No fuel to filter head after rebuild

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longball

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Jun 8, 2015
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A couple months ago I ran the GM Upper Engine Cleaner through my 04 LB7. Since then I've noticed a surge at idle after first start up in the morning. The colder it is the more it surges, enough so that the RPM gauge is visibly fluctuating. Friday it was slow to start when leaving work but I didn't think anything about it as it does that about once every 6 months. Drove it 300 miles yesterday with no problems but this morning it started, ran for about 5 seconds then died and would not start back up. I primed the system at the filter head and after about three tries eventually got it to start. I went to the local auto parts store and purchased a filter head rebuild kit, read the instructions, and watched Merchant Auto's video on the install. After getting it all back together the system will not prime at all. I tried loosening the bleed screw first, then tried to prime while the bleed screw was tight to no avail. After trying to prime with the bleed screw tight I can open it up and hear just a very small amount to air come out. I searched for a problem like this on the forum but didn't come up with any results. The truck has the Nicktane filter adapter and Cat filter if that makes a difference. Is there anybody who can point me in the direction I need to go from here?
 
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longball

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Jun 8, 2015
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Alabama
It may be entirely unrelated, but It seems as though over the last few months I've had a loss of power. I don't tow anything substantial but I do drive over a mountain in the foothills of the Appalachians every day. It seems to me like I've had to apply more pedal to maintain speed the last few months. Also, I haven't let the tank get below half full in over a year but yesterday, because of the long trip, it is lower than usual. Right now, on level ground, it's sitting about half way between the 1/4 and 1/2 mark. It may or may not have anything to do with the problem, just trying to provide as much info as possible.
 
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bmc1025

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Jan 25, 2013
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You likely have an air leak still. If you have shop air take out the bleed screw and use a blow gun in the filler neck. Use a rag to make a decent seal. That should at least get you primed enough to pump with the primer.
 
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longball

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Jun 8, 2015
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Alabama
bmc1025 said:
You likely have an air leak still. If you have shop air take out the bleed screw and use a blow gun in the filler neck. Use a rag to make a decent seal. That should at least get you primed enough to pump with the primer.
Click to expand...


Thanks for the suggestion, I will try that. If nothing else it'll get me to a proper mechanic if needed. All I have is a small DeWalt compressor. Would that work?


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longball

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Jun 8, 2015
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Alabama
I think in a few days I'll take the filter head apart again and triple check to make sure I got it back together properly. It seems odd that it went from losing prime only when I was parked on a hill to not priming at all. It makes me think there's something I done wrong.


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longball

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Jun 8, 2015
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Thanks. I'll give that a shot then. Is there a danger of pushing too much air into the tank?


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longball

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Jun 8, 2015
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Alabama
I just took the filter off and after probably 200 pumps yesterday there is no fuel in it at all. As horrible as it is to mess up something that simple I think I've screwed up the filter head rebuild. Even when it lost prime I had plenty of fuel after 4 or 5 pumps of the primer.


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Awenta

Awenta

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Sep 28, 2014
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If you fill the tank with air don't go crazy. Around 10psi.

Take the head apart and make sure you didn't mess anything up.

If it's fine it might be time to pull the pickup assembly out of the tank and make there's no debris clogging it. Check the lines back to the tank first.

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longball

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Jun 8, 2015
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Alabama
Big thank you to Awenta and bmc1025. I used both of your suggestions and found out a fuel line was NOT the problem. The problem was my paranoia about doing things right led to me doing things wrong. Long story short, I'm an dumbass and the second time I put the head together I left out an o-ring. Thanks again fellas, she's running tonight.


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Awenta

Awenta

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Simple fixes are the best! Good to hear

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Duramax One

Duramax One

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longball said:
I've noticed a surge at idle after first start up in the morning. The colder it is the more it surges, enough so that the RPM gauge is visibly fluctuating.
Click to expand...

This sounds like your fuel pressure regulator is getting sticky. They do this after a while on the LB7s. It actually causes a noticeable fluctuation in idle. If you have a way to watch your commanded versus actual fuel pressure you will notice it doing a sine wave from too little to too much as the fuel pressure regulator struggles to keep up.

The solution is to replace the fuel pressure regulator. You can do a direct replacement with stock, but will probably run into the same issue in another decade/200,000 miles. The LBZ regulator fixes the problem, but uses a different current rate to actuate, which requires an engine tune to correct. Either option should solve your idle issue.

Glad you got the fuel filter head fixed.
 
Awenta

Awenta

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Sep 28, 2014
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Running an additive usually smoothes it out as well.

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