I've been out working on my MC-8 today like I do almost every day. I decided to start it just to keep it lubed and, mostly, to hear it run. It's an 8V71 with a 4-speed manual. It's been sitting since May '05, but started monthly and moved around the yard some. The fuel tank was filled before it was delivered, so it has about half a tank of fuel in it still. Today, it initially started within 1-2 seconds of pressing the starter button. It ran for a couple of seconds, then cut off. It did the same thing a second time. After that, the engine would rotate but without starting. The bus started and ran great when I started it back in late April.

So, what's the best way to go about diagnosing this? I'm thinking it's a fuel issue, as the engine was rebuilt about 30,000 miles ago. I had the bus serviced before I had it delivered last year and all the filters were replaced. I'm wondering if I might have algae in the fuel and a clogged filter. If so, what's the best way to clean this fuel and get rid of the algae? What's the best way to check for fuel pressure? I'm thinking that a fuel pressure gauge would be useful to have for monitoring filters.

I'm glad this happened in the driveway instead of on the road, but what now? I'm new to big Diesels, but am mechanically inclined and have the MCI books (service and parts). I'd love to hear any suggestions! Thanks.

I'm not and MCI guy but this problem has come up a bunch of times on the board.

It is usually caused by fuel delivery failure caused by blocked filters or pump failure.

It can also be caused by accidentally hitting a "stop engine" toggle switch at the rear of the bus whcich is used by mechanics during maintenance.

Your problem sounds just like this and the exact same symptoms are caused by a partially blocked fuel filter.

GMCs have this but don't know about MCIs. This switch is air operated so the engine will start but once the air pressure builds up it stops the engine. It is a very frustrating thing, don't ask me how I know about it!

Please let us know what you find out once you get it running. Follow up helps us all.

Dave, sounds like the Emergency air damper might be closed. Check the 'reload' lever above the roots blower. If they can't breathe..they can't run. Other than that I'd look for a birds' nest or something in the air inlet system. It's 'spring' y'know, and these birds can get pretty industrious.

Have you cracked a vent on the secondary fuel filter to see if you have fuel on the cranking cycle? If you've got fuel and it'll turn it's an air problem.

David,Unless you have a lot of fuel in the tank that's been there for years, I don't think you have an algae problem. It almost sounds like the engine lost it's prime, possibly because of a leaky check valve, or even a loose fuel line connection.You didn't mention smoke, so I wouldn't think that it was the E-shutdown. Besides, with the E-shutdown closed, it will either not start or just barely start.Like NCBob said, pull the secondary filter and see if it has fuel up to the rim. If not, it's lost it's prime. Try filling it and starting it again.Check the primary filter and see if it's full. If not fill it too. If nothing else, try putting a hose from the incoming side of the primary into a jug of diesel and see if it will prime it up that way and run.

David an easy way to get it primed back up is to get a soap bottle and fill it with diesel fuel then take a plug out of the fuel filter block and press the tip of the soap bottle in the hole and sqeeze while someone cranks it for you, keep squeeze'n fuel in until the bottle is at least 1/2 to 3/4 gone the quickly pull the bottle and use your finger to cover the hole. have your help give a lot of throttle if it roars quickly and responsively it's probably picking up fuel on it's own., put the plug back in and yer set to go! I used to use a electric pump to prime 'em until "The Man himself MAK" let me in on the soap bottle trick! Thanks Mike it has been a time, and hassle saving tip! BK

A week or so ago the wife and I were down to Chuck Lott's for a visit. One of the things he showed me which he did to his bus was the fuel priming system. A relatively inexpensive Bendix type automotive fuel pump hooked into the fuel system which allowed him to close a switch and prime the entire fuel system. He told me he puts the new filters up empty...and just hits the switch and "bingo" it's primed. I don't know all the particulars yet, whether he's got some valves he needs to close in order to accomplish the task at hand, but you can bet your sweet 'bippie' I'm going to find out.

