Shark11408 Posted January 14, 2023 Share Posted January 14, 2023 Recently had a cylinder #1 injector cup changed and now my truck won’t stay running for more than 20 minutes. I grabbed my son to manually prime the truck while I started and ran the truck. The truck will stay running as long as you continue to manually prime it. The minute you stop it takes about 30 seconds for the engine to shut off. I am lost on this matter. Any and all help is appreciated Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/ Share on other sites More sharing options...
Joey Mack Posted January 14, 2023 Share Posted January 14, 2023 so it stays running if you pump the primer?? the tandem pumps on them are not something I like.. There is a drive coupler between the fuel and steering pump that is joined by a small round slotted coupler... it is a piece of junk. and when they wear, the drive can cut a hole onto the coupler and just spin.. They should have used a 'lovejoy' coupler like a Series 60 12.7 has........ seperating the tandem pump is a bit of a job.. are you familiar with the setup? jojo Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521285 Share on other sites More sharing options...
Shark11408 Posted January 15, 2023 Author Share Posted January 15, 2023 (edited) Not familiar with the setup at all. I work in Detroit motors mostly. Yes the truck will only stay running if you manually prime it constantly Edited January 15, 2023 by Shark11408 Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521303 Share on other sites More sharing options...
Joey Mack Posted January 15, 2023 Share Posted January 15, 2023 ok.. well stick around and wait for the guys that still work on these to help guide you.. jojo Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521304 Share on other sites More sharing options...
Onyx610 Posted January 15, 2023 Share Posted January 15, 2023 I thought you did all the cups on this truck? Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521306 Share on other sites More sharing options...
Joey Mack Posted January 15, 2023 Share Posted January 15, 2023 #1 only.. Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521307 Share on other sites More sharing options...
Onyx610 Posted January 15, 2023 Share Posted January 15, 2023 Has this problem started after you did the work? Have you check the fuel delivery system for any leakage? Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521308 Share on other sites More sharing options...
Shark11408 Posted January 15, 2023 Author Share Posted January 15, 2023 Was trying to do a 6 pack on cups but turns out every single cup is so stuck in the holes that getting them out would be removing the head and punching them out. I don’t have the equipment for that. I only got #1 out by tapping the hole and using a small slide hammer after about 1.5 hours of trying it finally gave free. I don’t know what to look for in fuel delivery. I am guessing a sending unit but not 100% never seen this issue before Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521330 Share on other sites More sharing options...
Mackpro Posted January 15, 2023 Share Posted January 15, 2023 Did you have install tool to form the end of the cup to the head ? Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521344 Share on other sites More sharing options...
Mackpro Posted January 15, 2023 Share Posted January 15, 2023 https://static.nhtsa.gov/odi/tsbs/2013/SB-10082932-6903.pdf Scroll down to the pics of the injector sealing areas. If any of the injectors looked “ unusable “ then the cup and injector needs to be replaced. This is a old bulletin but useful information. Mack now says don’t do the thread tap and pull on the stainless cups as the thread shavings were wiping out turbos left and right. Mack now has a expanding puller that grabs the sides/walls of the cup and pulls it out super fast. On copper cups you still have to use the thread and pull tool method. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521346 Share on other sites More sharing options...
Shark11408 Posted January 15, 2023 Author Share Posted January 15, 2023 Yes I have the proper tool to expand the injector cup and it was installed per Mack standards. Right now I can’t keep the truck started and running without manually pumping the prime plunger constantly. As soon as you stop pumping the primer the truck will shut off after 20-30 seconds Quote Link to comment https://www.bigmacktrucks.com/topic/71058-2015-mack-mp8-won%E2%80%99t-stay-running/#findComment-521402 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.