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Old 08-07-2018, 04:10 PM   #1
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Fuel starvation symptoms

I'm wondering if someone can tell me when a Lehman 80 has an air leak or a fuel restriction issue will the air accumulation always appear at the injector pump and last secondary filter in the line?

If someone was to say shut off the valve to the tank, then run the motor for a while (extreme example of fuel restriction) would air end up in the injector pump when the motor starved out?

Another example would be say a racor with a leaking oring letting air into the line, would that air end up accumulating at the injector pump causing shutdown?

I guess my question is if air gets in the line (other then empty tanks) or fuel starvation happens is the air always found in the same place at the injector pump and secondary filter?
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Old 08-07-2018, 04:21 PM   #2
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What are you really trying to figure out? What if the answer is, "Yes," how does that help you, or what will your next step be?


Are you asking if the location of the air is an indication of the air entry point?
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Old 08-07-2018, 05:13 PM   #3
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I'm asking if the air all ends up at the same place regardless of entry point.


I'm trying to determine why one of my motors ended up with air up at the injector pump, and I had to bleed it to get the motor started. I don't know why it happened, but the obvious potential cause was I replaced all of the fuel filters. So maybe I didn't bleed all of the air out (I sure think I did), or I have a oring or washer out of whack. Happened 2 hours of running after doing the filters. I might not have a problem at all but its a question Iv been wondering about, so figured someone here would know.


Also, reproducing the issue takes a while of running in gear, but if I can check for air accumulating at certain spot before the shutdown at a bleed screw Id be able to troubleshoot more effectively.
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Old 08-07-2018, 09:55 PM   #4
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Has it happened since then? If not, maybe just some Air was in there. If so, then it will most likely be your filters drawing air. I messed with some fittings and had to bleed the pump at the fittings. So Iím guessing yes, air will always be there since itís the reason your engine stopped in the first place. Had there been fuel on the rail it would still be running right? I may be wrong so others feel free to correct if I am.
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Old 08-07-2018, 10:07 PM   #5
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Yes the air winds up at the injection pump.

My engine shut down a couple dozen times last spring because of sticking antisiphon valves on the fuel tank pickups.

It would suck the fuel level down in the primary Racors too, as well as the secondary.
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Old 08-07-2018, 10:14 PM   #6
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My only experience was that engine could not reach full speed. Switching (turning one valve) to the unused of dual fuel filters solved that. (The fuel filter being used "died"/clogged doing its job.)
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Old 08-08-2018, 07:31 AM   #7
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The symptoms of air in the fuel line and a blockage in the fuel line are the similar but the mechanisms are different.

A blockage will often let the engine continue to run at lower rpms but won't rev any higher. I suspect this situation depends on the fuel system being vacuum tight. If it is then no air will get in the system, but fuel flow will be limited, thus limiting rpms.


But sometimes you have a partial blockage situation combined with an air leak and the symptoms are due to the air leakage sucked in by the high vacuum not necessarily the fuel blockage.


Air leakage causes the injector pump to lose prime and the engine usually stops then, even at idle. Some engines with an electric booster fuel pump (installed for just this purpose) can clear the air by turning on the electric pump which pushes the air blockage out through the fuel return lines. The engine should then start after running the electric pump for a minute or so.

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Old 08-08-2018, 01:07 PM   #8
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Thank you everyone that answers my initial question. Lets say I wanted to find an air leak would putting a pump up between the tank and the racor to pressurize the fuel lines so I could look for a leak be an ok idea? Is it ok to pressurize the line when the motor is not running or will it cause other issues?


Like I said I'm not sure yet if I have an issue, but I'm trying to learn how to find a leak if I have one. I have used oil pads in all the likely spots and have not seen a drop of diesel, but thinking if I pressurize the line Id find the issue if there is one. I have ordered the racor T vacuum gauge as an additional tool, but doubtful it would indicate an air leak motor side of the racor.


I'm thinking if it doesn't happen again there's a 99.9% chance something I didn't get right with the bleeding. I use a oil pump to pull the fuel up into the filters to bleed. I guess its possible the pump pulled some diesel from the injector pump side leaving air. I did not bleed the injector pump when I was done, so that might have been my source of air after the filter change.. I find it a little strange that it ran about 10 miles before shutting down if that's the case.
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Old 08-08-2018, 01:27 PM   #9
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Air leaks are often so small and they occur under a partial vacuum, that pressurizing the system often won't find them. Unfortunately it is a laborious process of tightening fittings, replacing bad fittings and sometimes hose until it stops.


