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STILL battling fuel gremlins


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let me start with this:mad: and this:banghead:...................ok now moving oni had problems with my truck somehow letting a tiny bit of air in....so i posted a thread before and all fingers pointed to the teflon tape i used on the fittings of the draw straw.so....i purchased myself a can of permatex prepping solution, and a tube of the high temp thread sealant. I sealed all the treads at the draw straw, and the one fitting at the pre filter. I allowed it 72 hours to dry and fired it, and it ran fine. I shut it down after 3 mins of running and started it back up 2 minutes later, same thing fired then chugged like it was missing for about 5 seconds. Today i came home and changed the fuel filter and to my suprise i found this..........post-10727-138698185497_thumb.jpgmy fuel filter looked more like an oil filter, it had black sludge all over it.post-10727-138698185505_thumb.jpg the truck has 168xxx on it and i dont know if the fuel filter was every changed, it sure didnt look like it. But the fun didnt stop there......post-10727-138698185513_thumb.jpgyep thats METAL SHAVINGS in the bottom of my filter housing. i have no idea how in the world they got there. bottom line is the fuel filters fresh and it started and ran fine. im going to go back out and start it again in an hour to see what it does. the one question i had is this, in doing all the things ive done thus far wih the fuel system, i havent removed the pre filter. if i start it and it runs like crap again does this mean that my pre filter could possibly be clogged???? i read alot about guys taking them off and never really finding anything in them.

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You seem unsure of when it was changed last so I am guessing you just got the truck. The previous owner could have been running waste motor oil (WMO) or something. If the screen in the prefilter is cracked (like mine) then the metal shards could get through and end up in the fuel filter. If he was running WMO, then shards are not exactly rare when people drain their oil. That would explain everything. If the prefilter isn't cracked then shards that big wouldn't be able to pass through the prefilter so that would mean the shards are coming from the fuel filter housing, prefilter assembly, or the lift pump. If it were me, I would clean the fuel tank (if you didn't already when you messed with the pickup tube) and change the fuel filter (think you just did) and inspect the lift pump/prefilter assembly. Then I would see how it runs.

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Isx- i did not clean the tank as it still has a 1/2 tank of fuel in it. I guess ill have to pull the pre filter off because i went out and startedit this morning and same results. Fired up then did the chug again. Ill have a video in an hour or so

--- Update to the previous post...

OTHER NOTES- there was never WMO run through this pickup. i talked to my uncle whos the second owner and after he bought it and started his company he gave the truck to one of his workers. he said it doesnt sound un likely that the fuel filter was never changed.

ISX- also i was curious, would you pull the whole LP and pre filter assembly or could i get away with just pulling the sediment bowl off ??? and do i need a new screen or anthing or can i just pull it clean it and put it back on.

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If it didn't have WMO run through it then thats not good since it probably means something is broken or cracked. I have some ideas but yes you can just take the screen off since it just unscrews and see if you have any metal in there or see if it is broken. That will give us some more clues.

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so today i took off the pre filter to check it out. this is what i foundpost-10727-138698185615_thumb.jpgpost-10727-138698185623_thumb.jpgpost-10727-138698185631_thumb.jpgpost-10727-13869818564_thumb.jpgnot exactly sure what was in pic 3. it looks like algae which i guess is possible seeing as how the truck sat a little while. in pic 4 that was a little bit of metal shavings and general dirt. all in all there really wasnt much in there as compared to the fuel filter. i got a great video of start up today and it really chugged for a good few seconds. ill have that posted up in a little bit. i have yet to re install the pre filter, im curious to know if i should check anything else.

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Not good. I would take the whole lift pump off and inspect it, only 2 bolts. They are a PITA 2 bolts well the center one is but easy enough. The problem I see is that there is nothing in the prefilter but there are metal shavings in the fuel filter and the only thing between the 2 is the fuel filter housing itself and the lift pump so one of those has to have shed the metal shavings and might be the culprit to where the oil is coming from since the lift pump is in direct contact with oil slinging around. It would be hard pressed to say it is sucking in oil but who knows, I would take it off and inspect it though. The fuel heater/prefilter comes apart moreso as well, you will see when you take the lift pump off since they are kinda attached to each other so you will be taking both out.

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Maybe. Sometimes the air leaks are a pain to find. It's just really weird that you have oil in the fuel filter. The lift pump really wouldn't be able to ingest oil and be able to pump fuel unless it had some sort of weird crack in the plunger. When you take the lift pump out, you can pull the plunger that rides the cam right out. I usually put a light coating of grease on mine and it seems to help it be quiet, though I think it just gets washed off but you will see what I'm talking about. Actually heres a vid I made a while back.

