Having trouble bleeding diesel system

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Siegfried
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Isuzu vehicle(s): 1985 P'UP Diesel

Having trouble bleeding diesel system

Post by Siegfried »

Hey all,

I replaced the fuel hoses in my P'UP forward of the firewall, from the tank to the filter, from the filter to the pump, from the injectors to the pump, and from the pump to the tank.

I was trying to bleed them using the method puttputtinpup describes in this thread: http://isuzupup.com/viewtopic.php?f=1&t ... 74#p270751
You can bleed also by taking a brake bleeding hand vacuum pump and connect it to the return fuel line (removed from back of injection pump). That'll pull fuel through the system and remove the air.
I've been trying this for some time now, I still get a lot of bubbles using the vacuum pump. I have the vacuum pump connected to the diesel pump, at the outlet hose that would normally go to the fuel tank. Am I doing something wrong? Any suggestions?
1985 Isuzu P'UP Diesel Long Bed
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Paul
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Re: Having trouble bleeding diesel system

Post by Paul »

Siegfried wrote:
Sat Dec 03, 2022 6:59 pm
Hey all,

I replaced the fuel hoses in my P'UP forward of the firewall, from the tank to the filter, from the filter to the pump, from the injectors to the pump, and from the pump to the tank.

I was trying to bleed them using the method puttputtinpup describes in this thread: http://isuzupup.com/viewtopic.php?f=1&t ... 74#p270751
You can bleed also by taking a brake bleeding hand vacuum pump and connect it to the return fuel line (removed from back of injection pump). That'll pull fuel through the system and remove the air.
I've been trying this for some time now, I still get a lot of bubbles using the vacuum pump. I have the vacuum pump connected to the diesel pump, at the outlet hose that would normally go to the fuel tank. Am I doing something wrong? Any suggestions?
The fuel return fitting on the pump is fed from a quite small orifice in the fuel return banjo bolt. This will make it difficult to pump enough air /fuel through the system to purge it.

There is an air purge bolt in the end of the banjo bolt that is fed directly from the pump housing, without going through the small orifice. If you can make a fitting to replace this purge bolt you will be able to pump much more air/fuel through the system and, hopefully, get the air out. The purge bolt is a 6x1mm thread.

Of course, if you still have an air leak this will not solve it.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
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Siegfried
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Re: Having trouble bleeding diesel system

Post by Siegfried »

Paul,

I backed up and tried bleeding only the filter by putting my vacuum pump on the filter outlet, same problem. Then I backed up even more and just tried to get all the bubbles out of the fuel line that supplies the filter, and I can't even bleed that. Maybe air is getting into that line somehow? What's the likely culprit?
1985 Isuzu P'UP Diesel Long Bed
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Siegfried
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Re: Having trouble bleeding diesel system

Post by Siegfried »

Right after I posted that I ran to the parts store and replaced the fuel hose between the tank and the steel line. Then I bled the filter without much trouble. Bled the fuel pump with my vacuum pump and now my truck is running again. It actually ran a little rough to start so maybe it had some air left over after all, but it's fine now so no harm done I guess.
1985 Isuzu P'UP Diesel Long Bed
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Paul
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Re: Having trouble bleeding diesel system

Post by Paul »

Siegfried wrote:
Sun Dec 04, 2022 3:49 pm
Right after I posted that I ran to the parts store and replaced the fuel hose between the tank and the steel line. Then I bled the filter without much trouble. Bled the fuel pump with my vacuum pump and now my truck is running again. It actually ran a little rough to start so maybe it had some air left over after all, but it's fine now so no harm done I guess.
Well, hopefully that is the only problem. Might be. You should know by tomorrow.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
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Siegfried
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Re: Having trouble bleeding diesel system

Post by Siegfried »

Paul wrote:
Sun Dec 04, 2022 11:34 pm
Well, hopefully that is the only problem. Might be. You should know by tomorrow.

