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replacing injectors on 1994 mack 350 motor


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Mechanical E7 or VMAC 1 electronic pump truck? does it have an engine brake?

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Before starting work completely clean off the engine of all dirt and oil. Especially get the area around the fuel pump and high pressure fuel lines clean. A spec of dirt can completely ruin a fuel injector. I suggest you have an E7 Service Manual handy while doing the injectors as I am describing how to do this by my ways from the top of my head.

The injectors are under the valve covers. You'll have to remove the air cleaner and air inlet pipe and the valve covers. If you have jake brakes, the brake housings will have to be removed, carefully remove the wire and disconnect the oil feed hose (the bolts that hold down the jake brake housing also hold down the rockers, I read in the repair manuals that these bolts should be replaced when removed but I've never had problems reusing them). If you don't have jake brakes then there is no need to remove any rocker bolts.

The fuel lines will have to be removed, I usually suggest that the lines be completely removed, cleaned and inspected for reuse. When the lines are removed cover the ports on top of the fuel pump to keep any dirt out. Dealerships usually have plastic plugs that go over the port but you can cover it with saran wrap or a lint free cloth.

The fuel injectors are installed under plugs between the intake and exhaust valves. A puller tool is needed to pull the injector from the bore. (The puller tool consists of a threaded shaft and nut, threaded tip, and spacer sleeve. The shaft is inserted through the sleeve and then the tip is threaded into the injector, tighten the nut carefully, you should feel the injector release from the bore with a couple turns of the nut.) Pull out the injector and inspect. It should have two O-rings and a metal sealing ring on its tip. If anything is missing check down the injector bore for it. The metal sealing ring usually is what gets stuck in the bore. A flat head screw driver can be used to knock it loose and remove it from the bore. Also check the fuel line ports in the side of the head for any accumulated dirt and blow out with a blow gun from the top of the cylinder head.

Prepare the new injectors for installation on a clean surface. The injectors from Mack are usually in a padded paper enevlope. Open this envelope carefully, the padding is a loose cellouse and can get into the injector if the envelope it torn open. The injector comes with o rings and metal sealing ring. Lubricate and install the o-rings on the injector, apply a light coat of oil around the tip and install the metal sealing ring (the oil holds the sealing ring in place for installation). Take the removal tool and remove the sleeve and thread the injector onto the tool. Place the injector into the bore with the fuel inlet port facing towards the exhaust side of the engine. Press down firmly on the tool until you feel the injector click into place. Check through the fuel line ports in the side of the head with a flash light to confirm that the injector ports line up. Install the injector hold down plugs and torque to 40 ft lbs.

Install the rocker shafts and engine brake housing (if removed) and check and adjust valve lash, Install the valve covers, Carefully install the fuel lines and tighten the nuts. Install the air cleaner and air inlet pipe. Check around engine to make sure all tools are removed before starting. The engine will be hard to start but should start within 20-30 seconds of cranking. Visually check (do not feel around, fuel spray from the lines can be injected through the skin and cause a dangerous infection) for fuel leaks around the high pressure fuel pipes. Let the engine run at a high idle for about an hour while observing for leaks. If no leaks are spotted then the procedure is complete.

Jeff - The Bulldog Doctor

:mack1: Master Technician

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yes the pump is a electronic governed pump what are the clearance on exhaust values and intake values?

It should be posted on the valve cover serial plate. The intake should be .016 inch and the exhaust should be .024 inch. I just checked in a service manual, some engines have an exhaust valve setting of .028 inch depending on the camshaft but that may have been done in later year engines. Just double check your serial plate to confirm the correct lash setting. You should be able to remove a plate on the bottom of the flywheel housing to see the position pointer. You'll see numbers 1-6 , 2-5 , 3-4 on the flywheel as you turn the engine over. You do not adjust both cylinders at the indicated position, just the one that is on its fire stroke (both valves should feel loose). The companion cylinder will be in overlap (both valves feel tight) do not adjust this valve.

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Jeff - The Bulldog Doctor

:mack1: Master Technician

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