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Injection Pump


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Hi I'm new here. I just purchased my first Mack. Its a 1980 DM686S TRI AXEL DUMP. I drove it home about 50 miles mostly freeway. And when I got home I noticed fuel that had leaked from what appears to be the lines at the pump. If it is indeed the pump. The throtle cable goes to it. The seller stated that he recently replaced the steering pump and pointed behind this ijection pump. I'm guessing that the lines proberly need to be snugged up after the 50 mile drive.Is this correct or should I not touch these lines? Also is the blowby that comes from the tube under the truck normal? It does not smoke at start up and feels real strong,should I be concerned? Thanks in advance Joe

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You should clean it up and try to see where the fuel is leaking from...it could be the lines leaking at the nuts and just need tightening, but it could also be cracked lines, bad delivery valves in the pump or the seats in the lines might be worn in which case you may need a new set of lines.

Barry - Watt's Truck Center Parts Manager and BMT Webmaster...1-888-304-MACK

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Also is the blowby that comes from the tube under the truck normal?


Once you start seeing an excessive amount of "blow by" from the crankcase breather, it usually means you've got worn piston rings, and the engine is getting close to overhaul time.

That said, "excessive" is the key word.

Without actually seeing the severity of the blow by, it would be difficult for any of us here to accurately assess the situation.

Check the air intake ductwork and the air cleaner itself to be sure all connections are tight and no holes anywhere, and be sure the top of the air cleaner is tightened down securely against the gasket.

I've seen a lot of perfectly good engines ruined very quickly due to a leak in the intake system allowing dirt & dust to be sucked in.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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I can uhderstand that you guys can only do so much from your keyboards and thats cool.I am no expert at all,but I would not consider the blowby excesive.The truck has 800,000 miles on it. As far as the fuel leak I'm going to try and tighten the lines and see what happens.The motor is cleaned upand the leak is not severe I just noticed a small spot on my driveway(6"x6") and found that to be the culprit.

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