I have acquired a 1987 26 foot Jamboree class C motor home, 460 V8 gas (7.5 L), E350 chassis,AT, with 22k Miles that has been unused for 7 years ( stored outside, uncovered, in central California).
Basically the main problem is that I am not getting gas pumped up to the carburetor, and would appreciate help in troubleshooting how to get this fixed. I have spend a full day on this already and will be going at it today too.

Summary of troubleshooting done and results:
cranking did not start the vehicle (however, adding gas directly through the carburetor throat did start the engine momentarily):

The 40 gallon gas tank read a little below ‘empty’ (I’m guessing someone siphoned the gas out during that time… no lock on the gas cap). Sniffing the gas filltube, it smelled like shellac. I put in about 6 ounces of Berryman B12 (injector solvent) and then added 6 gallons of unleaded gas, then another 6 ounces of B12. The B12 is supposed to dissolve any solid shellac. Still would not start. Added another 6 gallons of gas and 6 ounces of B12 to ensure I was up to the filltube.

-removed the inline gas filter (replaceable element in a 2.5 inch screw on base) that is under the chassis about half way between the tank and engine. It was half full or so of ‘old’ gas. There was no fuel in the line at that time. I left the filter element and case off and cranked for a while…. No gas came out… the first indication that there was a problem in the tank.

-used a small manual hand suction pump on the open gas line at the filter and got a couple ounces of ‘old’ gas, but could not suck out any more than that… I’m thinking the pickup tube is plugged. Ill try with more suction today after blowing it out first.

-hooked the manual pump up to the auxiliary fuel line coming from the tank ( goes to the on-board 120V generator) and was able to pull gas through until ‘fresh’ gas came through. This is a separate tube of course, with no pump, but comforting to see that it was ‘open’


-confirmed that there is no mechanical pump on the fuel line ( on the engine), apparently just a pump in the fuel tank (possibly more common with motorhomes because of the long distance between the tank and engine). The 40 gallon rear tank (behind the rear axle) has a 3 wire harness coming to the top of it (apparently for gas gauge sender and fuel pump)… these wires seem to be the same size , and not particularly thick (one with red, one with orange, and one with black, I think all have a stripe).

-there is also a fuel safety shutoff switch on the passenger side cowling that turns off the pump if you overturn the vehicle (ouch!)… this tested ok with the voltmeter.

-I turned the ignition on and went back to the tank, coud not hear anything.
Question- does the pump time out after a while? I am not aware if this vehicle has a ‘computer’ to control that type of action. I will retry today (Thursday) with another person turning the ignition on while I am observing the voltage, and with the plug hooked up, listening for pump noise.

-Removed the 3 wire plug from the top of the tank and turned the ignition on and, using a voltmeter, checked voltage between the three combinations (pairs of contacts) of the 3 wire cable. Results: 0 Volts, a brief 9.25 volts pulse every 2 seconds (possibly 0 volts between pulses), and a low constant voltage around .1 to .2 volts. I got the same results when testing each of the three wire contacts to chassis ground. I was expecting 12v constant on at least one contact (for the pump)… again, could this be due to a timeout? I will check that today.
Question- is the 9volt pulsing normal or suggest some other problem? Is this possibly for the sender?


--I want to leave dropping the gas tank as a last resort ( the 2” hose connection to the fill tube looks like it will be tough to reconnect because of lack of good access).


Additional Questions:

-what else can you suggest to help me get this fixed?

-any suggested way to confirm which contacts of the three wire harness are for the pump and which for the sender? Do they share a common ground wire, or is it normal for these kind of connections to use chassis ground through the tank? I would like to run wires directly from the battery to the pump contact (once I find out which one(s) that is) to see if the pump is ok. Im really hoping that the pump works and it is a (ugh!) electrical harness problem.

-Can I blow backwards with compressed air into the line leading to the pump to try and cleanout possible crud in the pickup tube? Any suggestions on Max psi?- I plan to start at maybe 5psi and take it up to 15-20psi if I can’t hear it bubbling in the tank.
-Question- does the pump have a one way valve in it that prevents fuel/air flow ‘into’ the tank? If so, can this be damaged by compressed air?

--If the pump turns out to be ‘bad’ is it possible to add another inline pump , outside the tank and not replace the one in the tank?

