1988 F150 -302 LB - Fuel Starvation
 

Recently I replaced the side fuel tank complete with a new in tank fuel pump, filter, sender, and hanger assembly. The fuel lines from the tank to the 6 port (diaphragm type) selector were thoroughly cleaned.

Reason for replacement was the tank was full of gunk, stale gas, rust, etc from not being used.

I had been running the truck on the rear tank only for a number of years, encountering no problems. After installing the side tank, installing 10 gallons of fuel, the truck ran fine on that new tank, the fuel gauge functioned properly, so I decided to run the rear tank dry to allow me to drop that tank to install a new sender float assembly.

Previously, when installing the new side tank, I had replaced the fuel pump relay on general principles. The truck has been running on both tanks okay since replacing that relay, depending of course on what tank I have the switch pressed to. However, when I ran the rear tank out of fuel to lighten it so that I could drop it to install a new float, and as it ran out of gas, I immediately I switched to the side tank... which never took effect. The engine died, would not restart, and I had to call AAA to tow me home.

I have since made sure that I have a proper amount of fuel in both fuel tanks, adding fuel to where they both are approximately half full of fresh fuel.

When grounding the diagnostic Data Link Connector (DDL) fuel pump terminal to manually apply electrical power to the pumps (all 3), I can hear the pumps run but obviously I am not getting fuel to the engine.

If I let the truck sit for a few hours, it seems that fuel is siphoning from a tank down to the main electric pump and the engine starts and runs for two or three minutes (approximately), then it runs out of gas again.

When turning the key on, the pump(s) run for about a second then shut down.

* Question (couldn't find answer in Haynes manual)... do the pump(s) come on again intermittently when the engine is running, coming on due to a change in fuel pressure?... Seems strange to me that the pumps are silent after that one second run.

I'm aware that the in tank low pressure fuel pump(s) are the power (pressure) that changes the fuel flow from one tank to the other within the 6 port diaphragm type selector reservoir.

As soon as possible I will be removing fuel lines from the 6 hose reservoir to see if the in tank pumps do indeed pump 6oz of fuel in 5 seconds as per the Haynes manual, and will also check to see if the reservoir is switching tanks properly.

Even though the engine runs for a few minutes after sitting, is it possible that the main pump has failed, or is failing even though it is running, at least when the terminal is shorted... or for that normal one second period when the key is turned on? I assume that the engine wouldn't run at all if the main electric pump was faulty... but that short one second run puzzles me.

My line of thought at the moment is that the 6 port diaphragm selector reservoir is possibly stuck between ports or somehow faulted, restricting flow to that main electric pump. Does that seem likely?
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Joe Reeves

Howdy and welcome to the basement. Yes, the selector valve is a common failure, along with the low/high pressure pump design being crappy overall.

I haven't had a rig with a failed high pressure pump still run, but have had a hard starting one that could pull through the dead low pressure pump if you cycled the key a few times.

If the EEC doesn't see a tach signal after a second, it'll trip the fuel pump relay off like if you just turn the key on without cranking. With a successful start the fuel pumps stay on constant pressure and what doesn't get used goes back to the tank. Ford didn't switch to returnless on demand fuel pump setups until I think the mid 2000s.

Harbor freight has a works fine for me fuel pressure set that will help ya figure out your numbers on the rail.

I'm switching my '88 Bronco to a single high pressure pump setup to avoid all this BS when I finish my 351 swap.

Adrianspeeder

Parts stores should have them in their loaner kits too.

Adrainspeeder... you mentioned "I'm switching my '88 Bronco to a single high pressure pump setup to avoid all this BS when I finish my 351 swap."

If that Bronco has dual tanks, I'd be interested in how the above is accomplished.

The manual speaks of plugging the fuel lines as they're removed from the 6 line selector reservoir... wonder what is used to do the plugging?

I'll check out the fuel pressure kits, Harbor Freight and the auto parts loaners. (Thank you both)

No, the Broncos up to '89 only have a single tank with the low pressure feeding the high pressure on the frame rail and a dummy "reservoir" lookin' thing like the selector on the dual tank pickups.

