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I have to agree with The Finlander that your symptoms and observations point toward the injectors. This is not to say that they will fail soon or in the next year or so, just that they are aged.
My 262,000 mile injectors are showing their age and will not allow ICP to stay at 2700+, but they still get the job done towing heavy up grades at high elevations. So, I have weighed the cost vs. benefit and put the injectors off until next year at the earliest.
Your analysis of comfort, mechanical wellbeing and longevity when looking at your 7.3L may be different than everyone here.
If you decide to go with injectors, Rosewood or Bitterroot only for remanufactured or new Alliant from a reputable source. BDP flow tests new Alliant for free and provides those results to the customer.
Yeah it's a question of how long I want to deal with that noise I guess.
A new piece of the puzzle though: I hooked an analog pressure gauge to the pre filter port of the fuel bowl and found idle pressure at 90 PSI!
Given that I got a new FPR, fuel pump, and resealed the fuel bowl, it must be due to an obstructed return line? The funny thing is if I key on and watch the gauge, it will go up to pressure and then slowly bleed off. I guess is returning to the tank but not quickly enough. Makes me curious if this is contributing to the injector knock.
Found B99 for 3.20 locally and filled up today (75% effectively as I had some petroleum diesel in the tank still). Engine seems to like it!
My injectors sound similar at idle. I will swap mine out as soon as I recharge my bank account. I would imagine much of the wear for me was due to air in the system over many years and previous owner didn't care or didn't know. Also fuel pressure starvation as it used to drop to like 20 psi when stomped on which was due to clogged screens in tank. It's quieter after the hutch mod but it's still there so damage is done.
In regards to the pressure I think you may be right and it does sound like the returns restricted. The poppet valve isn't in back to front by any chance? Not sure if it can be put in backwards, been 18 months since I redid my return. Maybe an o ring / bit of busted off Parker sleeve restricting the return? Correct spring in place etc? Can you disconnect the return line and blow air down it back to the tank?
When I rebuilt my fuel bowl I had a 100 PSI reading on my gauge immediately after reassembly. The first place I started checking was the FPR and just as I loosened the return line collar, the line moved. It appears that the line was off angle by 1/16 or 1/32 and that was all it took to throw off the pressure.
The parker sleeve was still sealed and the spring was properly seated.
I got lucky in the way that checking that line was the first thing I did. Four or more years later and the fuel pressure is right where it should be at 62 - 65 PSI.
It's hilarious that you mention that because, after I made my post, I removed the FPR to inspect it. Looked good, put it back in, tightened everything up. After starting the truck it idles at ~68 PSI pre filter. So bizarre. Suffice to say, making plans to purchase fuel pressure gauge.
Now I'm hearing a hissing sound from the fuel bowl when I key on the truck. No obvious leaks or hard time starting so I'm stumped.
It seems you and I may have had the same issue and I am grateful it was so cheap and easy to resolve. Looking at the return line you could not tell it was slightly off angle.
Regarding the hissing sound, I "think" my fuel bowl hisses a bit too. It could just be the sound of the fuel being forced into the stand pipe grooves, over the poppet or into the return line. If there are no leaks or adverse running conditions, you should be good.
One small bummer: the Rust-Oleum 2X paint I put in the valley didn't like the fuel and got a little messed up. Will touch up with a brush at some point.
I took it for a small drive. Still knocked but not as bad as it has lately. I think it'll probably knock just as bad once I go on a long drive.
Interestingly the timbre of the idle is a little different now, but I think that's due to the biodiesel.
On this drive I've discovered that, in addition to wiper electrical gremlins, the clock spring seems to've completely failed recently. Air bag light is on, horn doesn't work, cruise doesnt work. Another thing on the to do list.
One small bummer: the Rust-Oleum 2X paint I put in the valley didn't like the fuel and got a little messed up. Will touch up with a brush at some point.
I regularly clean painted parts with diesel and even brake cleaner without damaging that paint.
Surface prep is critical. Specifically no oil or grease present before paint. Use sandpaper to abrade the surface a little if you cleaned with wire brush.
The paint/primer is still adhered to the metal (my prep was good). More that the top layer of paint just liquified while the fuel was sitting in it.
Small update: we took a ~380 trip from Portland to Tacoma... mostly freeway miles with some around town stuff. Used a PHP 80 HP DD tune. Even going 75-80MPH on the freeway, with a canopy, running B99, we got ~15 MPG. Given this is a 20yr old CCLB truck with original injectors and a tired transmission, I'm very impressed.
With new transmission and injectors going 60mph, I'm sure I could get 17, 18.
Got new partially threaded 10.9 bolts and found a gasket at the auto parts store that seems to fit well.
Torqued both bolts to 30 ft-lb and did the soap water test. Seals completely! I put on the brakes and revved it in drive a little, still no bubbles. Have to take it for a test drive to know for sure if it'll hold under WOT... I'll look at it closely when we have the transmission out
Any updates on how the gasket did since you have the engine out? Having similar sealing issues with a CSD uppipe on my manifold. After install discovered the uppipe had an uneven spot on the flange from the pipe's seam
It worked well to seal it up. when I removed the uppipes the metal ring of the gasket was coming apart from the other material. I'm not sure that's entirely bad as it'd make sense for the gasket to become brittle from the heat cycles... I wouldn't be concerned about the gasket failing in a way that would send material to the turbo (as it'd be more likely to be blown out to the lower pressure atmosphere by the exhaust gasses), but how long it'd hold is unclear.
https://www.ebay.com/itm/165350268275 <- was thinking of having this person make a few copper gaskets (they do custom sizes)... not sure what thickness would be best though.
https://www.ebay.com/itm/165350268275 <- was thinking of having this person make a few copper gaskets (they do custom sizes)... not sure what thickness would be best though.
CRMB - Flanges / Gaskets / Custom Waterjet Cutting - is local'ish to us here in the Portland area and could probably give you exactly what you want. I have used them for other stuff, and it is good quality. Never any 7.3 specific stuff though. I'm sure they could probably cut any gasket you want and probably tell you the best thickness. Just a thought. They are out in St Helens off Hwy 30. Its always nice dealing with someone local for this kind of "1-off" stuff to make sure they get it right.