-The small engine manual that came with the motor home indicated that the fuel pump was hooked up with a 16 Ga (not amp) fusible link and was attached to the Starter solenoid relay. I found a couple of 20 Ga wires hooked to the solenoid relay, but no 16 Ga. I did find a couple of 16 Ga fusable link wires in the area, but could not see where they hooked up to power… it was not at the starter relay and apparently not at the fuse panel.

Question: the fusible link looks like a small rubber cocoon on the wire, and apparently cannot be opened. How do you ever find out if the ‘fusable link’ is open or closed as there is no access to the wire. How does a ‘fusable link’ operate?

Durning the testing I notice that the front disc brakes are rusted ... should i do anything with this , or just try to endure the screeching while the pads do the cleaning job?

 

For the troubleshooting above, how can I get a Ford wiring diagram for this vehicle? Jamboree motor homes only carries a diagram for the internal 'home' wiring.

--wiring diagram needed for 460cu inch gas engine, Econoline 350 (1 ton?) frame.


thanks

pwitort

 

-Try here for wiring diagrams,etc. for your motorhome (it's helped me numerous times when trying to figure out electrics & mechanics on my truck).

-I believe the fuel pump does have a check valve in it (at least that's the impression I have, because trucks with dual tanks had these valves fail in the past, is it the same pump in single tank vehicals? I dunno...), so you probably couldn't use air to reverse-blow through the fuel lines.

-The only way I know to check the fusible links is to find the ends or wiring harnesses and check for continuity with an ohmmeter (sometimes can be a PITA finding usable ends close enough for my leads though).

Sorry, but I can't think of anything else to help you out, except keep muddling away until you get lucky (at least that's what I do...). Please keep us posted with your progress. Good luck!

 

THanks for your comments.

We spent time today confirming the problem, and it is apparent that the in tank fuel pump is not working. Many of the questions above got answered because this time there were two of us ( my wife and I) and she could turn on the ignition and crank while I was under the chassis measuring the results.

Some findings:

- Of the three wires in the fuel pump harness, one is ground, one is for the positive voltage side of the fuel gauge sending unit, and one is for the + voltage to the pump.

-The pulsing 9.5 volts I was getting turned out to be the fuel gauge. I saw in a 1985 Ford manual that the fuel gauge gets pulses of voltage as part of normal operation. What I found is that the 9.5 volts was constant for the first 5-6 seconds after the ignition key was turned on, and then went into a pulse every 2 seconds approximately.

-As for the pump connection, in the previous days testing I would turn on the ignition key and then climb under the chassis and find no voltage on that wire. I found out why when I had my wife crank the engine while I monitored the voltage on the pump wire.. Amazingly, the pump voltage only came on during the cranking (12 volts)! And off when the cranking stopped. Apparently there is some sensor that sees if the engine is running (cranking is slow running) and only turns on the pump when that is happening. I fully expect the voltage to be present when we finally get the motor running ( recall no gas getting to the carburetor now).

-So, with known voltage to the pump, it was time to reconnect the pump harness and to listen carefully for the pump during cranking... couldnt hear anything. To make sure of this, we 'hot wired the pump ( traced the red/black wire from the pump back to the starter relay) and stuck a needle through the plastic jacket of the wire and touched the needle with a wire that was attached to the +12v side of the battery... still no sound.

-Next I measured the resistance across the pump terminals on top of the tank and found about .5 to .9 Meg ohms. ... virtually open circuit. Rechecked everything and confirmed that the pump is apparently bad.

--So now we are looking to replace the pump by dropping the tank.

Any suggestions on:

--How to reconnect the short length of 2" rubber hose that connects the filler pipe with the tank? This looks like it will be difficult at reassembly time.

--Any tips in general about dropping the 4o gallon tank?

-- does anyone know where I can go to get the plastic gas cables and unique brass connectors for the system used by Ford? One end has a brass tube about a quarter inch in diameter, and the other end has a female tube with two internal 'O' rings that seal on the brass tube once inserted. A 'circlip' shaped piece of plastic locks the ends together.

 

As predicted above by one respondent, I was unable to blow air back through the pump ... apparently a check valve.

