Fuel Issue

[kstossel]

I'm a new member here, sorry I have to start with a question. I have a 93 Dodge with 1st Gen Cummins engine. I had experienced some weird symptoms untilI narrowed it down this weekend. In short, when parked on a steep hill (my driveway), with thetruck pointing uphill, the fuel will drain back into the tank. It will not self-bleed (with the starter).Then, of course, it will not start. When I flip the truck, and have it pointing downhill, in about 24 hours the lines will bleed and I'mgood to go. Truck starts fine. (One the fastest starting and best running Cummins I have everowned). Rather than start replacing things left and right I was trying to determine where the checkvalveis located in this vehicle. I would think: Injection Pump, Lift pump, tank sending unit. My gut tellsme the Lift Pump, since a pump wouldn't really be a pump if it didn't have a checkvalve. But a friendly mechanic insists it is the injection pump. Can anyone help possibly save me some money and tell me it is the lift pump (or not!)It runs so well, I just can't imagine its the injection pump, but I figure I willleave it to the experts. Thanks for any advice you are willing to give.

[ISX]

You are on the right track but you also have to remember that it is a closed loop system. How will the fuel drain back when there is no air to replace the fuel in the lines? It would be one thing if the draw straw in the tank was exposed to air, then it would all drain back to an extent but not the case if it is always submerged. Somewhere it is getting air into it. When you park uphill, the fuel in the engine is above the tank so gravity can do what it does best. The overflow valves could not be seating fully or a return line is letting in air.

[Mopar1973Man]

Actually there is no check valve technically in the system. It just a air tight system that holds prime so if there is a bad O-ring, fuel line, etc it will bleed air in the system allow the fuel to drain back to the fuel take. Like the overflow valve is a check valve but even its got a tiny pin hole to allow to bleed air in or out of the system. Lift pump is not say fuel tight so once the ignition is off the sliding vanes can move to allow air to enter.. So like I said you'll have to back check the fuel system by adding a little bit of air pressure (1-2 PSI) to the fuel tank and having a friend look around the fuel line for wet spots or leaks.

[kstossel]

I appreciate the advice. Although it sounds like I have to actually work (as opposed to just bolting on a new part) it might end up being a simple loose fitting. I'll spend any amount of time necessary to avoid randomly replacing the injection pump. Although I guess the leak could still be in the injection pump. When I trace the leak, I'll post back, might help someone else if its an easy fix. Thanks again.

[kstossel]

I followed your advice and started looking for an air leak. I was lucky enough to find a probable leak without even having to put pressure on the system. I saw that what my book calls the 'Air Control Vent Tube' (connected to the Injection Pump) was extremely loose. I was able to tighten its connection with my fingers a full 4 turns, 1 more with a wrench. My guess is that this allowed air in. I will flip the truck around and see if it bleeds out the fuel, but somehow I think it won't. I appreciate the advice, I appreciate you guys guiding me rather than just telling me the answer, and as soon as next payday rolls around I will become a full member. I am sure I will need your advice again, next is a hot rod I am making with a Cummins diesel. Thanks again, you save me from simply getting a new Injection Pump, which when installed, I would have found that same leak and kicked myself $1500 times.

[ISX]

Do you have any more info on this air control vent line? I can't find anything on it on google. It sounds like it might be something for the AFC but I am not sure. Just a pic of where the line is on the pump would work but a physical description of where the line is will work as well. I am kind of doubting that fixed it based on what it sounds like that hose does, but I guess we will see.

[Mopar1973Man]

Remember there is all the suction line from the fuel tank forward to the lift pump that will not leak outwards and will require some air pressure to make it show.

[kstossel]

Do you have any more info on this air control vent line? I can't find anything on it on google. It sounds like it might be something for the AFC but I am not sure. Just a pic of where the line is on the pump would work but a physical description of where the line is will work as well. I am kind of doubting that fixed it based on what it sounds like that hose does, but I guess we will see.

I was waiting until the weekend to flip the truck around so no problem.

The Air Control Vent Tube (at least in my book) has one ended connected high on the block, or head actually. The other connects to the TOP REAR of the injection pump with a bolt that goes through an eyelet on the tube. It was SO LOOSE and so obvious I thought I got lucky at that one. Feel free to

tell me to keep looking for a leak if you know better. Thanks

--- Update to the previous post...

Remember there is all the suction line from the fuel tank forward to the lift pump that will not leak outwards and will require some air pressure to make it show.

I will check that also, thanks.

[ISX]

Are the 2 connections the same ones as what I circled? If so then that doesn't have anything to do with your fuel. I assume you didn't see any fuel leaks around it or anything either. That hose is actually for emissions in a way. It goes to the intake manifold and as the turbo builds boost, that hose runs to the top of the pump and as you build boost the is allowed to fuel more. So that line is nothing more than a pressurized air hose. You will probably have more power now that you tightened it :lol:Check all your return lines, fuel filter, etc. making sure everything is tight.

[kstossel]

Are the 2 connections the same ones as what I circled? If so then that doesn't have anything to do with your fuel. I assume you didn't see any fuel leaks around it or anything either. That hose is actually for emissions in a way. It goes to the intake manifold and as the turbo builds boost, that hose runs to the top of the pump and as you build boost the is allowed to fuel more. So that line is nothing more than a pressurized air hose. You will probably have more power now that you tightened it Check all your return lines, fuel filter, etc. making sure everything is tight.

Yes, the one on the right of the picture, circled, is the one that was incredibly loose. That's great that I will have more power, but it wasn't really down on power anyway. BUt I will run the pressure test over the weekend and hopefully I find the actual leak. I very much appreciate all this info. Thanks again.