'94 923A2 Fuel Issues

[Bluebeard]

We recently picked up a "new" to us, M923A2 that had 6000 miles on it since its rebuild. For the first couple of months, it ran great, but now we are having fuel issues. One day it ran great, the next we couldn't get it to start, it just cranked and cranked. We replaced the fuel pump and bled the lines and it started right up. It ran for a couple of hours, but when you turn it off for any period of time, it won't start again. We've been tracking the fuel lines, and it doesn't appear there are any leaks. Anyone have any ideas? I am not the mechanic, I am the guy who is translating what he told me so I could tell you.

 

[98G]

It may not appear there's any leaks, but that's what it is. You have pinholes in the fuel lines...

 

[Suprman]

Yup the line from the big cannister in the drivers footwell area to the lift pump is a possible culprit I have had them rub thru.

 

[MtnSnow]

If you still have the problem after replacing the supply fuel lines pull the fuel pickup tube from the tank and check it for cracks/leaks where the tube is soldered as well as the integrity of the whole tube.

 

[Bluebeard]

If you still have the problem after replacing the supply fuel lines pull the fuel pickup tube from the tank and check it for cracks/leaks where the tube is soldered as well as the integrity of the whole tube.

Thanks Guys, I will pass this info on to the guys working on it.

Rick

 

[Moto2four]

A leaking fuel line won't always drip fuel. I had a leaking line that sucked in air while the truck was running. As long as it was running it was ok, but as soon as I stopped it wouldn't restart without bleeding the air.

 

[Bluebeard]

A leaking fuel line won't always drip fuel. I had a leaking line that sucked in air while the truck was running. As long as it was running it was ok, but as soon as I stopped it wouldn't restart without bleeding the air.

So probably the best way to resolve this is either to replace all the fuel lines, or to (perhaps) do something that pressurizes the fuel line, rather than having it work from a vacuum? Like some sort of electric fuel pump? A pinhole leak can be ANYWHERE.

 

[MtnSnow]

Yep....Fuel line is cheap & easy to replace!

 

[Moto2four]

Putting 2 or 3 psi on the system and letting it sit would probably be the easiest. But I'd just replace it all and be done with it.

 

[Bluebeard]

Not knowing hardly anything about diesels, will common rubber gas fuel line work? or do I need something specific?

 

[MtnSnow]

Hit your local Napa parts store and tell them you want diesel rated fuel line. If using Parker hose it would be "Mfr Part #: 39708"

 

[Bluebeard]

What are all the white (green painted) plastic lines coming off of top of the fuel tank? Are they vents? or other pick ups for when the truck is at extreme angles? Also, there is this flared connector under the driver that goes into the frame, but isn't attached to anything- and it is right under the floorboards of the driver.
Any ideas what it goes to? In both photos it is in the center of the photos

 

[Moto2four]

Make sure it's fuel line rated for diesel. I had an asshat give me 1/2 heater (coolant) hose once and I being none the wiser put it on. It barely lasted a week.

 

[MtnSnow]

Blue,

The two small white lines are vent lines, The line closest to the frame is the fuel pickup and the line closest to the outboard (slightly smaller than the pickup line) is the fuel return line. As for the line with the compression fitting on it likely used to run to the filter housing but was replaced with the rubber hose that is now in use.

 

[Bluebeard]

Blue,

The two small white lines are vent lines, The line closest to the frame is the fuel pickup and the line closest to the outboard (slightly smaller than the pickup line) is the fuel return line. As for the line with the compression fitting on it likely used to run to the filter housing but was replaced with the rubber hose that is now in use.

So, I don't need to replace the vent lines, just the fuel pickup line, right? The fuel return line is pressurized, so if there was a leak there, it would drip, right? (and not be a problem, right?)

 

[MtnSnow]

Yes the line to replace would be the Tank to filter and then filter to IP. On my trucks I just replaced the hard line completely with the Parker Push-Lok hose and fittings. Just take the fitting ends from the ends of the existing lines with you to the store so they can match up the sizes and so in the end you will end up with two rubber hoses (tank to filter) and (filter to IP) When you take the existing hard line(s) off you will find that you actually have 3 hoses/lines currently which actually adds in additional locations for leaks and the hard line(s) have been known to get hairline cracks and thus allowing air leaks. Also if you do go with Parker Push-Lok type fittings you can reuse them years down the road when you change the fuel lines due to age (Preventative maintenance)

 

[MtnSnow]

And No There is no need to replace the vent lines or the return line (unless it is actually leaking)

 

[Bluebeard]

So, you guys are right about the flare fitting sitting out there by itself. Apparently, someone put a remote fuel filter in the fenderwell, and replaced that line with rubber back to some sort of coupler attached to the frame (heading back towards the fuel tank). So it looks like in order to replace that rear fuel line I need to run it from the in-between coupler, back to the tank. Is there a standard size for that fuel line? It looks like either 3/8" or 1/2" (most likely 3/. And maybe roughly 6', does that sound right?

 

[MtnSnow]

Use 1/2" for the fuel line as it is readily available along with the needed fuel fittings

 

[chrisrauch72]

I have a 1990 923a2 having same isuues, bleed the system it will start let it sit longer than like 20 minutes and you have to bleed it again! So let me get this straight replace the tank to seperator hose and hose to lift pump and go from there? How about the lift pump being the problem? is there any way to check it?