Caterpillar recommends that all their filters be installed dry since you can introduce contamination into the fuel system with relatively unfiltered pump fuel. While the fuel systems on the 2 stroke Detroits will allow some contaminates to go through with their bigger clearances, the new electronic engines are much closer in tolerances and have much finer filters to compensate for this. So priming your filters with a electric priming pump is the best way to change your fuel filters. Good Luck, TomC

Hi Dave,Check your fuel level with a stick or whatever and verify that your level better than a 1/4 tank. If an MCI lists to the left, you'll run out of fuel with in spite of a considerable amount of fuel in the tank...The bus has likely slugged air from somewhere. If you have the usual MCI dual fuel filter layout, the secondary filter has a fitting on the discharge side (line to the injectors) where bleeding is possible if you'll install a primer pump. I agree with Dallas, that unless you had some really old fuel in your tank, an algae problem is unlikely. Air in the mechanical pump will stop you in your tracks. This is a good time to add a primer pump and sufficient plumbing bits to prime the engine. At a minimum, you'll need a ball valve in the supply line to prevent pumpng back into the tank. The pump would split (T in before and after)the ball valve. If you buy an electric primer (highly recommended) don't buy a fuel injection or high pressure pump. Use one that is designed for carburetor use. High pressure pumps will push fuel around (or displace the seal) in the mech fuel pump and fuel up your oil with catastrophic results. The same fitting on the secondary filter makes a good point to bleed from and verify that the mech fuel pump has fuel. I keep a 2' piece of clear 1/4" tubing that will screw onto a fitting installed on the sec filter. Some coaches have a pressure switch located at the sec which controls the starter...prevents starter engagement with fuel pressure is present. If you have a small 2" Delco looking switch at the sec fuel filter, that's where the bleeding takes place. It's as good as any anyway. I assuming you don't have the bus aired up with house air? If so, you may have a skinner valve issue. The E cutoff should be checked just verify that it isn't partially closed or stuck in some odd position. Probably verify function for the future.Bleeding through the mechanical pump, depending on how much air is in the system, may take 15 or more minutes. And, don't assume that fuel dripping into the tank from the return line indicates it's bled...may not be. You need to get that bus out on the road and exercise it. Things will "happen" when sitting or run for just a few minites at a time.FWIW, you should be able to screw a pressure guage into the sec fuel filter fitting and see about 20-30 lbs when cranking at normal crank speed....don't melt the starter while doing this. It should come right up. If no pressure, change fuel filters, check for fuel in tank, and it will have to be bled. A 2 cycle will not self-prime. The mechanical pump must be provided fuel for it to run. Anytime air is slugged into the system and it gets to the pump, it dies. Once you get it started, keep the RPMs up for a bit until it settles down and runs smoothly on all 8 cylinders. It'll purge whatever small air pockets are left...if you let it run initially at an idle, you'll be dinking around all day. You could hit it with a small amount of ether and see if it runs....if not, bad...if it does, likely fuel issue. Could be mech fuel pump failure...not likely. Leaking fuel line, leaky return check valve is possible. Low fuel should be ruled out. Broken or damaged fuel pickup is possible...not likely. Time for a primer! If you have fuel pressure when cranking the engine over..the problem isn't the fuel filters. Water in the fuel is always a possiblilty, although, the filters would be full of water if that was the case. Again, not likely.Keep us posted, JR

Logged

JR Lynch , Charlotte, NC87 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.”

Thanks for the reply. I think you've hit on everything I need to check. I do have the pressure sending unit t on the secondary filter. That's where I was thinking of adding a T and mounting a fuel pressure gauge. I guess I'll remove this sender and crank and look for fuel squirting from the hole! If I don't see any, that would seem to indicate that it's a fuel prime issue. How do you filter the primer fuel, or does one not worry about that? Where is the check valve located?

My mus does lean to the left, but it should have at least half a tank. I had the bus aired up to 120 thanks to my new big air compressor ( to run that 1" lug wrench!). I doubt if it's the emergency cut-off, as it did run fine for a few seconds. It sounds a bit odd when it cranks. I'm guessing that's because I really never hear it crank much. It generally starts as quick as I can push and release the starter button.

