Losing Prime

The place to discuss problems and routine maintenance questions and tips. This is for topics that are specifically diesel-related.
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Dongshoreman
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Isuzu vehicle(s): 1983 diesel short bed

Re: Losing Prime

Postby Dongshoreman » Sun Jun 10, 2018 9:15 pm

Sadly I think my last post was a bit premature. After replacing the bleed screw o-ring and a successful test after 24 hrs, I got into my P'up a couple days later and I had lost prime again. I decided to change the fuel filter since it was due anyway, and what I found was kind of interesting. Threaded onto the bottom of the plastic sensor assembly that screws on to the filter is a brass hose barb that holds the fuel hose going to the hand pump. I decided to take it off and when I put my wrench on it I found it surprisingly loose. I probably could have taken it off by hand. Upon inspection I found that the barb was missing an o-ring. See the photo below, I put an arrow where I think the second o-ring should go. Please anyone feel free to weigh in on this if I am mistaken.
hose barb with arrow.jpg

Another reason why I am pretty sure that this hose barb needs two o-rings is because the lip of the edge of the threads is fluted and looks like it is designed to accept an o-ring. Picture below:
sensor assembly.jpg


I ended up replacing both o-rings on the hose barb and it seemed to make a nice seal once I installed it. Here's a photo of the hose barb with both o-rings and their sizes:

hose barb two orings.jpg

After installing two new o-rings on the hose barb I realized that the plastic bleeder screw is similar. I inspected the bleed screw and found basically the same setup: A gap on the top of the bleeder screw that fits an o-ring, and the same fluted lip on the threads on the hand pump. I installed a second o-ring on the bleeder screw as well. Here is a picture of the bleed screw with both o-rings and their sizes:
Plastic bleed screw.jpg


I ran out of time today to finish the job, but I will try to prime the system and start up tomorrow, and then test again after letting it sit for a day or so. I will try to post another update later on this week with a verdict on whether or not this fixed the problem.

Thanks,
Jake
1983 Diesel Shortbed

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puttputtinpup
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Re: Losing Prime

Postby puttputtinpup » Mon Jun 11, 2018 4:53 am

This is very good information! Thanks Jake. Ill save tjis in my. Personal archives for quick reference in the future.

SactoTodd
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Re: Losing Prime

Postby SactoTodd » Sun Jul 01, 2018 8:55 pm

2sk8 wrote:I have 2 new units for sale if you wanna buy one.


Do you by chance still have 1? Cost shipped to 95742

-Todd
1982 Diesel P'up - 5-sp, Longbed, Sweet blue herringbone interior

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puttputtinpup
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Re: Losing Prime

Postby puttputtinpup » Sun Jul 01, 2018 9:14 pm

SactoTodd wrote:
2sk8 wrote:I have 2 new units for sale if you wanna buy one.


Do you by chance still have 1? Cost shipped to 95742

-Todd

to make sure 2sk8 gets your question, you could send him a PM (private msg).

2sk8
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Re: Losing Prime

Postby 2sk8 » Mon Jul 02, 2018 3:06 pm

Hi Todd,

the primer pump is $39.99 with free shipping by US mail.

I have 2 units.

I just sent you a private message so you can send me a paypal.

masonandford
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Isuzu vehicle(s): 81 chevy luv 2wd diesel from slygopup, 84 diesel 2wd long bed , 83 4x4 diesel with grease conversion, 84 diesel 2wd flat bed parts truck

Re: Losing Prime

Postby masonandford » Wed Aug 01, 2018 8:21 pm

im having the exact same issue! my starter just quit on me because of it today. :( glad to have all these tips.
- Mason - 81 diesel Chevy Luv 2wd
84 diesel p'up long bed 5spd 2wd RIP

FiatSpider2
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Re: Losing Prime

Postby FiatSpider2 » Sat Aug 04, 2018 11:33 pm

Since I installed an electric lift pump I have missed out on all these issues.

This one is distributed under a number of name brands:
Image
FiatSpider2 (4FB1 Isuzu Diesel powered 1978 Fiat Spider)

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Dongshoreman
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Re: Losing Prime

Postby Dongshoreman » Sun Nov 18, 2018 10:10 am

So after much back and forth with my Pup, I am still having priming issues. There was still one last fuel hose that needed to be replaced, so I replaced it the other day. I primed the system, started up, and then let the truck sit for a two days. It sadly did not hold prime. I have now replaced every hose under the hood, changed the fuel filter, and replaced/installed multiple o-rings. I am kind of at a loss now as to why I keep losing prime. Anyone have any ideas?
1983 Diesel Shortbed

2sk8
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Re: Losing Prime

Postby 2sk8 » Sun Nov 18, 2018 10:57 am

Install clear fuel lines on all the hoses. Even on the return line going out from the pump.