I'll just order a '90+ in tank high pressure pump, and run new line up to the stock filter location.

The F series gas dual in tank high pressure '90+ setups are a bit different than a Bronco involving check valves on the tank sender mount, but still a much better way to go.

'85-'89 fuel system info

http://www.supermotors.net/registry/2742/66025

'90-'96 fuel info

http://www.supermotors.net/registry/2742/12737

You might want to play close attention to this image.

http://www.supermotors.net/registry/media/669586

Adrianspeeder

Indeed! All of those hyperlinks, especially the one quoted here were most informative that answered a multitude of unasked questions. A small but important one was the size of the reservoir ports of which I discovered are two different sizes (5/16" and 3/8")... needed to know to have plugs on hand to plug fuel lines should they siphon when removed. That bit of knowledge save me from sliding under there to measure them. Obviously this is the forum of Ford knowledge. Many thanks Adrianspeeder. (Joe Reeves)

Edit 09/16/13: Also Many thanks to Steve83, the keeper of many Ford TSB's.

Don't thank me on that one, Steve83 is the keeper of more Ford TSB's and info than I think Ford does now.

Adrianspeeder

I spent a good portion of yesterday (09/16/13) under my F150 marking fuel hoses, testing in tank pumps, making 5/16" and 3/8" greased wood dowels as fuel line plugs to prevent siphoning. Durning that time, I learned eight (8) new words, and at the ripe age of 81, learning anything can be considered a blessing. The end result was getting that six (6) port reservoir to my work bench.

Having been a serious minded marine mechanic since 1960, retiring in 1991, coupled with the detailed information and graphics forwarded to me on this forum, I had no problem in dismantling the reservoir. The interior of it did not contain a filter, everything was coated with a rust colored film but no actual rust, but there was no trace of any solid substance (goop, whatever) that would interfere with its operation. Upon close inspection, what I did find was the apparent failure of one of the valves.

One of the small "O" Rings at the bottom of one valve was sort of protruding slightly downward into the area where a filter might be located on some reservoirs. The thought occurred to me that possibly I could correct this problem, but I immediately dismissed this as should I be wrong, it was simply too much work to do twice (we've all been there). I belted the bottom of that valve with a punch and hammer to make sure that I wouldn't be tempted to go that route again.

So today I am off to various auto part stores to buy a new reservoir. The most reasonable one I saw on eBay (new) was $157.88... hopefully I will be lucky and find one locally somewhere around that figure.

Joe Reeves

81 huh? I was wondering why I was easily able to read your posts. All these young guns nowadays use pound signs, no periods, and ramble from their phones.

Adrianspeeder

Received new 6 port diaphragm type reservoir, in factory packed box, packed so well in bubble wrap that it could have been dropped from a chopper on my cement driveway and suffered no damage.

Installed easily and both tanks now feed to perfection (so far). I anticipate no further fuel tank feed/switching problems. Now, to drop that back tank to install a new brass float (next week).

Many thanks for the advice and graphic help fellows. I know where to go with my future Ford problems.

Back again for one last time with this fuel tank adventure. As I remember it from past removals of the fuel tanks, the rear tank was a breeze as compared to the side tank. Unfortunately and obviously, my memory sucks! However, with some difficulty I did manage to remove, dismantle, install a new improved larger float, clean and paint the tank, and get it reinstalled.

That vent hose is just about long enough when the tank is installed. With the tank dropped enough to get ones arm in there, I found the tank had to be up on the drivers side, dropped just enough on the passengers side, and encountered from the rear of the vehicle... tight quarters.

However, at the moment, all is well. The in tank pumps are both good, the six port reservoir switches fuel delivery and return flow as it should, and the dash fuel gauge works with both tanks. Hopefully this fuel tank scenario stays solved for a long time, but I'm sure I'll be back later on with other problems. Thanks fellows.......... Great Forum. I'll be back for sure.