Roadpower Posted December 2, 2021 Share Posted December 2, 2021 Greetings all, this is my first post on this forum. 2011 Pinnacle CXU 12.7L to the best of my current knowledge. The motor can be manually primed and will start almost immediately when this is done (when already warm, when cold it takes a little longer but that is to be expected). If the engine is not primed then the starting will be very protracted which is obviously not good. My do everything non specialist diesel mechanic has already replaced two fuel check valves to no effect. Current dialogue is either fuel pump or an injector problem. The owner of the truck just found a bulletin that states changing fuel pump won't help issue and something about a weep hole. Searching around I found something about a transfer pump. So needless to say I am at this point lost for a clue of what direction to go in. This truck must get sold next year anyway due to coming fleet rules but I need it to work reliably for this last peak season. Any help provided is greatly appreciated. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/ Share on other sites More sharing options...
Popular Post fjh Posted December 2, 2021 Popular Post Share Posted December 2, 2021 the complaint you have sounds like injector cup issues These tend to have issues with injectors leaking compression into the fuel gallery! 2 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483905 Share on other sites More sharing options...
Roadpower Posted December 2, 2021 Author Share Posted December 2, 2021 18 minutes ago, fjh said: the complaint you have sounds like injector cup issues These tend to have issues with injectors leaking compression into the fuel gallery! Thank you, searching I found a thread on this topic. From my reading there it appears that if it is indeed the cups then solving this is probably not going to be the kind of solution I had hoped for, but I'm going to ask my mechanic for a price anyway. On another note I find the symptoms interesting because the loss of pressure is so rapid but yet does not appear to be an issue when the engine is running. I can feel the total loss of pressure at the primer pump until I stroke it a few times and then the pressure builds, I think it takes about 8 to 10 strokes to get it to the point where it is very stiff to push back down into the lock notch. Thank you fjh 🙂 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483907 Share on other sites More sharing options...
Onyx610 Posted December 2, 2021 Share Posted December 2, 2021 We had and 08 MP7 with bad cups. Very Extended start times but otherwise ran fine after start up. Also the oil level was growing. Ended up replacing the cups and 3 injectors. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483908 Share on other sites More sharing options...
Roadpower Posted December 2, 2021 Author Share Posted December 2, 2021 3 minutes ago, Onyx610 said: We had and 08 MP7 with bad cups. Very Extended start times but otherwise ran fine after start up. Ended up replacing the cups and 3 injectors. Thank you. We have 748K miles on this truck. I'm wondering if we can get another 35K ish out of it in its current condition. Not that I'm asking you directly, I'm just wondering out loud. Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483910 Share on other sites More sharing options...
Onyx610 Posted December 2, 2021 Share Posted December 2, 2021 Consider yourself lucky, ours happened at 9k miles. Highly doubt you will be able to get much more out of it. I could be wrong though. Ours was all from one cup leaking. I looked back to see what was done and all six injectors were replaced as they need to be for the updated “steel conical” cups. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483911 Share on other sites More sharing options...
Roadpower Posted December 2, 2021 Author Share Posted December 2, 2021 6 minutes ago, Onyx610 said: Consider yourself lucky, ours happened at 9k miles. Highly doubt you will be able to get much more out of it. I could be wrong though. Ours was all from one cup leaking. I looked back to see what was done and all six injectors were replaced as they need to be for the updated “steel conical” cups. I assume you mean 90k but even still your point is well taken. I have been getting increasingly worried about this truck because of this issue seems to be slowly getting worse. The part that has confused me up to this point is the fact that it seemingly runs well once started. Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483915 Share on other sites More sharing options...
Onyx610 Posted December 2, 2021 Share Posted December 2, 2021 No you read 9k right…🤣 keep an eye on oil level, could be injector(s) 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483916 Share on other sites More sharing options...
Roadpower Posted December 2, 2021 Author Share Posted December 2, 2021 Just now, Onyx610 said: No you read 9k right…🤣 9k?? Yikes... Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483917 Share on other sites More sharing options...
Onyx610 Posted December 2, 2021 Share Posted December 2, 2021 By the way fjh is reallllly good with this stuff along with a handful of others on here. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483919 Share on other sites More sharing options...
Roadpower Posted December 2, 2021 Author Share Posted December 2, 2021 I'm going to ask my mechanic if an inspection will yield any useful info. Thanks all, I really appreciate the feedback. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483921 Share on other sites More sharing options...
Onyx610 Posted December 2, 2021 Share Posted December 2, 2021 Cool, keep in touch. A few of the other guys I was talking about will probably chime in with some solid advice. 🍻 2 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483923 Share on other sites More sharing options...
Roadpower Posted December 2, 2021 Author Share Posted December 2, 2021 12 minutes ago, Onyx610 said: Cool, keep in touch. A few of the other guys I was talking about will probably chime in with some solid advice. 🍻 Thanks, will do. Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483924 Share on other sites More sharing options...
Popular Post fjh Posted December 2, 2021 Popular Post Share Posted December 2, 2021 (edited) 1 hour ago, Onyx610 said: By the way fjh is reallllly good with this stuff along with a handful of others on here. Thanx however ! I will correct you Onyx! I am only a messenger on these new engines I do NOT Work on them or (Try not to)! I Am how ever around them All day long and pick up on (MOST )of the fixes going on in our shop ! To be an expert on these you have to work on them trouble shoot them on a daily basis !I just pass on what I have been seeing and how we are dealing with this rubbish! Also Roadpower observe This condition may worsen after hard pulls just putting around town with no load it may lessen in severity !this will confirm or solidify the diagnostic ! Just sayin Edited December 2, 2021 by fjh 2 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483926 Share on other sites More sharing options...
