Fuel Bypassing Injection Pump

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pitch4pd
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Fuel Bypassing Injection Pump

Postby pitch4pd » Mon Mar 05, 2018 6:21 am

This one has me stumped. I replaced the glow plugs yesterday and she started up first shot as expected but then stumbled and died within 5 seconds. Restarts were progressively shorter run times and the accelerator pedal did nothing to help. The truck ran perfect for 30 miles earlier that day before I changed the glow plugs (minus hard starting).

I have an electric lift pump that I leave off unless needed (priming). When I turned it on I could hear it wasn't building pressure like it normally does. It also didn't affect the run time.

I bypassed the lift pump to the stock configuration (hose from tank to the filter housing). Made no difference.

I tried using the manual primer and that's when I heard all the fuel returning back to the tank (I probably couldn't hear it over the electric pump noise and assume that's why it wasn't building pressure).

I checked all the hoses and ensured all clamps were tight. I removed the CSD and plated it off a month ago. Also drained the bottom of the filter twice just in case of water

Any ideas? I plan on taking the fuel lines off with the screens per the TSB and clean them but it makes no sense on why fuel is bypassing the injection pump.

Also I did double check the solenoid, it is getting voltage and is pulling about 1 amp. I don't know how else to verify it.

-Charles

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Re: Fuel Bypassing Injection Pump

Postby Pupfocused » Mon Mar 05, 2018 12:17 pm

My guess is that the check vales in the pump are no good. Paul has some details on the site on how to rebuild pump. I think in that posting he explains how the check valves work. You would also have to have an air leak for this to happen.
Jim
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JoeIsuzu
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Re: Fuel Bypassing Injection Pump

Postby JoeIsuzu » Mon Mar 05, 2018 12:24 pm

Charles,

Jim may be right, but whenever I hear about problems that pop up right after some work is done, my first and strongest suspicion is that it's somehow related. I can't quite figure out how glow plug replacement could produce these symptoms, though.

I think the glow plugs use washers of some kind (it's been a long time, and I'm not certain). Did all of the old washers come out with the plugs?

And a check valve should only stop fuel from flowing backward out of the pump. I'm not sure, but I think it should flow through the pump and out via the return fitting just fine.

Jack

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cocheeze
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Re: Fuel Bypassing Injection Pump

Postby cocheeze » Mon Mar 05, 2018 12:34 pm

The glow plugs don't have washers that I am aware of... in my experience the glow plugs just seal against the cylinder head with a slightly beveled sealing face about 3/4 of the way down the plug.

Are you sure that the lift pump you have installed is meant to pass fuel properly without being ran? I installed an accessory lift pump on my P'up when I converted it to run on WVO, and when it was losing power intermittently it was causing issues like what you describe.

I bypassed it, thinking that it would immediately solve the problem, but it actually took a bit of cranking and purging before the injection pump built pressure again... apparently the lift pump was starving the injection pump for fuel and air was being sucked in from somewhere as a result.

Just an idea!

Casey
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'81 Isuzu I-Mark Diesel (100% wvo) 220k
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pitch4pd
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Re: Fuel Bypassing Injection Pump

Postby pitch4pd » Mon Mar 05, 2018 12:49 pm

The glow plugs are slightly beveled, this is my 4th changing of the plugs in 2 years so I unfortunately have experience with this (another topic to come once I get her running again).

I ran without the electric lift pump running for about 6 months. I ensured it was a bypass type before installing it originally.

I will go over all the lines near the glow plugs again. I also have a/c so the farthest front glow plug is always interesting to get to and involves knocking around some lines and the injection pump when get a socket or wrench in there.

