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2008 mack ch mp8


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Im coming to you guys once again for help with this mack. First this truck was just purchased at an auction started and ran great there. it was an oilfield companies truck it has 49, 609 verified miles so obviously it has sat the majority of its life. Had it towed home got in it and maybe drove it 45 miles to have new rubber installed then it starts missing and wanted to die got it back home barely changed fuel filters then started noticing that it had a new looking filter head and a new looking fuel pump so i know mp8 engines had injection cup problems and thats is what im thinking. There are no codes and i changed the over flow valve pressurized the tank to help bleed out fuel system did not see any leaks etc. Truck was a long start and ran at idle fairly decent for 30 min. Then the miss returns and barely had enough power to back up 10 feet to get back in the shop. Just curious what you guys may think and if injection cups is having the truck sit for a long period could be what caused it with that low mileage or just that its dumb luck lol.  I appreciate any help you guys could throw at me. Thanks.. 

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Anyine got any ideas or has anyone ever experienced a similar issue i know that it could be anything.  I think that bad cups sometimes causes problems in the hand plunger on the filter head. Thats kinda where im at since it looks like everything was replaced up to the cups. I cant really see too much areated fuel in the tanks. Whats the best way to condemn the cups? 

If it is the cups can you replace with the upgraded cups without replacing the injectors or do u have to go back oem

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9 hours ago, Playinghooky13 said:

Anyine got any ideas or has anyone ever experienced a similar issue i know that it could be anything.  I think that bad cups sometimes causes problems in the hand plunger on the filter head. Thats kinda where im at since it looks like everything was replaced up to the cups. I cant really see too much areated fuel in the tanks. Whats the best way to condemn the cups? 

If it is the cups can you replace with the upgraded cups without replacing the injectors or do u have to go back oem

To look At cups you need to put a clear hose on the return from the head to the tank ! It sounds like cups If it has no codes! Also sounds like they were chasing this before dumping the truck!

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Ok i will do that when i can source a banjo fitting.  I appreciate the reply. I have a feeling its cups too but dont want to go through all that and it not do anything to fix the problem. If anyone knows about the upgraded cups vs oem injectors that would be great

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11 minutes ago, Playinghooky13 said:

Ok i will do that when i can source a banjo fitting.  I appreciate the reply. I have a feeling its cups too but dont want to go through all that and it not do anything to fix the problem. If anyone knows about the upgraded cups vs oem injectors that would be great

I am no Guru on these their are better sources on the site than myself   for this newer stuff How ever seen this stuff chased dozens of times at our shop!

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I finally got around to pulling the valve cover on this thing. Found a whole bunch if bare wires on the injector harness seems odd that its so brittle already but anyway of course mack nor volvo show to have it in stock maybe one dealer in new york has one waiting to hear back. Not sure if this would be the problem but i know it cant ride like it is. And i guess its the whole damn harness anyone got one laying around or know where to source one at?  2008 mack chu  mp8  last 8 8n003286

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1 hour ago, Playinghooky13 said:

I finally got around to pulling the valve cover on this thing. Found a whole bunch if bare wires on the injector harness seems odd that its so brittle already but anyway of course mack nor volvo show to have it in stock maybe one dealer in new york has one waiting to hear back. Not sure if this would be the problem but i know it cant ride like it is. And i guess its the whole damn harness anyone got one laying around or know where to source one at?  2008 mack chu  mp8  last 8 8n003286

They usually throw up injector codes for this! Not uncommon for the wiring to do this that is why there is no stock anywhere!

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Right i figured it would have some codes. It did have an inactive #1 injector code but none were active while it was running like crap. Im still thinking cups but going to have to do something with the harness. I know on 1 and 3 there were bare wires together. The engine kinda looks like it could have been into before  just because of paint stick markings on the injector rockers and so on like they marked them when they set them but its hard to say.  49k miles is nothing but i know guys for a different oil field company that were doing cups every 20 k they say.   49k miles with a bunch of idle time whike on the job cant remember the hours right now but its more than 49k miles.. just hard to say i know they had replaced parts and was really hoping to not see any signs of the valve cover being off before. 

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12 hours ago, Playinghooky13 said:

Right i figured it would have some codes. It did have an inactive #1 injector code but none were active while it was running like crap. Im still thinking cups but going to have to do something with the harness. I know on 1 and 3 there were bare wires together. The engine kinda looks like it could have been into before  just because of paint stick markings on the injector rockers and so on like they marked them when they set them but its hard to say.  49k miles is nothing but i know guys for a different oil field company that were doing cups every 20 k they say.   49k miles with a bunch of idle time whike on the job cant remember the hours right now but its more than 49k miles.. just hard to say i know they had replaced parts and was really hoping to not see any signs of the valve cover being off before. 

A short on one will shut down three ! That's why they run so shitty! 

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Im going to repair the harness for now and see what it does. I know repairs on the harness isn't the "right" way but it seems to be my only option with no available stock for right now.  I come  across some used ones at vanderhags that say will need repaired in a few places for 700 dollars i think ill just repair this one one for 50 and see if it will run.  The used ones are probably no better than what i got.  Ill post back with our findings. I appreciate your help so far..

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Those paint pen markings don't necessarily mean it's been into before. I've been seeing them on rockers that I know for a fact have never been touched. 

I've been seeing so many leaking cups lately that I've gotten really really lazy, to the point where if I don't see an obvious sign of the fuel system sucking air, I crack the fuel return at the head and if there is foamy fuel coming out, I go after cups. 

I'm sure it'll bite me in the ass at some point but the last 10 or so I've done, cups have been the culprit. 

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He needs to address the elephant in the room first bud! My thought! And yup you might get bit at some point how ever these can be chronic depending on whos doing the job before you! And how much attention to detail was paid! AND The odd time a filter head or transfer pump  goes fubar!

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