Sucking air/Losing prime

[Selahdoor]

Yep, agreed there. I guess my mind deals more with the physical, what I have actual experienced and seen with my own eyes happen, versus the technical, terminology and how things should work through principle. No hurt feelings, it’s just an exchange of ideas. It’s good to talk about these things so we can work out how to improve on the parts of our fuel system that is problematic.

Absolutely agreed. That's the way I have felt about this, the entire way through.

Have I said yet, I love to learn? You can learn without being presented opposing thought. But the learning always seems stronger and more valuable if you work for it.

Personally, I like to put my check valves at the lowest point of the fuel system, at the rubber hose between the frame and fp. It keeps fuel primed in the entire fuel system around the engine, and as long as you have no external leaks it keeps the engine starting right up every time.

Yep. I'd agree. The only reason I suggested just above the FP, is in case the diaphragm leaks.

 

[PROFG]

Diaphragm leak and early detection of same is what stop valve after LP is for. Manual or solenoid stop and gauge between will show leak down which has to be visible or into crankcase

 

[DaytonaBill]

Here's food for thought, but not to derail this thread...

Is there an overlooked point where we could lose prime?

I think so... My truck has been having hard start issues for past two weeks and I went through ALL of the usual rigmarole to fix it...

Found a burned out Beru, fixed that...

Starter was wore out from hard start issues, replaced under warranty...

Batteries were checked and passed..

Alternator checked and passed...

Replaced return from filter head with pressure gauge, nipple was just a nipple with small hole, NOT a check valve...

Pressure gauge never showed leakdown until hard start issues and I use a Duralift pump with check valve... Always stayed at 8lbs overnight... Now pressure bleeds off at an observable rate, sometimes to 3lbs and sometimes all the way to 0lbs... In less than a minute too...

When I swapped out the starter, I saw alot of what looked as if someone had sprayed a mixture of oil with some fuel on the right side of pan and might have something to do with the premature failure of starter... There was so much gunk on the starter that I had to clean it up before turning it in under warranty...

Strangely enough, when the hard starting issues started, my fuel consumption went way up. When I top off my back tank, it takes 60 miles for the fuel gauge needle to move to the full mark. It now goes past that in less than 20 miles and when starter was replaced, I checked oil level and was 2 quarts low, just filled it up 5 days prior and made a 120 mile trip... So it got 2 qts low... Never did that before so quickly, but again, it was all over the oil pan...

Can anybody see where I'm leading to?

It's the Injection Pump! I'm losing prime because it's dumping fuel down into the crankcase from the seal in the front. AND my oil is STILL frothy after sitting for hours...

Will be replacing it with a known good spare IP today and will replace the olives on the hard line from filter head to IP... While I'm at it, the o-rings on the injectors will get replaced... I've got 20 of them on hand...

BTW, replaced engine with one that had 80,000 miles and now it has 235,000 miles total... That means the IP has 235,000 miles too! It lasted a long time before it started leaking!

Will post back after job done...

 

[DaytonaBill]

Well, got it done...
Naturally it was pretty hard to reprime it but I got it running...
It's too advanced because the injectors are banging away... That never happened before...
Will time it in the morning, keeping it plugged in so it doesn't have to warm up that much..
The inlet pressure is staying the same, no leakdown in the fuel supply...
Will be changing out the orings in the return system... AND the oil...

Since I changed out the olives in the fuel line, I'm not going to be able to tell if the IP leaking out the front end caused it to lose prime... The good thing is, there's no more bleed down between the Duralift pump (it does have a check valve) and the IP supply line...

Any thoughts??? I didn't know I had a bad IP until all the usual suspects were investigated... No air bubbles with clear line from the IP return...