Uh oh. Wont start. Fass fuel pump- should there be a sound or silent? - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 11 (permalink) Old 06-14-2019, 10:45 PM Thread Starter
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Uh oh. Wont start. Fass fuel pump- should there be a sound or silent?

Good evening,
I didnt install the Fass Titanium Lift pump on my truck and am curious as to whether there is always a hum/noise. I currently hear absolute silence and nothing happens when I loosen the filter. I just wasnt sure if it shuts off until it senses a pressure drop or hits peak pressure...

Back story, I deleted the factory primer/filter tonight and I cant get it to start. It dawned on me that I may have been driving around and pulling fuel with the CP3... and that perhaps I dont have an issue with my turbo and subtle lagginess is... well because its been starving for fuel.

If it isnt working, perhaps I cut the power to the pump when I pulled the wires to the factory filter housing/primer??? I was under the impression it was typically powered through the fuse box...
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post #2 of 11 (permalink) Old 06-15-2019, 02:32 AM
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factory stuff should have no effect on Fass, mine when key is on it starts pumping. i sometimes have to bleed air out up by alternator on test port. i to deleted factory filter. Per Fass instructions there should be a wire going into your fuse box with a add a fuse insert on it, check fuse. get that pump running then maybe bleed it out all you can try for now.

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post #3 of 11 (permalink) Old 06-15-2019, 06:32 AM
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Originally Posted by righteousdude80 View Post

Back story, I deleted the factory primer/filter tonight.
That was your first mistake.......
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post #4 of 11 (permalink) Old 06-15-2019, 12:05 PM Thread Starter
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Well. Unbelievable- thank goodness I deleted the factory filter or I wouldnt have noticed- not the first mistake at all to remove the factory filter.

I took my voltmeter and tested the feed downstream- nothing. Had checked the fuse, it was fine. However, deep under the hood, the plug into the relay was diconnected....

This entire time it has been pulling fuel with the cp3- and driving pretty much fine, like a stock tune.

Its a night and day difference. As far as Im concerned, the only benefit of the factory filter is the primer, assuming the lift pump goes out. The cp3 pulls fuel just fine through the fass filters on its own, obviously dont expect your tunes to perform.

For the record, I had towed 8-10k loads without a problem on just the cp3. Man, I had been replacing things like the air mass, doing boost leak tests, compression & leakdown tests... and its the most simple 2 second fix.
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post #5 of 11 (permalink) Old 06-15-2019, 12:21 PM
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Originally Posted by righteousdude80 View Post
Well. Unbelievable- thank goodness I deleted the factory filter or I wouldnt have noticed- not the first mistake at all to remove the factory filter.

I took my voltmeter and tested the feed downstream- nothing. Had checked the fuse, it was fine. However, deep under the hood, the plug into the relay was diconnected....

This entire time it has been pulling fuel with the cp3- and driving pretty much fine, like a stock tune.

Its a night and day difference. As far as Im concerned, the only benefit of the factory filter is the primer, assuming the lift pump goes out. The cp3 pulls fuel just fine through the fass filters on its own, obviously dont expect your tunes to perform.

For the record, I had towed 8-10k loads without a problem on just the cp3. Man, I had been replacing things like the air mass, doing boost leak tests, compression & leakdown tests... and its the most simple 2 second fix.
I left the stock stock filter assy in place. One, it has the heater built into it. Second it makes it really easy to bleed the fuel system. Turn the ignition switch on to get the lift pump running and then just open the bleeder port. Some leave the stock filter in place, I decided to remove it and put a filter delete bowl on it instead. This gave me a 1/8th threaded port on it that I used to put a fuel pressure switch on to monitor my delivery pressure to the CP3.

I put the pump relay and fuse up by the driver's side battery. This makes it easy to check and work on if I ever have a problem. Dean
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post #6 of 11 (permalink) Old 06-15-2019, 01:24 PM Thread Starter
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Great advice. Those were all things I considered before deleting it. Ironically I ordered the Fass heater last week. As for the priming. I had a ton of air in the new fuel line i put in. It literally started immediately so I dont think the factory ability to bleed or prime is needed with a lift pump. Its also really easy to pull the line to bleed it if you need, just not as convenient. That being said, I dont have a backup.
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post #7 of 11 (permalink) Old 06-16-2019, 04:28 PM
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I would have to disagree to deleting the factory filter and head along with the WIF sensor after getting a bad batch of fuel with water in it and overwhelming the lift pump filters. I feel that the factory WIF sensor alerting us of a water in fuel might of saved use a load of money. JMO

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post #8 of 11 (permalink) Old 06-16-2019, 04:54 PM Thread Starter
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That is a good point. I wonder if there is an part or housing that will enable retaining the senor and loosing the primer. Only point of dropping the primer is to reduce the areas for air to get into the line. Otherwise Id just keep the thing and put in the filter replacement bowl. Hmmm...
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post #9 of 11 (permalink) Old 06-16-2019, 04:59 PM
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If your lift pump is between factory filter and tank, air shouldn’t be a problem. A fuel leaky filter head perhaps.
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post #10 of 11 (permalink) Old 06-16-2019, 08:16 PM Thread Starter
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Is that because the system is now under pressure from the pump vs being under a vacuum. So theoretically the primer and factory filter (from a failed gasket/o-ring would leak diesel as opposed to unknowingly sucking in air.
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