Air in fuel system after selector valve replacement

Greenie

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A local shop replaced the fuel selector valve, dropped both tanks and replaced the fuel (tube or sock) in each tank. When I picked the truck up it started hard, surged and bucked. The fuel filter/water separator was wet on the bottom so I replaced that and cleaned the fittings and schrader valve and drain. It runs much better but still is occasionally hard to start and has small surges when driving.
The return lines, injector pump & nozzles were all replaced 2 years ago.
How long does it take to purge all the air in the system that might have been introduced during this work? I've checked the replaced selector valve and all the fittings I can see and everything is dry - no seepage or leaks. Any ideas????
 

Cubey

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With a mechanical lift pump, 3-5 rounds of cranking for 10 seconds each. Let the starter rest a minute or two between tries.

An electric pump can purge air faster via the Schrader valve on the fuel filter head.
 

Greenie

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The truck is running but is surging - I've driven the truck at least 100 miles and the surging is better but still noticeable at times. Both tanks are full, I have switched back and forth from one tank to the other. I see no signs of leaking fittings. How long after the fuel system is disturbed does it take for all the air to be purged from the entire system?
 

Cubey

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Maybe the valve is already clogged up. Did they put filters like the valve instructions say to do? No warranty without them.
 

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Greenie

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No filters but they replaced the fuel pickups. A clog couldn't allow air into the system - it would stop the flow of fuel.
 

Cubey

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No filters but they replaced the fuel pickups. A clog couldn't allow air into the system - it would stop the flow of fuel.

And you're sure it's air and not fuel starving?
 

Greenie

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Under heavy load (high speed) there's no fuel filter light on or lack of fuel judging from the throttle. It sure seems like air in the fuel.
 

Cubey

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Air usually makes it surge as if it suddenly has more power
 

Big Bart

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Some thoughts-

1) Mabye you have air intrusion on one of the lines to the fuel selector now. May not leak out at standing pressure but under suction let’s air intrude.

2) Bucking for me has usually been fuel starvation. Air intrusion to the lift pump could cause a lack of fuel and bucking, especially at higher rpms with your foot into it.

3) When my fuel return lines leaked and caused hard starts, it only took 2-3 minutes to clear and no further problems till it sat. Your return lines are after the IP and under pressure, so a air leak there causes fuel to leak out. Only when shut off do they let air in.

4). If the bucking is consistent I would blow air from the rubber line going to the lift pump back to the gas tanks. Take off the gas caps, blow say 10psi, do it for both tanks, and see if things improve.

5) Some have put a 5 gallon gas can with diesel in their bed and hooked to the lift pump to test the fuel availability system. No bucking it’s lift pump back. Still bucking its lift pump forward.

Post pics and share what you are testing.
 
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