Air in fuel?

[Lorax]

A question for anyone that may have dealt with this in the past. My M818 doesn't want to start. The batteries are fine, and she'll turn over, but it's as if the fuel isn't getting to the engine. Here's what I've checked:
1. Both fuel tanks have fuel. About half each.
2. She puffs out a little smoke from the exhaust while turning over.
3. The fuel lines "look" OK.
4. I pulled the fuel filter and filled it with fuel. Not sure how much fuel was in it before pulling it, since I accidentally dropped it.
5. From reading other posts, I checked to make sure the EMERGENCY ENGINE SHUTOFF lever was reset above the injector pump.
6. Checked to make sure the fuel tank selector valve was NOT in OFF.

She made some smoke while turning over, then I pulled the fuel filter and filled it, then she didn't make any more smoke while turning over.

Everything else appears fine, so I'm guessing the engine lost it's prime, or got air in the lines somewhere. Does anyone have a suggestion for purging the air from the fuel lines? I would keep filling the fuel filter and cranking her over, but after half a dozen tries, the batteries were beginning to show fatigue.

 

[SasquatchSanta]

I've experienced the same problem with the original engine (LDT) that was in my truck and then the LDS. After getting the engine started in the morning it would start fine for the rest of the day but let it sit over night and I'd have to crank and crank to the point that I started resorting to giving it a shot of ether in the mornings --- even in the summer.

Recently, I tightened some of the fuel lines between the IP booster pump and secondary filters as well as some of the fittings on the IP pump and the problem all but went away. It still shutters a little on start up but it's a lot better. I'm also interested in what others have to say about this subject.

opcorn:

 

[WillWagner]

Is it a multi or a Cummins? Sorry, it's a 5T

 

[oilcan]

On the cummins, if the fuel line that goes from the filter to the IP gets a pinhole, you'll be sucking air. There are other places to look, but this one seems to be the most common from what I've seen.

 

[Lorax]

It's a Cummins. I figure it's a pin hole air leak...somewhere. There is a drain valve just before the fuel filter. Before dropping and filling the fuel filter canister, I opened that valve to see if there was fuel. 1 drop came out, so there may not have been any fuel getting to the canister. Also, before dropping the fuel filter canister, I opened the water drain valve on the bottom of it. 2 drops came out. Figured the canister was empty, but when I slipped and dropped (literally) the canister, there was a decent amount of fuel in it.

I'm busy reading through the manuals and reading posts, but does anyone know the best way to purge the air from the line? Everything else seems to work. The engine just needs fuel. Time to start getting new fuel lines?

 

[sermis]

I have Kwai's tractor here at the house. It is doing the same thing. I am leaning towards the fuel tank selector switch.
Really hard to start. Once started and you floor it and it has to think about it and when you left off the peddle it will surge the RPM’s up some time and then has to think about going back to idle. I know it is getting air. There is a new fuel line from the filter to the IP. I am thinking it was the same problem before it went to GL.

 

[Scrounger]

This is one of those issues that the Cummins and the 818 has, or any of the 800 series with a fuel selector switch.
The 800 series does not have an in tank fuel pump so it is very unforgiving of any air leaks and can loose prime every quickly.
First off any time one removes the fuel filter canister to check or replace the fuel filter the system need to be re-primed. That is done by opening the bleeder valve under the hood up by the air intake tube next to the cold weather stating plug. Work the priming pump on the dash till fuel flows from the bleeder valve then close the valve. Then when you go to start the truck pump the priming pump till the truck starts and you may have to keep pumping till it is running. You will know when the system is primed because you won’t be able to pump the handle.
Now there will probably be a problem with the six fuel lines that go into the fuel selector valve. They are notorious for dry rotting and allowing air in. Even if they look good change them when you get a chance. To replace them it is tight but can be done by only removing the fuel can holder and the tool box. Ask me how I know.

 

[WillWagner]

Could also be as easy as the rubber on the shut off disc worn real bad or missing a piece of it. Easy things first.

 

[Lorax]

WillWagner, could you be more specific about the shut off disc? Is that on the solenoid valve above the injector pump?

Scrounger, thats good information. I just read today in the manual how to bleed the fuel system after changing the fuel filter. Nearly word for word with what you said.

Looking at the fuel selector valve, there ARE a lot of hoses going to it. I'm thinking of taking a fuel line from the driver's side tank straight to the fuel filter, and bypassing the selector valve, in case all those hoses have a leak. Hopefully that would remove that possible leak until I get the truck home and can replace all the lines. Does the fuel return line go thru that valve too? Anyone know of any problems bypassing that valve could cause? I didn't get a chance to get a good look at all the hoses connecting to the valve.

Wish the truck wasn't an hour away. I'd grab a flashlight and get to work if it was here.

