use of prime/lift pump. 8.3 motor

ericp351 · Nov 23, 2019

Hi all. start.Basic question. My A2 needs a good amount of cranking after sitting and about 3 clicks on the hand throttle to start. Runs fine after start. Kill solenoid sometimes sluggish, but bump with thumb cures it. No obvious bad fuel lines or fittings. Frame fuel filter new and was careful with its o rings.
Should I use the little prime pump routinely, or just when I open the fuel system? My gut feel is that I am missing something basic. #2 fuel is more or less fresh and clean. Thanks! Eric

Elijah95 · Nov 23, 2019

8.3s are EASY starting engines, if it takes more than about 3 rotations in mild temperatures you have a problem, most likely the fuel system is sucking air. Save yourself a headache, add to vehicle value and make your maintenance cheaper by grabbing a Ken spencer fuel filter kit. It’s all bolt on and plug/play.

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ericp351 · Nov 23, 2019

Followup question. Should the "prime pump" take a rubber cover over the plastic thumb button? May invest in different fuel filter after I put some miles on my new element.

98G · Nov 23, 2019

The prime button should have a rubber cover over it. Missing cover is a possible indicator of an old pump.

Using the prime button should be a fairly rare event, after changing a filter or cracking the lines or something similar. Priming should not be routinely needed.

I suspect your lift pump is losing prime and/or sucking air.

With all the surface area of the on frame filter, most of us won't really benefit from a spin on conversion. It probably won't ever fill up in our lifetime. That said, spin ons are nice....

Elijah95 · Nov 23, 2019

98G said:
The prime button should have a rubber cover over it. Missing cover is a possible indicator of an old pump.

Using the prime button should be a fairly rare event, after changing a filter or cracking the lines or something similar. Priming should not be routinely needed.

I suspect your lift pump is losing prime and/or sucking air.

With all the surface area of the on frame filter, most of us won't really benefit from a spin on conversion. It probably won't ever fill up in our lifetime. That said, spin ons are nice....

Negative. The problem isn’t really the big filter, the problem is every. Single. Truck. I’ve ever worked on has at some point had issues with the fuel lines sucking air between the tank and lift pump then people send them down the rabbit hole incorrectly diagnosing and spending money on repairs that all would have been negated. Honestly, buying an 8.3 equipped truck the first thing within a week it would get a spin on kit because it replaces every line from the tank to the pump. In many cases that cheap little kit can save you $5000 in a tow home, believe my I fought my old trucks demons with sucking air and I was ready to torch it

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98G · Nov 23, 2019

Elijah95 said:
Negative. The problem isn’t really the big filter, the problem is every. Single. Truck. I’ve ever worked on has at some point had issues with the fuel lines sucking air between the tank and lift pump then people send them down the rabbit hole incorrectly diagnosing and spending money on repairs that all would have been negated. Honestly, buying an 8.3 equipped truck the first thing within a week it would get a spin on kit because it replaces every line from the tank to the pump. In many cases that cheap little kit can save you $5000 in a tow home, believe my I fought my old trucks demons with sucking air and I was ready to torch it

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Absolutely agree.

The first thing to do if having fuel issues is replace every soft line between the tank and the engine. The fittings are also suspect, as is the lift pump itself. Also the pick up straw in the tank.

It can be maddening and frustrating beyond words. I went through this recently with an M936A2. Even though the lift pump tested good, I replaced it. Replacement of the lift pump fixed it. So, if you get to the point you're throwing parts at it in an attempt to fix, lines and lift pump are the place to start.

If the spin on conversion is a quick and easy way to get new lines, so much the better.

ericp351 · Nov 23, 2019

Thanks guys. I'll go back thru the little lift pump and lines. No external leaks, but a little air plus time equals a "battery test" I guess. Like to improve it before needed to pull out neighbors in winter storms.

74M35A2 · Nov 25, 2019

Usually when the soft lines leak air they don't show anything externally. It will look like a perfectly normal hose. Even when pressure tested only some of them will bleed fuel, some will not. Cheap enough to just replace and be done with it.

use of prime/lift pump. 8.3 motor

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ericp351

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Elijah95

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ericp351

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98G

Former SSG

Elijah95

Certified Rookie

98G

Former SSG

ericp351

Active member

74M35A2

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