Hi. I just introduced myself and my '68 Polara in the new members page. https://moparforums.com/forums/f4/he...021/#post71207

The Polara is a 318 2bbl, 75K original miles. When running, the engine starts/runs great, but I've been experiencing a recurring fuel delivery problem and after troubleshooting the system from the carb to the tank, I'm pretty sure that something is causing repeated failure of the mechanical fuel pump (replaced twice this season after only a few hundred miles each time, thinking perhaps the first replacement was faulty).

As part of trying to solve the problem, I just replaced a 4' corroded/sightly leaking section of fuel line between the fuel pump and the rear section. I have siphon fuel flow from fuel pump inlet to tank. This has not solved the problem because the pump still isn't pumping.

Before reinstalling the fuel pump this latest time, I felt inside the cam space and noticed that the timing chain seemed loose, where the deflection was a fair bit more that the 3/16" recommended tolerance (according to the service manual I have). I had my wife repeatedly quickly crank the engine, resulting in the chain being sometimes tight, sometimes loose. I don't know if this is normal, but I suspect not. If not, I further suspect that either the timing chain needs to be replaced, and/or the camshaft could be slightly bent causing different tension on the chain depending on where it is in its rotation. If the cam is bent, I s'pose this could cause the eccentric to have less or more contact with the fuel pump rocker arm depending on where the bend is in relation to the eccentric.

The strange thing is, when this problem has happened in the past, a change of new fuel pump has solved the problem -- but only for a little while. To me, if there's a problem with the cam/chain, it's somehow damaging the pump within a few hundred miles causing it to fail.

I'd appreciate any advice to help me solve this. Thanks.

 

On a 383 I had, the cam eccentric for the fuel pump wore down and went flat to the point that it wouldn't push the pump arm for the fuel pump enough to operate the pump. The quick fix was to install an electric fuel pump, which I did.

 

Hey Welcome Eh! Cam won't be bent, for sure change the the timing chain set, it will affect spark timing and start to back fire through carb when you let of on accelerator pedal quickly. Rarely the eccentric will be the problem, almost always it is tank, lines or tank vents. Guys chase this all the time in these old cars. The rust sediment keeps coming and can even get through a paper fuel filter to the needle and seat. I would do the obvious like check tank vent, needle and seat and possibly rebuild carb, although it could be a waste if the sediment keeps coming. I would seriously think about a tank steam clean and internal coating or new. New complete fuel line, pump then rebuild carb. I'm the last guy to start throwing parts at a problem, I have seen and heard this same story too many times. Good Luck.
You can check that eccentric when you change the timing set too.

 

Thank you very much, Silverick, for your posts to my newcomer threads, and at my CarDomain site. I really appreciate it!

Your suggestion to install an electric fuel pump is a good one, which I have thought about, including to avoid any potential vapor lock issues. This will solve my problem, if as you say, a worn out eccentric is the problem, but I'm not sure it is. If it was, I would think that repeat replacement of new fuel pumps would mean that the new pumps would not work at all. But they do -- fior a short while.

Again, there's also the matter of the changing deflection of the timing chain. I'd be real happy to only have to install an electric fuel pump, but I still think the problem is beyond that!

Thanks again!

 

Thanks, and for your insight!

Even though there has been absolutely no back firing (the engine has been running great, with immediate accelerator response), I assume you're suggesting that the changing deflection is not right (strange that it would change from tight to loose though, no?), and if so, I agree that the timing chain set should be changed and I will look into that.

Even cause the fuel pump to fail so quickly? When I push down on the pump rocker arm, I can hear the diaphragm seemingly working right, and can feel the suction/pressure from the outlet. Before I bought the car which was located 3000 mi. from me, I had the previous (original) owner take the car to an independent garage. It wouldn't start and had to be towed. I spoke on the phone with the mechanic who determined that the fuel sending tube in the tank was plugged, so he soaked it to clean it out, and while the tank was off, he sent it out to be steam cleaned. He said, apart from that, the car was in great shape and it even passed a safety check when I got it, and required nothing. That was in Nov. Nov. '08. I have stored the car in a slightly heated garage each winter since then and get the car 'Krowned' (rustproofing) each spring. I'm not saying that rust could not become a problem since then, but if it is, would some rust colored gas in the fuel filter be an indication, and could this be enough to cause the fuel pumps to repeated fail? As part of the overall troubleshooting I've performed, gas I siphoned from the fuel line just before entering the fuel pump, and even back at the tank where I inserted the siphon tube as deep into the tank as I could, the gas was the color it should be, with no sediment settling after a good amount of time.

