I’m working on my Ford E-350 460 ambulance w/ dual tanks and in tank electric fuel pump sending units. Summit Racing carburetor that I just rebuilt. 67k miles on fig and has been well maintained its whole life as a fire dept rig. It’s been daily driven as a contractors work truck for the last 4 years.

I’ve tracked down my fuel problem to the pumps (I thought it was an electrical issue as the pumps sometimes run, sometimes don’t.) A newly installed fuel pressure gage indicates rear tank is pushing 2.5 psi and mid tank 2.5 psi. When I pounded several times on the mid tank, the pump motor slowed to a stop and pressure dropped to 0 psi. (Driving over bumpy roads has been causing issues which switching tanks solved.) Rear tank has no issue with pounding on it. I still don’t know why the rear tank sometimes won’t run when the front pump stops.

Alldata indicates factory pumps should run at 4.3 psi. My Summit carburetor requires 5-7 psi. I can drop both tanks and replace the fuel pumps sending units sending units, but I’ll still be 0.7 - 2.7 psi low. Plus the PITA can of worms of dropping tanks out of a 40 year old ambulance.

Is there any reason why I can’t just bypass those in tank pumps and run an electric fuel pump inline, after the tank selector instead?

Guidance is greatly appreciated!

 

I think part of the problem is pulling fuel through the in tank pumps.
Also electric pumps should mounted as close to the tank as you can and should have a wet intake, read below fuel level.

Now I know you said your carb need 5 to 7 PSI but I have heard of them over flowing with 5 PSI as the float cant close off the valve at that high of a PSI.
Are you running that carb with the 2.5 pumps now and other than the 1 pump stop working when you hit bumps has it acted like it was running out of gas?
Also note there is a difference between PSI and flow.
You can have high PSI and little flow or low PSI and high flow. If you are running the 2.5 pumps and not running out of gas you have low PSI and high flow in my book.
Dave ----

 

I’m definitely having fuel starving issues under full power, leading to stumbling and carb backfiring.

 

Ok then I wonder what new in tank pumps put out being yours are only 2.5 PSI?

It sounds like you have to replace 1 because it shuts off over bumps, are they the only pumps the truck have?
I know the tank drop can be a bear but if them pumps can put out the right PSI I would change them out.
Dave ----

 

AllData references the pumps at 4.7 psi. It’s a dusl tank truck, as I clearly stated in my OP.

 

Since bumps knock off the pump, double check the sender electric connector if you still use the stock connections. It could be a wiring fault. Check power at the connector when it fails. Quite possible these days you have a faulty fuel pump, even if fairly new.

 

I wondered if it would work when people on here add a external fuel pump and leave the in tank pumps in place. I think people have done it though and have it work. It makes you think though, what is going on with BOTH new pumps. I know they make junk now, it's hard to buy anything new that is worth installing. You could try it with an external pump, and then when you get time later and get one of the tanks empty, you could pull the tank, take the sending unit out, and then take the pump off and put a piece of hard line in it's place to eliminate it.

You would be surprised how dinky the pump can be and still supply that 460 with all the fuel it needs. One of those little square clicking pumps will supply it and work well.

 

Bumps cause the pump to slowly slow down to almost nothing. Then absolutely nothing. It’s not an on and off thing. As a I the tank it slows down till it stops… like a redlined engine with no oil. So strange!

 

The pumps in the stuck appear to be stock. I doubt if the tanks have ever been out of it. Definitely not new pumps.

 

The only thing I wonder is are the tanks and more so the pumps and how they mount, factory for the CC truck it was built on?
Sometimes when a body is installed different tanks are used and that could lead to different pumps too.

If you know who installed the body box, badge somewhere? maybe reach out to them and ask.
Dave ----

 

I wonder if going over bumps stirs up crap in the bottom of the tank, plugging the screen or sock on the pump intake. Same thing when pounding on the bottom of the tank? You want to make sure your tanks are clean. Replace old rusty tanks.

 

That is one thing that hasn't been mentioned yet to the thread starter. An ambulance will be a chassis cab truck, and they did use an oddball gas tank at the rear, not sure about the side tank. So oddball tank means oddball sending unit. These tanks are not going to be easy to find or cheap if they are a odd size.

 

It seems most go to a wrecking yard for OEM C&C rear tanks. But why not try a Truck rear tank and mount it sideways between the frame rails? The frame rails are narrower but a stock 19 gallon tank turned 90 degrees will probably fit. I haven't seen anyone report doing it. It will take some minor fabrication of custom supports and roll over straps. Seems the side tank would be no problem. But some careful measurements and fit check would be in order.

 

The problem is he is not dealing with a normal E-350 C/C truck it is E-350 460 ambulance w/ dual tanks so factory F truck C/C tanks may not even work for a E (van) C/C truck and being a AMBULANCE who knows if even a van C/C tanks were uses at all?
A van C/C is a whole different animal than the F trucks and I would not assume what they do to F truck C/C they do to E truck C/C.
Wonder how many Uhaul E van's have duel tanks to even to look at if the tanks are the same shape as he has?
That was why I said if there are any markings on the truck of why installed the body maybe reach out to them about the tanks.
Dave ----

 

Filler would take some thinking.