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puttputtinpup
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Re: Fuel Bypassing Injection Pump

Postby puttputtinpup » Mon Mar 05, 2018 1:12 pm

If you have original fuel lines or very old, they may have cracked when moving them around to get to that #1 glowplug.
I once had an 84 truck that had original fuel lines on it. I had taken lines loose to clean screen and little holes in the banjo bolts per TSB . Before I began, the fuel lines were secured by factory squeeze clamps and didn't leak. They appeared fine. I reinstalled them once I finished the service. After that, the injection pump would lose its prime if it sat a while. Merely loosening a squeeze clamp and rotating the dry fuel line cased the line not to seal well against the fitting and sucked air

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Re: Fuel Bypassing Injection Pump

Postby dorf » Mon Mar 05, 2018 6:03 pm

From experience I think that the fuel lines and or the water fuel filter are sucking air.
I went to gates barricade hoses....no more problems

pitch4pd
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Re: Fuel Bypassing Injection Pump

Postby pitch4pd » Tue Mar 06, 2018 10:02 am

I forgot to take measurements last night, anyone know the ID of the fuel hoses? I feel like the filter to injection pump is 5/16" and the rest 3/8" but I am more than likely wrong.

I was going to swing by parker on the way home since I don't think I can get eaton locally. Or the crazy idea of Swagelok soft copper since I have an infinite supply of them at work.

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Re: Fuel Bypassing Injection Pump

Postby puttputtinpup » Tue Mar 06, 2018 11:46 am

Frankly, I don't recall the fuel line sizes, but I do remember I had to use different clamps. The original squeeze clamps wouldn't work on the new hoses

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cocheeze
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Re: Fuel Bypassing Injection Pump

Postby cocheeze » Wed Mar 07, 2018 12:22 pm

All of the stock hoses are 5/16", except for the return line between the injectors and injection pump, which is 1/4".

If they are original, the hoses have a different wall thickness from what is commonly available nowadays... so when the original hoses are replaced you also need to upgrade to worm drive hose clamps like puttputtinpup mentioned. This has never been a big deal for me because I don't trust the squeeze-style hose clamps anyways and always replace them when I see them.

Doing so is especially important on diesel fuel systems, where air leakage accounts for a pretty large percentage of engine poor-running symptoms.
'81 Isuzu P'up Diesel 4WD (100% wvo) 310k
'81 Isuzu I-Mark Diesel (100% wvo) 220k
'81 Isuzu I-Mark LS Diesel (dual-tank WVO) 219k
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pitch4pd
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Re: Fuel Bypassing Injection Pump

Postby pitch4pd » Thu Mar 08, 2018 8:58 am

Thank you all. I replaced the feed hose to the injection pump w/ a new one and put a worm clamp on both sides. Unfortunately I didn't have 1/4 fuel hose handy so I just cut and replaced the squeeze clamps on all the return lines. This did it for now. BUT I also have the stock filter bypassed. I will put it back in the loop over the week and see if it was part of the problem too.

I was looking on upgrading to a heated fuel filter housing. Just trying to justify spending $100 on something that is "working". I've avoided tallying all my maintenance and upgrade costs on my 81 Luv since ownership as I know it is making the efficiency of 30mpg not so economical. If it wasn't for the fun/uniqueness factor of driving this little pickup everyday I probably would have to get rid of her. But there is something about driving these trucks that is fun in the weirdest way. They don't handle worth a darn, don't accelerate too quickly (with the turbo I at least keep up with modern traffic somewhat), they can't haul much, I'm 6 feet tall so the cab is not big at all. Yet, I love driving my Luv so much that I rarely take out my Golf R.

Anyways, thanks again guys. Sorry to create another thread that ended with a fuel line issue, I just never thought it would cause the IP to bypass back to the tank like this.

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Re: Fuel Bypassing Injection Pump

Postby JoeIsuzu » Thu Mar 08, 2018 10:12 am

pitch4pd wrote:Sorry to create another thread that ended with a fuel line issue, I just never thought it would cause the IP to bypass back to the tank like this.
Quite alright. No need to apologize. It may help somebody else, down the road. It's amazing how many symptoms lead back to fuel line issues. I'm pretty certain lots of trucks have been scrapped for this issue, misdiagnosed as bad injection pumps.

Jack

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Rjonesy
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Re: Fuel Bypassing Injection Pump

Postby Rjonesy » Thu Mar 08, 2018 11:29 am

Glad I saw this. Caught a faint whiff of diesel as I got home yesterday. Had just read this. Sure nuff. The return line was leaking. I'd have been all over the IP looking for the leak. The forum's a great resource!


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