1985 6.9 misfire

[6.9idi_sam]

I have a 85 6.9 I just did a facet pump on. Truck was running amazing for about a day and then it started misfiring like crazy up high and has gotten worse and worse now does it in the idle. Blows white and grey smoke. There was fuel leaking in the pump fittings tightened those up but no improvement. Truck has low miles and my grandpa took excellent care of it. Motor starts up no issues.this is the biggest issue I've ever had. Just changed my return lines about a year ago. Any help is appreciated thanks!

 

[MTKirk]

If you used a Facet duralift Check the o-ring seal at the filter bowl. Coat the o-ring with some vaseline (after you've made sure it doesn't have any nicks or imperfections) and tighten the bowl carefully. If that's not it; maybe check your water separator, you can bypass it temporarily with a 3/8" hose barb to hose barb fitting (obtain at any hardware store).

 

[6.9idi_sam]

I see little air bubbles in the filter bowl as well

 

[cpdenton]

Where did you mount the pump, and what line did you hook the fuel input to? I ask because it sounds like you might be sucking air.

 

[6.9idi_sam]

On the passenger fender. And it's just from the main line into the pump

 

[cpdenton]

Gotcha. Take a good look at that hose where you hooked to the hard line. Make sure it is good and tight.

Also, make sure your filter is good and clean.

I had a similar problem once, and it turned out to be a bad batch of fuel.

 

[6.9idi_sam]

It was just weird for like a day it ran so good and smooth. I did a wide open throttle run after that it ran weidd

 

[MTKirk]

I see little air bubbles in the filter bowl as well

That means you're sucking air somewhere between the pump inlet & fuel tank. You can isolate and check this by running the pump suction line into a container of diesel, after you've gotten the air out of the line the fuel in the bowl should be bubble free.

The Facet sucks harder than your mechanical could so it can turn a small leak into a big one. Mine turned out to be the water separator, the fuel in the bowl looked like a glass of beer with a head on it. Bypassed the separator and the fuel went clear.

Sorry to say there's lots of other places for air to creep in. Good luck!