So, here's the game plan for this evening, unless it rains:1) Check fuel level2) Remove sender unit, crank engine, and look for fuel3) If there's no fuel, remove and fill the filters, reinstall, and start - engine should run for a few seconds4) If it still won't start, post here and ask new questions!

NOOOOOOO! Don't remove the sender to crank and watch for fuel....it WILL require bleeding after that. At a minimum, get a cheap pressure gauge and insert into the switch hole. Be quick about it. You can get a cheap pressure guage from Lowes or HD for $8 bucks....look in the well section (water pumps etc) for cheap guage. BTW, this $8 buck guage is a temp diagnostic tool, and is not to be used as a permanent guage. It couldn't handle the heat or vibration...it will establish whether or not the mech pump is working. Also keep in mind that no pressure doesn't necessarily indicate a bad pump...may just need bleeding. No pressure does indicate a fuel related issue. Check valve is located at the bulkhead where the return line attaches to the hard lines. Also, someone could help here, there may be a check valve right behind the heads where the returns exit the heads...I'm not that familiar with the MUIs.If you're airing the bus up prior to starting, the skinner valve would cut it off if for some reason a bad electrical connection was made between the ignition master and the skinner valve solenoid. This action would be visible. You can see the skinner valve work...someone could watch it and verify that it stays in the "run" position once started. If the bus isn't aired up, the skinner valve won't close...it defaults to "run" when no air. MUIs will occasionally start, run up air, and cut off. You get the point. If youi change the fuel filters, even if filled with fuel, the fuel pump and engine lines will have to be bled. Unless something else turns up, bleeding the fuel system is the most likely temp fix. I say temp, because it shouldn't allow air incursion...so if that is your problem, look for loose fittings, hard or cracked fuel lines, maybe fuel pump seal, supply line. Keep check on your motor oil for fuel contamination. That would indicate a bad fuel pump or injector jumper. Feel free to pmail me if I can answer any questions...or call. Good luck, JR

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JR Lynch , Charlotte, NC87 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.”

Thanks for all the info, JR. Unfortunately, a thunderstorm kept me from working on it tonight. A while back, I remember a couple web pages showing primer pump installations. I'm sure I saved it as a favorite, but it must be on my pc at work. Does anybody remember seeing these? I thought it was somewhere on BNO, but I don't see it there either. I know it's not all that difficult to do, but it would be handy to see where all the connections actually go. Thanks!

It doesn't matter where the connections go, as long as they are in parallel with the supply line. You need to be able to shunt the fuel from the supply thru the pump while blocking the supply line. That is clear as mud. The pix you probably saw were posted on the Yahoo MCI site I believe. The concept is simple. The goal is to push fuel thru the filters and pump, while preventing return of fuel via the supply line. Your best bet with a complete coach is to access the fuel line just in front of the primary fuel filter. T off the connection and into the primer pump at the bulkhead fitting. T back into at the primary filter inlet. You probably already have a ball valve located above the filter assemblies that shuts off the fuel when changing filters. Just shut the ball valve off and turn on the primer. You may want to consider a ball valve in the primer line so that fuel doesn't feed around the primer when changing the filters. Just keep the primer ball valve closed when in normal operating mode, and open when priming. The ball valve in the supply line is just the opposite....closed when priming and open when in normal operating mode. I'm trying to figure out what I just said....this will work. I can send pix of the filter ball valve if you need. I'll have to go down and take a pix, but don't mind. Let me know if you want a sketch of a primer system. I could fax it to you. Pmail me for more. You've got my cell phone number? Cheers, JR

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JR Lynch , Charlotte, NC87 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.”

The best place for the primer pump is as close to the tank as possible with some kind of vavle to keep from pumping fuel back into the tank. Since this is a suction system it is easier on the small elect pump to be close to the fuel.

One reason for this location is that it will drive air out of the system if there is a leak somewhere and when the air is out it will pump fuel out at the same location and show you where the leak is.

If you have it near the filter and there is a leak between the filter and the tank it will just suck in more air.