 

Glad to here that you've tracked down the problem. Fuel pump failure seems to be a common occurance, including mine. Here's how I handled changing out my pump:

-Use LOTS of rust buster on the bolts holding the tank straps. I used almost a whole can, and then let it soak in overnite. I then gave it another good soak just before I started working on it. Even so, I still managed to strip one of the seized bolts (luckily I had loosened the bolt enough that I managed to get a small sawzall in and cut the bolt off)

-I used a hydraulic jack and a block of wood to lift the tank a bit and take the pressure off the bolts as I loosened them. I then was able to lower the tank enough to remove to fuel lines from the pump (if you don't have the tool to remove the fuel lines, you'll need to get one).

-As for new fuel line parts, maybe check your local ford dealership? The clips I did't bother replacing; the fittings seemed to hold the lines well enough.

-As for the hose...um, good luck? Maybe by balancing the tank on the jack you could manipulate the hose enough to get it back on.

hoped this helped a little bit...

 

Thanks for the info.

The wiring diagram was very useful. It confirmed that the fuel pump is only on during cranking of the engine. That suprises me. The tank is about 3 feet lower than the carburetor and about 20 feet away. With the pump operating only during cranking, this would provide only a quick priming of the gas line, and then there would only be suction after that from the carburetor to move the fuel along.
Does that sound right? Is there enough suction from the carburetor to do that?






To move the motorhome from the storage lot to my house, where I can work on it better, I am considering attaching a domestic aftermarket external low pressure fuel pump to the auxiliary gas line (goes to the generator) and connecting that to the gasline that goes to the carburetor. I could rig the electrical to come off the fuel tank harness although I think the low pressure pump is designed to be 'on' all the time. Any comments or suggestions on this?

The auxiliary fuel tube in the tank apparently has a shorter tube than the carburetor attached tube... I was able to draw out gas from the auxiliary tube until there was about 10-12 gallons left... doest this sound right?

 

I just finished replacing the intank fuel pump on my 91 Flair motorhome. I think I had just as much fun as you are having. When I dropped the tank, I just lowered the tank and then removed the entire fuel pump and gauge sensing assembly by removing the six bolts that hold it to the top of the tank. I never did undo the fuel lines. Then I went to ford and found out that they wanted $349.50 for the fuel pump. They told me that it only could be replaced by replacing the entire assembly, including the fuel level sensor. However, I was able to buy just the fuel pump at NAPA. That was about $90. My motorhome is fuel injected, but I have a hunch that the in tank fuel pump is similar.

Another thought, I used a syphon to remove the gas, but still had about 10 gallons in the tank that I couldn't get out when I dropped the tank. I made sure to get all the gas out of the tank before I lifted it back up.

Once removed, I could get the old fuel pump to run by conecting it to 12 volts. However, it would only run when I applied some pressure to one of the terminals. The terminal itself was loose. Since I have done this repair job, I have wondered why the thing didn't blow up with a loose terminal bouncing around in the gas tank!

 

Thanks for the suggestions.

I went ahead and put in a 4 to 7 psi external fuel pump that is connected to the auxiliary gas line. I hooked up the electrical to the new pump by tapping into the existing 'hot' wire for the old pump.... that way the pump is on when it is supposed to be and off otherwise. I also put in two clear inline filters in addition to the filter that was there. It appeared at first that this worked and I was able to drive a mile to the gas station without incident. However, when I went out on the freeway, the motorhome ran for a minute or so and then started hesitating. It turned out it was getting starved for gas , and If i just idled for a little while, the motor would run fine for about 20 seconds if I was trying to go fast, or several minutes if Iwas going slower. If i idled for 5 seconds, I could accelerate for about 4 seconds before I ran out of gas. If i went about 7mph on level ground I could maintain the speed for a reasonable while, but if I accelerated, it apparently drained the carburetor. I filled the tank fully at a gas station and added another 30 ounces of B12 solvent in the gas. No different response. I checked to see that the pump was still pumping , and it was.

Help! I need to understand why this is happening? I will try to measure the fuel pressure at the carburetor tomorrow ( sunday) and see if the fuel filter going into the carburetor is somehow clogged. Its as if the flow of fuel is somehow restricted to a low level and if you go faster than that flow will sustain, you temporairly run out of gas.