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to be honest i wasnt really concerned with the fuel filter condition, because it sat for so long and i was in question as to if it was ever changed. but now you have me curious, and a bit worried. ill see what i find tomorrow when i pull the lift pump. im hoping that it ends up being my air in fuel problem, i cant even begin to think what else could be letting air in as everything BRAND new and sealed well from tank to pre filter.

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They get black over time but that's because they get dirty from whatever is in the diesel fuel. Contaminants and things. NOT oil. Your fuel filter looks the same as mine exept the plastic is not coated in the black film as well and I cannot get oil on my fingers like you did and that is what concerns me. It is oil and not fuel contaminants. If he ran trans fluid in it as an additive or any other kind of oily thing then that might have done it as well. But the metal shavings is really a big concern to me. I forgot to mention you will probably have to take the fuel filter housing off as well (verrry easy) and then you can inspect the bottom of it as well (take the fuel filter off and look). If everything looks fine then the shavings might have been just from him crossthreading the banjo bolt in the housing and shearing some threads and the oil could be a time he forgot about when he added something thick like that. I mean if it all looks perfectly fine then what is there to fix. The air leak isn't really cause for concern too much if everything looks good when you inspect it. Mine chugs when I park it uphill and let it sit, even after replacing every return line copper washer and all the banjo bolt seals. I haven't touched anything behind the engine though so it could be something farther back. It's just one of those things that you can chase your tail forever on.

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gAg0bLW_a2Clfff6E4lVXrgupdnW7HY=ISX-this is what i was talking about with the chug. this is a video i shot today, coming off 24 hours of sitting un- fired. it sounds like a miss, you can see it in the Tach, it starts adn runs ok for a second or two, and then goes to crap , and back to normal after a few seconds.
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Yeah that's just purging air, mine does the same thing. Park it downhill and it won't do it. Actually mine almost dies so I gotta get to the road before it hits the air bubble so that the truck moving can drive the engine/lift pump when it starts to die. I hold it to the floor as it's chugging and coughing and the rolling truck being left in gear keeps the engine going so it keeps everything pumping until it gets the air out. I'm wondering if a check valve in the return line right at the back of the engine where it goes to a rubber line would fix this cause everything on the engine is new now. Maybe a check valve on the incoming fuel as well. Anyhow I think you might have 2 different issues so I would do what I said and check everything out. If everything is good then what more can you do other than find that air leak.

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Everything looked good there. That primer boot is just for show, you can actually it right off and see the white thing under it. There is an o-ring around that white thing that sometimes gets worn out and lets air in. That fuel heater can be taken apart further but having no moving parts it probably isn't going to be shedding metal shavings lol. I would check out the fuel filter housing underneath part for any signs. Other than that you can't really do anything else. Not sure how they got in there. I'm just going to guess that sometime during it's life someone stripped some threads between the lift pump and the fuel filter and left shavings behind :shrug: I would also venture to say they added something to the fuel tank at one time to do the oil on the fuel filter. Have you changed the oil in it yet and if so was the oil all the regular black crap with nothing else in it? See if the fuel is perfectly green when you take the fuel filter off to check out the housing, as in no oil in it. I want to check out some things myself so I am gonna go out and take my lift pump/fuel filter housing off as well right now.

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thanks again ISX.im wondering if its worth replacing the LP just incase, but i guess if it works fine then it cant hurt. ill take the filter off tomorrow and take another look at it now that it ran about 5 minutes since i replaced it. I think im going to take a mirror and check the underside of the filter housing, i dont feel like replacing all the copper washers quite yet as i have some other work that needs to be done. also i was curious is there ANY good way to scrape the gasket off the block? i stuffed a rag in the cam hole, i was thinking of putting RTV on the back of the pre filter assy. that mates to the block but i know if i do that with my luck itll end in a leak. And do small block chevy fuel pump gaskets work with these LP's like they did my first gen?these problems are really beating me up man, im a young guy who just wants to drive the "new truck" ive had sitting in my driveway for a year. its just really frustrating working my butt off the get this truck driving and theres always some monkey wrench thrown in my plan. :cry:

