Fuel restriction question

[Harley PHD]

Have you checked your fuel pressure?  I put a rebuild kit in my fuel pump using the new springs and check valves that came with the kit. The check valves didn't work, low fuel pressure, so I took it apart again and cleaned up the original check valves with the new spring and had too much fuel pressure.  I had to use only the new diaphragm and reuse the OEM original springs and check valves and got 4-5 lbs of pressure.

 

I've also had bikes die on me and when I opened the gas cap I could heard vacuum escaping.  leaving cap loose I could get home.

[Noonan]

You could try run the car with the pump pulling directly from a Jerry can? 

 

 HARLEY PHD... just an interesting thing i came across..    I rebuilt a fuel pump recently although not for a chrysler product... regardless in this case had I not read the factory service manual I wouldn't have done it properly.  The service manual stated the pump arm had to be held tight forced against the pump arm return spring while the two halves of the pump were screwed down securing the diaphragm.   Holding the fuel pump arm this way normally pulls downward on the diaphragm.  The factory stated premature diaphragm  failure would result if not done this way 

[Doug&Deb]

The cap is properly vented. The pump is new but that doesn’t mean it hasn’t failed already. It wouldn’t be the first time. Like most of the new pumps there’s epoxy on the ends of the pivot pin. I’m tempted to go back to the electric pump exclusively even though I don’t completely trust that option. 

[Sam Buchanan]

4 hours ago, Doug&Deb said:

The cap is properly vented. The pump is new but that doesn’t mean it hasn’t failed already. It wouldn’t be the first time. Like most of the new pumps there’s epoxy on the ends of the pivot pin. I’m tempted to go back to the electric pump exclusively even though I don’t completely trust that option. 

 

Why do you not trust an electric pump?

[Doug&Deb]

Sam it’s probably unjustified. It’s been on the car for 5 years as a part time pump and no problems. However it’s a Chinese made pump and I’ve had plenty of issues with their tune up parts. But I am beyond frustrated with this car and I just want it to work properly so I’m going to try the electric pump again.

[Dartgame]

For a mechanical pump there should only be one filter after the pump. You may have a suction (restriction) issue caused by the filters in line or perhaps the electric pump itself, before the mechanical pump. You might also look at your fuel tank gas cap. Is it a vented type, and have you verified its working, far east sourced parts (if so) aren't always great quality... 

Edited Monday at 02:56 PM by Dartgame

[Ivan_B]

11 minutes ago, Dartgame said:

For a mechanical pump there should only be one filter after the pump.

For the OEM setup - yes. I am running a standard transparent paper filter before the pump, and the fancy rock sponge after  

[JBNeal]

On 4/3/2025 at 5:00 PM, Doug&Deb said:

I was running a rubber line to the carb after I changed the fuel pump. I had been using the wrong pump. The problem never occurred until I made a new hard line. The problem is very random only happening when pulling a hill and even then it’s random...

That 90° fitting may be increasing back pressure enough to trigger the backflow check valve to close and possibly stick in the mechanical pump.  When the carb reservoir empties, back pressure drops, allowing that check valve to open.  When in WOT, the reservoir empties out faster, and the fuel pump cannot refill it fast enough to maintain non-stop fuel flow into the charge air stream.  So it kinda sounds like the mechanical pump is performing as required, protecting itself from that excessive back pressure.

[Ivan_B]

1 hour ago, JBNeal said:

That 90° fitting may be increasing back pressure enough to trigger the backflow check valve to close and possibly stick in the mechanical pump.

I believe that it was already quite scientifically confirmed that this is not the case, here 😅

[Doug&Deb]

I guess I have two options to try. I can bypass the electric pump and see if that helps or I can eliminate the mechanical pump and see how that works. I’m about ready to get rid of the car and walk away from the whole thing. The only thing stopping me is that my one grandson wants the car when he’s old enough. 

[Ivan_B]

Oh, come on, it's just a little stubborn problem, nothing out of the ordinary. The car is old and, well, sometimes it gets a little difficult to deal with. Do you think old folks are always easy to deal with, as they get older? 😁 It just takes a little extra time and dedication.

We are here to help... So, does the car currently run without issues with the electric pump or not?

[Doug&Deb]

I am old and difficult lol. The car did run good with it and I should have left well enough alone but I’m stubborn and wanted the mechanical pump also. I’m going to try a few things and go from there. I’m supposed to go on a tour with my AACA region on Saturday and I don’t trust it yet.

[Ivan_B]

Doug,

 

Let's take it one step at a time.  Let's test it with your electrical pump, if it works, you can use it for now until you have time to mess with the mechanical one.

I prefer the mechanical setup purely for authenticity reasons. There is nothing wrong with using either type, and I doubt that a back-up is ever needed. Either a good quality electric, or a properly functioning mechanical pump should function without questions for many-many years.

[Los_Control]

I'm just curious what tank you have installed? .... Many vehicles this age have aftermarket tanks installed.

I have a "Tanks" gas tank and it comes with a option to install a internal fuel pump .... They make a universal bolt pattern pump that you can install inside the tank and have a modern type fuel pump installed. ... that is cooled with the gasoline .... naturally there are different brands of pumps of different qualities .... you are stepping into a threshold of better quality pumps to fit your car.

 

What I believe to be a factory hard line from my pump to carb, has a 90 bend in it.

 

 

A fuel line has a more sweeping gradual bend then a brass fitting .... just not enough difference between them to make a real difference.

 

Just saying, there are quality electric pumps available that should be trustworthy, in line or in tank ... things still happen and parts fail.

Many people use a pusher electric pump through a mechanical pump with no issues ....

 

I personally feel a issue going up a hill is because the float is set to low, it runs out of fuel on a angle .... where a electric pump is capable of keeping up.

This has all been covered before though.

 

You want to feel better, follow my thread on the way off topic caravan .... you can see where I have been fighting a simple issue for over 6 months now.

I should make another report today on how I finally thought I found the issue .... just to realize I have been fighting 2 issues and now have one issue fixed .... not the main issue. .... I ordered more parts today   😕 

[Doug&Deb]

Los I feel your pain. I’ve been fighting this for a year now. And I’m still not sure whether it’s fuel or ignition although I did put my spare dizzy in and that didn’t change anything.

[Los_Control]

I know what you mean. I felt blessed when my issue got worse and I could reproduce it in the driveway. I was at least able to test and found out my issue was spark.

I had no idea though, until I could reproduce it in the driveway.

 

So far, I think we are all waiting to hear if the issue happens when using the electric pump?

 

Last I read, it works fine with electric .... you just do not trust your existing China pump.

 

I'm just suggesting there are quality pumps available that you should be able to count on.

There are so many cars being LS swapped today, they need electric to manage the FI .... just as many with a small inline pump like yours .... neighbor has a 1952 Ford shoebox with a 1990's FI 302 installed .... little inline pump has worked good for over 5 years I know the car .... they do work.

[Doug&Deb]

I’ll report back when I get a chance to get back in the garage. Because of my back problems I can only wrench for a little while then I need to rest for a day. Hopefully tonight.

[hepkat63]

one thing that caught me during a similar scenario was a very slight air leak in the fuel line.  I'd made up new fuel line and used a brass compression fitting to join them together.  It wasn't bad enough to cause a leak, but was bad enough to suck a little air upon load.  Two second fix

[Doug&Deb]

Okay so here’s what I found out. The new mechanical pump has failed already. I bought it from a very reputable vendor. I know they don’t manufacture but seriously I doubt I put 200 miles on it. I’m going to call them and let them know. For now it’s the electric pump. I still have some tweaking to do before I drive it.