Ahubbard Posted June 9, 2019 Share Posted June 9, 2019 Hey guys, I have a 1994 EM7-300 PLN fully mechanical motor in my truck. I am having a problem with the fuel. It is not as noticeable when the truck is cold in the mornings but after I work the truck for a while it gets pretty distinct. It will do it when it is cold but sort of clears up quickly, when warmed up I can set the throttle lock at 1200 and it keeps doing it continuously. The engine shakes/misfires around 1200 rpm. It sort of sounds like it is running out of fuel. Smooth at idle, runs good above that rpm. I put a gauge on the supply line going into the injector pump and have about 20psi at all rpm. Not sure what I should have there. After work Friday I set the throttle lock to 1200 and cracked open injector lines. They all chugged the motor good but #1 not as much. I swapped #1 and #3 injectors and that did not change. Cracking #1 still sounded like less of a chug. I started to think that maybe because #1 is farthest away from fuel supply that it wasn’t getting enough fuel. While checking things over again I see air bubbles in the return line. I have a clearish plastic/rubber hose on there and I can see through. Actually there doesnt seem to be air in the return from the head to the back side of the pump. But there is air in the short line form the back side of the pump to the front where the return check valve is. If I link that line off while the truck is running at 1200 it seems noticeably smooth up. Is that because I am cutting off those air bubbles or does linking that off raise the pressure and help keep it from running out of fuel? Anyway I am going to put new return lines on today and make sure that they are good and tight on the fittings. Also, I see that the return fitting on my side of the pump is a check valve with a spring in it. What is on the back side in by the engine where those 2 return lines meet? It is like a Y fitting where the return line comes from the head then a short line comes around to the front. Is there some sort of check valve in that too? Any knowledge of what I am looking at would be great!! Also any ideas of thinks I am not thinking to look at. I want to start with bigmacktrucks first! Any shops around I think will throw in injectors then if that’s not it try a new injection pump. I don’t have the $$ to be just guessing at big parts and downtime. I want to get it diagnosed first. Thanks Guys!! Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/ Share on other sites More sharing options...
Ahubbard Posted June 9, 2019 Author Share Posted June 9, 2019 Oh man I meant Kink the return line not link it. Damn autocorrect lol This line has airWhat is this ? Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-424884 Share on other sites More sharing options...
Ahubbard Posted June 9, 2019 Author Share Posted June 9, 2019 After further inspection that 2 prong banjo fitting just has a small orifice behind it. Nothing seemed blocked there. I looked harder at the return line from the head and am not really getting any fuel coming back through that line. Just the first couple inches have fuel in it. But that lower line flows a ton of air through it. I ran the suction line into a pail of diesel and then also ran it with the outlet line from the lift pump direct to the injection pump. No change either way. Is my lift pump or flowing enough or should I be thinking something with the injection pump? Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-424901 Share on other sites More sharing options...
Mack Technician Posted June 9, 2019 Share Posted June 9, 2019 (edited) Don’t have the pressure spec for that engines fuel lift, someone does, sounds about right, at low end of good spec, to me off the top of my head. In the old days they bridged each injector for internal spill fuel returning to tank. Now you just have that one circuit plus a head crossover tube. Those little tubes have a tendency (actually are notorious for) to leak and let fuel drain away from the pump back to tank and lose prime. Cracked stand pipe in the tank is also a possibility for air leak under suction. Fuel is swaying in the tank all day, against the stand pipe, trying to flex it. Time can take a toll. If your maintaining 20 psi at the pump rail your lift is providing enough volume of fuel. if you have a system pushing air through you will want to also consider replacing all fuel lines before the transfer lift pump. After pump they leak fuel with a hole in line, before transfer they suck air into system with a hole in line... and drain back causing hard start. Be cautious about using certain hyd lines as fuel line replacements. Hyd psi lines are not engineered to experience suction, suction lines are. It’s surprisingly easy to pull the inner liner of a hyd psi line into a drawn-collapse due to engineering. Edited June 9, 2019 by Mack Technician Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-424907 Share on other sites More sharing options...
Ahubbard Posted June 9, 2019 Author Share Posted June 9, 2019 Just now I pulled the return line off my head. I put my thumb over the line to keep fuel from feeding back from the pump. It cleared up the air in that lower line. I am getting no fuel out of the front head. There is pressure there when I put my thumb over but no fuel. I took the little crossover to tube off from between the heads. Ran truck with it off. Back head consistently spills fuel out and front head has nothing. Unless I put my thumb over it then I get a big shot of air and a small surge of fuel when I let my thumb off. Is it possible to have a bad injector or cup that is letting compression in the system causing my air problem in the return lines and pump? Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-424908 Share on other sites More sharing options...
