Duramax Diesels Forum Truck of the Week
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Old 01-18-2013, 05:14 PM
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Exclamation Kinked fuel return lines and no fuel cooler!!!

So I was under the truck today cleaning and painting and I noticed this:

Someone had deleted the fuel cooler and now both braided lines are kinked almost shut if not all the way shut. Could this have anything to do with the loss of power problem I've been having with my truck. I was thinking if it wasn't returning all the fuel then the computer would limit the fuel. I could be wrong because I'm by far no duramax technician. I also remember reading that high fuel temps ( no cooler) would also cause it to limit fuel. If anyone can offer me any help I would greatly appreciate it. I just lost my job 2 nights ago so if its not the problem I'm not gonna mess with it yet but if it is I can splurge to fix it
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Last edited by Stevenmc89; 01-18-2013 at 06:24 PM.
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Old 01-18-2013, 05:20 PM
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Definitely wouldn't hurt to fix kinked lines. I did a write up on diesel place a while back to fix the lines, GM had a tsb on this. I'm not sure that the return lines could hurt the performance but maybe? It is a little hard to tell exactly what is going on and how everything is routed in the one picture though. Here is the write up.

http://www.dieselplace.com/forum/sho...062&highlight=
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Old 01-18-2013, 05:24 PM
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They just removed the cooler and hooked the two quick connect fittings together with something that I've yet to figure out what it is and zipped tied it to the cross member in front of the tank
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Old 01-18-2013, 05:25 PM
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Just read a post from a guy on the diesel place regarding deleting the fuel cooler. He said that deleting it will make the temperature raise and stay higher, than the ECM will start pulling fuel from the injection process. I have had help from this same guy before and I believe he knows what he is talking about. Seems it might be worth trying to get it hooked back up correctly fixing the dryrotted/kinked lines in the process.
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Old 01-18-2013, 05:28 PM
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Does your truck have a loss of power all the time or just after its been running a while?
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Old 01-18-2013, 05:42 PM
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If any of it is a problem I would think it was the lines because evidently its never had a cooler since I've owned it and the power loss started about two months ago. It used to smoke my 37s and blow black smoke and now it feels like I have a mobile home behind it all the time and never blows black smoke which makes me think its limiting fuel since it won't over fuel and blow smoke anymore. It's had a cp3 7 months ago, injectors a month ago, ff head rebuild, new rubber fuel lines, and multiple fuel filters
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Old 01-18-2013, 05:45 PM
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Also actual vs desired rail pressure is dead on, MAF reads as it should, no boost leaks, and there is nowhere behind the MAF that air could be getting in because its got a K&N intake and I've looked over all connections MANY times
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Old 01-18-2013, 06:46 PM
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It's hard to tell but since the lines are kinked you'll most likely have to cut them there anyways so just take a piece of 1/2" fuel like and connect the 2 ends back together and see if it helps your power problem. Then you can look for a new fuel cooler.
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Old 01-18-2013, 07:02 PM
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If I cut off the quick connects to run the 1/2 fuel hose then how will I hook the cooler up once I buy one?
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Old 01-18-2013, 09:03 PM
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The lines are only 3/8" on the return side, and teh stock cooler uses 1/4" pipe threads going into it. What somebody did was take the fittings out of the stock cooler, and hooked them together via a pipe union. And if your return gets blocked there is a chance it could affect your injectors opening. The injectors are a differential pressure valve, so they NEED an unobstructed fuel return system to allow the injector bypass to free flow. I doubt you could get enough of a blockage in the return side to cause an issue, but it might.
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Old 01-18-2013, 10:04 PM
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Just the man I was hoping would comment on this! I just crawled back under it and they used a union like you were talking about to connect the lines but the u shape it made has caused 3 complete kinks in the flex lines so I doubt fuel is going in to the tank at all. I really appreciate all the help you've gave me since I've been a member here!!!
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Old 01-19-2013, 07:32 AM
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If no fuel was going to the tank, it wouldn't run at all. The BOSCH HPCR injection system MUST be able to return fuel to even run. I boub those kinks will stop fuel under 23,000 PSI of pressure from passing by. I know it sounds crazy, but the injectors are differential pressure valves. Meaning they used bypassed fuel to cause the injectors to open. When the injectors are triggerred to open, that opens the bypass valve in the injector, and that difference of pressure inside the injector is what allows the injector to open. So if no fuel is returned to the tank, there can be no pressure differrence, and no fuel injected. you can go down and buy a B&M 8.5X11 cooler, a set of 1/2" to 1/4" pipe reducers, and a set of 1/4" pipe thread 90's and hook it inline. You'll have to make some sort of bracket to hold it in place, but it will be very similiar to the stock fuel cooler for alot less money.
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Old 01-19-2013, 08:39 AM
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So is the K&N setup an oiled filter? If so it would probably be worth trying to clean the MAF with CRC Mass air flow sensor cleaner if you haven't tried (For the power loss). I'm not disregarding the lines or anything, it would just be a good thing to check.
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------------------------------------------
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Old 01-19-2013, 09:33 AM
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Yea it's oiled, but I clean it every oil change and a few days after I clean and oil the filter until I can get an s&b or aem with a dry filter. No one can figure out the problem on this truck. I've stumped all the local shops in my area with it because everything checks out fine but it's a complete dog and barely has enough power to move but somedays it gets a wild hair and gets a little more pep in her step than usual but never back to normal
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Old 01-19-2013, 02:28 PM
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We'll I went and bought some hose, 1/4" unions, and 1/4" barbed fittings and tied the factory lines straight to remove the kinks then connected them with the hose and fittings. Took it for a test drive and she's got a lot more get up and go than before but not like it was and it still sounds like its straining. The only thing I can think of is someone hooked an invisible mobile home behind my truck because everything else looks fine!
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