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Author Topic: What do I check next  (Read 1467 times)
bobsw
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« on: September 22, 2007, 03:26:55 PM »

I tried to take the bus out for a ride today and have no power. The bus has been setting about 6 weeks ran fine last time out.The only things that I have done to it was change the water pump and put in a new alt.  The engine starts right up sounds good. As I started up the little rise in the driveway as I pressed on the throttle no increase in speed or RPM some black smoke out of the exhaust.  I checked for obstructed air filter it looks OK I checked for fuel leaks and didn't find anything. The bus is a MCI-7,   8-92TA, 5 speed auto with air throttle. Any suggestions of what to check next.
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JackConrad
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« Reply #1 on: September 22, 2007, 03:57:18 PM »

When running, transmission in neutral, will it rev up past an idle?  Just a guess, but it could be plugged fuel fliters or a partially blocked fuel line. I would also check the air throttle operation. With the bus running and aired up, have someone watch the air throttle actuator on the govenor while you push the air throttle pedal.  Jack
« Last Edit: September 22, 2007, 03:59:36 PM by JackConrad » Logged

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« Reply #2 on: September 22, 2007, 03:59:24 PM »

Hi Bob,

Check the fuel shut off selonoid on top of the injector/throttle box to the left of where your throttle cable connects to.

Sometimes they get stuck and you will have to lube the shaft. The same thing happened to me after I power washed the engine.

If that is the problem. you might want to replace the selonoid because it is suppose to completly shut off the fuel.

Good Luck
Nick-
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bobsw
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« Reply #3 on: September 22, 2007, 04:06:05 PM »

In neutral the throttle works fine rpms will go up to about 2100.
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JackConrad
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« Reply #4 on: September 22, 2007, 04:17:18 PM »

That is how ours acted when we had clogged fuel filters and also how it acted when we had an internally collapsed fuel line in the engine compartment (the rubber fuel line from the bulkhead fitting to the primary filter).  What happens is that you get enough fuel to allow the engine to rev up with no load on it, but not enough fuel when there is a load on it. Takes more fuel with a load on the engine. I would check filters first. (easier & cheaper).  When you open up the filter, if it has black snot in it, that is algae that is growing in your fuel tank. If so add an algaecide (available at truck stops) and plan to change filters several times until you get all the dead algae (killed by the algaecide) out of your fuel.  Jack
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bobofthenorth
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« Reply #5 on: September 22, 2007, 04:19:23 PM »

Is it possible it is staying in too high a gear?  I don't know anything about automatics other than PRNDL2 but that could explain the behavior you described.
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« Reply #6 on: September 22, 2007, 05:00:46 PM »

As Jack describes if you have some black stuff in the fuel filter, it is alge (actually not alge but I cannot remember the real name) the filter does not have to be plugged with it, just a little bit will destroy your day.
 Buy a Biocide from a Marine supply store ie West Marine ect. and follow directions. I do not care what the label on the magic elixers at truck stops or the auto parts places say. Buy the right product and end the problem.
 After having this problem one time I now use Biocide from West Marine on a regular basis.
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bobsw
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« Reply #7 on: September 22, 2007, 05:41:25 PM »

I just pulled the fuel filters and they look pristine no gook at all and full of fuel. Is their a shutoff for the fuel line on a MCI for when you remove the filter?  I am starting to see why we are bus nuts. Our buses drive us their.
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73 MCI-7
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« Reply #8 on: September 22, 2007, 07:01:26 PM »

On my 5C there is a shut off right at the fuel filters. No black stuff, be happy Cheesy
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« Reply #9 on: September 22, 2007, 07:35:11 PM »

I had a similiar problem last month with no power with our 6v92 turbo. I changed the fuel filters and treated the fuel, still no power. It ended up being the shutoff on top of the engine sticking on the shaft. I oiled it and it works great now. I also plan to oil it on a regular basis from now on.
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bobsw
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« Reply #10 on: October 14, 2007, 06:17:35 PM »

I think I found the problem.  After a lot of head scratching I found a small crack in the fuel pump housing. I think air was getting sucked into the system. I changed the fuel pump and took it out for a spin and everthing ran fine.
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73 MCI-7
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« Reply #11 on: October 14, 2007, 07:17:19 PM »

Is it possible that you may have tripped the emergency shut down air block while you were working on the engine?HuhHuh??
  just a thought Dwayne
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gumpy
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« Reply #12 on: October 15, 2007, 05:48:19 AM »

Is it possible that you may have tripped the emergency shut down air block while you were working on the engine?HuhHuh??
  just a thought Dwayne


Dwayne,

92 series engines don't have that feature. Only on the 71s.


Bobsw,

Sounds like you found the problem. A small crack in the pump would result in air being pulled in at higher RPMs, and would seem to
cause exactly the symptoms you describe.

craig
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