Cummins loss of prime, can you pressurize a fuel tank??

[70deuce]

On my M818, it loses prime now after sitting for only a few days. Until I can replace all the fuel lines, would pressuring the selected tank with a few PSI work to get a positive supply of fuel to the pump. NAPA has these real short bolt on tire valve stems that could easliy be installed on a fuel cap. Any thoughts on this???

 

[jwaller]

It would prob work if you could open the vent at the filter or something but you must have flow to move fuel up to the pump not just press on the tank. kinda depends on where your problem is I guess.

 

[CGarbee]

I've done this more than once by removing the vent line and putting my blowgun (with the rubber tip attached) up the tank vent and giving it a shot of air. Works well, especially if you have somebody else in the cab who can crank the truck while you apply the air (so that it is pumping while you are pushing the fuel up...).
Just be careful to not overpresurize the tank, only a couple of pounds will have the sides bulging...

 

[Jones]

The problem would be too much pressure finding any weak seams and rusted spots for you. Three or four psi would be the max I'd want to play with-- and to make sure I wasn't tempted to put just a few more pounds in if that didn't work. Pressurizing the tank wouldn't necessarily prime the system if you have no place for the fuel to go upstream. There are enough pumps, filters, closed chambers, and tight passages to act as restrictions; keeping all the pressure in the tank.
If you do go ahead; make sure your pressure cap is made from a non-vented one. I know that's bone-head mechanics but little details like that DO get overlooked.

 

[98hd]

I did this once to a dodge cummins w/ a bad lift pump. Just be careful not too much pressure.

If you look at the top of the injection pump, there should be a large fitting. Take out the plug and fill it w/ diesel.

Fill the filter housing w/ fuel and reinstall.

Try and start w/ some ether.

This is what the roadside mech did to mine when I accidentally ran it out of fuel. It died shortly after it fired the 1st time. Fired again, and ran rough for a few seconds, then all was well.

 

[jasonjc]

There is a primer pump right on the dash.

 

[jcappeljr]

I have did this many of times on my trucks and equipment toget them started.

 

[Stalled]

A can of spray Scotts Liquid Gold fires em right up.Did it today on one of our co. trucks.Honestly,you can even smell it in the exhaust when she fires.

 

[ENCS_DEI]

The problem I see with pressurizing the tank is that if you're drawing air through bad fuel lines, you will now be pushing fuel out of these same lines.

 

[Gamagoat1]

Check the fuel filter gasket. Seems the trouble started when the filter was changed. TIGHT. TIGHT, TIGHT.........But, don't squash the rubber O'ring on top.

 

[bob130ab]

I had the same problem, mine turnrd out to be the fuel system was sucking air through the primer pump. I disconnect the lower line under the dash and pluged it with a brass fitting. This solved my problem.

Bob Martin
Brooklet, GA

 

[WillWagner]

Pressurizing the system will get it started, but, there is definatly an issue. You should troubleshoot it. It could get worse and leave you in the worst possible spot.

 

[70deuce]

Thanks for all the responses. I'm not trying to make this a regular use thing. For now just trying to avoid alot of cranking and starting fluid until the problem is corrected. The primer pump could be a culprit for sure. Need to take a look at the fuel filter gasket and O ring also. It might be a good thing to have fuel seeping out somewhere with the tank slighly pressurized. Might point towards the problem and help with troubleshooting. More to follow.

 

[GIJoeCzar]

I just went through this with my M818. Batteries were new, battery cables were new, battery cable connections were perfect, starter was good, starter switch was good. The truck would crank real hard at start, then the starter motor would pick up a bit of speed, but it wouldn't start without ether. Plus, I could only get about 20 seconds of cranking and the batteries needed to be recharged. I put a very small amount of pressure on the driver's side fuel tank and began inspecting the fuel lines everywhere. Sure enough, one of the lines underneath was leaking fuel, which meant it was sucking air. I fixed the line and now the truck starts perfectely. Put a small amount of pressure to the selected fuel tank and look for your leaking fuel line or connector culprit.

 

[beaubeau]

I had problems with the lines at the Switch for changinf from left tank to right tank. Several of the hoses were cracked. I just hooked lines to the left tank.

 

[ARMYMAN30YearsPlus]

When I was a truck mechanic on the NYTW I made up several fuel caps of various sizes with shrader valves mounted through them. They were the only way to start a trailer mounted reefer unit up high with a saddle tank on the trailer under the van. Used it too on the road as some of the truckers would try to climb one last hill before stopping to buy fuel. Only put a couple of PSI in it and worked every time

 

[70deuce]

Thanks for the last two posts. I plan on taking off the tool box so I can see the fuel selector valve and he maze of fuel hoses there and pressurize one tank at a time and look for fuel coming from somewhere. Hopefully it be obvious. Any know of any commercial fuel cap I could modify with a shraeder valve??