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1972 F250 4x4, 78 d60/d60, 3.55, np205, 200hp 4bt nv4500 superHX30w
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Discussion Starter · #1 ·
Changed fuel filter a week ago, filled it up. Bled line to banjo bolt used lift pump and clear tubing to make sure of no air. Bled filter to inj pump line, did numerous injector line bleeds at idle, leaving one at a time cracked for 10 seconds (with a rag close as possible to injector and fire extinguisher handy). I have done 2 sets of line bleeding.

Each day it runs ‘great’ until 15-20 minutes in when it starts to sound pulsating like an injector is missing and seems to idle somewhat rough. Sometimes it has shut off at idle fortunately after pulling into the driveway. Higher rpms pulsating/clang sound not as noticeable but lower rpms under load very noticeable and a bit rough under load. A while back before the fuel filter change there was a few times when it was sluggish at idle and it shut down at idle in traffic but started right up.

Usng the fancy hvlp lift pump from dieseltuff (with cummins part # scratched out), simple as possible AN fittings direct to tank. New Bosch injectors on rebuilt engine.

Other than going through all fittings and snugging them up does anyone have suggestions.
 

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Trying to isolate an air leak can often be quite a challenge. Might try a few things. First try to figure if the leak is before the lift pump or after. Disconnect the fuel supply from the tank and hook up a temporary supply. Might also install a short section of clear fuel line in the return. If when running you see air bubbles in that return then the issue is likely on the engine and not the fuel tank and feed lines. If the problem clears up then you know the issue is before the engine. If it is on the engine there are a couple places to check. The banjo bolts have 2 gaskets and a tiny crack in one could be the culprit. Also, a loose fitting fuel filter can be at fault. The weird thing about air leaks is you don't always see any fuel leakage. There could also be a tiny crack in a fuel line where the banjo fittings are. If the engine parts check out then the demon is elsewhere. Check all the hose clamps and of course the issue can be inside the fuel tank. Does you fuel return line go all the way to the bottom of the tank? Air has been known to feed back in that line. These are just a few ideas. This witch hunt often takes time.
 

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1972 F250 4x4, 78 d60/d60, 3.55, np205, 200hp 4bt nv4500 superHX30w
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194 Posts
Discussion Starter · #3 ·
Char1355, I appreciate the checklist for air in fuel lines. Funny thing is every single o ring and seal in the fuel lines was replaced and checked for correct assembly off the parts diagrams.

Before continuing the hunt, here is a sound recording of 1st, 2nd, 3rd, then 4th gear under load. The pulsing sound started after changing the fuel filter and as I've mentioned there's not as much power as before. The recording device was held on the gear shift knob so there is a bit of a vibrating sound made. I don't have a trained ear for diesel engines, does this sound like air in the fuel line(s) or something else before going further?

The pulsing sound is most pronounced about 26 seconds into the recording. If anyone had a moment to listen, I'd appreciate any comments on what you're hearing.

 

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If it started after a filter change then I would suspect the highest probability is with the filter. Two common filter related issues are either a mis aligned filter ring gasket or the old filter gasket remained stuck to the engine when the new filter was installed. Also check the center gasket on the threaded nipple that attaches the filter to the block. Then there is the problem which i experienced. Sometimes the attaching nipple will back out of the threads in the block. It does not take much to cause the filter's outer ring gasket not to completely seal. It feels tight but it really isn't. The older attaching nipples are torqued using a large flat blade screwdriver attachment to a ratchet. The newer ones are keyed for an allen wrench.
 

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1972 F250 4x4, 78 d60/d60, 3.55, np205, 200hp 4bt nv4500 superHX30w
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Discussion Starter · #5 ·
I Appreciate the suggestions to check gaskets and tighten threaded portion, thanks.

Time for me to get the step ladder and show some serious plumber's rear end. Sometimes I consider buying a special tool like a 'topend creeper' but then the cost and finding the space to store it limits that.

Automotive parking light Tire Vehicle Wheel Motor vehicle
 

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Hook the engine up to a separate gas can trust me. I fought a issue pretty similar to this and it ended up being nothing to do with engine and all to do with the tank and lines to the engine. It's really easy and I wish I would have tried that first would have saved me months of frustration.
 

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1972 F250 4x4, 78 d60/d60, 3.55, np205, 200hp 4bt nv4500 superHX30w
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194 Posts
Discussion Starter · #7 ·
Thanks Dr1rrr. I have a clear line on the return off the engine to a tank. Lift pump connected to truck fuel tank. No air bubbles in clear return line, solid column of fuel.

Am I correct that any air leak would result in bubbles in the return line?

I understand that tank to lift pump would be a vacuum air leak condition, anything from lift pump to injectors would be high pressure fuel leak.
 

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honestly what you are saying in theory sounds correct but I would still strongly urge you to hook the feed and return up to a separate tank or gas can. I'm not sure how difficult that would be in you particular situation but that is the best way to eliminate the fuel system in the truck the engine is put in. I fought something like this and drove myself dang near crazy thinking something was wrong with my engine itself. I was extremely irritated considering Cummins engines are some of if not the most reliable engines ever made and of course my luck, I got lemon but I should have listened to my own advise it had 0% to do with the engine and everything to do with fuel system even though I would have swore that couldn't be the problem.
 

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if you do find a solution it would be greatly appreciated if you updated what was actually wrong to help others in the future I definitely don't want some to go what I went through for such a simple dumb issue
 

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1972 F250 4x4, 78 d60/d60, 3.55, np205, 200hp 4bt nv4500 superHX30w
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194 Posts
Discussion Starter · #10 · (Edited)
Ended up checking fuel pump inlet screen, didn't see any problems. On this bleeding procedure did a 'most thorough' bleed, and it appears to be running consistently well. Clear tubing on return line and top fuel banjo bolt. Loosened / bled fuel filter, top banjo bolt, inj pump inlet, then idling injector lines. Did it all a 2nd time, probably pressed priming bulb 300 times running maybe 3 gallons through the system. Fuel return goes to the bottom of the tank using old 5/16 gas supply line maybe 6" away from the supply line.

With new fittings and lines, didn't want to tear into it assuming it's good and snug before doing a most thorough bleed procedure. I believe the solution has been to do this extremely thorough bleed procedure. I didn't do as thorough the first time and got by OK. Power is back up and noise back down even though it's a little smoky at idle.
 

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hopefully that is the fix one thing I did with mine to to help eliminate parts on the engine itself was i pulled all the injector lines completely off and vacuum tested them with a hand held vacuum pump which in my case showed no problems but could be something to try in the future if this problem persists.
 

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hopefully that is the fix one thing I did with mine to to help eliminate parts on the engine itself was i pulled all the injector lines completely off and vacuum tested them with a hand held vacuum pump which in my case showed no problems but could be something to try in the future if this problem persists.
Why would you vacuum test the injector lines? If there is a leak in them you will have fuel everywhere.
 

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Not necessarily I haven't seen this on diesel engines yet mainly cause im fairly new to them but I have seen very high pressure hydraulic lines have extremely small cracks on the side that is pressurized and when you put positive pressure to them you can't find any leaks but under a vacuum you can I've also seen that very same situation allow air in even though the line had positive pressure it's only happened to me a hand full of times but a vacuum pump is a easy cheap way to diagnose it. I know that sounds not possible I wouldn't believe it if I hadn't seen it happen for myself but I would assume something similar could happen to injector lines
 
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