There is something a little puzzling to
me and that is how they never had any problem with the add on gas tank over filling the regular tank..

So let's look into why I ask this.
If the higher tank just keeps adding fuel to keep the regular tank filled to the brim is clearly a NO_NO !
If the regular tank is filed to the brim even at the gas pump, liquid gasoline now goes into the vapor lines and can flood the engine, just not a smart thing to do.
Your vehicle may really have a flooded problem and not an electrical problem. Is there any way to shut off the aux tank from overfilling the regular tank?
Until I have the answers to some of these questions , we will have to take these things one at a time.
There is still the question of why you cannot hear the fuel pump run for the 2 seconds when the key is first turned on. You do have to wait a few seconds before turning the key on again to hear the pump run.
I have some reservations about this aux tank installation especially if the installer was not aware of the overfill problem it could create. So we will take things one at a time , OK ?
I have a special request if you will, when the engine will not start, please remove any spark plug and see if it is wet or dry.
Will wait for your reply, thanks.

 

The aux. tank doesn't fill the lower tank to overflowing. It simply adds fuel when the main tank gets below a set limit. It has never overflowed or showed past full. I do not think there is a way to just switch the aux. tank off. Also, I think this was done at an RV center, so I don't think they or the manufacturer would overlook the potential for such a problem. At any rate, it has never overflowed or smelled of gas and has never presented the current problem of not starting until the last couple of months. It has a module installed on the bottom edge of the dash that indicates if it is functioning correctly and how many gallons are in each tank. The main tank holds 30 and the aux. holds 50. I can check a plug, that's not a problem. I just keep on going back in my mind to the thought of why it will start and run with the starting fluid. If the fuel pump is not pumping fuel, then how can it continue to run after it starts with the fluid? That fact would also seem to eliminate power not getting to the pump and/or a blown fuse or relay. Not trying to be argumentative, it just makes zero sense to me for it to run if any of the components are bad. It just seems to me like it might be a pressure problem. I'm sure these systems have to have a fuel pressure regulator somewhere in the line but I have no idea where it would be on this truck.

 

The question also comes up it there was a fuel pressure problem the engine most likely would not perform as well as you say it does once started, right?

When it will not start the appearance of the spark plug will tell us either it is getting fuel or not.

There is nothing wrong with questioning anything since at this time we are not sure of what is really happening.
I appreciate your replies and try to see if there is something we may be overlooking. Not familiar with the aux fuel set up , so I ask how does it know when to stop adding fuel? Does the module control that also and could it be malfunctioning? It does not need to be spilling gas out anywhere , just possibly overloading the system.

A little FYI, the PCM provides a temporary ground (2 seconds) for the fuel pump relay to close and power the fuel pump when you first turn the key on.. If it does not see an RPM signal the PCM will not allow the relay to stay closed.Sometimes the fuel pump will need that extra bit of power the alternator delivers and run, and yet if not all it requires will not run.. The fuel pump and relay seem to be working once it starts running. Again , we will need to check each possibility one at a time.

 

Yes sir, it runs absolutely normal when it does start. I'm not sure how it meters the fuel to the lower tank but will see if I can find some information on that. I would think that this is a fairly normal set up in the RV world. I will continue to follow your logic with this as it looks like you have far more experience with these trucks than I do. I very much appreciate you taking time to help figure this out and just want to make sure that you don't take anything I say as me being a wise guy or smart aleck. My wife is constantly reminding me that "it's not what you say, it how you say it". Alas, I know she's right but I just don't see anything wrong most of the time. What would we do without them?

 

I ain't goin there, no matter how hard you try , lol.

Again, appreciate the challenge your vehicle is presenting and can only do so much without being there to actually see everything.
Your thoroughness and efforts are a big help. Hope we are not coming across too strongly, but together we should find the cause

Still , concerned why you cannot hear the fuel pump run when you first turn the key on. If there is any break in the chain the engine should not start at all.

Might be able to come to a decision after we know what the plug(s) look like when it will not start. Thanks for your assistance.

