changing injectors

[mikke60]

I bought my second bus last year. she was completed converted and done very well. my issue is with the 6-92. it is turbo with oversized injectors. The problem is, when i take off, the black smoke is insane. once uner way,not and issue. My question is, is this unhealthy for the engine, and how big a job is it to change them out? I will assume power loss at top end will be one of the effects of a swap out
.thanks, mike

[Bill Gerrie]

Black smoke is unburned and wasted fuel. It will contaminate oil faster then normal with the carbon particles. It also has other determental effects on the engine. I assume you are talking a mechanical engine. Check all exhaust connections to the turbo. Black sooty marks indicate exhaust leaks. The turbo needs to spool up fast to provide air for combustion to burn the fuel. If you are mechanically inclined it is very easy to change the injectors and set the rack afterward. Check the books to see what injectors you should be using and the settings afterward. You will need the special tools to set the injector height.     

[chessie4905]

What is the letter and number on the injector?

[luvrbus]

All depends how the 6v92 is equipped could be you have a throttle delay that is bad or out of adjustment if the engine is equipped with one or you could have the wrong turbo for the injectors ,it would help if you posted what bus the engine is in too a little more info please 

[TomC]

When I first turbo'd my engine and changed the injectors from N65 to 7G75, I tried it for a very short time without fuel modulator. I had Don Fairchild install one. The adjustment is very sensitive-in that there is a fine line between eliminating smoke and have the engine accelerate. I got the adjustment down to the point of putting out a little smoke on acceleration-a big improvement compared to putting out a large cloud of very black smoke.
On the 6V-92TA there were two types of smoke inhibitors. One was a throttle delay-which looks like a little shock absorber built into the left fuel rack that slows the opening of the fuel rack allowing time for the turbo to spin up to speed. The other is the fuel modulator. This has a small air line going from the intake side by the blower to the left cylinder head. This is the most accurate in that it works directly off the turbo boost. Both need to be adjusted properly. You can pull your left cylinder head and see which one you have. It was common to remove altogether the throttle delay (I know, I did it). Also, this will give you a chance to see what injectors you have. Good Luck, TomC

[busfan]

Air Cleaner / oil bath clean and not restricted?

[Utahclaimjumper]

 Also you would NOT have to "pull the left cylinder head" just the valve cover.>>>Dan

[Templar52]

Slow down on the fuel pedal is the key. It will be better than every device.

[HB of CJ]

Before about 1976 the fire apparatus had 6V71N and 8V71N engines with insane N90 injectors.  Also a 2500 rpm governor setting.  About 2700 rpm or so no load.

Very slow road gearing.  Thus the high rpm.

The manual transmissions were a mix of Fuller T905 five speeds and unknown specific Spicer granny 5 speed trannies.  Easy to blow CLOUDS of black smoke starting up.

No Allison automatics yet.  That was to come later.

We learned to keep our foot out of the engine until the rpm spooled up.  The early 8V71T engines were even worse.  Black smoke.  Easy throttle increases stopped the smoke.

This was a learned technique.  After some time it was easy.

Then the shops changed out the injectors to something more sane and added the dash pot throttle retarders.  No more smoke.  But ... one could stop the smoke with practice.

Long ago.  A learned technique.

[mikke60]

Thanks for all the input
I have been learning to keep my foot out of the pedal on takeoff I was told the bigger injectors were installed to supply more fuel at the higher rpm,s.is there an truth to this?

[Utahclaimjumper]

     

[chessie4905]

Yes it will supply more power, but if other parts of total package aren't changed also, you end up with what you have. Plus, then you can have overheating issues when engine is working hard if cooling system is marginal. Also, don't lug engine with big injectors. Sure way to cause internal damage as combustion temps soar. You need to pull the easiest valve cover and report numbers and letters on small round tag on an injector. Example: N90 or G110 or C60. If they are way oversize, will give nothing but grief over time. If they are a commonly used size, tune up, adding some model of fuel control Detroit makes, turbo change, etc. can help or totally alleviate issue. The engine tag with model number would be helpful if it is still on valve cover, or stamped on cylinder block on older engines.

[luvrbus]

If you have a Williams air throttle it makes matters worse without a delay