Roadpower Posted December 2, 2021 Author Share Posted December 2, 2021 24 minutes ago, fjh said: This condition may worsen after hard pulls just putting around town with no load it may lessen in severity !this will confirm or solidify the diagnostic ! Just sayin Thank you. Typically this truck (route) pulls light loads on mostly level ground but peak season will (and is) definitely see the weight increase. I will be keeping close contact with the driver to monitor the situation. Worse comes to worse I will have to put the driver into another truck but I'm avoiding that as much as I can for a variety of reasons. The plan was for a replacement unit next year but we may not have that long. Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483929 Share on other sites More sharing options...
steeler Posted December 3, 2021 Share Posted December 3, 2021 Usually when the cups start leaking, it will run fine after you get it started. I've seen engines with 3 Badly leaking cups run great, just hard to start. When it gets to the point you start noticing an engine miss under load, that's when you're running out of time with them. Sadly there really isn't any way to get by on the cheap. Pretty much just fix it or run it. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483975 Share on other sites More sharing options...
Popular Post Joey Mack Posted December 3, 2021 Popular Post Share Posted December 3, 2021 any chance you have access to a banjo fitting that is the right size to fit the fuel pressure regulator on the front of the head?, if so, you can attach a clear hose to it that is long enough to go back to the filler cap and in the fuel tank, down into fuel, run the engine and see if there is air in the returned fuel. it will look like suds/ beer foam.. make sure the line is in the fuel so you can see the bubbles in the fuel. if you see a lot of air, darn good chance the injector cup o-rings have failed.. There really isnt any repair shortcut's for this issue. If you cut corners, you will just be 'pissin in the wind'... jojo 2 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483982 Share on other sites More sharing options...
Roadpower Posted December 3, 2021 Author Share Posted December 3, 2021 7 hours ago, steeler said: When it gets to the point you start noticing an engine miss under load, that's when you're running out of time with them. Thank you, that is very useful to know for monitoring this situation. Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483986 Share on other sites More sharing options...
Roadpower Posted December 3, 2021 Author Share Posted December 3, 2021 1 hour ago, Joey Mack said: any chance you have access to a banjo fitting that is the right size to fit the fuel pressure regulator on the front of the head?, if so, you can attach a clear hose to it that is long enough to go back to the filler cap and in the fuel tank, down into fuel, run the engine and see if there is air in the returned fuel. it will look like suds/ beer foam.. make sure the line is in the fuel so you can see the bubbles in the fuel. if you see a lot of air, darn good chance the injector cup o-rings have failed.. There really isnt any repair shortcut's for this issue. If you cut corners, you will just be 'pissin in the wind'... jojo I looked up banjo fitting. I've seen those many times but I wasn't aware of the name. I mostly understand what your doing here but I'm not sure why the line has to return all the way to the fuel tank and not just a nearby jug, unless it is the length of the line that is useful for seeing the bubbles/foam? (Forgive me, I'm the curious type as I like to understand the process.) I'm going to show this to my mechanic, I suspect that he will find it educational info. Thanks Jojo! Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483987 Share on other sites More sharing options...
Popular Post Onyx610 Posted December 3, 2021 Popular Post Share Posted December 3, 2021 Yea, it’s to help really see the agitation. Plus it’s just easy to return the fuel back to where it came from and let it repeat the process as long as you would like. 3 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483988 Share on other sites More sharing options...
Popular Post Vmac3 Posted December 3, 2021 Popular Post Share Posted December 3, 2021 Does this vehicle have a primary fuel filter (fuel water separator) Davco or Racor type brand? If the primary side (suction side of the fuel system has a breach, then the symptoms will be identical as bad injector cups. I am not saying that the cups are a wrong diagnostic, I am just saying that there are other issues that will cause the same issue. Just make sure you get the correct diagnostics done as mentioned above. V 1 2 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-483990 Share on other sites More sharing options...
Roadpower Posted December 3, 2021 Author Share Posted December 3, 2021 2 hours ago, Vmac3 said: Does this vehicle have a primary fuel filter (fuel water separator) Davco or Racor type brand? If the primary side (suction side of the fuel system has a breach, then the symptoms will be identical as bad injector cups. I am not saying that the cups are a wrong diagnostic, I am just saying that there are other issues that will cause the same issue. Just make sure you get the correct diagnostics done as mentioned above. V I'm going to look into this means of diagnoses. Thank you V. Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-484000 Share on other sites More sharing options...
Joey Mack Posted December 3, 2021 Share Posted December 3, 2021 a 'jug cant handle the volume of fuel that will be pumped... 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-484010 Share on other sites More sharing options...
Onyx610 Posted December 4, 2021 Share Posted December 4, 2021 3 hours ago, Joey Mack said: a 'jug cant handle the volume of fuel that will be pumped... Yup, more then likely what would be heard is “Shut it off! Shut it offf!!” 2 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-484034 Share on other sites More sharing options...
Joey Mack Posted December 4, 2021 Share Posted December 4, 2021 Amen! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/68861-rapid-fuel-system-pressure-loss-after-shutdown/#findComment-484035 Share on other sites More sharing options...
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