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FUEL PUMP

45es said:
I have a bunch of dumb questions so bear with me. The conversation appears to be moving away from your original question with the change moving toward an electric fuel pump. But I would still like to know, what is the cause of the mechanical pump's failure?
You told us you rebuilt the engine and it ran fine for quite a while before this problem developed. The 360 engine is not the original engine to the jeep as originally it would have been a 304. Yes, I know they are the same family of engines.

When you rebuilt the engine, was this the engine in the Jeep when purchased?
If the original engine, what fueling related parts did you reuse? Fuel pump? Fuel pump eccentric. etc.
What pumps have you purchased? Brand and model numbers? I ask this because I have noticed a slight difference in physical appearance for the pumps listed as compatible to either the 304 or 360. The difference that caught my attention appears to be the pump's actuating arm shape. This gives me the sense that the arm to eccentric contact could be slightly different. Is this possible or effect the pumps diaphragm, I don't know?
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This is the same engine that was in the jeep when I bought it. It was in poor condition so soon after I bought it, I decided to rebuild it. The fuel pump eccentric is the same one that was on the engine when I took it apart. Upon reassembly, I replaced fuel pump, water pump, alternator, etc.
I have used different brands of fuel pumps,
Carter M6505
Delphi. MF 0042
Crown. J 8124460
USMP 16263
GMB. 520-8130 Most recent
The 1st pump after engine rebuild was a Carter M6505 and after looking at my records, that pump lasted approximately 15k miles and nearly 6 yrs. That pump failed with a bent arm.
1772394150795.jpeg
Seemed simple enough so I replaced with another Carter M6505. That pump would not start the jeep. I pulled it off and clamped it in my vice and hooked my vacuum gauge to it. It pulled 0 vacuum on the inlet side. Every pump after that has failed basically the same way, either gas or oil out the weep hole.
I pulled the front cover after 3 or 4 pump failures and checked the pump eccentric and it was fine.
1772395563302.jpeg
I did find after looking closer at my records that 1 of the Delphi pumps lasted about 1400 miles.
I’m not 100% certain but I think the pumps are interchangeable between the 304 and 360. I really really hope that you are on to something with this thought.
If I failed to answer something, hit me again please.
EDIT
I commonly use 1975 J20 as a subject vehicle when I'm ordering engine parts.
 
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PeteL said:
Agreed.

My thought is that while running the diaphragm should by design be just getting tickled by the cam and lever. Since the diaphragms are failing, I wonder if something is causing them to"full stroke" constantly, and fatigue prematurely?
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I think I understand your thoughts but I surely don’t know the answer.
Keep asking questions.
 
I'm inclined to agree with Pete.
Something caused the pump arm to bend. I would flat out replace the eccentric. While doing that, check closely the end of the cam, the timing gear, timing chain for stretch and oil pump drive gear for any signs of distortion. I feel something may not right in that area. As Howard said, open up a few of the failed pumps. There quite possibly could be a useful clue when evaluating the area of the eccentric. Good luck.
 
If you still have the first failed pump, could you take a couple more pictures of it? If looking down from above or from the side of it, are there any indications of what may of bent the arm?
 
That one in the tailgate picture looks bent too. The arm is hitting something too hard.
 
PeteL said:
That one in the tailgate picture looks bent too. The arm is hitting something too hard.
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I thought the same thing until I looked at pictures of new pumps. Do that and you will see they all have that offset.
 
Totally inconclusive as to why the failures, but here are some pics.
Delphi
1772569596974.png
USMP
1772569693585.png
1772569723811.png
1772569743644.png
If you look close you can see the rubber seal notched, at the tiny stem in the center, that failure was oil out weep hole
1772569829987.png
1772569863429.png
 
As I said earlier, I would replace the eccentric. It has been on the engine for a long time and even though it has functioned well in the past, it was there when this problem began. I spent a little bit of time looking at another time set replacement project. I noticed in that project, the eccentrics wear pattern was a bit different than yours. The pattern started at about the middle of the eccentrics face as yours does but, it did not extend fully to the outer edge of the eccentric. The wear pattern was only about two thirds as wide as yours leaving the outside edge of the eccentric unworn. I am guessing if you were to measure the face of the eccentric, you would find a slight tapper towards the outside edge.

Whether I am right, wrong or otherwise as I said, I would replace the eccentric
 
45es said:
As I said earlier, I would replace the eccentric. It has been on the engine for a long time and even though it has functioned well in the past, it was there when this problem began. I spent a little bit of time looking at another time set replacement project. I noticed in that project, the eccentrics wear pattern was a bit different than yours. The pattern started at about the middle of the eccentrics face as yours does but, it did not extend fully to the outer edge of the eccentric. The wear pattern was only about two thirds as wide as yours leaving the outside edge of the eccentric unworn. I am guessing if you were to measure the face of the eccentric, you would find a slight tapper towards the outside edge.

Whether I am right, wrong or otherwise as I said, I would replace the eccentric
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I think I will pull the distributor and check the wear on the cam/distr. gears and go from there.
If I see no evidence of wear, I may possibly have EFI sooner than I had planned, which would do away with the problem altogether.
 
That is true.
 
PeteL said:
What caused it to bend?
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I just recently re-read most of this V8 fuel pump thread. I have a 304 on an engine stand, a 360 is a corner, and a 360 in my LR Defender project. When I refreshed the Defender 360 (about 12 years ago), I had a hard time finding a new fuel pump for it. Every one I bought had a different length lever/arm from my original. If I recall, I bought like 3 different pumps, a couple the same external configuration, and one early AMC that looked similar to a Chevy style, but all the lever/arms weren’t the same as my original. I think ended up putting my original fuel pump back on. I have never started that engine (stalled project).
I can’t help but agree with PeteL’s reply in post #38 that your arm is over-extending causing all your failures. I have run into this same issue on some Chevy engines where there is a 1/4” spacer between the engine block and fuel pump on some engine configurations. If you bolt the pump on without the spacer, it bends the lever/arm, or tears the diaphragm, or breaks the fuel pump housing. Spacing the pump further from the drive eccentric results in less stroke, or as PeteL put it, “just tickling” it.
I can’t help but think the lever/arm is not the correct shape/length. If I get some time, I might try to get the fuel pump off my 360 to get a part number and compare the lever/arm.
 
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