I haven't done this. Any tips how to go about testing for this?

Although I could certainly be wrong (I don't pretend to be a mechanic, just trying to apply logic from basic understanding of old car engines), I don't think there's a carb problem. Fuel isn't reaching the carb. I have ran it before by running a line from a gas can into the carb.

 

Try putting a glass type filter in line before the pump so you can see exactly what is being drawn up to the pump, if you see a lot of sediment, a thorough cleaning or possibly replacement of tank and metal lines may be necessary, if it is a matter of not getting any fuel, look into the tank vent being plugged as the possible problem. Either way a glass filter will help you see what is going on.

 

Sounds like your on top of your game 68. The vent I would find the end and use a hand held liquid transfer pump, the kind you would use to fill a rear end, and suck don't blow. My 70 has 2, one goes in about 2" the other runs along the top to the back, both open ended not turned up or down, not sure on the 68. The back fire will eventually come when it's really,really loose you might be ok for awhile.
The eccentric: If you can take something long and turn the engine until you "feel" it at it's lowest, take the pump and put in the lever and see how much the pump is tilted up. Push the pump body down and see if it puts pressure against it like its pushing the diaphram. If you really need to compare I can take mine apart and see how many degees the pump flange moves away from the cover as the engine is rotated. I hope that made sense.
Oh, the tight then loose could be broken teeth on part of the cam sprocket, if it has nylon teeth.

 

Thanks about the vent. I will check that.

Re the eccentric, each time I have installed the pump, I have no other option but to place the tip of the lever (rocker arm according to service manual) under the circular part that the eccentric is part of. To be able to secure the pump to the block, I have to put upward pressure on the housing (where it bolts to the block) to get the bolts to align to the threads. I know this pressure is pushing the rocker arm down (tensioned by the spring), and seemingly to me, the correct installation.

Thanks very much for your offer to take yours apart. That's more than I would ever expect anyone to do, so please don't. But you're a great guy to offer!

For information, as this problem has persisted, although I have been doing what troubleshooting/work I can myself to solve it, I've also had the car at two garages to see if so-called 'old school' mechanics could solve it. One was a local Chrysler dealership who told me that a few of their older mechanics even have old mopars of their own. No luck. I'm on my own.....with support from helpful folks like you guys!

 

I've had a problem with the push rod off the cam excentric to the fuel pump arm,mushroomed in the the block,causing the mechanical fuel pump not to pump.I purchase the fuel pump rod from Mopar performance parts,and they told me that there was a defect with the metal rod on 1,000 that they made.So I picked an original 1 up at a swap meet ,that solved my problem.

 

Sounds to me like you are sucking crud from the rusty lines and tank and this is why a new pump fixes it for a short time. You need to clean or replace the tank sending unit and lines. The timing chain is probably fine for now as it runs when a new pump is put in. get it running and then go from there.
The chain will indeed be slack at times and less at others. The reason is where it stops on the compression stroke. The compression will cause it to back off slightly=slop. No compression on exhaust stroke and it will be more likley to remain where it stopped=tight.

 

This is not that hard to find, IF the problem is fairly constant.

An example of a DIFFICULT one was that years ago a cousin had a pontiac which would occasionally stop. FINALLY after backing over a stump and bashing in the tank, they pulled the tank and found that the pickup tube was cut off "straight across" and the type of strainer on the tube had gotten loose and could slide up and down. It would suck up!!! against the end of the pickup tube.

Get yourself an auto store vacuum gauge. Hook it to the pump inlet and crank the engine. It should pull AT LEAST 10-12" vacuum.

Since you are having so much trouble, I would suspect everything and eliminate nothing until you get it fixed. "Rig" the fuel pickup tube by plugging one end with a short length of hose and a smooth bolt/ clamp, and pressurize the other end. With 20 psi or so in there, look for leaks all along the tube.

Pull the filler cap to prevent buildup and blow out the pickup with air.

Hook the pickup tube back up and use a new piece of rubber connector hose. Jack up the car, and with a scrap hose hooked to the delivery tube up front, start a siphon, look for rust, crap, poor flow.

Make sure you tank is vented. You have a shop manual?

Worn-out cams are rare, but if it is, it might be that the pumps are not so much failing, as they are not getting "stroked" as far as they should, and are right on the border line of pumping or not.

 

Thanks for your ideas 440RR. I really appreciate it. The problem is solved. It turned-out to be the cam eccentric. An electric fuel pump is now installed and the car is running better than ever. Thanks again!

 

Great!! Glad to hear your rolling again!