air in fuel issues

[frauhansen]

Hi togetherI

I have, so I guess, a diesel / air / line poblem.

The history:
My truck ran after a long tour in quite warm outside temperatures and after very heavy rain only with about 80% of the power.
I didn't notice it right away, but it was noticeable.

So I guessed water in the diesel. It had been raining very hard for days and I was refueling in the country.

So I put "Dry Fuel" additive in the tank and went to take a sample at the front left drain cock. With the engine running, as I know it.

To my surprise, however, no diesel came there. But I heard air hissing. And I suspect the came not out but in!

As a result, the engine went out and did not start again. Air in the system.

My question 1:
Why can there be a vacuum there? The diesel filter should be under pressure from the pre-feed pump on the engine yet!

Further history:
Since I now had air in the system was the opportunity good to change the diesel filter.
I noticed that there was already in Barstow times botched. A screw sat only in a helicoil. And that very loose.

Question 2:
That this was still tight I can not imagine.
But then I should have seen that diesel leaks.
Because I assume that the feed pump here generates a certain excess pressure.
Or is it so minimal because it is just reduced again via the return?

Question 3:
Whereupon the third question arises for me.
Can it be that the IP has sucked via the probably no longer correctly sealed diesel filter?
If so, can this lead to the observed loss of power?

For the rest of the story:
Inserting a new helicoil was not possible. Not enough meat there. So I drilled through the thing and closed with screw / nut.
Should now be tight now.

Question 4:
For me, the question now is how to check.
That I have to bleed the whole system now is so far clear. So pressure on the tank and fill the diesel filter before via return line manually.
Open an injection line in front, crank the engine, and wait until I am wet.

But can I check whether the pre-feed pump in OK? Can it be that this has delivered too little and therefore the IP has drawn air via the defective seal of the diesel filter?
These mechanical pumps should actually be indestructible. Especially with well lubricating diesel.

I don't like it when I can't figure out the original problem. But I only know the current symptom, not the cause. Translated with www.DeepL.com/Translator (free version)

 

[Mogman]

The IP has an internal pump that will kinda/sort of run the engine if the lift pump is bad, that is why you had a vacuum at the filter drain.

 

[GuntherRommel]

I had something similar to this happen not to long ago, turned out there was a kink in the supply hose right before the lift pump. There is a severe bend there where it crosses the frame. Found a preformed hose to replace it, re-pressurized the fuel system with this homemade contraption.

 

[frauhansen]

Sounds logical. I should have thought of it myself.
If the pre-feed pump part is clogged (by a broken pump or blocked line), then the IP pulls what she can.
And if I then open the drain line, it also draws air.

Thanks a lot... Will write if I still get problems or it is solved.

 

[Coug]

Mine did the same basic thing (lack of power, and died when fuel filter drain opened)
Installed new lift pump and that fixed it.

I doubt it's the check valves as that would require near complete blockage, as that would keep the engine from getting any fuel at all, so it wouldn't run.

 

[Retiredwarhorses]

It’s common for the diaphragm to fail, as long as no air is in the system, the injection pump will act as a lift pump, as soon as the
water separator is opened though, your done.
I tell my customers, don’t ever check your water separator unless your prepared to be stranded, I’ve had more than my fair share of trucks
at the shop die on the other side of the property when I should have done the maint in the shop.
As a matter of fact, I test all customer trucks when they come in to make sure the lift pump is in good health….I’ve never gotten water out of the separator, just the random dead engine.

 

[Mogman]

I had something similar to this happen not to long ago, turned out there was a kink in the supply hose right before the lift pump. There is a severe bend there where it crosses the frame. Found a preformed hose to replace it, re-pressurized the fuel system with this homemade contraption.View attachment 904159

You have to be VERY careful, you can blow off vent lines or damage the tank, a red rag around a blow nozzle will give you as much pressure as you should ever use.

 

[frauhansen]

Okay, so lift pump replaced. What a dirty job! Why can't the idiots put studs in there. Getting the pump down there and hitting the bolt holes is exasperating.
But okay... now it's in.