I limped home ... very slowly up a hill

 

Just to clarify my post above, when Idling, the fuel line would supply enough gas (more than enough gas) to the carburetor to keep it running. Depending on how long I left it idling, it would build up a reserve of fuel that could be expended in 5 to 20 seconds of medium to high rpm use of the engine , depending on how long I let it idle. It was as if there was only a limited amount of fuel getting through to the carburetor bowl (for reasons I need to find out) and the bowl held about 20 seconds worth of fuel at medium to high rpm for the engine (460 v8).


Other activitities on the slow uphill climb ( 2-3mph):
I still had the old original (replacable) filter element in the original inline fuel filter, and I thought i might have been clogged (although I previously rinsed it with the intent of replacing it after I ran through the tank with all the B12 in it). So I unscrewed the fuel filter cannister (between the fuel pump and carb), removed the element (no new one inserted), flushed the cannister, and reassembled... basically eliminating any pressure loss through the filter cannister. There was no difference in the actions of the carburetor... it still ran out of gas just as quickly.

I need to troubleshoot if the problem is:
1. before the fuel pump (located about halfway between the tank and the carb.... eg. restricted flow from the tank.

2.In the fuel pump (eg. too low a pressure developed: currently the rating on the pump is 4-7 psi)

3. after the fuel pump (eg. clogging at the inlet filter to the carburetor- made out of tiny ***** of metal, or a very restricted needle valve opening in the carburetor.


I currently have access to all of these points and am afraid I will have to eventually pull the carburetor ( I cant believe how my beloved Ford Motor Company put the carburetor halfway between the front of the hood and the inside dashboard... in other words, totally under the enging cowling and virtually inaccessible!I think I'll go ballistic if I ever hear that this happened because the Ford design folks wanted a more distictive nose on the front :-) My last motorhome had a Dodge engine/cab and you could look right down into the carburetor throat from inside the vehicle.

So, Ill appreciate any help anyone can give at this point. We are supposed to be driving this 700 miles to Portland within a day, so the one who figures this out and gets us going on schedule gets 10 pounds of freshfrozen Tuna steaks ( I went tuna fishing in Northern California recently).

 

So here is what I am planning to do when the sun comes up:

First, note that the fuel goes through the following path on its way from the tank to the carb:
From the tank into the pickup tube for the auxiliary fuel line , through 2 feet of 1/4 inch hose, through a see-through inline gas filter, through a 12 foot 5/16ths line to the inline fuel pump, through 1 foot of 5/16 line to another see-through inline gas filter, through 1 foot of 5/16ths line to the original inline fuel filter (now with no filter element), then about 12 feet through the original 1/4 in line to a brass 'T' fitting in front of the carburetor where the return line to the fuel tank is located , and finally into the side of the carburetor where, I am told is the thimble sized filter element made up of little ***** of metal. Whew! some path.

1.disconnect the fuel line by the carburetor and see how powerful the stream of fuel seems; measure the pressure with a fuel gauge if possible. I will need to hot wire the pump because it is not normally on except when cranking or engine running.
Note: in an earlier post I said it appeard that the fuel pump was only on during cranking, this is wrong. It is on during cranking , but also when the engine is running (possibly when there is sufficient oil pressure); however, the pump does not run when just the ignition switch is turned on and the engine is not running.

Confirm that the pressure is 4-7 psi and a healthy flow of fuel is coming out.


2.-measure flow out of (into) the fuel pump (open the fuel filter cannister up and catch the fuel coming out. Confirm it is enough.

3. measure vacuum in the fuel line by the tank to see what level of suction is present there when the fuel pump is running.

4.Insert a manual pump bulb in place of the electric pump (or inline after it to augment it) and see if I can keep up manually with what the engines needs; see what pressure is generated by the manual method to get an idea of how high the pressure needs to be to work properly with the carb.


Note: It appears that the gas gauge (sender unit?) is faulty. After putting in 18 gallons the gauge still read 1/8 full; when I filled up at the gas station it still read less than a quarter tank after I filled it up to the cap (fill tube filled). I expect I currently have about 35 gallons in the tank; along with about 48 ounces of the B12 which is about 30% more than recommended to add.
Does anyone know if you can replace just the sender unit (float and variable resistor) ?

5 When I get time ( probably not before this trip), drop the tank and replace the in-tank pump and gauge sender unit; replace the inline fuel filter element , and reconnect with the factory hoses. THis of course may not solve the problem if the cause is in the carburetor.

6. What else should I be doing?