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Sucking Air!!!!


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I have a 1999 2500 24 valve.. Approx a year and a half ago I replaced the injection pump with a remaned one from thoroughbred diesel and a fass ddrp lift pump. About 3 weeks ago I fired up my truck after it was sitting for about 2 hours. I drove about a block and it started spitting and sputtering. I opened my water valve on the filter housing and air came out then fuel. It fired up and ran fine after that and was back to normal for a day or two. It then did the same thing again and I again opened the valve and air came out, it then fired up and ran fine. Now it's happening every time I go to drive it. There are no codes and my life pump pressure is superb at 15 idling and 13 WOT. It starts fine. I let it warm up. Listen for it to start running rough, turn it off, bleed the air, fire it up then drive it as long as I need with no problems. I also have just turned the key on and opened the valve before ever starting it and it blows fuel out with great pressure. So it only sucks air when it is running. I can not find any fuel leaks anywhere and my gas cap appears to be functioning properly ( judging by the air pressure when I open it).

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It's all stock except for the FASS DDRP and a remanufactured vp 44 about a year and a half ago. It won't stay running when it starts to act up. It will eventually die and to prevent and damage to anything I turn it off when it starts to act up. Then get out and open the valve and air drains out. I've called my local shops and they have no clue either.

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It was only once in a while a couple weeks ago, now it's every time I start it.

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If the op's fuel tank is pressurized, that might be where he is able to get air and fuel out of the drain valve after engine shut down.. Correct me if I am wrong, but the tank should not be pressurized.

If so he's possibly got...

[*]Injector copper shim damaged

[*]Cracked head

Compression test on a hot engine possibly show it. Also checking if there is pressure in the fuel tank.

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If so he's possibly got...

[*]Injector copper shim damaged

[*]Cracked head

Compression test on a hot engine possibly show it. Also checking if there is pressure in the fuel tank.

What would cause a copper shim to damage?

Also it is not chipped and I don't hot rod it or do any towing. So what would cause the head to crack?

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Also, if those were damaged how would air pressure build up in the stock fuel filter canister? It does it cold or hot.

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What would cause a copper shim to damage?

Also it is not chipped and I don't hot rod it or do any towing. So what would cause the head to crack?

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Also, if those were damaged how would air pressure build up in the stock fuel filter canister? It does it cold or hot.

I understood in your first post that the gas cap worked because of a release of pressure when you opened it. If so, when you shut your engine down the fuel system will be pressurized allowing fuel to flow from the drain valve. Normally there is no pressure in the system after engine shut down, the pressure bleeds off very quickly. As far as the causes MM listed above, I would to defer to the more knowledgeable.
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What would cause a copper shim to damage?

Also it is not chipped and I don't hot rod it or do any towing. So what would cause the head to crack?

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Also, if those were damaged how would air pressure build up in the stock fuel filter canister? It does it cold or hot.

Some how you getting compression gases from the cylinder into the fuel system. The only 2 I know of is a copper shim on the injector is damaged or the head is crack allowing compression gases to leak into the fuel return rail.

The other though is maybe this is all backwards. What if this is a vacuum you hearing? If the tank vent is plugged and the lift pump is pumping till the tank is pulled into a vacuum and quits. Then you open the filter drain release the vacuum and good to go. How about loosening the fuel cap and and see if the problem goes away?

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Some how you getting compression gases from the cylinder into the fuel system. The only 2 I know of is a copper shim on the injector is damaged or the head is crack allowing compression gases to leak into the fuel return rail.

The other though is maybe this is all backwards. What if this is a vacuum you hearing? If the tank vent is plugged and the lift pump is pumping till the tank is pulled into a vacuum and quits. Then you open the filter drain release the vacuum and good to go. How about loosening the fuel cap and and see if the problem goes away?

Genius! Pure genius! Why didn't I think of trying that! I will try it when I get back to my truck this evening. Ill let you know. Thanks for all the input thus far.

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The gas cap did not make a difference.

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Ok. so thinking deeper on this.Does it do it with a full tank of fuel?Is the fuel gauge functioning properly? Like mine would get down to about 1/2 tank and actually was near empty.My problem thinking out loud here is that you claim there is air flow from the filter can. I've got a hard time with that knowing that the pressure is dumped rather quickly form the fuel system once the engine is shut down so that means the pressure would have to be in the tank as well. But loosening the cap did fix it. :think:Anyone else want a stab at this one too?

