Non-Ford, old car question

[wickedmerc]

My 442 has been cutting out on me during drives. It starts and idles OK. I have a clear fuel filter between the fuel pump and the carb. I'm seeing a lot of air bubbles coming through the filter. If there was a hole in the line or if the line was compromised, wouldn't fuel come out as opposed to air coming in? Something up with the pick-up in the tank?
Talk to me folks.

[Comin' in Hot]

where is the fuel pump?

[wickedmerc]

Stock mechanical fuel pump, front passenger side of block.

[Comin' in Hot]

Stock mechanical fuel pump, front passenger side of block.

then yes, I think its totally possible to pull air into a fuel line due to the suction without it leaking.

let's see what the others say

[wickedmerc]

But wouldn't I have a fuel leak when the car is off?

[Comin' in Hot]

not necessarily. air molecules are far smaller than fuel molecules, I just did a quick search to reinforce my thoughts

http://www.thirdgen.org/techboard/tech-general-engine/625458-lots-air-bubbles-fuel.html

[Merrill]

More definition on "cutting out" , under acceleration, etc. ?

[blackhueys]

what kind of carb? what fuel are you running? is the fuel filter correct size and flow rate for car? what is your fuel psi at idle what is it when the issue happens (may need to tape a fuel gauge to the windshield while your driving), does the car get driven a lot or has it been sitting for along time, any fuel part ie lines pump fitting etc not OEM but aftermarket, how hot is it running, anyone work on the car that may have caused this issue to come up, electric or mechanical cooling fan? just some questions that might help narrow it down some. and yes I have seen fuel have air in the lines and cause issues but no fuel leak externally even though there is a leak somewhere what I have seen is under vacuum from tank to pump can suck enough to open a small hole then seal back up after the vacuum drops.

[wickedmerc]

More definition on "cutting out" , under acceleration, etc. ?


what kind of carb? what fuel are you running? is the fuel filter correct size and flow rate for car? what is your fuel psi at idle what is it when the issue happens (may need to tape a fuel gauge to the windshield while your driving), does the car get driven a lot or has it been sitting for along time, any fuel part ie lines pump fitting etc not OEM but aftermarket, how hot is it running, anyone work on the car that may have caused this issue to come up, electric or mechanical cooling fan? just some questions that might help narrow it down some. and yes I have seen fuel have air in the lines and cause issues but no fuel leak externally even though there is a leak somewhere what I have seen is under vacuum from tank to pump can suck enough to open a small hole then seal back up after the vacuum drops.

Thanks for the info blackhueys! I guess a little more description would've helped from the start...
It's a 350 Olds (I know, I have a 455 block waiting) with an Edelbrock 600 on an RPM manifold. Pump is original type mechanical. I installed a Spectre 2369 inline fuel filter, it's not a high performance engine and I don't see any reference to flow rates. I'm watching it collect pieces of rust as the poor car sat for over 7 years with gas in the tank and lines. I see air right from cold start so I'll assume temp is not a factor. Car starts (after 5-7 pumps which seems excessive) and idles relatively smoothly. The car hasn't been shutting off unexpectedly but rather it bogs down as if fuel gets cut down, then it stalls while driving, not at idle. She doesn't start right back up immediately but will after a few more pumps. Almost like it gets air-locked. I don't have fuel pressure gauge but it's a fair assumption that it drops off once the car bogs down.
I guess I asked the question because I found it odd that there is air coming in but no fuel going out when the car is off. I'm thinking fuel pump or something is up with the pick-up in the tank. the gas gauge works but is not accurate. I don't get lots of spare time to work on the car with little kids running around so I guess I'm looking for areas to attack 1st when I have 20-30mins here and there....before having to pay to have the tank dropped.
I appreciate all of your input.

[mrjones]

I'm having the exact problem with my 77 F150. I'm guessing it's a problem with the pickup tube in the tank. It's sucking air and blowing bubbles into the clear plastic filter I put on mine. When it runs for even a short time, it's sucking enough air to create a vacuum in the tank. After running for just a bit, you can take the cap off the tank and hear a significant rush of air into the tank.

My problem was man made! I accidentally locked one of the locking gas caps on that tank. I couldn't get the cap off, so we pried it off, but the substantial center section fell into the tank. I'm sure it's been bouncing around in there knocking rust and scale off the inside of the tank, and has probably damaged the pickup tube. I'm gonna pull the tank, have it cleaned, and replace the pickup tube and sending unit.

[Curless]

There are several places along the stock lines that have rubber connection them. At the tank, right at the lower control arm mount on the right hand side in the rear, at the front of the frame behind the front wheel and at the pump. Replace them all, after that I'd do the pump. Yes it will pull air in and not leak...I happen to have a 71 on my hoist right now getting a 575 horse 455 and this is one of our concerns!

