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'79 F350 xlt extra cab 7.3 auto dually. Stock. 240,000. Bought new.
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Discussion Starter · #1 ·
Hello guys. 1st post.
Dilemma: Removed filter housing to replace drain valve O-rings since it was easily accessible while doing other work. Noticed a heavy build-up of crud and RUST under the heater plate. In reading through this forum (great resource) I deduced that my pick-up screens probably were shot and I've been carrying around a bunch of water for many years. The rear tank started acting up @ ¼ tank about 12 years ago and I put a lift pump on it 5 years ago. (Wish I had read more here before slinging parts at it lately. You guys have some great ideas) I am now the proud owner of a new Motorcraft filter housing with 2 tanks arriving Thursday. THIS IS MY PLAN: Blow air back through the lines toward the tanks, cycling the tank selector valve as needed to clean lines, clean out lift pump with air independently, putting it all back together, with fuel, and lightly pressuring each tank using compressed air and rags at the filler neck (with the corresponding valve selection) to force the fuel through the system for bleeding.
I have a feeling it may not go as planned? If anyone can poke holes in my idea, please let me know? Thank you.
 

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I would also occasionally bleed air through the shrader valve on the fuel pressure regulator when trying to start. I'm not sure you'll get much through the piston stage of the 2-stage mechanical pump, plus there will probably be air in the fuel rails anyway. Cheers!
 

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'79 F350 xlt extra cab 7.3 auto dually. Stock. 240,000. Bought new.
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27 Posts
Discussion Starter · #3 ·
I would also occasionally bleed air through the shrader valve on the fuel pressure regulator when trying to start. I'm not sure you'll get much through the piston stage of the 2-stage mechanical pump, plus there will probably be air in the fuel rails anyway. Cheers!
Thanks for that thought. What would you recommend for the pump? Bleed everything leading up to the pump, attaching the hoses, then crank it until flushed before hooking up the filtration? Or...?
 

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Make sure your WATER IN FUEL (WIF) light flashes when cranking. It will not light up and stay lit like a normal idiot test light, it only flashes for a second when first cranking. Easy to miss it not working, then bad things happen.
 

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'79 F350 xlt extra cab 7.3 auto dually. Stock. 240,000. Bought new.
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27 Posts
Discussion Starter · #5 ·
Make sure your WATER IN FUEL (WIF) light flashes when cranking. It will not light up and stay lit like a normal idiot test light, it only flashes for a second when first cranking. Easy to miss it not working, then bad things happen.
Thank you. I don't remember the last time it came on? I haven't been worried about the water so much because the drain valve had a slow leak, so it was constantly draining. All this time, I thought the fitting on the side of the fuel regulator was the WIF sending unit, but it turns out that's for the fuel heater? No wonder it wouldn't plug in after replacement? Wrong part, right hole? The truck had been running pretty good despite my fuel issues. A buzz test showed 2 weak injectors...20 years ago, but it hasn't really affected the running. I'll have to find out the WIF light sending unit location and make sure its working.
UPDATE: Now my tanks won't be here until 10/18. A bummer for sure, but if that's the worst thing I deal with today, I'm doing great. Thanks again for your input.
 

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As mentioned, when cranking (and if it doesn't start right up), just stop cranking and go press the shrader valve to bleed any air and then continue trying to start. Lather, rinse, repeat until it starts. I've really only had it happen once where it took 4 or 5 cycles of this before it started. Cheers!
 

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'79 F350 xlt extra cab 7.3 auto dually. Stock. 240,000. Bought new.
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27 Posts
Discussion Starter · #7 ·
As mentioned, when cranking (and if it doesn't start right up), just stop cranking and go press the shrader valve to bleed any air and then continue trying to start. Lather, rinse, repeat until it starts. I've really only had it happen once where it took 4 or 5 cycles of this before it started. Cheers!
Gotcha. My big concern is making sure the lift pump doesn't spew rust/crud into the new system and I'm not entirely sure how to clean it well?
Thanks again for your thoughts on this.
 
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