 

[Scrounger]

The return line(s) go back thru the fuel selector valve. When the valve is in one position it feeds and returns the fuel from and back to one tank. When it is in the other position it does the same for the other tank. I would only by pass the return if there was no other way. The pump draws more fuel than the engine can use and sends the excess back. Bypassing the return line would probably result in to much fuel going to the engine. Even if one of the fuel lines going into the fuel selector valve is leaking air the truck is still drivable. It’s not easy, however all one has to do is keep the rpm’s up. Those lines can draw air it just makes the truck a “you know what” to drive.
Without looking at it I should think that the fuel lines just needs to be primed to get the truck started. After that it will still idle a little ragged because of air in the lines, and the only way to get that out is to drive it. And if it won’t idle steady after you get it home it probably has a fuel line(s) leaking air at the fuel selector valve. Even if it doesn’t, do yourself a favor and replace them when you can, you won’t regret it.

 

[WillWagner]

Here's a pic of it, #2 is the disc, there could be a piece of crap on it or a big worn spot on the seal areas. It can cause the fuel to bleed back after long periods of shut down and can cause a slow shut down. Number 3 is the shield, if it is cracked, there could be an external fuel leak, and it will cause a bleed back.

 

[Lorax]

Thanks fellows. A wealth of information. I look forward to trying this out.

 

[CGarbee]

I've bypassed the fuel line on the suction side (supply) using a six inch long pipe nipple and left the return flowing back through the selector switch for the ride home on a "new" truck. That way, you know that you are not sucking air into the system and you save yourself some wrenching. Just make sure that you have the switch set to dump the fuel back into the tank you are pulling from...
I had one truck (the M817) that had a slight pinhole in the suction tube in the driver's side tank. Once you got to a 1/4 tank, it started to suck a little air... I fixed that at the same time that I redid the tank sender. Before that, it sorta worked as a poor man's fuel guage.
One trick that I picked up from AMGeneral when we snagged my M817 was to put an air line (his blowgun) onto the fuel tank vent to pressurize it a tad when cranking it up the first time...helpful if you have a source of air and the primer pump is suspect...

Memphis Equipment has the little rubber lines that go on the fuel selector switch. I know one dealer who uses barbed brass nipples, generic rubber fuel line, and hose clamps on these (haven't tried this approach on mine...), and I have one friend who has rotated his switch and just hardlined the supply and return lines to it with some new brass fittings who says things have been working well and that cab flex/vibration doesn't seem to be having an adverse affect on his lines...

 

[Lorax]

When pressurizing the fuel tank, how many pounds do you pump it up to? 1 or 2 psi? More?

 

[madsam]

I like the idea of pressurizing the fuel tank. If there was a big leak, you could find it quick. If it is a pinhole, you might find it. It bypasses the primer pump.

All my hoses on the fuel selector were change before I got it. (I think by timtrucks.) My drivers side tank does not work. My passenger does work.

So if it does not work no matter which tank it is switched to, then the leak should be the selector valve or the lines from the engine to the selector valve.

One question. Has any one ever tried to hook it up like the large trucks? The one I drove, had a fuel line between tanks which transfers from on tank to the other and only has one line from one tank going to the engine. I know these trucks are setup to have a secondary tank for emergency, but the way most of us use them, we don't hit emergences to much.

 

[Lorax]

Does anyone know what size fuel hose goes from the tank to valve to filter to engine? I haven't yet found that info in the tech manuals.

 

[CGarbee]

One question. Has any one ever tried to hook it up like the large trucks? The one I drove, had a fuel line between tanks which transfers from on tank to the other and only has one line from one tank going to the engine. I know these trucks are setup to have a secondary tank for emergency, but the way most of us use them, we don't hit emergences to much.

I've thought about this a lot, but didn't like the routing that a hose (or pipe) would take... If tucked up high enough to not get snagged when going over obstacles (I know, it's up there, but I'd hate to high center my M817 and honk my fuel line) you'd not be able to utilize all the fuel in the secondary tank. If run lower, you could snag the line...
I have a Walbro 24v diesel pump from a boat (got it surplus) that I have thought about hooking up as a transfer from the passenger side to the driver's side tank on the M817. It wouldn't be hard to fit as I can use the existing lines with just a little modification (run the existing supply line to the pump instead of the selector switch, tee into the return line to the other tank for the pump output (or if that caused backpressure problems to the injectors--need to check the Cummins specs on the return line pressures--run a new line to the tank).

I've never put a guage on it when I've put a little air to the tank to help prime... Not a lot, just a couple of pounds... If you see the tank bulge a bit, you've put too much air in...

 

[bob130ab]

I have had the same problem with my M-817. Some times it would crank the next morning, other times it would not. Some times it wouldn't crank 30 minutes after being shut down. It didn't make any difference which tank I was using. I notice when tring to re-prime that while pumping the hand primer, fuel would leak out the stem of the hand primer also it wouldn't hold pressure on the gage.

I disconnected the lower line going to the hand primer and caped it. I have been using it all week 6-8 hrs a day with no starting problems.

 

[Gamagoat1]

The 543A2 has a transfer pump from one tank to the other and one fuel line to the multifuel.
Makes sense.