Symptoms of a failing mechanical fuel pump?

[ArtemisI6]

My girlfriend's '67 runs and idles fine for the most part, but when I'm driving it, it'll sometimes just flat out stall out of nowhere. Sometimes it'll stall, and if I keep the ignition on and keep it in gear with it still rolling with my foot on the gas a small bit, sometimes it'll buck to life and continue to drive for a few hundred feet, then die again.

It seems like after it happens the first time while I'm driving, it'll happen several more times in the same drive. When I shoot starter fluid down the carb throat the car always starts up without issue and will sit there idling smoothly. I found a medium fuel leak in the rear of the car and figured that the car was sucking air and causing it to stall out intermittently while driving so I replaced all the fuel lines in the car since they were all pretty bad to begin with. Figured I'd fixed it... then it happened again a couple hours later in the same night. I also replaced the fuel filter since it's like $2 and when I pulled the old one off expecting to get my hands covered in gas I realized the thing was bone dry inside. Zero gas came out. This was immediately after the thing had stalled pulling it into place in my driveway.

I have not noticed speed or RPMs as having any significant affect on this issue, either.

With an electric fuel pump it's easy to diagnose - just jumper the two leads to + and - on a 12v source... but I've never had experience with a mechanical fuel pump failing... does anyone know if this sounds like it might be the issue?

 

[Anonymous]

You are experiencing failing fuel pump.
Ken

 

[Harte3]

Best get it changed because if it is leaking in to the crankcase...the engine does not lube well (understatement) with a gas/oil mix in the crankcase.

 

[ArtemisI6]

Yeah, after speaking with my boss he explained to me the reasons behind exactly why and how mechanical fuel pumps fail. It definitely sounds like that especially because this seems to happen MUCH more often when attempting to climb a hill. What made me not so sure about this being the issue is that it doesn't seem to affect it when I floor it down the road, which seems weird because a failing fuel pump should show up during any engine load at all, not just a hill... and the fact that it's intermittent. It'll happen on level ground too although a hill causes it to happen more frequently.

But, at $30 for a brand new one, I figured I might as well just change it because if it's not the cause, it'll be the next thing to fail on this car. The fun of getting a car reliable again after being neglected for well over a decade...

I bought a new one today through my job and will be installing it tomorrow. Thanks for the input guys. I hope this fixes it so I can move onto the steering components next.

 

[The Plankster Prankster]

i've seen similar symptoms from a leak between the tank and the pump. drove 7 hours once to fix my truck that my brother was driving across the state when it sprung a leak and started sucking air.
if the pump doesn't fix it, check all the lines again.

 

[ArtemisI6]

i've seen similar symptoms from a leak between the tank and the pump. drove 7 hours once to fix my truck that my brother was driving across the state when it sprung a leak and started sucking air.
if the pump doesn't fix it, check all the lines again.

That was the first thing I checked. I've redone all the fuel lines except for about two feet coming off the gas because I couldn't be arsed to bend those at the time and they're the only lines in halfway decent shape anyway.


I just installed the new fuel pump. Basically I pulled the first one out and just popped the new one in with a new gasket. The instructions mentioned something about having to pry a cam bar (or something) onto the fuel pump's plunger or some crap like that, and if you don't then damage can occur. It didn't seem nearly that complicated with this motor but I haven't started it yet... I stuck my finger inside there to see what kind of drive this fuel pump was and it just seemed like an offset cam lobe driving the pump. It seemed like with this one all I do is pop it in and crank the motor but I don't want to crank the motor and blow the thing apart. Is it as simple as it seems or is there a risk of messing this up? I'm no moron but it's not my car so I want to be extra careful and make double sure before I risk damaging something.

 

[mustang6]

It sounds to me like you installed it correctly.

 

[GrantD]

on the plus side though, the fuel pump on a 200 has to be in one of the most convenient places I've ever seen. The hardest part is holding it in the block while you get the screws started.

 

[ArtemisI6]

Well, I drove it 15 miles to my girlfriend's school last night without a hitch. On the way home tonight, it did the same thing as described in the original post. Stalled about nine times in the 15 mile trip home.

I'm beginning to think it's the Pertronix module, but the thing idled in my driveway the other day for 20 minutes straight without stalling at all, but as soon as I pulled it onto a main road it died. I don't understand what would change in the behavior of the module between idle and just cruising along.

 

[PaulS]

If her fuel tank has a drain plug on it try pulling it and fill a glass quart jar with what is in the tank. I bet your gas and alcohol has separated and at times you are getting straight alcohol to your carb. The engine is not running rich enough to run at all on the alcohol.
If what I suspect is true there will be a layer of what looks like water in the bottom of the jar with gas sitting on top. If you find this you can find out if it is water or alcohol by sucking the clear liquid from the bottom and try lighting it. If it burns then the alcohol has separated - if it doesn't burn then you have an accumulation of water in your tank. Drain a gallon or two from the tank and your problem should be solved - at least until the water builds up again.

 

[Lazy JW]

....

I'm beginning to think it's the Pertronix module......

Swap the points back in, it's easy to do and will eliminate that as a variable.
Joe

 

[ArtemisI6]

If her fuel tank has a drain plug on it try pulling it and fill a glass quart jar with what is in the tank. I bet your gas and alcohol has separated and at times you are getting straight alcohol to your carb. The engine is not running rich enough to run at all on the alcohol.
If what I suspect is true there will be a layer of what looks like water in the bottom of the jar with gas sitting on top. If you find this you can find out if it is water or alcohol by sucking the clear liquid from the bottom and try lighting it. If it burns then the alcohol has separated - if it doesn't burn then you have an accumulation of water in your tank. Drain a gallon or two from the tank and your problem should be solved - at least until the water builds up again.

Would that happen from the car sitting? Because I've refilled this fuel tank three or four times from three different gas stations with this still occurring.

Swap the points back in, it's easy to do and will eliminate that as a variable.

D'oh! Of course! Will do that tonight!

 

[ponyrider200]

I had the same problem with my 66 Mustang. Turned out there was a piece of fabric, like rubber floating around in the gas tank. The fuel pump would suck it over the inlet to the fuel line and cut off the fuel supply. The engine would die. As soon as that happened, the piece of fabric would float free, away from the inlet, and the car would start up and run fine until the thing got sucked into the inlet again. I drained the tank and removed the gas sending unit, and when I flushed out the tank, out can this piece of rubber sheet. It was abou the size of a small balloon, which is what I think it was. Problem solved.

 

[ArtemisI6]

I had the same problem with my 66 Mustang. Turned out there was a piece of fabric, like rubber floating around in the gas tank. The fuel pump would suck it over the inlet to the fuel line and cut off the fuel supply. The engine would die. As soon as that happened, the piece of fabric would float free, away from the inlet, and the car would start up and run fine until the thing got sucked into the inlet again. I drained the tank and removed the gas sending unit, and when I flushed out the tank, out can this piece of rubber sheet. It was abou the size of a small balloon, which is what I think it was. Problem solved.

Yeah, the fuel tank was pretty gross when we got it... like, you couldn't see steel because of all the black gassy sludge. Had to get a new fuel sender because the original looked as if it'd been undercoated. We should've freaking just bought a new one when we had the chance, but we tried to clean it instead. Thought we got it pretty clean, but that's really the last thing I haven't investigated yet. I hate pulling gas tanks, and I just filled this one up too. It would make sense, too. The girlfriend wants to do it on Thursday when she's in town.