Need Help, Fuel draining back

[alexx1060]

(09-11-2016 )Rawze Wrote:  

(09-10-2016 )alexx1060 Wrote:  hey guys, 3 days in and I'm running out of options.
2011 KW T660
CM871 with electric low-pressure pump

Current symptoms:

Turn key to Ignition ON position, fuel drains into tanks from both Clear Housing filter (many air bubbles clearly visible) and from the on Engine filter. Seems to be free flowing as if someone is just pouring it out.

Tried Bypassing the Chassis filter, same result.

Can hear the low-pressure pump motor running for sure.

Any advice would be appreciated!

WTF??!?! Are you trying to say?

Clear housing filter??-- EH??!? Do you mean your DAVCO FILTER ??? -- THERE IS NO DRAIN LINE FROM THE DAVCO BACK TO THE FUEL TANKS!!!

on Engine filter??-- EH??!? Do you mean your THROUGH-FLOW FILTER? ??? -- THERE IS NO DRAIN LINE FROM THE THROUGH-FLOW FILTER TO THE FUEL TANKS!!!

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In an attempt to descern what you are trying to say...

Are you saying that there is LESS FUEL in both the davco AND the through-flow filters after you turn the key and the electric fuel pump runs?

Will the engine run or not?-- Does it run erraticly?

What are the circumstances surrounding this problem?? -- Engine suddenly loose power? -- Were you changing the filters? -- HOW DID YOU END UP WHERE YOU ARE AT WITH IT?

haha, okay let's start with that last question. last weekend my dad had a hard time starting his truck. on after about the 3rd try cranking it would start. he decided to change the white cylinder-shaped filter that threads onto the engine (i'm assuming here thats the through-flow filter as you called it, on the diagrams it's just a Fuel Filter). also he checked the DAVCO :) filter found there to be some sort of debris but not a ridiculous amount. replaced that one as well.

after the replacements, truck not only had a hard time starting but would stall out as well. this is about when he discovered the air bubbles in the Davco filter.

At that moment in time, the truck did not run like dad was used to but drivable. problem was, he would get the truck to start with the help of starting fluid, then whenever he would reach his destination, the truck would stall out once he would idle.

Did a bypass around the davco filter, and got about the same results. except that after we helped it get started, truck would actually run standing at 850 - 1000 rpm for a good 20 minutes sometimes less then stall out.

onto the electric pump. so when you turn the key the motor runs as usual, the fuel is being primed while simultaneously draining into the tanks (but fast) this we observed with the davco filter connected still. when dad did the bypass and still couldn't start i had the suspicion that the engine didn't have enough prime fuel to start on its own. i had him turn the key and after the pump was done priming i took the through-flow filter off and there was less than half of the appropriate amount of fuel in it.

i've tried pressurizing the lines and determined there's no leaks in the main fuel lines from the tanks to the davco filter and from the davco filter to the pumps.

okay onto our results. so i've found a crack in the fuel transfer tube on the low pressure pump, on the side where the main fuel line comes in. retrofitted our own tube because everything was closed. we will buy original probably tomorrow. but once i put everything back together, still can observe the fuel escaping the davco filter BUT the engine has no trouble starting on it's own.

also had it running last night at 650 rpm for 20 minutes and it never stalled, we shut it off ourselves.

the davco filter drains but never fills back up, but you can see some fuel below where the clear housing threads onto the body. and you can observe bubbles coming up.

can still hear something going on in the tanks but not as bad. i can't figure out by ear if its just air bubbles or fuel draining into it.

i think that's everything....