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Is your lift pump running when you have your key is on? by that I mean when you first get in your truck and turn the key on you should just have a bump in pressure and it then bleeds off quickly. The pump should not start running until you either start the engine or bump the starter with no engine start. Just trying to see if the system is functioning properly. When you open the gas cap are you hearing air escaping or being sucked in? Just so I understand, you removed the fuel cap and ran the engine with the cap off and it did the same thing.

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sure fire way to test each system one by one. get a length of new hosefill a fuel can full of dieselhook fuel line to suction side of lift pump put other end in fuel canlet it start suckingif no air after prime then you have something leading to lift pump causing air.sometimes you got to get caveman when troubleshooting lolthe trick is start at one end and work your way to where there is no more trouble. then you will know where the problem is

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sure fire way to test each system one by one. get a length of new hose fill a fuel can full of diesel hook fuel line to suction side of lift pump put other end in fuel can let it start sucking if no air after prime then you have something leading to lift pump causing air. sometimes you got to get caveman when troubleshooting lol the trick is start at one end and work your way to where there is no more trouble. then you will know where the problem is

I like. I will have to remember this if I ever have trouble like this. THANKS
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i had the same issue two years ago. I got the kit from http://www.vulcanperformance.com/category-s/182.htm. I fixed the issue. I had a crack int he supply some where i never could find it. i had i seal leaking on my transfer case so i had oil everywhere. I highly recommend get the draw straw also if the do the big line kit since you will have the tank out anyway.

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  • 1 month later...

Thanks guys... I hadn't been on here because it randomly quit acting up shortly after this post until approximately 1 week ago. Now it's doing the same thing again...

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i had the same issue two years ago. I got the kit from http://www.vulcanperformance.com/category-s/182.htm. I fixed the issue. I had a crack int he supply some where i never could find it. i had i seal leaking on my transfer case so i had oil everywhere. I highly recommend get the draw straw also if the do the big line kit since you will have the tank out anyway.

I have a fass ddrp.... A local diesel shop said they wouldn't put a draw straw because it wouldn't be able to suck enough fuel???? Opinions on this?
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A draw straw (enlarged pickup tube) may not be strictly necessary but any working lift pump will suck through hit as well as the OEM pickup. There are some problems with later After market draw straw quick connects tend to get loose. Old style hydraulic fittings do not. A plugged tank vent is or a failed fuel line or fitting is where I would start. You should not get air into the system if acting correctly. Check simple stuff first. A failing lift pump... a bad filter housing leaking air?

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Gotcha. I was thinking my fass ddrp should be able to provide adequate suction.... Now as far as my truck, the ddrp is putting out enough pressure. It's 14-15 at idle. When it first kicks on with ignition is 10ish.. Vp 44 is new as well. There are no leaks I can see. I've replaced my overflow valve. Crawled under the truck and inspected the tank and module and followed the lines. No leaks. I don't know what to do besides burn it. Lol

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I understand that the Dodge does not use a vented cap but reportedly has a tiny vent in the module. What results did you have when you loosened the cap. I'd try running it with cap loose (if you haven't, I don't see the report) & see the results.

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I've tried that. Here is what doesn't make sense. I turn on the ignition. My lift pump moves fuel with 10+psi. I've opened the water valve on the filter housing as it was doing so and no air. It starts up fine. A minute or so into idling or driving it starts to surge like it is running out of fuel. Then if I let it go it will die. I get out, open the water valve on the filter housing and air comes out and I let it bleed until fuel is flowing. It then fires up and runs fine. So here is where it doesn't make sense. If it was sucking air from a fuel line that is cracked or module fittings or anywhere before the lift pump. It would pump air by just turning the ignition on and fill the canister. But since it pumps just fine until its running doesn't lead me to believe its a hose or fitting issue. I've checked the fuel pressure upon ignition activation and when the engine starts. It has adequate pressure. It's frustrating.. I don't want to take it to a shop because the few I've talked to have no clue and said it'll take a couple of hours. So for roughly 200$ in shop labor I might end up where I started. Thanks for all of the advice thus far everyone!

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I had a 12 valve in my driveway that would quit from sucking air ONLY when the temperature was about -10*. Anything above that it would start and run just fine. It took me a while, but I finally found the line coming out of the tank module was rusted and cracked right where it goes into the module. The way I found it was lift the bed and pressurize the fuel tank. Once I fixed it the truck ran great and still does! It is my daughter's truck..... Anyhow, maybe that is where the problem lies? It will suck air there.

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