Hard/Long start issue, supply fuel line corrosion? - 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.

  • 1 Post By stevewaclo
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post #1 of 4 (permalink) Old 06-02-2019, 02:27 PM Thread Starter
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Hard/Long start issue, supply fuel line corrosion?

So for the last couple of months (I know, I know), I have noticed a fuel leak under the tank. I never crawled under enough to fully identify the source. But it seemed to not leak when the tank wasn't full. I have also experienced an occasional longer crank (less than 2 seconds or so), and I assumed it was related. But it wasn't bad at all, so I put it off for another day...

Fast forward to a few days ago and after the truck sitting for a few days (vacation), I had a very long crank before it fired. But it started, so I just assumed it was because it sat for so long, with the leak...whatever. While driving, my fuel range was low (<70 miles). Well when I got to my destination and shut it off for about 30-45 minutes, it would NOT restart. I didn't have any tools with me to remove the prime screw, but I pressed the prime a few times and tried to fire it. It did fire, but then quit after 10 seconds or so. I also saw the "low fuel" light on. And I was parked an a decline (front pointing down), and thought damn, maybe I am out of fuel??! I ended up having it towed home.

Not sure if any/all of that is relevant, but adding for completeness.

At home I replaced the fuel filter (needed to anyway), added 5 gallons of fuel from a portable tank, primed it. It took a good 6-10 seconds to start, but it did. It ran fine. Now anytime I start it, it takes a good 3 seconds or so of crank, but it does fire and it runs perfectly; no hesitation or surges, no smoke, etc. I had never noticed any issues up until this hard start.

Back to the leak. I finally climbed under and this is what I see. Now everything is dry, because I kept the fuel level low I guess. But this corrosion and likely place of the leak seems to be in the supply line right at the quick connect. Could this be the source of my problems?

I would like to replace this with -8AN fittings; has anyone done this? From what I have researched, this is a 1/2" line. I was thinking I could use a 1/2" compression to -8AN fitting on the steel tube. And use a 1/2" barbed fitting to -8AN on the black braided line (cutting off the quick connect). Seem reasonable?

Any other thoughts would be appreciated!
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2004 Silverado 2500HD Crew Cab 6.6l Duramax Diesel LB7 Stock
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post #2 of 4 (permalink) Old 06-02-2019, 09:07 PM
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Oh, you did start a new thread!

As you probably noticed in the return test video I posted, those fittings near the tank can become corroded and extremely difficult, if not impossible to release, even with the proper tools.

Im sure they exist for ease of component assembly at the factory and the solution you suggested (which mentioned parts Im not familiar with) should get the job done. Just looking for a good seal and diesel safe plumbing.

That on again, off again fuel leak is a bit of a head scratcher, but maybe fluid pressure from a full, 32 gallon tank is high enough to open what is an otherwise tiny hole.

You could probably use low air pressure at the filler neck (sealed with a rag or some such) to provoke leakage, but that line looks so bad, I would go with replacement.

Best, and thanks for the picture!
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2003 GMC Sierra 2500HD SLE ExtCab CA Emissions; 155k; Allison 1000 w/Transynd X2 Flush & Fill; 8' bed; AFE/CAI; MBRP 4" Exhaust; Side Tint, 33% VLT, rear, Limo; Smittybilt Stainless Side Nerf Bars; Sprayed-in Bed Liner; MadJack Fuel Filter Access Door; Regular Used Oil Analysis (latest available on request), Blackstone Labs; EGT/Boost Gauges; Dual Chrome Dipsticks, JC Whitney; Stainless Steel fuel filter head bleeder screw; New WP and Hydroboost; Billet Aluminum Fuel Filter Housing Spacer; Professionally repaired instrument cluster (new steppers and lamps); Does anybody ever read this s%#t?; Injectors under warranty @ 70k; 2nd set DIY @ 155k
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post #3 of 4 (permalink) Old 06-04-2019, 06:32 AM Thread Starter
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Thanks! I'm learning a lot. It looks like because there is so low pressure (or vacuum as you mention) on these lines, even a simple hose clamp is enough. So I have arriving shortly a list of parts including a 1/2" quick-connect to barb fitting to attach at the supply side of the tank, and a few feet of braided stainless hose and a compression fitting to re-attach at a good clean part of the supply solid tube.

I also purchased a fuel filter head rebuild kit from Merchant Automotive that was inexpensive and seemed worthwhile. After priming when it wouldn't start I noticed fuel leaking, but I hadn't unscrewed the bleeder. Not sure where it came from, but I installed a new metal bleeder screw with O-ring also.

And finally, I came across the Nicktane fuel filter adapters and purchased that with a new filter; I wish I had known about that years ago. Would have saved me $$ on filters alone, and maybe more. Better late than never.

2004 Silverado 2500HD Crew Cab 6.6l Duramax Diesel LB7 Stock
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post #4 of 4 (permalink) Old 06-05-2019, 01:58 AM
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Don't use the Nicktane adaptor and different filter...the Nictane will eventually start to leak at its O ring. Besides, the stock filter from AC Delco is just as good in filtration down to about 3 to 4 microns as the Cat filters that the Nictane uses. Don't get wrapped up with the advertised hype of the Nictane adaptor and filters that go with them.

Your truck aged, and so did the fuel lines. You are getting air induced into the fuel system from aged rubber fuel lines. Replace them with good blue (diesel rated) fuel line and you will be good to go.

2003 2500HD 6.6 duramax (LB7) all stock (no mods)
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