[Krytin]

then yes, I think its totally possible to pull air into a fuel line due to the suction without it leaking.

let's see what the others say
+^^
I broke down in Boston - engine kept cutting out.
Steel fuel line along frame rail between tank and pump was cracked - sucked air but did not leak fuel!! 6 hrs on a Sunday and it was fixed!!!
You wouldn't believe that could happen in Boston (it was over 30 years ago!)

[Vortex]

Does it have vacume advance? If so, check that.

[blackhueys]

well me myself I would drop the tank and clean it check it out as you say you have rust and its been sitting for 7 years clean all the lines out carb needs to be rebuilt as 7 year old fuel will destroy the inner seals etc. if you see rust then that needs to be gone through first as rust pieces from the tank could get to the carb and plug one of the ports or passages. Your stock mechanical fuel pump should be rebuilt or replaced as well as the rubber diagram is more then likely bad as well from old fuel this can cause weak operation at above idle or in your case a bog this can also cause air in the system to appear. if you want to try and see where if you do have a leak you can apply a small amount of compressed air into the fuel fill neck and hold a rag around it very low psi though not more then maybe 10 psi max as most carb setups only need about 8 to 14 psi while running. there is no amount of running good fuel or cleaners through a system that's been sitting that long with hopes of cleaning everything out. oh also every carb equipped car I have owned normally starts after 1 pump to set the choke then turn the key and they fired your amount seems excessive to me (now this did take me a bit to get dialed in right so take your time). also is your timing set right, also what year car, do you have points? sorry to say this but it is what I would do you should have no rust any where in the system getting to the filter.

[wickedmerc]

Thanks for your input everyone. There's some good info to move forward with. All signs are pointing to me having the tank dropped and either cleaned or replaced.

OR....
Conveniently, I just put a new tank with sending unit in my '72 Cutlass Supreme not too long ago. I really didn't want to start picking parts off of it to use on my 442 but I can think of several parts I could use from that car. I was hoping I could keep the '72 whole, swap the motors/trans and sell it. Gotta think about this one......

[TFB]

I'm yet to see a clear fuel filter in a carb system that was more than 3/4 full or didn't have some bubbles...

[Wags]

Take a peek at the short rubber hose that connects the fuel outlet on the top of the tank to the metal fuel line going up to the fuel pump. These have a tendency to rot over time. When running at idle and slight acceleration enough fuel can get through without issue, but when more flow is needed, the cracked hose will let in air. No fuel will leak out when sitting, as this is located on the top of the fuel tank. If not that, then I would say the rubber diaphragm in the pump.

Wags

[MyBlackBeasts]

Inline glass filters never fill 100% and always have bubbles in them. That said, yes you could have a "sucking air" issue. Steel fuel lines rotting (especially at clamp spots) are very common for this and will not show a liquid leak. Easy way to diagnose is to run a bypass line (pump to tank) or alternate line to a temporary fuel source (this works best as it also rules out an intank issue) and then test drive.

A partially plugged fuel sock in tank can cause symptom also.

Is the fuel pump a 2 line or 3 line lump?

Have you done a fuel pump pressure and volume test?

Did you do an OEM GM HEI conversion? If yes, you could be describing either beginning HEI rotor burn-out or coil pick-up wire failure. Both were very common issues.

[wickedmerc]

Take a peek at the short rubber hose that connects the fuel outlet on the top of the tank to the metal fuel line going up to the fuel pump. These have a tendency to rot over time. When running at idle and slight acceleration enough fuel can get through without issue, but when more flow is needed, the cracked hose will let in air. No fuel will leak out when sitting, as this is located on the top of the fuel tank. If not that, then I would say the rubber diaphragm in the pump.

Wags

I'll check that. You described exactly what I'm seeing. Start and idle are OK but on acceleration the rush of air becomes too much eventually and it shuts down. Thanks for the tip!
BTW.... sharp Chevelle in your profile pic!! :drool:


Inline glass filters never fill 100% and always have bubbles in them. That said, yes you could have a "sucking air" issue. Steel fuel lines rotting (especially at clamp spots) are very common for this and will not show a liquid leak. Easy way to diagnose is to run a bypass line (pump to tank) or alternate line to a temporary fuel source (this works best as it also rules out an intank issue) and then test drive.

A partially plugged fuel sock in tank can cause symptom also.

Is the fuel pump a 2 line or 3 line lump?

Yeah, there's always some air in the filter, that doesn't bother me. It's the air that keeps coming in that is my problem.
I like the "temporary fuel line" idea. That will help narrow down potential problem areas. I hope to give that a try. I also wondered about the pick-up in the tank....if it was clogged, even partially, it would certainly be a problem.


Thanks for the input guys. I really appreciate it. :cool: