Starts the dies - But......

[Rupert8]

Hello all,

1986 F250, 6.9. I did a lot of work to eliminate air intrusion about six months ago or so. Olives, o-rings, new lift pump, checked all the fuel lines - and more. Truck ran great.

Then about a month ago it started pulling a little air. I'd be driving and after an hour or so I'd get surging - a sudden little increase in power. Unscrewing the fuel filter, it would be only half full. I'd get to where I was going then purge it before driving home....

This has been getting worse - the filter is filling with air faster than before.

I could handle that since I don't have a lot of time but now - suddenly - I'll start the truck, it will fire up first time, every time. But then it dies about two seconds later and I have to crank it multiple times to get it to start. (Purging air, I guess.).

My question - where do I begin here? Kind of lost since I did all the work above.

One thing to mention - Since this problem got worse I bypassed the fuel selector valve and am only running from the front tank. The truck feels like it has so much more power. Is this air getting in or just more fuel? (Bypassing the selecvtor valve has not improved the start-then-die problem....)

Thanks in advance to the hive mind! The help is always appreciated.

 

[franklin2]

The start then dies sounds like classic air intrusion, what you did all the work for. Just get up there and look very carefully at all your return hoses and connections. If you see any dampness, that is your leak. It does not have to be dripping.

You surging problem is not the classic air intrusion, it is a air leak on the suction side of the lift pump. A very common place for this to happen is the metal lines on the sending unit. They get rusty and get pin holes. Again, look for dampness. If you need to, take brake cleaner and spray a suspicious looking damp spot down to dry it up quickly. Then after a couple of days go back, if it looks damp again, that is a problem.

 

[Old Goat]

Did you replace the curly Q rubber hose to the Lift Pump.
When I changed my LP several years ago, mine was pretty cracked on both ends.
Do you still have the Water separator? or the 2 hoses connected together? I read it can be a problem.

It could be your Lift Pump, been reading they are short lived now days.


Goat

 

[chickenpot]

do you have a hose connection from the filter head that goes to the return system? great place to start if so by deletting that, then the filter has a lot harder time draining out while sitting. after that, id be looking at the lift pump, and the entire span of suction supply line from tank to lift pump. including the tank pickup and sending unit!

hook a jerry can directly up the the lift pump and see if it fires and runs fine. if it runs you can route the return back to the jerry can to run it longer otherwise it will go back to truck tank. this will tell you if you have fuel pipe system or lift pump problems

 

[Jesus Freak]

When I got my tow truck, I didn't have to start driving it right away, so I took opportunity to redo the entire fuel system including dropping and cleaning the tanks. It's tanks had an inch or more of hard slime in the bottom, the consistency of buffet style jello (ya know, a little thicker than you might make at home). Anyway, along with Franklin2's pinhole in the sending unit thought, I might add that there could be a clog somewhere( even your fuel filter) that has the injection pump emptying the filter while the lift pump isn't able to suck or push more fuel into the filter.

You got this, it's just the classic case of "the only reason a 6.9/7.3 won't run is because it ain't got no fuel getting to it". I think that we should train Chihuahuas to crawl thru our IDI trucks to sniff out and bark at air intrusion, it would save a lot of time and provide an invaluable service to our online community.

 

[IDIBRONCO]

I think that we should train Chihuahuas to crawl thru our IDI trucks to sniff out and bark at air intrusion, it would save a lot of time and provide an invaluable service to our online community.

That sounds like a great idea as long as I don't have to keep any of the little barking rats at my house!

 

[Daddy Tanuki]

That sounds like a great idea as long as I don't have to keep any of the little barking rats at my house!

I can smell a business opotunity a mile away... I can see the ads now... Fuel Sniffing medium sized punt rats for rent!