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Old 08-08-2018, 02:26 PM   #10
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Using pressure to find a vacuum leak in the fuel line works, but you need more pressure than the average fuel pump provides. Another way is a vacuum pump and gauge. You pump down the vacuum and check/tighten fittings until the vacuum stays steady.
A couple common leak areas are a worn out Racor housing gasket and the fuel bowl drain not closed tight or worn out. Drain doesn't leak fuel but under vacuum, you sometimes see bubbles rising from the drain. The Racor drain assemblies last a long time, but not forever.
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Old 08-08-2018, 04:27 PM   #11
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If it happens again I will switch that motor over to the other tank, bleed and give it another try. If it runs without issue off the other tank I have a blockage between the port tanks pickup and valve. If it continues to happen its from the valve to the motor. Ill post back if it happens again and what I find out.


Thanks for all the advice and help.
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Old 08-10-2018, 12:17 AM   #12
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Iím a firm believer in what did you last before it died. If you changed filters go back through the fittings and bolts that were moved. Most likely you will find the problem.
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Old 08-10-2018, 01:05 PM   #13
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Yes 100% I agree but there’s more to the story that I left out for simplicity sake as my question was already hard to convey. It’s possible there is restriction somewhere in the port side lines.

Lepkes post about slight restriction causing vacuum and sucking air with no apparent fuel leak really summed things up for me. With so many filter o rings, bleed screws, and line connections it seems it’s one of the more difficult issues to find - especially if there’s any restriction going on.

I’ll be taking the boat out over next few days hopefully it’s non issue. Otherwise first thing is checking everything I touched last. My gut is telling me I got air into the line up by the racor when I pumped air out of the secondary’s. That would explain why it took so long to accumulate at the injector pump. The air bleeding process has the need for a checklist I think, so I’m putting one together for my boat.

I read as many posts as I could find befor posting this one.The reply’s from you all have helped me understand more on troubleshooting the fuel system so thank you.
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Old 08-16-2018, 09:50 PM   #14
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The saga continues. Took boat out twice this weekend ran around 3 hours and on Sunday port motor stopped. This time I looked at a few things. First the last filter in line closest to the injector pump had air. Also the racor was full of air.

Tonight I decided to put a squeeze bulb in line tank side of racor on the inlet. First thing I noticed no fuel came out when I cut the line. I used the bulb in revers to blow back into the tank quit a bit to check flow. Seemed fine no restriction. I put the bulb back the right way and pumped about a gallon of fuel through the racor with lid off and drain open. Seemed to flush it well.

Next I bled every bit of air from all 4 spots. Motor started right up ran smooth at idle like I’ve never heard. Tomorrow I’m going to go have a look. If the squeeze bulb is not full or has air I think I need an anti siphon?

Seems strange the air would be in the racor and the motor filter, but I guess if the line to the racor from the tank is draining back into the tank it would seem I have an air leak between the racor and the tank right??

Any pointers on my symptoms above and what it might be are much appreciated. I took Simms filters off and checked all seals looked good and were in place.
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Old 08-16-2018, 11:59 PM   #15
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I've just skimmed this thread but a couple things come to mind.

--Racor? was it disassembled just before the trouble showed. Mike Negley has written many times about the ball check seat in the filter housing. There is a right way and a wrong way to install that seat. If wrong it can cause trouble like you describe, It is marked but not clearly so it gets installed the wrong way. Check it out carefully.

Described many time on B.D. Forum is the use of a piece of clear vinyl tubing. Install between the last filter and the fuel pump. Purge the system of air and start the engine. There may be a few bubbles initially and then subsiding but if a stream appears then there is an air leak.

Move the tubing to just before the filter and see if the bubbles stop or continue. If they stop then the device just before the move was done is the culprit, ie the filter. If they continue then move the tubing again to inspect for the bubbles. Whenever the bubbles stop then the device it was just moved from is the culprit.

