Question for MCI 9 Owners

luvrbus · January 11, 2010, 05:50:09 AM

A friend stop last night and his engine was shutting down we traced it to fuel switch on the filter. MY question is why does MCI have one no other buses do I have been around, his doesn't now and we changed his shutdown over to a 1 piece shutdown (no skinner valve) because he was having problems with the skinner also when shutting down and not starting . Got answers?

good luck

Ed Hackenbruch · January 11, 2010, 06:18:34 AM

I have a 5A not a 9. Is there a switch for it on the dash? manual shutdown of the fuel in case of runaway engine? Curious.

NewbeeMC9 · January 11, 2010, 06:32:46 AM

Do you have picture of this switch? I don't think I have one but will gladly check.

mikelutestanski · January 11, 2010, 06:35:35 AM

HELLO: If I understand what you are referring to correctly then the flollowing applies:
First; The fuel switch will not shutdown the engine but it will prevent the starter from engaging as it is in the starter solenoid circuit.
2nd: The switch is part of an override system that allows the driver to run the motor during an alarm condition to move the bus to a safe position ie off to the side of the road . If you push the starter button and hold it the starter will disengage when fuel pressure is sensed but holding the button down manually overrides most or all shutdown functions.
THis gives the driver who is responsible for his or her passengers safety the power to override any shutdown feature.

If this is the switch you are referrring to then it is there to close the flapper in the air intake (the flapper is spring loaded and when you press the switch a solenoid releases the flapper ) that will be shut if the engine runs away or overspeeds and the only shutdown option is to choke off the air supply. That is why the red cover is over the switch. It is a last resort effort. I dont know if this option will damage the engine but the overspeed may cause a self destruction in any case.
FWIW and this is my understanding of the functions others may have a better explanation
Regards and happpy bussin mike

Jriddle · January 11, 2010, 06:39:39 AM

I had starting problems with my 9 and found that the wire from this fuel pressure switch to be the problem. I ran a new wire from the fuel pressure sensor to the starter solenoid relay and bus started. I took the wire back off while bus was running and it didn't shutdown. I am not sure why it is there but believe it will not allow a start with fuel pressure above 8 lbs.

luvrbus · January 11, 2010, 06:52:26 AM

His would run good at anything above idle then at idle the switch became hot and would shut the engine down.
He has 6V92 MUI and no switch for emergency shut down and DD's have a lot more fuel pressure than 8 lbs.
FWIW Eagles have a override system for the shutdown but is not tied to the fuel system
I can not see the purpose expect to cause more headaches for owners could be just somebodies creative wiring but he called this morning from El Paso and is a happy camper no more shutdowns and the engine starts

good luck

Jriddle · January 11, 2010, 07:03:47 AM

Headache for sure. Mine lasted over a day.

John

Jriddle · January 11, 2010, 07:07:41 AM

This might be better

mikelutestanski · January 11, 2010, 07:53:57 AM

Hello: if this is a DDEC then I dont know how the system works ; Never worked with that one only the older hardwired systems.
THe other gentleman talking about the pressure switch is correct . The switch is closed @ 0 psi fuel pressure (allowing the starter to engage) and opens when the pressure rises above 8 pounds. I have removed this switch and bench tested a few and if the switch was working correctly they all opened around 8 psi. This particular switch is on the secondary filter which is after the fuel pump and before the injector feeds.
FWIW
regards and happy busssin mike

gumpy · January 11, 2010, 07:59:13 AM

Mike and John are correct. This is part of the safety shutdown system (low oil, low water, high temp) and allows driver to override by holding in the start button. It is connected between ground and the starter solenoid and simply disengages the starter when fuel pressure is reached.

If his is shutting off his bus, it has probably been rewired. Is it possible someone put a tempstat in and wired it to the safety shutdown system? Are you sure it's not one of the tempstat switches that's shutting it down?

luvrbus · January 11, 2010, 08:08:50 AM

No Craig when the switch was hot on both sides it would shut the bus down at idle like it was wired into the fuel pressure some way.
His starter would always engage but it had set for about 15 minutes before it would fire
Makes no difference now we removed it and pluged the hole and he is on his way fwiw Mike it is not a DDEC engine

good luck

gumpy · January 11, 2010, 04:36:49 PM

Quote from: luvrbus on January 11, 2010, 08:08:50 AM
No Craig when the switch was hot on both sides it would shut the bus down at idle like it was wired into the fuel pressure some way.
His starter would always engage but it had set for about 15 minutes before it would fire
Makes no difference now we removed it and pluged the hole and he is on his way fwiw Mike it is not a DDEC engine

good luck

It's not uncommon for the safety shutdown system to get bypassed, rewired, "fixed" (pick one). When one sensor goes bad, it's a pain to figure out which one, and in revenue service, I think it was common to simply disconnect it and go.

It seems your friends was probably not wired as original, so removing it does nothing other than make him happy

And that's what's most important for now...

Chopper Scott · January 11, 2010, 06:42:45 PM

The switch you are refering to on my 7 started spewing diesel fuel. I removed it, plugged it off and had to ground it out to make the starter engage. It does override the shutdown system I found out earlier when I had heating issues.