I can tell you from experience that unless you have x ray vision you won't be able to know where the air is coming from.

Temporally you can use vinyl tubing from the Home Depot or Lowe's.

5/16" ID for all the fuel hoses except the return line that is 3/16" ID.

Get the clear lines install and run the truck and watch carefully all the lines.

You will see where the air is coming from, it may even come from the tank, who knows but unless you have clear lines you won't know for sure.

In my opinion clear lines are a must.

I also I think that your hand priming pump could be causing the air leaks.

If later on you decide to stay with clear lines I recommend any of these:

** I'm using this one ** MOTION PRO 12-0065 MP CLEAR PVC FUEL LINE,5/16 ID X 3 FT

$7.69

https://www.ebay.com/itm/MOTION-PRO-12-0065-MP-CLEAR-PVC-FUEL-LINE-5-16-ID-X-3-FT/192593320059?epid=1822168883&hash=item2cd774d87b:g:-TEAAOSwRuVbQsqt&vxp=mtr

Clear Polyurethane Fuel Line Tubing 5/16

https://www.ebay.com/itm/Moose-Racing-Fuel-Line-3ft-5-16in-Clear-0706-0113/122835771938?epid=171131272&hash=item1c99952222:g:ZRQAAOSwF8lbGrvA:rk:3:pf:0&vxp=mtr

Let us know what you find.

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puttputtinpup
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Re: Losing Prime

Postby puttputtinpup » Sun Nov 18, 2018 11:05 am

Is it relative to amount of fuel in the tank? A pinhole in pickup tube sucking air? There are 2 rubber hose to steel line connections at the tank. Hard to get to. Perhaps glow issue and not fuel related.

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Dongshoreman
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Re: Losing Prime

Postby Dongshoreman » Sun Nov 18, 2018 11:32 am

Thanks for the input guys.
As for the clear lines, would you recommend I install them and then look for air while the truck is running, or just while I am priming the system?
The reason I am led to believe that this is not a glow issue is because i am not getting any unburnt fuel out of the exhaust while cranking. A while back I was having glow issues and I replaced a fusible link and all four glow plugs, and the glow system has been working fine since. I will double check the system though just in case.
1983 Diesel Shortbed

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Dongshoreman
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Location: Southern California
Isuzu vehicle(s): 1983 diesel short bed

Re: Losing Prime

Postby Dongshoreman » Sun Nov 18, 2018 4:57 pm

So I double checked everything again after reading the previous posts, and I think I may have found the problem. After inspecting the soft lines on the tank (everything looks good), I double checked the injection pump again, and found a vacuum hose that came off of the pump. Here is a photo of the hose reinstalled:
injection pump diaphragm.jpg


Once I reattached this vacuum hose and pumped the hand pump I felt a significant difference in the back pressure on the hand pump. I primed the system and gave it a test drive and it ran great. I will let it sit for a day or two and see if it holds pressure. Does anyone know exactly what the purpose of that vacuum hose on the IP is?
1983 Diesel Shortbed

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puttputtinpup
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Re: Losing Prime

Postby puttputtinpup » Sun Nov 18, 2018 5:02 pm

That is merely a vacuum motor the pulls the throttle to fast idle in cold weather

2sk8
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Re: Losing Prime

Postby 2sk8 » Sun Nov 18, 2018 9:24 pm

Dongshoreman wrote:Thanks for the input guys.
As for the clear lines, would you recommend I install them and then look for air while the truck is running, or just while I am priming the system?
The reason I am led to believe that this is not a glow issue is because i am not getting any unburnt fuel out of the exhaust while cranking. A while back I was having glow issues and I replaced a fusible link and all four glow plugs, and the glow system has been working fine since. I will double check the system though just in case.


Yes check the clear lines while the truck is running. And also check the next day or so after the truck has been sitting for a while.

You will see right away if your problem is air relate.

Regarding the glow plugs: I think you may have a glow plug issue as well.

Like you said cranking and no smoke is a clear indicator of glow plugs no working or no fuel reaching the pump.

Fuel cut solenoid sticking/not working, could also be something to look at.

Every time I have had starting problems (No smoke while cranking) it was either the glow plugs not working or no working fuel cut solenoid or both at the same time.

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Halden
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Re: Losing Prime

Postby Halden » Mon Nov 19, 2018 8:57 am

2sk8 wrote:Every time I have had starting problems (No smoke while cranking) it was either the glow plugs not working or no working fuel cut solenoid or both at the same time.


Generally if you have bad glow plugs you'll see white "smoke" which is just unburned atomized fuel. If no "smoke" you're not getting fuel.
It's not pronounced "Ih-soo-zoo", it's pronounced "It-screws-you"
83 LS Long Bed Diesel
64 Chevy C20 w/ 283 & 4 speed.
05 Sonata with a standard