Help MCI won't Fire

fredcliff · December 20, 2010, 05:30:43 AM

Our 1984 v6-92 Detroit Diesel won't Fire! We have checked all fluids and charged batteries,we rebuilt starter and replaced the fuel filters and still she won't fire. . We preheat the engine to no avail. What are we missing

bevans6 · December 20, 2010, 05:47:16 AM

Is it a mechanical or a DDEC engine? What happens when you crank it? Any smoke, or it just spins over? When did it run last, and why did you feel you needed new batteries and starter? How did you prime it after changing the fuel filters?

Brian

fredcliff · December 20, 2010, 06:10:24 AM

When we try to start it, it smokes and turns over and spins but doesn't fire. Yes we primed it after changing the filter by pumping fuel into the filters, the starter was rebuilt after we had it check and it was found to be on its last leg. The batteries kept getting worn down as we tried to start it. It was last run two days before we started having problems. it ran fine with no problems

DMoedave · December 20, 2010, 06:19:23 AM

Its getting fuel if it smokes. You dident answer if its a ddec or not. If you have an emergency shutdown flap make sure its not activated and shutting off your air. Did you just change the filters? Has it run since you changed them?

Busted Knuckle · December 20, 2010, 06:47:11 AM

Fred
do you have air pressure?
If so the cylinder for the fuel shut off to the rack could be extended.

If the cylinder is extended there are two ways to temporarily solve this one is to take the air hose loose from it. Or you can remove one of the mounting screws on the side of it out and twist the cylinder to the side. (either way once the cylinder is removed from the shut off lever it should start "if this is the problem."

Have you tried giving it a shot of either to see if it will "hit" or not?
If it hits on either it means your either not getting proper fuel to it, or it's not turning over fast enough to build enough heat to fire it.

BK

moonrakerbus · December 20, 2010, 07:01:48 AM

Mine did exactly what you described but mine is an 8v71. MY problem turned to be nothing more than being cold. Did you plug in your block heater the night before starting? If not, you may want to warm the engine compartment and it may help. Once the temperature warmed up outside, mine started right up..Detroits HATE Cold weather. I hope this helps.

robertglines1 · December 20, 2010, 07:08:57 AM

First of all it happen to me.....is rear switch in correct position? she will turn over but not start if it is in the wrong position.

luvrbus · December 20, 2010, 07:22:23 AM

The MCI has a low pressure fuel shut down I think it has to have 7# before it opens not sure about the pressure check the filters again and be sure they are full and reprime, the engine has a gear driven pump and will not pick up fuel if the filters are not full and no air leaks smoke doesn't mean that much on a 2 stroke and what size batteries do you have are they large enough a Detroit will fire when down to about 20 with the right batteries,follow BK about the shut down sometimes they stick in shutdown

good luck

fredcliff · December 20, 2010, 12:23:26 PM

Alright just got back from a visit to the 84 MCI. first thing I did was check the resistance of the leads to the low pressure pump and it read about half an OHM and then testing ground it read 0 OHMs. so I'm assuming it gets power second i aimed a heater into the engine bay to raise it over 30degrees, got it to probably 90, primed it again and gave it a tiny shot of ether and it fired! but after about 5 minutes of running it got shaky and sounded like it was only firing a few cylinders and then it proceeded to die. I'm not sure where to go from here kind of at a loss and anymore help would be greatly appreciated. Also i would like to know if what i think is the low pressure pump actually is that, it's the only round object with a positive and negative lead on the fuel system that i can see but it's confusing because I thought a pump should have an inlet and an outlet but it has just one outlet leading into the fuel filter assembly. thanks so much.

luvrbus · December 20, 2010, 12:38:35 PM

The fuel pump is mechanical it is on the front of the blower behind the water cross over pipe it has a inlet line from the filter and a outlet line going to the heads check for air leaks those pumps will not stay primed if you have a air leak on the suction side check the pump area if you have fuel wetness around that area the seal in the pump has gone bad then you need to change the pump

good luck

bevans6 · December 20, 2010, 12:46:31 PM

Your little round thing is the fuel pressure sensor that was discussed earlier. If your system is even close to stock, fuel comes in from the tank to the first filter, closest to the front of the engine, from there up to the fuel pump, back down to the secondary filter (the one with the pressure sensor on it) from there up to the cylinder head (driver's side) back and across to the passenger side cylinder head, then returns to the tank. There is a close-off valve in the line to the first filter, make sure it's open. I agree it sounds like you are getting air in somewhere and losing prime.

Brian

robertglines1 · December 20, 2010, 02:32:35 PM

Haven't had a visit from a fuel thief? I have had a weak transfer pump act the same way.(twice)

gumpy · December 20, 2010, 03:02:43 PM

Quote from: luvrbus on December 20, 2010, 07:22:23 AM
The MCI has a low pressure fuel shut down I think it has to have 7# before it opens not sure about the pressure check the filters again and be sure they are full and reprime,

Ummm, no it doesn't.

The sensor you are describing, and in the later post, which is located on the secondary filter is part of the emergency shutdown system. It's purpose is to cut off the current to the starter solenoid after the engine starts and fuel pressure comes up. This is there so that one can hold on the starter button to override the safety shutdown system while moving the coach to a safe location.

If the bus started, ran for 5 minutes, and then slowly died, the safety shutdown system is working. It shut down when air built up enough to activate the fuel shutoff cylinder.

You need to check your low oil pressure, low water sensor, and engine temp sensors (and maybe low oil level sensor). Remove the wire from each sensor and keep it from grounding to the engine or frame. Start the bus after removing each wire. When it runs longer than 5 minutes and air pressure builds up full, replace the last sensor whose wire you removed.

gumpy · December 20, 2010, 03:04:28 PM

BTW, you should put your location in your profile. Heck, if you were close to me, I'd probably come over and help you figure it out....

MARKMC7 · December 20, 2010, 04:18:14 PM

i had the same experience just last week when i changed the low pressure fuel switch. then she ran just a few min then got shakey and died again, after repriming and a bit of eather each start she finally stayed running. don't know why but i had to prime it 3 times before it stayed running just my experience and i hope this helps ya.