A1 liquids Posted October 11, 2014 Share Posted October 11, 2014 Hello from Manitoba.... 1988 mack R688ST with a E6 350Took in shop for a miss, cracked lines and sure enough #6 dead in the water. Tested injector and fail....6 new injectors and fuel lines later reassembled still a miss. Cam is good, compression good.... Noticed when cracking fuel lines #6 looked (foamy) yup I said foamy.... Now I don't know my mechanical injection pumps. When these pumps wear out .... Is it possible that # 6 line hasn't got the pressure to fire the injector? Is this common to pump failures.....Little History of truck.....Literally sat and did not move for 3 years in a Quonset. Shouldn't matter but thought I'd point it out.... Thanks in advance.... Love the forum by the way... Colin Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted October 11, 2014 Share Posted October 11, 2014 Colin: there is basically a cam shaft inside the pump it could of had a lobe go flat or the barrel and plunger are too scored to build sufficient opening pressure to fire the injector Quote Link to comment Share on other sites More sharing options...
b61mack Posted October 11, 2014 Share Posted October 11, 2014 It could be a broken spring under the fuel line in the pump. there is the nut that the fuel line screws into that you have to take off and the spring is under there. had one break on a 300+ Robert Bosch pump. Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted October 11, 2014 Share Posted October 11, 2014 I saw a injector line stopped up about two years ago. 1 Quote glenn akers Link to comment Share on other sites More sharing options...
A1 liquids Posted October 11, 2014 Author Share Posted October 11, 2014 Thanks for the quick reply guys... I actually checked that spring under the fuel line in the pump and it was fine.... Thanks b61mack ( we're on the same page) was looking for something simple but I'm starting to lean towards gearhead204.... Taking the ambac 300 off my 85 today to try it Tuesday on the 88. Beats coughing up 2 grand for another pump. Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted October 11, 2014 Share Posted October 11, 2014 check e-bay also for used or reman pumps Quote Link to comment Share on other sites More sharing options...
farmer52 Posted October 11, 2014 Share Posted October 11, 2014 What is the part number of your injection pump? I have a spare pump (history unknown). Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment Share on other sites More sharing options...
A1 liquids Posted October 11, 2014 Author Share Posted October 11, 2014 (edited) What is the part number of your injection pump? I have a spare pump (history unknown).The pump I just finished taking off my 1985 is a Mack model 300 PLM 450051B . Edited October 15, 2014 by A1 liquids Quote Link to comment Share on other sites More sharing options...
farmer52 Posted October 11, 2014 Share Posted October 11, 2014 Sorry, mine is 300 PLM 450211B. Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment Share on other sites More sharing options...
A1 liquids Posted October 12, 2014 Author Share Posted October 12, 2014 It's all good, I appreciate the attempt farmer52. Quote Link to comment Share on other sites More sharing options...
A1 liquids Posted October 15, 2014 Author Share Posted October 15, 2014 The pump off of my 85 had a different BTC... So took the pump in yesterday to get tested. Should know a lot more today. 1 Quote Link to comment Share on other sites More sharing options...
A1 liquids Posted October 17, 2014 Author Share Posted October 17, 2014 Pump tested ok but low idle was 1/3 of spec..... Lap valve and snubber removed on #6 new gaskets everywhere.... Reassembled.... And all cylinders firing...... It's a good day. Thanks for all the suggestions and help guys..... I'm a hole lot wiser on how these pumps work now.... Thanks againColin and family 1 Quote Link to comment Share on other sites More sharing options...
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