Paul
Paul, that wasn't the problem after all (well, not the whole problem). I am pretty sure it is sucking in air where the hand pump is on top of the fuel filter. When I put my hand pump on it, I hear a sucking sound from that area, and if I wiggle the pump button a little bit, the sucking sound changes or stops if I hold it just right. Is there a way to reseal this?

I tried taking out the phillips head screw on top of the pump button, thinking it might reveal an o-ring or something, but the screw just spins and spins.

I saw this guide you wrote, hoping I don't have to tear it all down like that since the pump actually seems to function fine, it's just sucking in air: http://isuzupup.com/viewtopic.php?f=36& ... 4017222f0d
1985 Isuzu P'UP Diesel Long Bed
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Paul
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Re: Having trouble bleeding diesel system

Post by Paul »

Siegfried wrote:
Sat Dec 10, 2022 8:20 am
Paul wrote:
Sun Dec 04, 2022 11:34 pm
Well, hopefully that is the only problem. Might be. You should know by tomorrow.

Paul
Paul, that wasn't the problem after all (well, not the whole problem). I am pretty sure it is sucking in air where the hand pump is on top of the fuel filter. When I put my hand pump on it, I hear a sucking sound from that area, and if I wiggle the pump button a little bit, the sucking sound changes or stops if I hold it just right. Is there a way to reseal this?

I tried taking out the phillips head screw on top of the pump button, thinking it might reveal an o-ring or something, but the screw just spins and spins.

I saw this guide you wrote, hoping I don't have to tear it all down like that since the pump actually seems to function fine, it's just sucking in air: http://isuzupup.com/viewtopic.php?f=36& ... 4017222f0d
That guide is to open the hand pump up so as to be able to service the check valves inside.

Seems like your pump must have a leaky diaphragm. This is unusual as I have never seen this. I don't know of any way for you to fix the diaphragm. However, there are lots of folks on here who may have a filter/hand pump housing that is good and available.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
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JoeIsuzu
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Re: Having trouble bleeding diesel system

Post by JoeIsuzu »

My 1980 VW Rabbit had a Racor filter assembly. I'll bet something like this (or a small model) would work well.
https://www.racorstore.com/racor-215r2- ... embly.html

Jack
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puttputtinpup
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Re: Having trouble bleeding diesel system

Post by puttputtinpup »

Maybe changing out the filter housing would help. Here's one for an NPR Isuzu truck that has the hand primer on top. I 1st looked at pictures of ine for a GM duramax (Isuzu engine) truck and it looks like it has a priming motor or lift pump, or something on top where the hand primer would be located. Here's a link to AutoZone NPR filter housing. https://www.autozone.com/fuel-delivery/ ... 482080_0_0
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Siegfried
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Re: Having trouble bleeding diesel system

Post by Siegfried »

puttputtinpup wrote:
Sun Dec 11, 2022 8:28 am
Maybe changing out the filter housing would help. Here's one for an NPR Isuzu truck that has the hand primer on top. I 1st looked at pictures of ine for a GM duramax (Isuzu engine) truck and it looks like it has a priming motor or lift pump, or something on top where the hand primer would be located. Here's a link to AutoZone NPR filter housing. https://www.autozone.com/fuel-delivery/ ... 482080_0_0
I ordered this part from RockAuto (much cheaper), I will let y'all know how it works out.
1985 Isuzu P'UP Diesel Long Bed
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puttputtinpup
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Re: Having trouble bleeding diesel system

Post by puttputtinpup »

Siegfried wrote:
Sun Dec 11, 2022 3:59 pm
puttputtinpup wrote:
Sun Dec 11, 2022 8:28 am
Maybe changing out the filter housing would help. Here's one for an NPR Isuzu truck that has the hand primer on top. I 1st looked at pictures of ine for a GM duramax (Isuzu engine) truck and it looks like it has a priming motor or lift pump, or something on top where the hand primer would be located. Here's a link to AutoZone NPR filter housing. https://www.autozone.com/fuel-delivery/ ... 482080_0_0
I ordered this part from RockAuto (much cheaper), I will let y'all know how it works out.
I wouldn't guarantee that the original filter would fit, but it might
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