Mack Technician Posted June 9, 2019 Share Posted June 9, 2019 Don’t give much thought to injector cups on your engine. God bless it, you got a good engine Volvo didn’t screw up. Think leaking copper fire ring @ nozzle tip. Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-424911 Share on other sites More sharing options...
Ahubbard Posted June 9, 2019 Author Share Posted June 9, 2019 I think I am pretty set that I have a problem there and I should pull injectors and see what’s up. They do have 25,000 hours on them. I just didn’t want to jump to conclusions and not diagnose. I feel like if taking that return line off the head eliminates the air cycling around my injection pump then I probably have narrowed it down to injectors. Too bad...I should have planned ahead. Last winter would have been a good time to do injectors. Dump truck suppose to be running in summer!!!! Thanks for the help I will keep you posted what I find. I figured I had a lot of information but I didn’t know exactly how to use it. Guys in here always seem to know their stuff!!Sent from my iPhone using Tapatalk 1 Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-424912 Share on other sites More sharing options...
Mack Technician Posted June 9, 2019 Share Posted June 9, 2019 25,000 hours on the injectors!!!! Man I still love Renault’s PLN... Your not lacking anything on your analytics. Everything you’ve said so far, down to cylinder closest to return being affected by combustion air intrusion makes perfect sense. Be sure you put a closer on this thread. Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-424921 Share on other sites More sharing options...
Ahubbard Posted June 11, 2019 Author Share Posted June 11, 2019 Ok... here we go. I took a trip to Antrim Diesel today. Kevin checked my injectors and didn’t find one good one. Lol. MAYBE number 6 was decent but still bad. #1 and #2 were terrible. Think just streaming fuel on the pop tester. Yikes. Guess I got my use out of those. Traded them in for a reman set he had on the shelf that have a little better flow. Came home this afternoon and installed them. That solved my return fuel problem. Nice clear fuel with no bubbles in the return line. Took that running out of fuel sound away. But I still have the shake/chug at 1200 rpm. That’s a little frustrating. Can’t figure out why it is at only one specific rpm. Smooth as silk at idle. And smooth above that..even at 1250 for example. Wonder if this could be in the pump. Someone else suggested a cracked line between the pump and injector somewhere. I didn’t have them totally out I just backed the nuts out and pulled then back an inch to clear the injectors when I switched them. I should have picked kevins brain a little more about it at Antrim. But with a 4 hour ride one way I guess I got a little hurried to get home and install my new toys. I wish I could post a video here so you could hear it. On the bright side the new injectors are great! Test drive shows a noticeable power gain and I feel like (other than 1200 rpm) the engine has less vibration. Took my turbo boost pressure from about 28 psi to 35. Gotta watch the pyro harder now!!! Probably will have to get a bigger turbo... might as well have the pump worked over while they check it..... lol ANY MORE IDEAS?! I am going to work the truck tomorrow. Gonna have to keep running it. I am just not sure where to go from here. Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425077 Share on other sites More sharing options...
steeler Posted June 12, 2019 Share Posted June 12, 2019 1200 rpm? Sounds like it could be a resonant ride issue with the pump? Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425085 Share on other sites More sharing options...
Ahubbard Posted June 12, 2019 Author Share Posted June 12, 2019 1200 rpm? Sounds like it could be a resonant ride issue with the pump?I am not sure what this means Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425086 Share on other sites More sharing options...
Ahubbard Posted June 12, 2019 Author Share Posted June 12, 2019 Like governor fluctuating at this rpm?Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425087 Share on other sites More sharing options...
steeler Posted June 12, 2019 Share Posted June 12, 2019 Yes, resonant ride in the pump feels kinda like the fuel rack in the pump is bouncing back and forth, usually right around that rpm. I remember it being a big pain in the ass in the early/mid 90s at the dealership I worked at. Sent out many pumps for this problem, but rarely was it ever fixed. I remember Mack coming out with some kind of contraption that mounted to the front of the pump to fix it, but man its been a long time! Does yours almost feel like you are bouncing the throttle real fast at that rpm? And usually if the engine had a strain on it, you wouldn't feel it. Only happens when there is steady rpm with little to no strain on the engine. Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425089 Share on other sites More sharing options...