So then pressurized the tank as described, opened an injector and let it run. But the truck wouldn't start.
Then one way back. Pulled off the outlet of the diesel filter and looked to see if anything was coming out of it at all. Neither!
I try to narrow the error further... the supply hose of the lift pump pulled off and rear pressure on the tank...then it should run out in front cheerfully. But it does not... nothing... a slight whistling from the remains of the DWF system was audible, but nothing more.

That can not be that now "spontaneously" still the line to the lift pump is blocked. That would be too much coincidence for me!

But first checked whether the system works from the lift pump.
So to the supply line of the pump a hose on it with a funnel and so filled. Before with ner small inline pump the system "filled" that no more air is in it.
Works... starts... and also sucks the fuel from below its height from the funnel.

So I assumed that the line to the rear is blocked.
So we give compressed air from the front to the back... then it should bubble in the tank. But it doesn't... I don't get any air from the supply hose of the lift pump into the tank.
Strange... should the line really be closed? Or does it have a check valve? Would make sense. However, none is drawn in the plans.
So I attached the brake bleeder to the hose from the tank to the lift pump. It generates a vacuum (to bleed the brakes) and after 10 seconds diesel comes in... and that a lot. So the line can not be blocked. And my thesis of the not drawn back valve seems to be right.

The only explanation I have now is that the new lift pump is either defective or incorrectly mounted.
From my point of view it can only be that the lever is next to the cam and is not actuated at all.
Hard to imagine because then I would have had to bend the lever to be able to set both screws.
To check this would be if I take off the inlet and outlet of the pump and see if it also pumps.
Since the outlet on the pump but a huge cramp was to get back straight on it I have not yet done.

The lift pump there now once again out and back in ... very unwillingly. Rather out, close the hole with a plate and replace it with an electric one.

What does the community say about the whole thing?

 

[Mogman]

If you did not pull the plate behind the pump and grease the pump rod so it would stay out of the way , the pump rod is now broken.
Yes there are check valves on the fuel lines coming and gong to the tank they should be removed, both these issues are discussed quite often here.
EDIT, most just remove the check valves as they are problematic, you can also take them apart, clean and re-install them.

 

[frauhansen]

WOW, I was not aware that there is something to lubricate behind it. It is not the first mechanical lift pump I change on an old V8, but they were always driven via camshaft and thus in the engine oil.
But in this case I will remove the pump again and close the hole with a plate. Then installed an electric lift pump. Once again I do not do the work with the mechanical.

 

[Mogman]

WOW, I was not aware that there is something to lubricate behind it. It is not the first mechanical lift pump I change on an old V8, but they were always driven via camshaft and thus in the engine oil.
But in this case I will remove the pump again and close the hole with a plate. Then installed an electric lift pump. Once again I do not do the work with the mechanical.

The SBC and the BBC has the same setup, only they have a threaded hole in the front of the block where you can pull the short bolt and carefully install a longer bolt before pulling the pump to gently "jam" the pump rod so it does not fall out of place while the pump is installed.

 

[frauhansen]

Here is my final report.

You wrote about a "pin" that connects the camshaft and pump arm. When I took off the plate, it came towards me. Had expected something in the dimensions of a cigarette. But this is a cigar! This is a full grown bolt

How I could have missed this fat bolt during the first installation is a mystery to me. But I have the feeling that the bolt was at the bottom dead center. So that I may have put the pump arm over the bolt instead of at its tip. Only explanation I have as you can not hit that.

Anyway, now the pump is in. But definitely with an adjustment!
Because how on earth does one get the idea to use screws instead of studs? This fumbling is a nightmare! Then still in conjunction with the sealant? Then the sealant is everywhere, but not where it belongs.

I cut the head off two 3/8" bolts and cut a thread across the shank. So built me studs.
Now you can push both the plate and the pump very pointed over the studs without it slipping. And you can no longer cant the pump and end up over the push stud instead of at its tip.

The tank I no longer have to put under pressure. Took about 15sec with an open injector then it started right up.

Thanks for your help guys...
Without your encouragement, I would probably have installed an electric pump a long time ago and would not have learned anything.