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B61 Mack 673 Injection pump problems


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Hi guys. Wanted to start off with so happy I found this forum and joined hoping I can help people out and hoping people can help me out! lol. I have a b61 mack truck. Its been sitting for years. I pulled it in the garage, turned the motor over and found out I have a stuck valve, which bent the push rod. Fixed all that. While I was in there I checked the pistons and everything and everything looked good and moved great. I got the head redone, all new gaskets and everything. Went to start it again and found out the plungers in the injection pump are stuck. Seen a guy on here said to put a screwdriver in the spring and tap them down. I did that with a lot of pb blaster and all the plungers are free. Went to try and start it again and it fired up. However its missing on the last cylinder (closest to the cab). I sent all the injectors out to get tested and of course they are all bad. So got all new tips, and pressure tested and we are good. Installed them today and again, last cylinder still wont fire. Piston looked good when I was in the motor, cylinder walls aren't scored. Im lost. So I checked the top of the injection pump where the fuel lines meet the injection pump. Cracked them and fuel shot out of it, and its shooting out where the injector goes into the motor. So its getting fuel. How much pressure I don't know, and I don't know how to tell; (which could be the problem also not enough pressure). So my two questions are....How do I tell how much pressure im getting (where can I put the gauge at) And worse case scenario, how to I pull my injection pump. (details please) lol. I seen one post the guy said loosen the injection pump screws, and make sure motor is top dead center. I would like more details than that being this is all new to me. Thank you very very much!

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The best way to check and see if each pump is pumping is get another fuel injector line and connect it tro the pump with a injector connected to the other end.Hold it up some way out and crank over watching the injector spray.Do each one that way.Cracking a injector line does not tell you much as you have already found out.

glenn akers

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I agree with Glenn. You are getting fuel to the injector, but might not be getting enough pressure out of that particular plunger to lift the needle off  the seat in the injector, by the way where did you find head gaskets for the 673?

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Thank you guys for all the great info. So how do I fix that last plunger on the injection pump to get more pressure out of it. Can I fix it in the truck, or take the injection pump out and get it redone. If I take it out, can anyone help me threw all the steps of taking it out.

I found the head gaskets and all the top end gaskets threw http://www.wattstruckcenter.com/store/index.php?route=product/category&path=59 ask to speak to barry. He is excellent and sends everything you need. Not cheap at all. But what else you going to do? haha.

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To remove the pump set the engine on its timing mark  roughly 24 drgrees BEFORE TDC! Usually marked on the flywheel or the Damper on the front!

Try Glens idea first coud be a stuck /pluged injector!

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Ok sounds good. I really appreciate all the help. I already got over 1,500 bucks into the motor and it's still not running right. So I'm giving it a break for the moment to restock some money. In the meantime I'm running all new wires, and switches. Way cheaper lol. Thank you everyone. I greatly appreciate all the help. Get to learn something new everyday and that's why I got this old pig (;

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I pulled the last injector out and the first injector out. Last one is definitely not shooting enough fuel out. There is fuel coming out of the last injector. But not near as much as the first one. So I think it's going to be time to pull the pump off and send it out to get rebuilt. 

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  • 4 years later...

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