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johnpstoll Member
Joined: Aug 19, 2016 Posts: 19 Location: Dent, Minnesota
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Posted: Thu Feb 16, 2017 11:36 am Post subject: Fuel pump question |
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I have a question about the fuel pump. I installed a rebuilt pump on my M38. I checked the psi and all I could get was 1 psi. I took it apart and checked everything out, visually it all looked fine. I tried a different diaphragm and the same thing. The vacuum side was at 5 psi. I bought a rebuild kit for the fuel pump side. While I was putting it back together I noticed that the new spring was noticeably stronger then the one I had removed. Now I get 5 psi out of the pump. Is the spring tension crucial to the pump pressure? Or did I answer my own question?
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16260 Location: Wisconsin
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johnpstoll Member
Joined: Aug 19, 2016 Posts: 19 Location: Dent, Minnesota
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Posted: Thu Feb 16, 2017 2:28 pm Post subject: |
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Yes, it was the N spring. I was curious what controlled the pressure. I almost put the old spring back in. I think I'll just get rid of it so I don't unknowingly use it in the future.
Thanks WES |
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4x4M38 Member
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16260 Location: Wisconsin
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johnpstoll Member
Joined: Aug 19, 2016 Posts: 19 Location: Dent, Minnesota
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Posted: Fri Feb 17, 2017 7:28 am Post subject: |
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I didn't have the tool shown in the TM, so I used the primer handle to flex the diaphragm and then tightened down the screws. It seemed to work. SO far so good. |
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4x4M38 Member
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
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RonD2 Member
Joined: Oct 02, 2014 Posts: 1921 Location: South Carolina, Dorchester County
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Posted: Tue Jun 19, 2018 8:36 pm Post subject: |
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I've read the TM 9-1828A page 119 carefully but it's not clear to me. There are 10 screws around the perimeter of the top cover on the pump, and two screws by their lonesome in the middle of the cover. Are these the 2 screws that must be loose to pre-load the pump?
And 2nd question: can pre-loading be done with the pump installed?
I appreciate the advice! _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16260 Location: Wisconsin
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RonD2 Member
Joined: Oct 02, 2014 Posts: 1921 Location: South Carolina, Dorchester County
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Posted: Wed Jun 20, 2018 7:26 am Post subject: |
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That clears it up perfectly. Thanks Wes! _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
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Jason86 Member
Joined: Sep 19, 2015 Posts: 43 Location: Maine
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Posted: Thu Jun 21, 2018 10:59 pm Post subject: |
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Then and Now Automotive was asking on his Facebook page if there were any videos that people wanted him to make, so I asked him to make one showing how they preloaded the pumps when they did a rebuild so he made a video posted it to their Facebook page and onto YouTube a month ago or so. It's not the way the book describes doing it with the special rod but it's apparently how they do it.
Not sure how you feel about links Wes but I will post the link just to get the message across and then you can go from their and edit or delete as you need or redirect people in that direction. I'm not sure how correct this method is but it's what they recommend. The Google link to YouTube is: https://youtu.be/v0yLWQvjrPg
Or you can do a search on YouTube to find the video type in "Preloading the diaphragms" should be first video. _________________ Jason
1953 M38A1 |
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16260 Location: Wisconsin
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RonD2 Member
Joined: Oct 02, 2014 Posts: 1921 Location: South Carolina, Dorchester County
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Posted: Sun Jun 24, 2018 2:33 pm Post subject: |
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Followed the directions and believe I successfully pre-loaded the pump (9810 on the flange, has priming lever, correct spacer). It puts out plenty of fuel but my pressure gauge only indicates a tad over 3 PSI when cranking the engine, maybe 3.1 or 3.2 PSI. I know the TM spec says 4.5 to 5 PSI with the engine running at 600 RPM. I can't start my engine at the moment due to a distributor issue. Never had this pump on a running engine before, it's a rebuilt unit from one of our reputable suppliers. I have no reason to suspect my gauge isn't accurate but have no way of knowing for certain. Am not inclined to buy another gauge just for that.
Searched and researched this question with no joy. Nothing in the TM I could find. Is 3 PSI out of a cranking fuel pump ok? Or will I just have to start the engine to know for sure? _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
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wesk Site Administrator
Joined: Apr 04, 2005 Posts: 16260 Location: Wisconsin
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Posted: Sun Jun 24, 2018 8:41 pm Post subject: |
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There is nothing published except the required minimum which is obviously for an engine at 600 RPM running.
Don't mis-understand the purpose of pre-loading the diaphragm. It is not done to help make more pressure. It is done to ensure the diaphragm is seated evenly the full circumference of the cover and is pre-stretched to ensure it does not develop too much pressure. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php |
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RonD2 Member
Joined: Oct 02, 2014 Posts: 1921 Location: South Carolina, Dorchester County
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Posted: Sun Jun 24, 2018 8:56 pm Post subject: |
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Hi Wes. Thanks! Yes, I understood the need for pre-loading as you described. I'll measure it when I have the engine running. _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
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