PIA , yes, but has worked for many.
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Old 08-17-2018, 03:02 AM   #16
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In my case, wasn't able to reach speed (symptom). Turned Racor lever to switch filters (solution).
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Old 08-17-2018, 08:47 AM   #17
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When you open the Racors to do service, did you scrupulously clean the cover gasket surfaces and install a new gasket? Did you do the same for the T-handle or gauge in the top of the filter? A common source of air ingress. Keep in mind you can pressurize the line and no leak will show, if you apply vacuum, an air leak inward can occur where no fluid leak outward shows. INVISIBLE!! Air leaks are the bane of the diesel fuel system. I chased leaks for MONTHS, I can rack up 500 hrs in a year, if you're only running a couple hours a month, it can be worse. There is no magic bullet. It's trial and error, and it's a tedious process of elimination. The clear tube is the most effective tool. Suspect filters, valves, threaded connections, flare connections, manifolds, in that order. Any fitting that shows a sheen is a suspect. Clean it all up with simple green to remove all traces of fuel, then look for a shiny spot. A dirty engine room makes it real hard to locate problems. Don't use cheap valves, make sure they're vacuum rated.
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Old 08-17-2018, 09:35 AM   #18
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[QUOTE=CEC;690023]


Also the racor was full of air.
Should not happen. Air leak on Racor or fuel line from tank. Check Racor gaskets, check underside of lid for cracks, and replace fuel line from tank to Racor. Make sure you use properly sized clamps that do not distort the hose seal.


First thing I noticed no fuel came out when I cut the line.

Does the fuel line come from the tank top or bottom? Your symptoms say top. Fuel line empty. Even blocked off at tank, like your finger over the top end of a straw, some fuel will come out unless empty.



I used the bulb in revers to blow back into the tank quit a bit to check flow. Seemed fine no restriction. I put the bulb back the right way and pumped about a gallon of fuel through the racor with lid off and drain open. Seemed to flush it well.

Proves no longer restricted IF it was.



Seems strange the air would be in the racor and the motor filter, but I guess if the line to the racor from the tank is draining back into the tank it would seem I have an air leak between the racor and the tank right??
Not strange at all for an air leak. Is it uphill from the tank to the Racor? How do you fill it?
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Old 08-17-2018, 01:28 PM   #19
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To all of your replies:


The racor was not rebuilt just cleaned the lid and channel for gasket. New gasket and new T handle gasket. I put the T handle guage in last night. Thinking the check ball in the racor could be the issue so I put the squeeze bulb tank side of the racor as a anti siphon to see if the line empty's between the tank and the bulb. The shut off valve is above the squeeze bulb and yea the tank level is below the racor and the lines are above the racor. The shut off valve is at the top of the system up at the top of the tanks level.


The clear tubing is going to be used today. I'm suspicious of the three gate valves in series and the hoses up there. If I use the squeeze bulb tonight and air comes out it means the line to the tank has lost its prime and I think my issues lye's tank side of the squeeze bulb.


The reason I'm suspecting the lines and valves tank side of the bulb is I did not like the feel or sound of the squeeze bulb. Like Maerin said its becoming the puzzle I never thought Id have. I'm trying to segment the system to rule things out. There's a chicken and the egg thing going on with this fuel system.


Its my assumption that there needs to be fuel in the lines from the pickup tube at the bottom of the tank all the way to the injector pump at all times no air right? Loose prime in the pickup line and air is in the line coming from the tank. It then it moves to the racor and gets sucked into the lift pump once the racor is sucking air. Is the racor ball check the only thing that accomplishes that or is there (or supposed to be) an anti siphon valve in the pickup elbow on the tank?


If there's an anti siphon valve in the pickup why was I so easily able to blow backwards into the tank with the bulb? The hose I cut for the bulb that had no fuel was 10" below the shutoff gate. If I replace the line from tank to racor Ill be replacing all of the gate valves as well. Ill know more tonight Ill post up what I find.


Thanks for the help everyone.
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Old 08-17-2018, 01:41 PM   #20
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A packing leak of air into the fuel valve is a common leak. Are any of those gate valves very easy to turn? The hand wheel should have resistance to turning due to the packing. There should be a gland nut around the valve stem that can be tightened if necessary.
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