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Old 11-14-2020, 12:24 PM   #1
Mini-Skoolie
 
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Air in fuel system - squealing sound after shutdown

Hello.
i have the well known problem of stalling, followed by a hard ~20-30sec start when the bus was driven hot and then sits for some hours.
When i get it to start with cold engine and shut it off again before it gets hot it can sit for days and still start without problems.

During debugging i replaced the hose from the filter on top of the engine ( the last of 3 filters, from which the hard line goes tot he IP) to the return lines with a clear hose.

some seconds after shutdown i hear a sqealing sound from the filter and airbubbles can be seen traveling from filter down to return lines. I already replaced the filter, handtightened it, then tightened it real hard - no difference, issues persist.
When removing the filter after it cooled down it is only 2/3 full.

I made a video here:
https://youtu.be/zW_ULI9nZoA
Any ideas where to look for leaks? Return lines have been replaced recently by the previous owner. I checked some and the o Rings look good.

Regards,
Michael

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Old 11-14-2020, 01:39 PM   #2
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Some info your bus and its mechanicals would help (can put this in your account info).

Squealing on shutdown sounds like fan bearings.
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Old 11-14-2020, 03:06 PM   #3
Mini-Skoolie
 
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Ah, forgot that. I'm sorry:

International 3700 from 1990. 7.3 IDI V8. I also managed to fill out my details

The sound is definitely not the fan. If you put your ear next to the filter assembly you can hear that it comes from the filter / the lines next to it. You can hear it on the video i posted - Sounds like air being sucked in. The same sound you hear when you have a Thermos bottle with hot tea inside with the lid not screwed on firm enough.
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Old 11-14-2020, 03:46 PM   #4
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Details aren't showing up, perhaps they didn't take...


It's possible your lift pump or sending unit lines in the tank are sucking air. Sending unit lines can crack inside the tank and suck air, and lift pumps do strange things at times. You might also check your hoses in the fuel feed.
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Old 11-14-2020, 04:11 PM   #5
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I had an IH road tractor at the shop recently for a similar issue (one with the clear plastic housings with a cartridge). It was sucking air in/around the fuel filter housing. The techs replaced the O-ring, cleaned the sealing surfaces very carefully and had to try 2-3 times before they finally stopped the leak.
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Old 11-14-2020, 04:29 PM   #6
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You've got the classic air intrusion issue that plagues all IDI's. The filter being 2/3 full is the source of your start and die situation. You need to figure out what's causing that.

On mine, I had the same issue you have a few years ago. I installed a return kit, and then discovered the seals on the hard line between the filter and the pump was leaking. Those seals are called olives and can be replaced separately, but I actually replaced the assembly with fuel hose and brass barbs and fittings.

Not sure what you've all done so far. I see you said return lines, but the O-rings on the injectors and the return caps will also leak, so if they weren't replaced with the lines, I'd buy a return kit and install that.

With it running, is there any air in the clear section of line?
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Old 11-14-2020, 11:49 PM   #7
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Thanks for the replies so far.
There is no air in the clear section. I will remove the filter and clean everything again. Caps and rings are fresh.
I already suspected the seal in the hard line but i just cleaned it and screwed it back on firmer than before...

Just curious: I don't understand why the filter is half empty. It is hanging upright, the lines connect at the top. If the fuel would simply "fall" back to the tank , the filter should still be full and only the lines empty. Why is the fuel sucked out of it?
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Old 11-15-2020, 01:18 AM   #8
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It's fairly common for these types of fuel filters to have a bit of "empty" space, especially when they are newly replaced. In fact, when the fuel it "at the top" it is often considered a sign the filter is nearing replacement time.
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Old 11-15-2020, 01:59 AM   #9
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I was referring to the feed tubes inside the tank.
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Old 11-15-2020, 02:04 AM   #10
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Would the fuel drain back all the way when there was a leak on the low pressure side of the lift pump?

I will drop the tank and have a look when other options fail. I'm a beginner and removing the fuel tank during winter does not sound like something i want to do ��
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Old 11-15-2020, 06:24 AM   #11
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Quote:
Originally Posted by mikadobrain View Post
Would the fuel drain back all the way when there was a leak on the low pressure side of the lift pump?

I will drop the tank and have a look when other options fail. I'm a beginner and removing the fuel tank during winter does not sound like something i want to do ��
It's certainly possible. I've seen it on a gasser. Also, the tubes inside the tank ca crack an cause air bubbles when fuel level is below the cracks.
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Old 11-15-2020, 08:19 AM   #12
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Quote:
Originally Posted by mikadobrain View Post
Thanks for the replies so far.
There is no air in the clear section. I will remove the filter and clean everything again. Caps and rings are fresh.
I already suspected the seal in the hard line but i just cleaned it and screwed it back on firmer than before...

Just curious: I don't understand why the filter is half empty. It is hanging upright, the lines connect at the top. If the fuel would simply "fall" back to the tank , the filter should still be full and only the lines empty. Why is the fuel sucked out of it?
There is definitely air in your clear section. I can see it in your video.

You can't clean the olives, you can barely see the olives so I'm not sure how you cleaned them. Plus, they normally aren't dirty, they're dry rotted, so cleaning won't solve anything. Replace them.

The fuel filter needs to be full, It's on the pressure side of the system so all air should be forced out and through the pump or through the bleed orifice and into the return system. The piece of hose you replaced attaches to the bleed orifice on the filter. The only time I've seen a filter partially full and operate okay is when it's on the vacuum side.

What's happening is his engine starts, sucks in the big gulp of air at the top of the fuel filter, and then dies. He'll then have to crank for 20-30 seconds to purge all of the air out of the system before it will start and then run correctly.

The filter is half empty through siphoning, that's the squealing sound you hear. It siphons because there is a leak present in the system. The leak causes the fuel drain back. The leak could be anywhere from the lift pump to the return, but you can be sure you have a leak somewhere.
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Old 11-15-2020, 09:21 AM   #13
Mini-Skoolie
 
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That is exactly what i thought, too. The sound should come from the leak somewhere near the filter. But i cant track it down further by just listening. I'm after hints where to look.

The olives are a good start. To prevent misunderstandings: olives are the cylindrical seals under the nut? like o rings but way thicker and in cylindrical shape? thats what i cleaned. wiped them carefully to remove debris, then lubed, then screwed the line back on. they looked good to me.

Edit: This is what im talking about. olive or not?


anyways, i will try to get a replacement. hopefully german shops have them in stock.

how much torque for the nuts? the more the tighter the seal? or would high torque prevent a good sealing?
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Old 11-15-2020, 09:29 AM   #14
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It doesn't take much for a small air leak like that.

Olives are the cylindrical rubber seals. I've heard people use hose in place, but I doubt that would last too long.

Being in germany, it's hard to say where you'll find them. They include them in an Injection pump install kit, which is cardone # 2k-203, if you can find a source over there.

They also sell the olives individually at certain agriculture and industrial shops.

You can also get them individually -
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Old 11-15-2020, 09:31 AM   #15
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The fittings don't need to be all too tight, just fairly snug with a line wrench should be good.
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Old 11-15-2020, 09:33 AM   #16
Mini-Skoolie
 
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Agriculture is good. ill give it a try, thanks a lot.
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