4104 671 Hard Starting

pennuja · March 14, 2018, 01:17:54 PM

For about a year now I have been having starting issues, when I try to start up the bus the motor fires right up, then after a few seconds it dies. Then I have to crank the motor over for a short while and it starts up and stays running.

It seems like there is a very slight leak in the fuel line and there is air in there. This happens after a few hours of sitting.

Some other things I noticed. The previous owner bypassed the original fuel line and ran a new one, I am guessing it was clogged or leaking.

From what I can tell the fuel comes from the new line into the fuel pump (I am guessing that os what it is, it is on the blower I think) Out of the fuel pump into a spin on filter, out of the filter and into the head.

I was thinking about adding a primer pump, even before this happened, but didn't want to add it as a fix and find later on there was a bigger issue.

So my question is do I have an air leak in the line, and should I add a pump or fix the problem first.

What is the best way to add in the primer pump with what I have, I searched and saw a few different ways, but not sure which is best.

Thanks, Jim

Templar52 · March 14, 2018, 02:51:06 PM

Don't put any primer on the engine. Check primary for air comming on your fuel line. You are suppose to have a one way valve on the fuel supply line from the tank. Maybe this one is no good anymore.

Utahclaimjumper · March 14, 2018, 04:21:29 PM

If you are sucking air from the delivery line than you will also have a leak in that line. A steel line will corrode from the inside out and start leaking fuel & air.>>>Dan

HB of CJ · March 14, 2018, 04:25:55 PM

If you have any rubber fuel lines after time and old age the rubber will swell up on the insides reducing the fuel flow. The rubber fuel line may look brand new or near new on the outside but the insides are swelling up.

Perhaps the wrong type of rubber line was used? This would also be between pipe lines or steel fuel lines. Just takes a couple inches of rubber. Cold they may pass fuel but once heated up to fuel temperature they swell up.

pennuja · March 14, 2018, 04:39:51 PM

Quote from: Templar52 on March 14, 2018, 02:51:06 PM
Don't put any primer on the engine. Check primary for air comming on your fuel line. You are suppose to have a one way valve on the fuel supply line from the tank. Maybe this one is no good anymore.

Where is that valve located at the tank or at the pump side?

The fuel line looks like it is a straight run from the tank to the mechanical pump. I will have to see if I can see anything there at the tank side.

pennuja · March 14, 2018, 06:04:48 PM

Here are some pictures, I do not know what one way valve looks like. The fuel line is about 8 years old. I doubt it is a swelling issue, seems like fuel runs back towards the tank after a while and then it takes some cranking to draw it back up the line. If some one can point me to what looks like the one way valve I will try and get a replacement. I had a lot of crud in the fuel tank when I purchased it, for the first few tank of fuel I had to replace the spin on filter every hour, so it sounds right that maybe that crud is in the check valve and maybe stopping it from sealing well. When I first purchased the bus it always started right up, but during the time I replaced the filters all of the time it started doing this.

Fuel Tank: The line here runs all of the way back to the pump, no fittings that I can see along the way.

The pump, the one line is from the tank the other gos to the filter.

The filter, one line to the pump the other to the head.

Dave5Cs · March 14, 2018, 07:17:18 PM

Sometimes in a bigger nut just a spring and a ball. Most will have a small arrow on them showing which way they flow. HTH
Dave5Cs

luvrbus · March 14, 2018, 07:20:19 PM

Use a Detroit 2351618 check valve at the filter about 50 bucks on E bay

chessie4905 · March 15, 2018, 03:41:20 AM

Inspect the area where the fuel lines come through the engine bulkhead. The check valve may be there.

pennuja · March 15, 2018, 04:08:14 AM

Quote from: chessie4905 on March 15, 2018, 03:41:20 AM
Inspect the area where the fuel lines come through the engine bulkhead. The check valve may be there.

Thanks, unfortunately the person that ran the new line took a different path, it comes through the opening where the driveshaft is, so it really is just one long line.

chessie4905 · March 15, 2018, 05:23:09 AM

If that new line is one piece braided, obviously he had a problem with this before. I would unhook line at tank and remove and inspect pickup tube if it was me. I had trouble with my 4104 once, found a big hunk of solder in pickup tube from previous tank repair. Acted like fuel filters would plug quickly. You could rig up a piece of vinyl line before fuel filter and look for air bubbles while it is running to verify problem before removing pickup tube. If it is not one piece braided, carefully inspect any connections mid point.

birdarchitect26 · March 15, 2018, 07:01:51 AM

I would say you are burning the fuel sitting close to the rack, then you hit air and you have to pump to fill the line and your golden. You have a pin hole air leak near the pump IMO. I would let it sit and start disconnecting lines starting closest to the engine. If you take it off and its full of fuel, I'd say that area is still ok. If you take a line off and fuel doesn't pour out, then that line is draining backwards via gravity and being replaced by the air. Often times there is a check valve near the pump to permit the fuel from draining the line.

Mine kinda did the same thing, although it died under load because the pickup tube was clogged in the tank, you better hope its a line instead, removing the tank is uneventful. Take a look at my thread about removing my fuel tank.

J

Geoff · March 15, 2018, 08:11:40 AM

Quote from: pennuja on March 14, 2018, 04:39:51 PM
Where is that valve located at the tank or at the pump side?

The fuel line looks like it is a straight run from the tank to the mechanical pump. I will have to see if I can see anything there at the tank side.

The fuel line is supposed to route to a high point in the engine compartment with a check value. If not, the fuel will drain b ack to the tank. The line MUST be high up, not straight to the engine.

chessie4905 · March 15, 2018, 08:14:08 AM

I don't know how difficult it is to remove the tank from a MCI, but a 4104 is not that bad, as I've done both 4104, to find a fuel supply issue,and 4905, which was to install the longer tank. On the 4104, it gave me the opportunity to thoroughly clean the many years of sludge build up on bottom of tank. That alone will save many fuel filters over time. I used small gravel, kerosine and lacquer thinner. Just kept sloshing the mixture around by gently tilting tank side to side and end to end. Cleaned it nicely.
Empty tank before removing! When I replaced fuel, I made a note of how much fuel it took to reach fuel pickup, and how much it took for each increment in fuel gage. Marked it down. One of the main reasons for these notes was that my 12kw Koehler drew from the main tank.

chessie4905 · March 15, 2018, 08:18:27 AM

Seems wet around fuel pump....could be leaking seal at pump coming out of weep hole? Have you installed new pre-filled fuel filter? Was/ is the old filter full of fuel, or only partially full?