Troubleshooting a fuel feed problem

[Hemicbx]

Hey all, My car started acting a little wierd so I thought I'd throw this out to see what others think. This might get wordy, but I'll try to get all the pertinent facts down the first time through.

The engine is a 383 w/ a TF, it's got a Carter mechanical fuels pump (the rebuildable type, M4862), and an AFB. From the tank to the carb, there's the sock on the end of the pickup tube, a 3/8 pickup tube, a basic 3/8 fuel filter right there at the pickup, 3/8 fuel line to the pump, the pump, 3/8 fuel line to a see though fuel filter (basic in-line paper type), and the carb.

I just got the car back after 10 years and it was running decent. I ran a few hard pulls through the gears. It was noticeably laying over a little bit at the top of second gear so I decided to rebuild the fuel pump. I installed the complete rebuild kit without incident. It went together nicely. I also went back to the filter right off the tank and replaced that as well as any rubber line in the suction side of the system. Initially it was running great. Noticeably better pull through all gears.

Then after 20 or so miles of running around, it started acting kind of like a vapor lock or a run out of gas. I'd jump on it in first and at the top of first or just after the shift into second it was sputter, practically die, and by that time I was out of the throttle, feathering it hoping it would catch, it would fire & I'd behave like a normal person for a while.

So I get home and look at the pressure side clear fuel filter and it was essentially empty. I could see little spits of fuels coming into it occasionally, but not nearly enough to feed anything. So I figured something had gone wrong in my fuel pump rebuild. I pulled the pump off & apaprt. All looked well. The dry side was dry, the internal valves were all in place and would seal against me blowing or sucking on them (no commentary needed on that statement), so I put it all back together. I measured the fuel pump pushrod at 3.220.

After it was reassembled I cranked the engine through from under the hood and in a very un-scientific fashion I held my finger over the fule pump's suction port. I could feel some suction but very, very light. I should put a vacuum gauge on it to get a number. However, I don't think it's enough to pull fuel all the way from the tank.

I stopped at that point

Before I go dump $$ into a new fuel pump, I thought I'd get your thoughts.

Any input would be appreciated.

-Hemicbx
York, PA

 

[mattsmopars]

May be a stupid question, but how does the lobe on the camshaft that drives the fuel pump rod look?
Not any chance it might have gotten wiped down or anything of that nature?
Just a thought or something else to check.
Matt

 

[lewtot184]

why a fuel filter at the pick-up? restrictions on the suction side of a mechanical pump can create fuel flashing, basically vapor lock. do a test with the filter removed and let us know what happens.

 

[Hemicbx]

I felt I needed on back there to help pre filter anything coming out. I had the tank steam cleaned when the car was built, but I wanted a little extra. I built the car in 2000 and the one I installed back then was still in the car up till this week. I cut it opened and there was a decent amount of powdery, rusty stuff in the pleats. I installed a brand new one.

I understand what you're saying about restrictions on the suction side, but I've had one in there all along with no ill affects.

I do intend to do a test with it out.

 

[Hemicbx]

I checked vacuum on the suction side of the pump this morning. Line from tank disconnected, vacuum gauge right at the pump. I got 7" vacuum.

 

[67 coronet]

I checked vacuum on the suction side of the pump this morning. Line from tank disconnected, vacuum gauge right at the pump. I got 7" vacuum.

that seems low.it might not hurt to reopen your pump and check to see if new diaphram is split.the powder you found in the prefilter sounds like old dryed out fuel residue.might try to clean tank.if fuel was allowed to dry out inside it will leave a residue that will slowly plug up your filters and reduce octane rating of your new fuel.also make sure any rubber lines between tank and pump have no small cracks.

 

[70rr-brian]

you should be able to pull the fuel line to the carb, in leiu of a gauge and hold the hose over a coffee can or gas can or w/e and have someone crank the car and see if you are getting good fuel squirts.

 

[Meep-Meep]

I agree that a filter on the suction side can be an unnecessary restriction but I have seen plenty of cases where it affects nothing. I would look at your tank vent, or if you have a gas cap that is not under the license plate, take it off and go for a ride. Another thought is the rubber hose on the suction side in good condition? Could the inside wall of the hose be collapsing?

 

[ram250098]

My 68 Runner had a rubber fuel line above the tank that had been bent to run along the frame rail and over time kinked. The car would run but as you hit the gas the pump sucked the hose shut.
AL

 

[1toolguy]

Does the fuel in your area have ethanol in it? Here in FL all we can get now is E10 (10% ethanol) and it's playing hell hit rubber fuel lines. It softens them and allows them to be sucked closed in high demad situations (i.e. full throttle). My Cordoba does exactly what you described and gave us fits for weeks about two years ago. The best solution I found was a fuel injection hose marketed by Goodyear and Prestone with a blue teflon line, it's more expensive but it works great. Goodyear still has it but they have changed the blue liner to black, look for Goodyears SAE 30R9 hose.

There is also a "green" hose (so named because of the green lettering on the outside) that's supposed to be compatable. I had to try it when the local stores ran out of the teflon lined stuff. It'll work longer than the old syle hose but it'll eventually do the same thing, it did it to me at the track yesterday.

 

[Hemicbx]

Hey guys, it's been a bit and I just wanted to give an update so maybe others can use the info in the future.

Up above I said that vacuum on the suction side of the pump was low-ish at about 7". Others on the net have indicated that it should be up around 14. I got 2 stock replacement pumps and they both developed 7" or so on the suction side so I feel my carter pump rebuild is OK.

My fuel filter is horizontal just before the carb & is one of the clear plastic universal replacement types. I was noticing (and then started worrying about) a bubble that always was in the filter. I never saw the filter fill up. And then there was that intermittent "spitting" of fuel into the filter that I mentioned above. I tee'd in a pressure gauge to check it and I'm developing plenty of fuels pressure, 8-8 lbs even when the filter appears empty.

I relocated the filter to a vertical position for a test. The line comes up off the pump and I positioned the filter up & down figuring it would let any bubbles out. Wel, it still holds a bubble in there, but on the outside of the filter element. Fuel moves from outside to inside then out of the filter.

I also removed the filter from back at the tank. With all those changes, I'm happy to say it's all good to go; pulls hard. Now I'm gonna start undoing chnges to see if it re-appears. I'm first going back to my horizontal fuel filter location. I like that better because any crap that gets into the filter body stays there versus the vertical position where it all drains back into the fuel pump.

Ultimately I do believe that is was the fuel filter at the tank. I think Meem-Meep said it best that sometimes it matters & sometimes it don't. This car had a filter back there from 2000 to 2011 and was fine. After I swapped it it wasn't right. Maybe the new filter had more restriction than the original that was in there; who knows.

The comments about the line & ethanol are all good. When I took the rubber lines off while doing this work, they looked worse than some 30 year old lines I've dealt with. All rubber lines are new now.

Anyway, hope somebody can use this info in the future & thanks to everyone whoe chimed in.

-Hemicbx
York, PA