Fuel problems

[John S.]

My 1969 350/300 is having a few fuel problems.

1) Occasional fuel starvation I noticed when driving up a steep hill.
2) Occasional knocking noise. Sounds external like a fuel pump.
3) Gas smell only after refueling.

Early in 2010 I replaced all rubber fuel lines and replaced the fuel pump gasket to repair an oil leak.

The car was driven over 3,000 miles since the work was completed. The gas smell has been there all along. The other two items (1&2) are new problems.

Suggestions? The knocking doesn't happen at idle, so it's hard to debug.

[Edward J.]

Re: Fuel problems

John, have you check the fuel filter lately, when traveling up hill under a load the engine requires alittle more fuel demand, the knock you hearing could it just be pinging possiably from a fuel filter clogged.

Fuel smell is common since the tank is vented at the top of tank and gas cap is vented there also.

[Tom H.]

Re: Fuel problems

Don't by any chance have a kink in one of those rubber lines do you ????

[Jack H.]

Re: Fuel problems

Also, there's 'sock' that filters gas inside the tank. Excess stray 'crud' can collect and plug the sock making the problem come/go with cumulative fuel flow from the tank into the forward line...

[John S.]

Re: Fuel problems

Thanks for the suggestions. I'll check them out this wkend.

The knocking has a fuel pump sound, not engine pinging, exhaust leak or internal engine sound.

Would the fuel pump make noise because it's failing or could it also make noise if starved for fuel (pumping air)?

It'll be easier to debug once the noise is constant - probably why AAA is a good idea when you regularly drive your 41 year old car.

[Edward J.]

Re: Fuel problems

John, I have seen fuel pumps make noise a few times over the years, Its when the return spring on the pump arm breaks. It will almost sound like a lifter noise. You can take a long screw driver and place the tip in driver on pump and put the handle to your ear and listen to the pump as the engine idles.

generally an exhaust leak at a exhaust manifold quiets as the engine warms up.

Also when the fuel pump spring breaks the noise should be there all the time.

Jack also has a good idea the sock on the end of sender unit in tank sometimes will crud up overtime. cause fuel starvation.

[Joel T.]

Re: Fuel problems

My 1969 350/300 is having a few fuel problems.

1) Occasional fuel starvation I noticed when driving up a steep hill.
2) Occasional knocking noise. Sounds external like a fuel pump.
3) Gas smell only after refueling.

Early in 2010 I replaced all rubber fuel lines and replaced the fuel pump gasket to repair an oil leak.

The car was driven over 3,000 miles since the work was completed. The gas smell has been there all along. The other two items (1&2) are new problems.

Suggestions? The knocking doesn't happen at idle, so it's hard to debug.

John;

Something you might check... I had a similar problem, had your symptoms 1 & 2... (all the old cars smell of gas when you fill them..) It turned out to be the fuel pump, more specifically the pivot shaft on the pump semi detached. The pump still worked, made some noise... The car would run fine until I put stress on the motor and then it would buck a bit, starving for gas. Once I took my foot off the gas, it would straighten out. Drove me nuts! I did what most guys do... I headed straight to the gas tank and the fuel pick up. I blew out the line, I changed the filter (which was basically new) to no avail. My last resort was the pump and guess what...

Taking a pump out of a SB is no easy task so check other stuff first... It was a repop pump. When I finally got it out of the car, it basically fell apart!

Happy hunting!

Joel

[David Z.]

Re: Fuel problems

I also had symptoms 1&2 , but noise became constant. Do as suggested with the long screwdriver trick.... mine was the fuel pump as well.
I can also attest to the PITA that replacing the pump was.... Good Luck regards, Dave

[John S.]

Re: Fuel problems

I'm just finding time to get back solving this problem.

The fuel starvation happens under hard acceleration as well as uphill. The car runs fine until I accelerate hard and it starves around 4,000 RPM.

I replaced the internal carb fuel filter (start with the easy stuff) - no change.

So it could be:

- external fuel filter. those GF432 filters are $50. Mine was change 3K miles ago.
- fuel filter sock in the tank
- fuel pump
- carb

Where do you suggest I start?

- Testing the fuel pump pressure? With the hard lines I'm not sure where to connect a T?
- Replace the fuel pump?
- Send our the Rochester for a rebuild?

The carb seeps a bit of fuel and percolates after running. I haven't done any work on the carb.

[John S.]

Re: Fuel problems

The problem ended up being the fuel pump.

I also ended up rebuilding the Rochester so the car is running well now.

Thanks for all of your info.