Fuel pump pushrods-Again

Mackman

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In the spring of 2021 I installed a new OE style fuel pump on my newly rebuilt 440. 2,000 miles later, it quit running and I found the original fuel pump pushrod was wore almost a 1/4" and was not pumping fuel. I replaced it with another original equipment pushrod I had on hand. Sunday, 2200 miles later, it left me on the side of the road. Not pumping fuel. I find that the pushrod is wore about .200. What's my solution? I didn't really want to go to and electric pump. One thing I did notice is that the pump seems to be very stiff. Is it the cams fault? It is a mild Comp cam.
 

khryslerkid

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Are you using a Carter M6903 pump? The springs are found to be really stiff.

Mechanical Fuel Pump 101

My concensus is that the worn pushrods are happening from a stiff spring found in some of the aftermarket pumps or the aftermarket push rods are junk or both when used together.
 

hunt2elk

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I can verify kk's statement about the 6903's having to stiff of spring. I had more than one that was putting out 11 pounds. I think they are supposed to be 7 max.
 

khryslerkid

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I can verify kk's statement about the 6903's having to stiff of spring. I had more than one that was putting out 11 pounds. I think they are supposed to be 7 max.

I posted the link to the thread "Fuel Pumps 101" which when talking to Mike @ Then and Now Automotive, he stated that the spring in the 6903 that I sent him was way too strong. He replaced it with a new diaphragm and a lighter spring.

In the thread we go over how some of the 6903s that Carter built for certain vendors can have a lighter spring. Knowing that Edelbrock and Carter carbs don't like excessive fuel pressure, they were more than likely ordered with a lighter spring by these vendors.
 

gary h

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Is there a Good Aftermarket Push rod for a stock engine (Big Block) ?
 

hunt2elk

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Is there a Good Aftermarket Push rod for a stock engine (Big Block) ?
None that any of us have found. You are far better off finding an original one.
 

padam

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I would love to see a close up of the surface finish on some of these camshaft fuel pump lobes that are actually wearing out the push rods.
 

Mackman

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I've come to the conclusion that it is probably NOT the pushrods fault, either too much pump spring pressure, or rough cam finish. More to follow.
 

Don Frelier

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Are you using a Carter M6903 pump? The springs are found to be really stiff.

Mechanical Fuel Pump 101

My concensus is that the worn pushrods are happening from a stiff spring found in some of the aftermarket pumps or the aftermarket push rods are junk or both when used together.
Hmmm
Now I'm wondering about the pushrod in my Plymouth.
I have a 6903 Carter pump in it (same pump I ran in my Charger for probably 15 years or more with no issues).
Perhaps I should take a look at it it's maybe got 4-5,000 miles on it.
If it still measures good then it may point at the cams as both of mine are Mopar Performance purple shafts.
 

gary h

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Here is a pic of a push rod i removed from my '66 Imperial (440) about three weeks ago. I had long crank times after sitting a few days,So i replaced Fuel pump and filter and noticed a well worn rod.Luckily i had a another used rod to install.Engine was Professionlly rebuilt about 15 years ago.Maybe 10 k miles on it.
IMG_20220614_191932194_BURST000_COVER_TOP.jpg IMG_20220614_191952028_BURST000_COVER_TOP.jpg IMG_20220614_192017878.jpg
 

wagonman

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After wiping out an original in 1500 miles went with a Comp lite weight with Cromoly tip. So far so good. Used with a Carter hipo pump and Comp cam.
 

khryslerkid

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Hmmm
Now I'm wondering about the pushrod in my Plymouth.
I have a 6903 Carter pump in it (same pump I ran in my Charger for probably 15 years or more with no issues).
Perhaps I should take a look at it it's maybe got 4-5,000 miles on it.
If it still measures good then it may point at the cams as both of mine are Mopar Performance purple shafts.

I wouldn't worry about one that you've had that long. It's more than likely the newer pumps that were built with the heavier springs.
 

Don Frelier

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I wouldn't worry about one that you've had that long. It's more than likely the newer pumps that were built with the heavier springs.
Sorry my post was poorly written.

To clarify:
1. The fuel pump in the Plymouth is about 4 years old (it was new at the time)
2. The fuel pump from the Charger was removed when I switched to EFI about 6 years ago (that one is in a bag in my parts room).

I said same pump meaning it was the same "model" not the same piece of hardware which is what my post indicated.
So I think it is possible I have a developing problem that I should investigate.
 

khryslerkid

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Sorry my post was poorly written.

To clarify:
1. The fuel pump in the Plymouth is about 4 years old (it was new at the time)
2. The fuel pump from the Charger was removed when I switched to EFI about 6 years ago (that one is in a bag in my parts room).

I said same pump meaning it was the same "model" not the same piece of hardware which is what my post indicated.
So I think it is possible I have a developing problem that I should investigate.

Gotcha.

Possibly the Carter pumps that Mancini and Edelbrock sell were made for use with the Edelbrock carburetor with those needing a 5.5 to 6.5 rating. They were more than likely a special request for Carter to insure their pumps didn't exceed these pressures. Other than that other 6903 pumps that have been manufactured may not have use the strict guidelines for whatever reason. The one I currently have, I bought from Summit and was found to have an extremely strong spring, causing extreme pressure of 8lbs or more.

Now how hard is this heavy spring pressure going to be on the pushrod. The pushrod that I installed in the newly rebuilt 440 was the Howard's one and it didn't last long at all. Further inspection and other people's testimonials says that they're junk. I replaced it with a 50 year old pushrod that still measured close to the 3.220. One day maybe I'll check its condition but since Mike replaced the heavy spring in the 6903 with the lighter one I'm not too concerned.
 

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