Hard start - suspect fuel bleed down

[bobofthenorth]

My 8-92 has always fired right up IMMEDIATELY.  Sometimes you could hardly hear it turn over before it was running.  Lately it has taken a lot of cranking.  Occasionally it will start and then die and be a bit hard to restart.  I'm looking for some troubleshooting tips.  It can't be bleeding back much or it would never start.  I think there is a check valve ahead of the water separator - my eyes aren't what they used to be so I need a magnifying glass to see if I can read anything stamped on it but it looks like it could be a check valve.  I'm tempted to pull it out and replace it.  Probably more because it is relatively accessible than because I have any big reason to suspect it. 

Any suggestions - anybody?

[Dallas]

Bob,

This may not be your problem, but, I had a 6V92 in a GMC cabover that would do that. it kept getting worse no matter what we did.
We finally, after about 2 months of trial and error figured out the secondary fuel filter housing had a small crack where one of the fittings went in. It would allow a bit of air back in when we shut down, but wouldn't leak any fuel when there was pressure. Over night it allowed the prime to slack off enough to make the engine hard to start but would pick the prime right back up again once the engine was running.

IHTH

Dallas

[Ncbob]

Bob, I was quite surprised when Ned Sanders was up here in our home territory recently and he seemed to be having the same problems with a 92 Series..and it had only sat for a couple of days.  Chances are he'll jump in on this if he's found the source of his problem.

To me it sounds like, as Dallas said, a possible leak somewhere between the tank and the pump. There should always be a solid column of fuel available to the pump.

One of the items on my TDO (things to do) list is to add an electric fuel pump into the fuel circuit with a guage wherein I can close a switch momentarily and see fuel pressure in the system before starting.  I'm also adding a Pre-luber pump for the same reason. 

Detroit's normally start with just 1 or 2 revolutions is everything is right and I don't like surprises when starting out on a trip.

That's my way...

Bob

[bobofthenorth]

I'm going to take it into town tomorrow & give the engine a really good bath.  Maybe then I'll be able to see a leak somewhere. 

[gus]

Bob,

A leak before the fuel pump on the engine will not leak fuel since it is suction. This will let air into the fuel supply line but no fuel out.

If the check valve before the primary fuel filter is leaking the fuel will drain back into the tank as the air enters at the leak. This happened on my 4104 when my primary filter was not sealing at the big O ring.

You could hook up a small electric fuel pump to a small diesel container at the fuel tank outlet and check for diesel leaks in the supply line since the supply line will then be under pressure.

[Sam 4106]

Hi Bobofthenorth,
An easy way to check for an air leak between the check valve and the tank is to remove the fuel line at the tank and plug it. Remove the fuel line on the tank side of the check valve, install a tee fitting to the fuel line, a guage in one leg of the tee, and a schrader valve in the other leg. Pressurize the fuel line with shop air and watch the gauge. If the pressure drops you know you have a leak. The speed at which the pressure drops will give an indication of the size of the leak. Be careful how much air you apply since there isn't much volume in a fuel line and the pressure will go up fast. I learned this test method from a retired bus mechanic.
I used this method to find a leak in my fuel line. As soon as I applied air to the line I could hear fuel dripping into my pit. After I replaced the leaking section I tested again and the gauge stayed steady for two hours so I knew I had found the only leak. If your leak is as small as I suspect it is you may need to use soapy water to locate it. That's if you have access to your fuel line its full length. Check any fittings first. I had to remove my LP tanks, Fresh water tank, and water pump to reach a place where I could splice my fuel line. My leak was in the area behind the rear axel and was caused by a rusted through pin hole.
Good luck, Sam 4106

[gus]

Sam,

An even better way is to remove the supply line at the tank and attach a small 12v fuel pump to it with the pickup end in a small jug of diesel. Or you can attach it to the tank via fittings and a rubber hose.

This is very easy and any leak will be wet with diesel since this line is normally under suction.

It won't leak diesel under normal use because it sucks in air.

[uncle ned]

bob

good morning.
Still recovering from my week with all of the guys.
Just coming down from a real high.great time

Hope to make it to bk's in sept. Want me to come by and get you and jackie.

My Slow starting was from the fuel shutoff sticking.Seems like my detroit does not leak enough oil to keep it lubricated. Had to oil it an have had no more problems.

Uncle Ned
"Huggy Bear"