Need Help, Fuel draining back

[alexx1060]

(09-10-2016 )schISM Wrote:  Did ya fill both filters and see if the engine would pick it up again?

just have to fill the one clear filter to get it to pick up after

[alexx1060]

(09-10-2016 )Signature620 Wrote:  Lift pumps can sound normal but be very weak at the same time. If you tip fuel into the IFSM inlet, does it suck that in?

we took it off to see if the flow direction is correct, and it is. by placing finger on either end you can feel that works, though the suction end feels weaker than the send side. without pressure tester i don't know how to be sure.

[alexx1060]

I just realized i forgot to mention that once we get it running, it last about 10 to 20 minutes before stalling out if we have run at 850-1000 rpm. at 600-650 it would stall out instantly.

okay update on the situation. took the low pressure pump off. found a cracked tube that goes from main line inlet to the electric motor on the suction side (fuel transfer tube). so i've cleaned everything, air sprayed all ins and outs, all available hoses, and put it all back together. had to retrofit our own transfer tube with what we had at home because i found it when everything was closed. i'm sure it needs oriignal but we had to try and see if it would fix our problems.

still have the same conditions with the fuel escaping the clear housing but the engine gets primed enough to start on its own. still seeing air bubbles in the housing and still hear it in the tank, either air bubbles or the fuel draining back into them. its not as rapid anymore, though.

sorry was working from morning to night yesterday which is why my answers are taking forever.

[alexx1060]

(09-10-2016 )Signature620 Wrote:  Lift pumps can sound normal but be very weak at the same time. If you tip fuel into the IFSM inlet, does it suck that in?

sorry i'm not good with all the truck acronyms yet, where can i find the ifsm inlet? i have access to all the diagrams, just point me in the right direction :)

[Rawze]

(09-11-2016 )alexx1060 Wrote:  I just realized i forgot to mention that once we get it running, it last about 10 to 20 minutes before stalling out if we have run at 850-1000 rpm. at 600-650 it would stall out instantly.

okay update on the situation. took the low pressure pump off. found a cracked tube that goes from main line inlet to the electric motor on the suction side (fuel transfer tube). so i've cleaned everything, air sprayed all ins and outs, all available hoses, and put it all back together. had to retrofit our own transfer tube with what we had at home because i found it when everything was closed. i'm sure it needs oriignal but we had to try and see if it would fix our problems.

still have the same conditions with the fuel escaping the clear housing but the engine gets primed enough to start on its own. still seeing air bubbles in the housing and still hear it in the tank, either air bubbles or the fuel draining back into them. its not as rapid anymore, though.

sorry was working from morning to night yesterday which is why my answers are taking forever.

Fuel is supposed to drain back to the tanks from the IFSM when the pump and/or engine is running. This helps to purge air from the system. Also, there will ALWAYS NORMALLY BE air in the return fuel going back to the tanks due to internal cavitation. -- Therefore you cannot use the fact that there is air bubbles in the return fuel, or the fact that fuel is returning to the tanks to troubleshoot ANY fuel related problem if you have no frame of reference.

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Put 10 psi (but no more than that) air pressure on the fuel tanks! -- you will find all your leaks in the suction system to the pump!.

[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....

[Rawze]

That clears up a lot,.. thanks. This thread was beginning to be very cryptic, hard to follow.

Some things to check,...

If the level of the davco is falling off after you fill it up with fuel, it is either sucking air somewhere, or the filter is bad. I had someone not 3 days ago have the same issue with their davco unit and power loss. The fuel level would drop to BELOW the filter itself (actually, the very bottom metal edge of it). It was a cracked filter,.. and ironically, they had changed it twice.

I have also seen this happen if someone forgets to take off the black rubber gasket for the old filter, because it is very common for it to stick to the stem on the davco unit, then stack the new filter on top of it, making for 2 gaskets at the bottom of the filter. When you remove the filter,.. there should only be the bare metal stem sticking up where the filter sits, and the rubber gasket is part of the new filter at its bottom. I also recommend to others to always use a 10-micron filter instead of the Bulls$#T 50 micron one. 50-micron filters offer very little protection towards keeping ashfaultine and algea buildup out of the fuel system.

I have also seen people install the o-ring for the clear plastic bowl on the wrong side of the flange for it. Very easy to make this mistake. It will suck air and have problems, and the next person who changes it, puts it back on the same way,.. solving nothing. The o-ring goes between the clear bowl abd the top of the metal flange of the davco unit.

Here is the correct way to install it (at 2:15 in the video)...




Next,.. ensure you didn't accidentally leave the rubber gasket for the old through-flow filter (the white filter on the engine itself) stuck up into the housing where it mounts. This is a very common mistake too. I see them do this all the time at speedco. Then you put on the new filter,.. and you get double-gaskets,.. and you get engine starting problems just like you are describing. It is very possible that it can be done 2 or 3 filter changes ago, and the problem only showing up now. I have seen this more than a few times where someone has double gaskets by mistake. The only way to check this, is to remove the filter and look up into the mount to make sure it is not hidden up in there.

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If you are getting air in your suction system, (lots of bubbles coming into your davco) then it is either the davco itself, the lines (pressurizing them will find leaks),.. or in the pickup tube(s) in the tank itself.

As well,.. you may be facing multiple problems. It could very well be that you are chasing some air bubbles, but you may have bigger issues like a failing shutoff solenoid, a stuck pressure relief valve, or a bad fuel/gear pump. The IFSM is designed so that if a bit of air gets into the fuel, it will be bled off through several small leak passages throughout the IFSM before it reaches the injectors unless it is excessive.

[alexx1060]

wow! thanks so much! this is going to help clear up a few things for sure! i will get on it and let you know the results. My dad is thinking the same thing about the pickup lines in the tanks. not sure how to test or check them because the angle they're at on this truck makes them not visible from the caps.

[Nilao]

You'd need a mechanics mirror and a flashlight. You can then extend the adjustable mirror into the tank and use the flashlight to reflect the light to the tubes to examine them. You won't be able to see them on both sides.