Is fuel system losing prime?

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Dbordenb

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May 15, 2014
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I replaced a fuel filter delete block with a stock filter housing and when I removed the feed line from my fass pump to the cp3 it did not drain a lot of fuel like I assumed it would. I assumed the line would be full of fuel. Is the fuel somehow draining from this feed line back to the tank?

After the instal and reconnecting everything I primed the system by letting the lift pump run until it shut off and then bumped the starter and let it run one more time until it shut off I turned the starter and it fired right up with no trouble. After I checked the lines for leaks I turned the truck off and cleaned up and went to start it again but this time, the fass pump was making a pulsing sound. Rail pressure is the same as before the new filter and the new fass noise and when the engine is running the pump sounds normal. What could be causing this sound.

Thanks for any input.
 
I would take the line and the fitting off the output of the fass system and check the ball and spring to see if there is any crap in the seat of the check ball. I had a similar issue and that's what was causing my pulsing problem. Might want to rig up a gauge in the low pressure fuel system and see what your pressure is doing. Should be an 1/8 inch pipe plug on the elbow fitting to plumb a gauge into.
 
OK, I'll check that in the morning. Will that part be something that I can clean it or do I buy a new one if it's dirty?
 
I didn't get a chance to pull the line at the fass to clean the check ball today because of the weather here. I will get to it sometime this week.

I am still trying to figure out why the feed line to the cp3 was not full of fuel. If I understand the fuel system there are two parts, low pressure before the cp3 and then high pressure after the cp3. Is that correct?

If that is the case there must be a leak somewhere pre cp3 right? Loose connector tubes are one thing I read about that causes the fuel system to lose prime but that is in post cp3 part of the system and so I don't see how that would cause the fuel supply line to drain. I could be way off with this, though. Let me know what yall think.
 
Did you have this trouble before you took the filter delete plate off? Does the fass line go directly to the cp3 pump or through the filter housing you put on? Could it be sucking air on the suction side of the fass pump?
 
No trouble before I put the stock filter housing on.

The fass line went directly to the cp3 with the delete plate on the truck but I now have it going to the filter housing and then to the cp3.

It could be sucking air but I don't know what would have caused it to start doing that because I did not change anything in the tank or with the fass pump. I have just over a half tank so it shouldn't be having any quarter tank issues.
 
Today I had a chance to look at things a little more but still haven't been able to take off the return line to inspect the check ball. I have a new filter and a fuel pressure gauge ordered and on the way.

After listening to the pump today, the motor in the pump is not making the pulsing sound. It still makes the same sound it always has. I think the sound is actually coming from the return line coming off the fass so it very well could be the check ball in the fitting. I will check this weekend when I have more time.

I am confused about how changing the setup under the hood caused something back near the lift pump to change. If the banjo bolt to the return line on the filter housing is loose and letting air into the return line would that cause the sound?
 
I would say your problem does have something to do with the filter housing. Maybe there is to much restriction going through the filter housing causing the check ball to unseat. I can't really remember how mine is plumbed up, but I'm pretty sure mine goes directly to the cp3. I'll look at it and refresh my memory. I would also say a loose banjo fitting on the return could be causing your problem. I would try checking all the fittings again and maybe try to hook your fass back up the way it was and see if your problem goes away.
 
I was afraid that it would cause too much restriction. I have read about others running the lines through both filters and being ok but maybe my lift pump isn't strong enough.

I will check all the fittings again and hook up the fuel pressure gauge to see what the pump is actually doing. If I am lucky a new clean filter will lighten the restriction and fix the issue.

What exactly does the check ball do?
 
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