Ahubbard Posted June 12, 2019 Author Share Posted June 12, 2019 Yes I will get that feeling when I drive. Almost feels like the spring is too light on the throttle return even though it’s not. I will let my foot of the throttle some and lay back in to correct that sometimes. When this does it at 1200 it almost is like a horse galloping. Rhythmic and kinda shakes the motor. Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425090 Share on other sites More sharing options...
steeler Posted June 12, 2019 Share Posted June 12, 2019 1 minute ago, Ahubbard said: Yes I will get that feeling when I drive. Almost feels like the spring is too light on the throttle return even though it’s not. I will let my foot of the throttle some and lay back in to correct that sometimes. When this does it at 1200 it almost is like a horse galloping. Rhythmic and kinda shakes the motor. Sent from my iPhone using Tapatalk Yup sure sounds like resonant ride. Unfortunately I'm not sure there's much you can do to fix it. We've sent pumps out before, some were better, most weren't. I'll do some digging about that contraption Mack came out with. Maybe someone else here knows of a fix? Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425091 Share on other sites More sharing options...
Ahubbard Posted June 12, 2019 Author Share Posted June 12, 2019 My problem definitely isnt under load. It actually does it most prominently when I rev the motor up past 1200 and then let it back to 1200. Or for example when I come to a 35 mile per hour zone and don’t downshift if my foot is lightly pushing the pedal as i coast through it starts the gallop. Is there potential for this condition to damage anything if I run it? I am hoping to get through my busiest season and get to October/November before I take the pump off and send it to the shop. Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425093 Share on other sites More sharing options...
steeler Posted June 12, 2019 Share Posted June 12, 2019 No, it won't damage anything at all. It's just annoying. Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425096 Share on other sites More sharing options...
1965 Posted June 12, 2019 Share Posted June 12, 2019 Probably little hard on drive train, doing that bucking Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425099 Share on other sites More sharing options...
Ahubbard Posted June 12, 2019 Author Share Posted June 12, 2019 I appreciate all the help guys. We will get this fixed!!! I would love to get any info people have on a fix to this resonant ride problem... makes it easier when I talk to pump shop if I have an understanding about things. Sent from my iPhone using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425100 Share on other sites More sharing options...
Mack Technician Posted June 12, 2019 Share Posted June 12, 2019 14 hours ago, 1965 said: Probably little hard on drive train, doing that bucking Keeps torsion springs of clutch center plate in constant motion. Clutch life is usually determined by the spring life. Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-425134 Share on other sites More sharing options...
Ahubbard Posted January 10, 2020 Author Share Posted January 10, 2020 Hey I have somewhat of a conclusion to this thread. I traded the injection pump in for a reman one this week-Finally had some down time. This fixed the problem with my gallop at 1200 rpm. Haven’t had a load on yet but the test drive seemed to go fine. So I don’t know what specifically was the problem in the pump... probably something in the governor. Thing was worn out either way. Almost 26,000 hours on her. So I am a happy camper. I still have a bit of a shake/ vibration in the engine overall. Not sure what. It’s not bad but noticeable. Nothing that more time and $$$ can’t fix I suppose. I just wanted to follow up so the guys who were helping me diagnose could know that my gallop problem was in the injection pump. Resonant ride, worn parts, high speed and overload are my conclusion. Thanks again everyoneSent from my iPhone using Tapatalk 2 Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-439938 Share on other sites More sharing options...
Ahubbard Posted January 10, 2020 Author Share Posted January 10, 2020 Keeps torsion springs of clutch center plate in constant motion. Clutch life is usually determined by the spring life. I put a clutch in three weeks ago. That thing started making a bunch of chatter under there. Worn all to hell around those torsion springs when I got it out. That was old too... but this summer of running the truck this way didn’t do me any favors there I suppose. Sent from my iPhone using Tapatalk 1 Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-439939 Share on other sites More sharing options...
JoeH Posted January 10, 2020 Share Posted January 10, 2020 Interesting to read about the resonant ride... Might explain that weird flutter my 95 e7-350 does around 1200 when I'm maintaining speed with minimal power application. Almost to 20,000 hours. Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-439955 Share on other sites More sharing options...
fjh Posted January 10, 2020 Share Posted January 10, 2020 12 hours ago, JoeH said: Interesting to read about the resonant ride... Might explain that weird flutter my 95 e7-350 does around 1200 when I'm maintaining speed with minimal power application. Almost to 20,000 hours. This resonant ride condition was a bit of an issue on the v8 with the ambac pump as well! The fix was a light spring om the right side rack acted as a damper for this condition ! I have never run into it on any Vmac Pumps entirly possible thou! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-439999 Share on other sites More sharing options...
JoeH Posted January 11, 2020 Share Posted January 11, 2020 10 hours ago, fjh said: This resonant ride condition was a bit of an issue on the v8 with the ambac pump as well! The fix was a light spring om the right side rack acted as a damper for this condition ! I have never run into it on any Vmac Pumps entirly possible thou! My 95 isn't vmac it's completely mechanical. Quote Link to comment https://www.bigmacktrucks.com/topic/57605-return-fuel-problem-misfire/#findComment-440040 Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.