Fuel loss issue, vapor lock? Fuel boiling?

[Runner12]

Hey Guys,

this is my first post so bare with me
I have done some research on other threads but I can’t find exactly what I’m looking for I don’t think….

picked up my 69 Road runner with a 75 block 440. Ran fine, did some timing adjustments, high octane fuel and the basics. (Oil change etc)
Pumped I have this running car not needing much….
Next thing I know the car dies while driving. Will crank but not start. Wait 10 minutes it will fire back up. No other issues for about a week or so of driving. Now I can’t drive 3 blocks without the car dying. I can idle in park or neutral and rev to the moon for 5-10 minutes and the issue will not occur. Only under load.
New dist cap, rotor, and ignition coil doesn’t fix it. I eliminated the old fuel filter and it added flow and power but still died. As I sit there, I hear this bubbling noise from the fuel tank and I open the cap and sounds like pressure released. (Boiling?)
Sometimes it will limp home but most of the time it will die out.
I just switched to a better 91 low or no ethanol fuel (i was told) before this all started. I bought a new vapor separator/fuel filter but I’m not sure where it goes at the tank? I don’t have a 3rd nipple on the sending unit to hook into… could I replace the factory vent line with this return line and install a vented gas cap?

Am I on the right track to eliminate this issue?

Everything is appreciated

 

[beanhead]

I hear this bubbling noise from the fuel tank and I open the cap and sounds like pressure released. (Boiling?)

While it may or may not fix your trouble, it sounds like you need to clean out or replace the tank vent lines.

 

[davek]

only 6 pack and hemi cars came with the vapor separator/fuel filter set up. to me it sounds more like a wiring issue or even coil or plugged pickup in the tank..but could be wrong. You said you changed the timing was the car not running good? is your car running hot? Whats the temp been were you live?

 

[hunt2elk]

only 6 pack and hemi cars came with the vapor separator/fuel filter set up.

I had a 69 Charger R/T a few years ago that came with the return line and vapor separator, it was a 440 car.

 

[Runner12]

While it may or may not fix your trouble, it sounds like you need to clean out or replace the tank vent lines.

i can look into that for sure. Seems easy, best way to do that would be to make sure tank is empty and pull it out I’m assuming?

I’m an electrician, not an auto tech so sorry if any questions seem silly.

 

[davek]

I had a 69 Charger R/T a few years ago that came with the return line and vapor separator, it was a 440 car.

Im wrong. its all HP 440 and hemi.

 

[beanhead]

i can look into that for sure. Seems easy, best way to do that would be to make sure tank is empty and pull it out I’m assuming?

I’m an electrician, not an auto tech so sorry if any questions seem silly.

Not silly at all Sparky! They connect to the tank via a small length of rubber hose. Just un-clamp and completely remove them so nothing gets blown/pushed into your tank.
There is the possibility that the tank's internal vent tubing is clogged, so in that case you'd be best off to drop the tank (it's not too difficult) and douche everything out real good. I'd start with the external tubes though (because it's easier!) and they tend to get plugged and rusted easier due to being out in the elements, at least in my experience..

 

[Runner12]

only 6 pack and hemi cars came with the vapor separator/fuel filter set up. to me it sounds more like a wiring issue or even coil or plugged pickup in the tank..but could be wrong. You said you changed the timing was the car not running good? is your car running hot? Whats the temp been were you live?

timing was fine, just a recommendation from another b body family member to get some better performance. Only 2 degrees different. It ran fine before and after timing for a while. car is definitely not running hot. Stays pretty cool…on the gauge anyways. Barely gets to half.
it’s been 30-38 degrees C here in Alberta the last 2 weeks so that could help the issue.
My Main question then is why the issue only with load and not with high rpms in park??

 

[davek]

i can look into that for sure. Seems easy, best way to do that would be to make sure tank is empty and pull it out I’m assuming?

I’m an electrician, not an auto tech so sorry if any questions seem silly.

NO silly questions,yes drop tank and pull the sending unit and see whats in the tank.

 

[davek]

driving could stir up the dirt/rust in the tank and start to starve the carb.

 

[Runner12]

NO silly questions,yes drop tank and pull the sending unit and see whats in the tank.

Sounds like a plan I should tackle! Good think I only have 45 litres left in there haha

 

[Runner12]

Thanks all, I’ll drop the tank and see what I’m looking at for debris. There was a layer of dust on the car when I bought it so definitely possible that there could be some crap plugging things up.

I will repost if issue still occurs.

 

[Tony Tee]

Get a laser thermometer from harbor freight. So you can pinpoint where your Hotspot problem is.

 

[twecomm]

You running a mechanical fuel pump on that big block ? You may want to check your fuel pump push rod length. Had an issue with my 383 many years ago, turned out being an excessively worn push rod. Pump was barely being stroked enough to be reliable. New one is about $ 35

 

[Runner12]

You running a mechanical fuel pump on that big block ? You may want to check your fuel pump push rod length. Had an issue with my 383 many years ago, turned out being an excessively worn push rod. Pump was barely being stroked enough to be reliable. New one is about $ 35

similar symptoms to me ?
Yes mechanical fuel pump. What should the push rod length be for that pump?

thanks

 

[twecomm]

I believe it 3.25 in. but I would verify that. Think it's in the shop manual.
Mine was worn by close to 3/8 inch when I had my problem.
Here's a link to push rod from CompCams. Details on thgis part below state 3.22 in.
https://www.jegs.com/i/COMP-Cams/249/4626/10002/-1

 

[XCELLR8]

Is your new fuel filter clear? If not, get one that is clear. I had a problem in the past that the filter would be full of gas, but when I went to drive the car, it would suck the gas out of the filter to the point that there was hardly any gas in it. I ended up having a plugged sock on the end of the sending unit, put a new one on and problem went away.

Edit to add info: When I had the plugged sock the filter would be full and stay full when I was in the garage trying to find out the issue, but as soon as I took the car out to drive it, it would run like crap. Come back to the garage and the filter was almost dry.

 

[451Mopar]

I no longer trust 50 year old fuel tanks and fuel lines.
I pull the tank, and at least flush it out clean if re-using it.

A new Spectra CR9C tank is only $172.99 from Autozone.
https://www.autozone.com/fuel-delivery/fuel-tank/p/spectra-premium-fuel-tank-cr9c/163323_0_0
The Tank sending unit (FG68B) with 3/8" Pickup with 1/4" Return is $94.99
I don't know why the 3/8"$ 1/4" set is $170.00 from SSTUBE The kit might come with the fuel line to body clips?
https://www.sstubes.com/pages/searc...s&page=1&rb_product_type=Fuel+Lines\,+Chassis

My Coronet with EFI:
Spectra Preimum Fuel injected tank with pump, the CR9CFI, but it is about $470.19
https://www.amazon.com/Spectra-Premium-CR9CFI-Classic-Injection/dp/B00LPIP7J0
New 3/8" Stainless fuel line from SSTUBE is $68.00
And 5/16" Fuel line for return (the spectra tank uses a 5/16" return) $68

Making connections with Gates Barracade EFI Fuel line and the Fuel Injection Hose clamps:
https://www.gatesaustralia.com.au/~...products/gates-fuel-hose-flyer--june-2018.pdf