I would inspect the larger supply line all the way from the front sender, through the valve, along the frame, to the lift pump. Look for any minor damp looking areas. Also, have you ever temp bypassed the FSV and tried it? Still sounds like a fuel delivery problem to me. You might want to see if you have a place to put a small gas can somewhere and fill it with diesel, and temp hook it directly to the lift pump. Go for a short drive and see if the problem goes away.

 

Seems that all these troubles have gotten worse after the fuel lift pump was replaced...along with a tap tap tap like a bad tappet...any chance a defective pump, or an improper install could cause all this?

 

The IP needs a minimum of fuel pressure to function correctly so a bad lift pump may cause some of the issues. The lift pump should supply 4 PSI Minimum and 1/3 a pint with 10 seconds of cranking on fully charged batteries. Both can be easily be checked. But the more likly scenario is that the new pump is high lighting a worn IP and injectors. The tap-tap what you are hearing is likely a nailing injector, this happens when injectors are leaking or the pop pressure has degrading enough that is it opening too soon causing pre-ignition, in diesels this heard as a tap tap tap like a hammer hitting a nail, hence the term nailing.
No Mech injected diesel will ever run correctly with worn injectors or a worn-out IP pump. All the symptoms you are describing point to a worn IP and injectors. Especially the full-throttle hesitation, this is classic worn Rotary IP symptoms, and that with the nailing injector point to a worn-out injection system.

Do a volume and pressure test on the lift pump, but if it passes the injection system is likely just worn out.
If you can post a video of the engine running so we can hear the tapping, we will be able to definitely tell you if it is a nailing injector.

This fix will not be cheap figure $500 for the IP, $500 for new or $250 for reman injectors, install kit at about $75 and then having the injection pump timed this will easily be just about $1K with reman injectors and around $1250 with new ones. But once done it will run and start like new and be good for at least 100K miles.

So before sinking any more money into it check the lift pump pressure and volume and then you will know where you at and if you are going to be willing to put the money into the truck or just sell it.

 

Unable to post video...or audio...none of my file types are supported...OGG, MP4... If I can find a proper format, will post...

 

Ok, learning curve...new conversion software....here's audio... I did run the RPMs up about halfway thru...

 

I have also had faulty lift pumps make a tapping noise. It would be worth investigating that I think. You could even spend a little bit of money and temp install a electric lift pump before diving into that injection pump thing.

We had a 89 f350 with the 7.3 diesel in it, and someone had put one of these up on the pass side inner fender. While we had various troubles with everything else on the truck, never had a bit of trouble with fuel delivery. It just sat up there and made a ticking noise for years and always worked, even in cold weather. And it sucked the fuel up fine mounted up high on the fender.

 

You think it would cause engine to lose prime overnite? Also hard to start even with full filter...checked this am, was half empty, filled it up, still hard to start, and when it did start, a HUGE cloud of grey smoke came out the exhaust, and revved up for a couple seconds, then settled down. Posted audio of engine running...

 

Usually other things cause it to lose prime. I guess it could. I would do anything I could before getting into that fuel injection pump and injectors though.

 

Another thought...wonder if my glows are going bad...just replaced them last year...

 

Glowplugs are only for heat to get it started. They are not doing anything while driving down the road.

 

Ja, I know they are for starting in cold weather...but it has been hard to start lately...even after holding glow button for 10 seconds...even in 60 degree temps...wonder if they have gone bad already...

 

That sounds just like a nailing injector,the frequency is to low to be the Fule pump and In 50 plus years of messing with vehicles, I have never heard mech lever arm fuel pump make a tapping sound SBC style pin plunger pumps yes lever arm no. The loss of prime can be an indication of failing injectors and IP Pump (provided the rest of the system is sound)

As for glow plugs, they are needed even in warm weather, your smoke on start-up is unburnt fuel. You probably have one or a few failed glow plugs.
Regardless no point in spending the money to fix the glow plugs is you are not going to do the IP and injectors...

Yes I know not great news, But given the mileage of the truck and unknown service history, the most likely culprits (by a very wide margin) given the symptoms are the injection pump and injectors.

 

Ja..think it's headed to the scrap pile, or maybe **** Creek machine gun shoot...make for a good target for the M-40 recoilless rifles that show up......to do what you listed is another 2500 at least...

 

I would try selling it if the body is in decent shape someone will snap it up.

 

Update...runs fine on the front tank..rear tank not so good...time for new tank (1985 for a 3.5 inch hole)and sending unit...which now are available . Think I'll keep the ol gal... FMSU-6DER can be had at
MTS COMPANY, L.C.
1-800-522-1622
MTS COMPANY, L.C. - Plastic fuel tanks for Jeep, Ford, Chevy, Scout, ******, and Toyota
Tank at any parts house...just shop for the best price...and make sure it is a 1985 model...not the '84, which has the smaller sending unit hole.
Will post on progress...