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If it runs fine after that initial stutter then I wouldn't replace anything. The mirror deal would work. I really think it must be nothing since it runs fine and am betting on the things I said in my last post. If you don't find anything there then I would hook everything back up and drive it. I am going to do some advanced NASA engineering and figure out how to find these air leaks. I seem to have several but I notice my return lines are leaking so I guess I need to tighten them more. Copper takes some finess to get it to seal right. The lift pump probably seals the same as a 1st gen lift pump so I wouldn't see any reason why the chevy gasket thing wouldn't work. Don't worry about it breaking on your or anything, the filter did it's job and stopped the metal shavings from wherever they came from and the lift pump is obviously still pumping so I wouldn't break a sweat. When I got my truck I didn't know a thing about it and the next day it wouldn't start. I had no clue what to do but read and read and figured out what the fuel shutoff solenoid was and found the wire going to the battery was corroded and just happened to fall off the terminal completely the day after I bought it. Then the whole truck just started to fascinate me. I have taken the engine out for basically no reason, same with the trans and just about every part on the engine I have taken off for no reason, just to learn about it. You have the same truck and if you ever tinker with it like I did you will figure out that there is basically nothing that will go wrong with it. As long as it has oil and it starts in the morning, your pretty well guaranteed it will work until you turn it back off. These little air leak gremlins are the only things that get you and they are just a sign of age or working on it too much. I really enjoy any issue my truck has. Its a chance to take stuff apart and learn about it and why whatever failed failed.

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ISX- i understand where you are coming from. my first gen was my first vehicle ever and i did countless things too it, and modded it and dolled it all up. and i LOVED every second of it.....okay maybe not EVERY but most. that's why when i sold it, it only took me 2 weeks to jump into buying this one. I think the other reason i love owning a cummins so much is not just because its an amazing engine, but because of the people you get to meet and interact with, much like yourself.i appreciate all the help you've given me in this thread, and in others. i look forward to you NASA engineering project :lol: and i cant wait to see what you come up with. thanks again NICK

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I just took the lift pump completely apart, even the main pumping side of it. It's very interesting and I got video and stuff I'll have to show you. Basically the fuel will NOT backflow through the lift pump. I think my problem is that on an uphill (only time it happens) the air is allowed into the return lines (fuel leaks out) and when you start it (always starts fine) it eventually sucks the air into the fuel filter (if you trace the injector returns they go to the fuel filter, not to the fuel tank, so any air goes right to the filter then injection pump then chug chug chug) causing all the chugging until it purges it. The return lines are pressurized so fuel leaks out while running so it doesn't really let air in until I turn it off and park uphill. On a downhill the fuel in the return line "rail" may dry up but only until it makes the bend to the fuel filter and since that is higher than it, it cannot let fuel continue to replace fuel with air. Check valves would all solve this if they made them for banjo bolts. I think a way to test would be to just take the return line rubber hose off and put your own rubber hose on it and supply 40psi and just start spraying soap on all the fittings. Only problem is that it goes straight to the overflow and it would just keep the thing shut since it is pushing the ball in there shut. I do have a crappy overflow with no balls though so I would stick that in for testing purposes, though the overflow itself could be a possible leak as well. Actualllllllly, I got it. This is really NASA engineered lol. There are 2 fuel inlet ports on the P7100, one of which is unused and is on the front of the pump behind the timing cover. If you put an elbow in there with a simple barb fitting or even get fancy and put an air hose for an air compressor fitting in there so you could just unhook it when your done but hook the air hose to it and set the regulator on the compressor for 40psi. The overflow on the truck is once again a problem so you would take the rubber line off the steel line that goes to the overflow and use your own rubber hose that goes to a 50psi blow off valve (just in case, high pressure can crack the fuel filter housing, though I think it might even take more than 50) so the overflow could open but would just go to your blow off valve so the entire system would be pressurized. This would only get to the lift pump and not the fuel heater which is another common air leak but you can actually use a clear rubber hose between the fuel heater and the lift pump (replacing that 3" little piece of crap) and then you could watch the air bubbles. I'll put this contraption together tomorrow and see what I can see. Hope diesel doesn't eat those air line connector o rings.

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I've been following along with this... I'm still borthered by the color of the filter housing I really do wonder if some added a batch of waste engine oil just once. It would possibly explain where the metals came from. The only other though would to drop the fuel tank and inspect the tank for more debris and that would answer the metal problem.I know ISX is the guru of 12V and you great man helping you... :smart:

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Hard to tell from the video,but does it run rough then smooth out then run rough then run smooth and continue this pattern? If so you have an air leak. Put a peice of clear plastic hose(long enough so you can see it several feet long ) where your lines from the tank conect to the fuel filter. Pump your lift pump. The lift pump should pull fuel through the clear hose from the tank. If it does not pull fuel you have an air leak ,big leak. If it pulls fuel through the clear hose but has bubbles in the hose(bubbles =air), you have a small air leak. Do not drive around with the clear hose,this is only for testing. It is late hope this makes scence I am half a sleep.Sent from my SCH-I405 using Tapatalk

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