[Gator67]

Originally Posted by 68bird400HO

I had fuel pump issues a few years ago and started a thread on it. I had replaced my leaking fuel pump and the new one died after about 100 miles. I did find the reason for the pump failure and started discussing it at about post #58. Here is a link to the thread at page 3.

https://forums.maxperformanceinc.com...=868529&page=3

In short, the failure isn't the diaphragm, it is the arm. The repops are using the wrong arm. It appears the repops copy the Delco body but are using the Carter arm which is a little different and sits a little higher at the eccentric contact point. This puts too much pressure on the arm when compressed and they eventually break, and the car dies instantly. There are some out there with the correct arm, the "Muscle Car Fuel Pumps" from Summit or Jegs but I am not sure if they are produced anymore.

You also could try to buy a repop and swap the arm. I was messing with that a little and just don't have the correct tool to uncrimp the aluminum to get the arm pin free. I think it would slide out if you could do that, though.

BINGO!

Removed the fuel pump and found two little pieces which came from the end of the arm that depresses the spring. I removed the arm myself to make sure there were no missing pieces that could have made their way into the engine. I got lucky. Good grief...

[Shiny]

Glad you found a reason for the pump failing. Thanks for sharing the painful carnage.

You can see some forming wrinkles in the sides of the arm in the section photo right where yours broke.

Maybe the steel they use is weak or the forming operation is just bad quality?

Unfortunately, there's no way to inspect that part of the arm on a new pump. The factory probably likes that!

What brand pump? It looks brand new....

You think this has anything to do with the unexpected fuel in the vent return line? Maybe there was more destruction inside the pump?

[68bird400HO]

Originally Posted by Gator67

BINGO!

Removed the fuel pump and found two little pieces which came from the end of the arm that depresses the spring. I removed the arm myself to make sure there were no missing pieces that could have made their way into the engine. I got lucky. Good grief...

Yep, I had those same broken pieces fall out of mine too. I bet if you put the correct arm on, the pump would be fine.

Any tips on getting the arm out? I was trying to uncrimp the aluminum around the pin so I could recrimp in a new arm. I'm not sure what tool to get in there with.

[Gator67]

Originally Posted by 68bird400HO

Yep, I had those same broken pieces fall out of mine too. I bet if you put the correct arm on, the pump would be fine.

Any tips on getting the arm out? I was trying to uncrimp the aluminum around the pin so I could recrimp in a new arm. I'm not sure what tool to get in there with.

I used a hammer and large screwdriver I have no plans to reuse the pump, or buy another new one. My wife drives this car around town, so it has to be reliable.

I'll probably order up a RobbMc pump for this car as well as my GTO, since that one's down with a bad Delphi pump as well.

[Shiny]

I just sent a note and thread link to Delphi about this failure mode just to find out if they will actually respond. I don't expect anything back beyond "if your part fails, return it and try again.... you might get lucky next time".

But I noticed my pump was MF0155, not MF0154. I found it odd to have a unique PN (MF0154) for 1968 applications.

Anyone know the actual differences in the pumps for 1968 vs 1970? Is it only the apparent difference in vent line configuration (straight vs elbow)?

Their online specs do show a slight performance difference, which I also found interesting and unexpected. The 68 pump says max 8 psi, the 70 says max 7 psi. Really? Does this mean the 68 pump arm is stressed more for some reason?






I also found a note in their installation instructions to grease the inside of the arm cavity. I certainly did not do this. Anyone else put grease in that cavity and how important is this?



Mike

[HWYSTR455]

I have never heard of putting grease in the cavity, and not sure it would make a diff anyway. Pump should get plenty of lube from splash, and the grease would wash out in a short period of time.

Maybe it is meant for other makes/models? Still can't think of what would use that step.

I have heard of people using grease on SBC engines, but it's just to aid in holding the pushrod while installing the pump.


.

[scott70]

Originally Posted by Gator67

I used a hammer and large screwdriver I have no plans to reuse the pump, or buy another new one. My wife drives this car around town, so it has to be reliable.

I'll probably order up a RobbMc pump for this car as well as my GTO, since that one's down with a bad Delphi pump as well.

The robbmc mechanical pump has to have a regulator with it. I didn’t realize that,, they used to be self regulated but they changed it a few years ago

[Gator67]

Originally Posted by scott70

The robbmc mechanical pump has to have a regulator with it. I didn’t realize that,, they used to be self regulated but they changed it a few years ago

Interesting. This seems to contradict the information on the website/instructions, which indicates a regulator is not typically needed with the 550hp version of the pump (it is needed on the 1100)...it says 7psi +/- 1 and that using the vapor return should reduce it by 1psi. This seems to be in the ballpark of what I need for a Qjet. Was your experience different?

The instructions also suggest that if a regulator is needed, it should be a non-return version placed between the pump and carb. The problem here is that I seem to recall to function correctly, the pressure to the regulator should be like 3psi greater than the desired pressure.

[scott70]

Originally Posted by Gator67

Interesting. This seems to contradict the information on the website/instructions, which indicates a regulator is not typically needed with the 550hp version of the pump (it is needed on the 1100)...it says 7psi +/- 1 and that using the vapor return should reduce it by 1psi. This seems to be in the ballpark of what I need for a Qjet. Was your experience different?

The instructions also suggest that if a regulator is needed, it should be a non-return version placed between the pump and carb. The problem here is that I seem to recall to function correctly, the pressure to the regulator should be like 3psi greater than the desired pressure.

Yes sorry… the 1100 pump used to be adjustable and they did away with it the save on costs.