo, is this possible, when i start bus up there is no smoke but while running even on flat ground there is black smoke, unburnt fuel i would guess ? runs good on flat surface 75 mph or better, but its just a dog going up hills, im not tryin to be king of the hill but when semi's pass me loaded, its embarresing, open for any ideas.
  Randall  (onemule)http://[i][b][move][/move][/b][/i]
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Sammy
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« Reply #1 on: April 09, 2006, 05:35:39 AM »

Randall, check the air filter, all pipes and clamps that lead from the turbo to the air filter too.
You are correct - black smoke is too rich - not enough air getting into airbox.
I recommend to do some basic checks and repairs first - don't worry about turbo.it's working. If your turbo was not making any boost you would not be able to do 75 mph.
Check your fuel pressure, change the fuel filters if you don't know when they were last replaced.
Let us know if your 6V92 has DDEC, will be able to help you some more.
Best of luck with your repair.
Sammy Cool
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rv_safetyman
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« Reply #2 on: April 09, 2006, 07:26:02 AM »

As Sammy points out, we need to know if your engine is mechanical or DDEC.  It would also help to know what bus you have.  If it is a non-transit and is pretty well outfitted, you are probably in the 34-40K pound range and going slow up a big hill will be the norm with all but a specially set up 6V92. 

Most bus 6V92s were set up in the 280 HP range.  You can take a mechanical 6V92 up to 350 HP by changing the injectors and turbo to specific DD specifications.  You can find those details in a 6V92 manual or some of us can help you with that upgrade.  Before you do this work, you will need to know how your engine was built in the first place.  If you give your engine serial number to a DD dealer they can tell you how the engine started life.  Modifications after that will not be documented.  If your bus has black smoke under full throttle, someone might have put bigger injectors in it.  If they did that without changing the turbo to match the injectors, you will not benefit from the injectors adding extra fuel.

If your engine is DDEC, you might be able to talk DD into reprogramming the ECM.  They are getting reluctant to do that because of emission issues.  If they will reprogram the ECM, expect to pay at least $500.

My guess is that it is mechanical.  If so, you need to make sure that you do the things Sammy suggests, plus have someone who knows two strokes "run the rack".  DO NOT let anyone touch the engine unless you are sure they have a ton of two stoke experience.

Once you are sure that everything is adjusted properly and filters are clean, we can help you upgrade your engine and do it properly.
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Jim Shepherd
Evergreen, CO
85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
NJT5047
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« Reply #3 on: April 09, 2006, 08:03:34 PM »

When you run the rack (assuming an MUI), ID the injectors while you're under the valve cover.   Someone may have installed big injectors and your engine cannot digest the fuel.  That isn't good for the engine   Shouldn't smoke black smoke unless lugging.  The size of the injectors and year of coach and engine would help make a plan.  Do you have a tach?  You may be under turning the engine due to final drive ratios.  A tach would ID that problem.   You should max out at about 2100 RPM. 
DDECs shouldn't smoke at all.   You could also have a bad, or possibly several bad and leaking injectors. 
I must have missed the part about what bus Randall is operating.   If it will go 75 MPH, it isn't so bad...the speed would also rule out transits, and ex-NJTs.   Without mods, they won't go that fast. 
Good Luck, JR
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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
onemule
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« Reply #4 on: April 09, 2006, 10:46:49 PM »

Thanks everyone for your input, when i purchased the coach from mak, he stated to me that it had the small injectors ? not sure how many different sizes there are,as far as  ddc,am i to assume you mean detroit diesal. my bus is an 84 made in November of that year with a detroit 6v92 and even at takeoff on level ground it is slow,very slow but mak said this was normal because of the injectors, that is what led me to beleive the turbo was not functioning propery ? or not enough boost. I will change all filters ,should i be concerned about loosing prime, Im sorry for all the questions but i have yet to find or obtain all manuals for my coach yet, any ideas , im waiting on one guy who has two but not the engine manual.he wants 160.00,  Thanks in advance, you guys are GREAT.  Randalll
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rv_safetyman
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« Reply #5 on: April 10, 2006, 07:57:08 AM »

Randall, while you will want a manual on the bus, you should have access to a DD manual on the 6V92.  Even if you don't plan to work on it yourself, it is probably worth looking for one.  They are on Ebay all the time.  You would probably have to pay less than 50 dollars.

When we talk about DDEC, we are talking about an electronic engine.  Your '84 should be a non-electronic or what we refer to as a mechanical engine (referring to the controls). 

6V92 engines in that era had what is called a throttle delay system (two different kinds).  They delay full throttle until the turbo has a chance to spool up.  This prevents the black smoke on take-off.  It also make for fairly slow acceleration for the first few seconds.

If you are pretty sure that your bus is slower than other buses of the same size and era, I again strongly recommend that you have the engine "tuned up".  This is called "running the rack".  This  must be done by a very qualified two stoke mechanic.  When that person does the work, they will also be able to tell you what the injectors are, and what your engine is rated at.  They will also check the other maintenance items that have been mentioned (especially the air filter)
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Jim Shepherd
Evergreen, CO
85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
NJT5047
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« Reply #6 on: April 10, 2006, 05:08:25 PM »

Regarding losing the fuel system prime...the answer is yes.  Very likely if you don't completely fill the fuel filters prior to instralling them.  If you have a fuel cutoff valve on the primary filter, turn that off and then the line won't drain wihile the primary is being changed.   Use clean fuel, and be clean with the install.   Clean the area proximal to the filters.  They are top heavy and slick to hold on to. 
Once the engine starts, set the high idle.  if it dies, you'll have to bleed the system at the secondary filter.  Generally, a gear pump won't self-prime if aired up. 
Your bus is probably an "intracity" based item that has about 270 HP.  Small turbo, small injectors, cat converter, various throttle delays...and maybe retarded cams.   Probably redlined at 1800 RPM.   If it has "Clean Air Bus" on the rear...that's a positive sign of the small HP engine.  They work well, just slow.  It can be bumped up to 300 + with injectors, and turbo.   The 75 MPH is a little odd...you may have a 300 HP engine and a high (low numerical) diff.  That would give you high road speed, but make hill climbing slow.   Have you got a tach?  You may be overrevving the engine.   That would add to the road speed at the expense of an engine.   
Something is not correct with the fuel system, it shouldn't blow black smoke on a flat road at 75 MPH.  Someone may have change the injectors already.  If you find you're getting 4 MPG, you'll have some idea. 
It's unlikely that MAK would actually check for injector size, he's stating what the unit should have, and was spec'd with when new.   Was the coach taken out of bus service?  Or has it passed through private ownership?  Another thing, is what are you expecting on hills?  A bus isn't going to charge up a mountain pass....unless you got some 450 or 500 HP engine.   Often 35--45 is good as it gets.   
It'll all get sorted out. 
Best, JR 

I will change all filters ,should i be concerned about loosing prime, . Randalll
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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
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