 

The plug looked fine. I also went to start it again. I decided that I would listen for the fuel pump again, so got down right next to the tank and had him turn the key to "on". This time, I heard it. No mistaking the sound - like somebody turning something on for 2 or 3 seconds and then silence. It was pronounced enough so that I don't think you would have to have your ear right next to the tank. I believe it could be heard from just standing near the driver's side rear wheel. I then asked him to start it and it fired right up. This leads me to think that it is losing power to the pump at some point. Wondering if the relay may be bad? Won't have much opportunity to mess with it for a few days as it's raining now and supposed to keep on doing so for the next 3 or 4 days. I'll msg back if I come up with anything else...

 

Well, after 7 days of constant rain, it has finally cleared up. I changed the relay - and yes, it is behind the radio - to no avail. I can hear it clicking. I changed it anyway, just to be sure but still no fuel pump sounds. I've pretty much resigned myself to the 99% chance that it is the pump itself. I ordered an OEM pump and gasket to just go ahead and replace it. They sure are proud of these, but I'm not one to go with cheap junk for something like this, that appears to be quite unpleasant to begin with - not something I would like to do two or three times. Now my concern is how to empty out what gas is in the tank. I keep the truck full all of the time, so I'm sure it has at least 25 gallons in the tank. Looks like good old fashioned siphoning with a simple hose won't work because they now have a blocker somewhere in the bottom of the filler neck. The pump won't be here for a few days, so I have plenty of time to think about getting that gas out. I'm absolutely no novice to this type of thing but I really am not looking forward to fooling with this! Thank you for your suggestions, they were a help. Considering that this original pump is 21+ years old and that it's pumped probably 12 to 13 thousand gallons of gas in that time, I shouldn't squawk too much about having to replace it or the cost to do so. I've been quite fortunate that the truck has never given any other problems, other than a rear window popping out of it's track a couple of years ago, but that was an easy fix. Otherwise, it's had zero issues and is quite pleasant to drive, other than the gas mileage that is...

 

Playing around with gas tanks is bad enough, but an almost full one is crazy ,especially if you don't have the equip to do the job.

You could be right suspecting the fuel pump in the tank, but before starting that project , we make sure power is getting to the fuel pump right at the tank AND we make sure the ground is good. If we don't do this,we do the job, put fuel in it ,turn the key on and get the same result, and that ,,,,, is no fun.
There is a fuel pump relay in the engine compartment fuse /relay panel. You might switch that relay if you have no test light to verify it's operation.

One thing I could never explain maintaining a fleet of these vehicles was ,,,,,,,,,,,,,,,,,the pump always quit right after the driver filled the tank, damm it.
I did manage to get a piece of windshield washer hose down past the baffle and get it to siphon, but it took a few hours to get enough out to make the job manageable.

Just don't want to see you go through a lot of work when you can get the problem solved easier.

 

OK, thank you for another good suggestion in regard to the other relay. I will most certainly check that one too. It did occur to me about the other relay under the hood. I popped the cover off and found that there is no diagram on the inside of it showing what is what. Should be easy enough to find something online to see the layout. As for the siphoning...I saw a post where somebody had used some copper refrigerant tubing to do the siphoning. It apparently is easier to get it past the baffling and it actually makes sense, since it would be stiff. I think I'll try that first. I'm sure it will still take a LONG time since that tubing would also necessarily have to be small diameter too.. Thanks again for taking time to think on this and respond. It is a help! I'll let you know about how the siphoning goes. Been quite a while since I've had a mouthful of gas...I've been pretty good at it in the past, but sometimes it just doesn't work as you'd like!

 

There are 2 things you might consider.
One is the turkey baster and the other is an enema ball.
Of course once used for gasoline that is now a permanent tool in the garage toolbox.
No need to rinse with gasoline , it really doesn't taste that good. lol

Please make sure you verified power at the pump and a good ground also, there are better ways to use your time than replacing a possibly good fuel pump.
Don't forget the pump only runs for 1-2 seconds when the key is first turned on AND only if the computer sees an RPM signal that the engine has started , otherwise it stops running because the computer takes away the ground for the fuel pump relay.