M923a2 fuel pump issue

[Elijah95]

Hey y’all, just replaced the lift pump on my truck w/brand new one, the old one was leaking fuel (and allowing air in) by the primer bulb. Didn’t touch the filter as it was just replaced a few weeks ago and truck ran fine until the primer started leaking.

Got everything swapped over, buttoned up, then cracked the 10mm bleeder on the front of the pump inboard side next to the engine, pumped the pump around 150 times until nothing but clean fuel ran out, tightened bleeder valve, started her up and it ran great for 30 seconds and died...

Okay, must be more air in lines right? Pump it another 100 times or so, with bleeder valve cracked, until all air bubbles gone, then fired it up again, ran smooth for 30 seconds, then died once again.

Repeat this process for about 10 times, getting up to nearly 200+ pumps each time and truck continually does the same thing. Seems to get a ton of air in it when running off the cam lobe side.

I’m stumped at this point, please advise

 

[Elijah95]

 

[simp5782]

Hey y’all, just replaced the lift pump on my truck w/brand new one, the old one was leaking fuel (and allowing air in) by the primer bulb. Didn’t touch the filter as it was just replaced a few weeks ago and truck ran fine until the primer started leaking.

Got everything swapped over, buttoned up, then cracked the 10mm bleeder on the front of the pump inboard side next to the engine, pumped the pump around 150 times until nothing but clean fuel ran out, tightened bleeder valve, started her up and it ran great for 30 seconds and died...

Okay, must be more air in lines right? Pump it another 100 times or so, with bleeder valve cracked, until all air bubbles gone, then fired it up again, ran smooth for 30 seconds, then died once again.

Repeat this process for about 10 times, getting up to nearly 200+ pumps each time and truck continually does the same thing. Seems to get a ton of air in it when running off the cam lobe side.

I’m stumped at this point, please advise

Let it suck on some ether if it stumbles till it can idle on its own

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[Elijah95]

Let it suck on some ether if it stumbles till it can idle on its own

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Be right back, will return with results

 

[simp5782]

Be right back, will return with results

Sometimes the 8.3 needs that motivation since it takes only a slight bit of air to shut it down

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[Elijah95]

Sometimes the 8.3 needs that motivation since it takes only a slight bit of air to shut it down

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Didn’t get it going, i believe the new pump is either junk or I’m sucking air somewhere so I’m done for the night, going to disassemble the brass fittings again and add much more Teflon this go round and see how she does

 

[simp5782]

Didn’t get it going, i believe the new pump is either junk or I’m sucking air somewhere so I’m done for the night, going to disassemble the brass fittings again and add much more Teflon this go round and see how she does

Ill be thru your way Wednesday if you need help i can drop by

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[WillWagner]

Make a line from the lift pump into a bucket of clean go juice. See if it will run on that. If it runs 'till the bucket dries up, your issue is before the lift pump.

 

[Smckerigan]

I just went through the same problem last week, I ran it dry and tried the prime hand pump for ever. So I put a tire valve on the fuel cap and opened the 10mm bleeder and pressured the fuel system tell fuel ran out the bleeder screw. Turned the switch and she ran right off the bat.

 

[porkysplace]

.............

 

[WillWagner]

You'd be better off by putting the bleeder at the outlet of the pressure filter, the fittings are the same and it is a higher point. Good idea installing a bleeder. Just a tidbit of info, Bosch inline pumps are self bleeding. Hold the pedal to the floor and the engine will fire.

 

[Elijah95]

You'd be better off by putting the bleeder at the outlet of the pressure filter, the fittings are the same and it is a higher point. Good idea installing a bleeder. Just a tidbit of info, Bosch inline pumps are self bleeding. Hold the pedal to the floor and the engine will fire.

I can’t take credit for the bleeder on the top, it came like that from Uncle Sam as such. I just transferred everything over accordingly, and I’m going to install a fuel pressure gauge in its place soon after i get it going again.

 

[frank8003]

Is there a place on your truck to put a bleed tygon tubing that you could see?

 

[Scrounger]

Even though you didn’t mess with the secondary fuel filter it may still be your problem. It can’t hurt to loosen then re-tighten it to make sure it is sealing. Ask me how I know.

 

[WillWagner]

Secondary is pressurized. A messed up gasket makes a mess. 20 to 30 PSI there

 

[Scrounger]

I had a secondary filter that was just tight enough to seal but was just loose enough to leak. The truck would loose prime every so often. Did and went through the usual checks and could not track it down. One time when I was priming the system after it lost prime I slipped and my hand bumped the lower end of the secondary filter. There was a sound of air from the gasket area. After loosening then re-tightening the filter I haven’t had any problem with losing prime since. I will add it would only loose prime after a cold start.

 

[Elijah95]

Thanks for the tips guys, I don’t have an air compressor that I can get the truck near so I grabbed my gauges and bottle of nitrogen along with an adapter to hook onto my fuel lines at the tank and threw 10psi into it. Found the mini in line filter had a pin hole under pressure, and a brass fitting had cut away too much Teflon letting it suck air. Addressed both, primed it, and let it run for 30 minutes @ high idle to recharge the batteries a little

 

[silverstate55]

Since I started using "The Right Stuff" to seal threaded connections on fuel, oil, air lines, I haven't had a single problem with those connections. I no longer use any kind of tape to seal threaded connections. They are easy to unscrew afterwards if necessary, but TRS helps seal against any kind of leakage.

YMMV.

 

[Elijah95]

Since I started using "The Right Stuff" to seal threaded connections on fuel, oil, air lines, I haven't had a single problem with those connections. I no longer use any kind of tape to seal threaded connections. They are easy to unscrew afterwards if necessary, but TRS helps seal against any kind of leakage.

YMMV.

Please elaborate on the product? I’d like to see what you’re using

 

[silverstate55]

Please elaborate on the product? I’d like to see what you’re using

Available through NAPA.

I love this stuff.