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How To Bleed Your Engine

Reprinted with permission from Bob Pone

Often, engine problems are caused by small amounts of air in the fuel. Even if you run out of fuel, for example, you will need to know how to "bleed" your engine, which rids the fuel lines of air so the engine can start.

If you are an owner of a diesel engine bleeding is an essential skill, so let's review the entire process. If you are familiar with the manufacturer's recommended procedure for bleeding your engine, follow it, but generally, the procedure follows.

When bleeding the fuel line, especially when the starter motor is used to operate the fuel lift pump, wrap rags around all venting units to collect excess diesel fuel that splashes out.

Open the fuel supply valve and use the manual pump found on all diesels to pump fuel into the lines until you see it successively bubbling out of the bleed nipples on the secondary filter, and fuel injection pump if you can, and then the connection points at the top of the injectors. Try to pump until you get clear fuel without bubbles from each fitting. If you succeed, tighten this connection and repeat the process for the next nipple or injector in line. You may not be able to get clear fuel, without bubbles, but do not despair. We'll deal with that shortly. If you are fortunate enough to get bubbleless fuel flowing out of each and every injector, you are indeed blessed and ready to start your engine. All of the fuel line connections to the tops of the injectors should be tight by now, so go ahead and try to start your engine. Did it start? Great! You can skip the next paragraph dealing with how the rest of us, not similarly blessed, will deal with getting our engines to start. The procedure you will follow next picks up after we get ours started.

All of our injectors are tight in their bases and all of the fuel line connections to the top of the injectors are loose so that fuel and air will spurt out of them when the starter motor is engaged. Have the proper size wrench in hand, ready to tighten the fuel line connections. Now, turn the engine over with the starter motor with the throttle open. At first you should see fuel and air bubbles coming from the injectors. Focus on the number one injector. When it shows clear fuel with no bubbles, tighten the connection and focus on the second injector. Again, when it shows "bubbleless" fuel, tighten it and go on to the next one. Continue this process until all injectors are cleared of air. Your engine may start before you have all injectors cleared. This is not a problem. Just release your pressure on the starter button or key and let the engine run while you continue to monitor the fuel flow from the remaining uncleared injectors. Do not crank the starter motor for more than 30 seconds at a time, however. You can also put the decompression lever in its decompressed position and hand crank the engine to move fuel to the injectors. When all injectors are cleared of air and their fuel connections tightened down, you are complete. Don't over tighten the nuts, and check for fuel leaks when the engine is running.

The information contained herein is provided by Bob Pone. Neither ABA nor Bob Pone assume any responsibility or liability for events that occur due to actions you or others on your behalf take based on the information given. You are proceeding at your own risk.

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