6.9 loss of power stalls then dies

[mackmack]

I have a 86 f350 with 6.9 ats turbo and four speed. Wile driving it will lose power . If I feather the throttle I can kinda keep it running for a short time but it will stall and die.after this you have to really crank it to get going again. Both my fuel tanks are full. Fuel filters and lift pump are new. I'm thinking I have a air intrusion problem. I'm hoping someone here can chime in.

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[franklin2]

The normal air intrusion problem these trucks have with leaks in the engine area only causes trouble when you let the truck sit and not run it for awhile. It won't cause a problem when the engine is running.

You can suck air on the suction side of the system. That would be from the lift pump back to the tanks. Usually though that causes surging, the engine will keep running it just bucks and surges while driving.

Sounds like you have a major fuel feed problem, the whole system is running dry. I think the first thing I would do is get a piece of hose and temp put it on the lift pump, and suck out of a diesel can. See if the problem goes away. I am not sure if you will be able to rig this up so you can drive it though.

 

[franklin2]

P.S. There was another guy on here who had this same problem, he could let it sit and cool off, get it running again, it would stop, let it cool off, get it running again, same thing over and over. Come to find out he had some wires on top of the engine crossed up. There is a wire going to the injection pump to activate it to run. There is another wire coming from a temp sensor that goes to the injection pump that advances the timing in the pump only when the engine is cold. He had these swapped so the injection pump was only activated when the temp sensor was cold. Soon as the temp sensor activated it would kill the power to the injection pump and stop the engine.

Only thing is, with his problem it would probably be like turning the key off. Not sure about your problem since you say it gets weak before it shuts off. Getting weak sounds like it's running low of fuel supply.

 

[The Bus]

You have fuel "filters" as more than the factory one?

If so, the factory pump may not be able to keep up. There are some threads on about the demands, filters setups, volume checks post filter - could be your issue.

Another thing to look at is how much fuel is actually getting to the pump (franklin2's post). If I'm not mistaken there are some problems with the fuel p/u tubes in the trucks. They fail and your not able to draw enough fuel when moving (sloshing around). Also the p/u screen or opening can be block by debris (dirty fuel or rust in tanks).

When I had an issue like this with the old gas engines, I would disconnect the line after the pump and check for flow by having someone crank the engine (disable) while I held a container - like a two liter bottle and check flow.

On these engines, you would need to deactivate the injection pump just in case you have enough fuel to spin the motor around a couple of times.

Once again, search the previous post on the subject. Sorry, just not much help in the procedures.

If your getting air into the system, fuel would most likely be getting out. You would smell diesel and/or see diesel puddles. I know I did when my return o rings were starting to fail.

Don't rule out a bad pump (incorrect size on the diaphragm - no leaks, couldn't draw enough fuel, it happen to me once on a gas engine) or a collapsing rubber line either. I'm not familiar with the fuel line set up from the tanks to the pump on the trucks. But you could have a collapsing hose.

 

[mackmack]

By fuel filters I mentioned to say fuel filter and water separator the stock set up on a 86

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[steelheadguy]

I had the same problem. I dont know what fixed it, but I changed my return lines, tees and clamps. New fuel filter and cleaned the air filter. Got it running again and stays running.

 

[steelheadguy]

Also I cranked the engine while holding the schrader valve open on the fuel filter. Hold it open until a good amount of fuel comes out. It is the highest point of the fuel system. If there is air there it will come out, almost like the bleeder valve on brakes.

 

[steelheadguy]

By fuel filters I mentioned to say fuel filter and water separator the stock set up on a 86

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I dont know from experience, but I heard the water seperators fail and it is common to bypass them when trying to fix a problem like this.

 

[The Bus]

By fuel filters I mentioned to say fuel filter and water separator the stock set up on a 86

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Just wondering since all kinds of setups are posted here.

Can't really thing of anything else since these fuel systems are fairly straight forward.

 

[riphip]

Either put a 3/8" bolt in the drain hose of the water separator or bypass the WS all together.
These had a problem with the seat not sealing after ring was pulled.

Rick

 

[BDCarrillo]

What brand of fuel pump, and how new is it?

There's quote a few stories on here about parts-store pumps crapping out quickly. I had it happen too.

 

[IDIoit]

to address a fuel supply issue like youre having.
(yes it is a fuel supply issue)
you must first address the condition of the tanks.
inside the tanks are pick ups that should be addressed on any truck recently in your possession.
these crack and break up lodging pieces of plastic into the pick up.
pull both senders. blow air through them, and replace pick ups

from there is the ever so problemsome fuel switch valve that likes to catch debris. some have taken them apart and cleaned them, myself I destroyed it and had to replace the switch valve.
I preach direct replacement for ~$300 bucks. others like to get the 75 dollar vatozone special
that needs a lot of extra attention to fuel connections and electrical.

after the fuel switch valve, is another problematic device, which is the water fuel separator. DELETE THIS PIECE OF JUNK!(located on the driverside firewall inbetween the brake booster and fender)

and find an aftermarket waterfuel separator.
I have messed with about 5 of these now with ZERO percent success rating.
these direct replacement parts are no longer available, and once they are unsealed, you will bash your brain in before solving the issue.
delete and replace.

while your addressing all of these issues make sure you blow air through all of the nylon lines.
and replace all of the rubber fuel line.
this is from the main fuel supply line to the water separator, and from the steel line on the front cross member to the lift pump.

it is also common to get a weak stock lift pump.
and when you run out of fuel, and or have a dry supply line it takes forever to prime the system.
a lot of us like to run electric pumps, it saves time and mental anguish.

to determine if you indeed have a supply issue, run a line from the lift pump into a 1 gallon can of diesel,
secure the fuel can somewhere, and go for a drive.
if it acts normal, you know there is a clogged line somewhere.

I do every single step I just laid out before I even consider the vehicle for daily driving.

another favorite mod i like to do is to delete the saddle tank and run a 33-38 gallon tank in the rear.
deletes any further issues with expensive replacement parts.

good luck.

 

[laserjock]

Check and make sure the tanks are venting. If they aren't, it will pull a vacuum after a while and stop supplying fuel.

Crack the fuel filler caps and see if it still does it.

 

[mackmack]

You guys are great thanks for all the info . Hopefully I have some time to work on it this weekend . The previous owner of this truck installed a 50 gallon extra fuel tank in the bed of this truck . I thinking maybe the fuel tanks are not vented right like idiot suggest.

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[IDIoit]

that would be laserjock,
I left the vents out. but covered the rest.