Bubbles in Fuel Pump Bowl (was "Rebuild fuel pump in place?")

[Alpine 1789]

Since my previous thread hasn't been about rebuilding the fuel pump for a while, I thought it best to start a new one. To recap, my car died a few days ago when the fuel pump stopped functioning. Once I got it running again, I noticed many fine bubbles in the fuel bowl coming out of the inlet just left of the filter. Kevin/Puff4 indicated this was a sign of air being sucked in somewhere downstream of the pump and I have been looking for a solution ever since. Here is a photo showing the bubbles:

I have replaced the pump with a newer (although not new) one and replaced the fuel line with a stock one I had laying around. I was fairly certain the problem wasn't with the line (subsequent testing showed it was not) but suspected it might have been the hose connector I had been using and my spare line was uncut and still had the stock compression fitting.

Each time I change something I think the problem is solved, but once the car is fully warmed up (20-30 minutes on the highway) the bubbles return. Everything I have done so far needed to be done for one reason or another, but at this point I am getting ready to decide that bubbles in the bowl are fine. Can someone take a look at their engine when it is hot and tell me if they also have bubbles?

Thanks.

 

[65beam]

fuel pump

the fitting on the fuel line going into the pump is going in a long way which could be due to the ferrel on the line being worn out.it may be allowing some air to be pulled in. have you checked the cap to see if the vent is working?

 

[puff4]

Hang on. You say this only happens once the car is warmed up... is that fuel line getting hot anywhere along the way? The bubbles could be as a result of vaporized fuel if that line is getting pretty warm.

 

[65beam]

fuel pump

if the line runs up the right side of the car,how could it get hot? it's no where close to the exhaust. the line should go up and clip to the area above the rearend, turn right and go thru the x frame,follow the x frame and go thru the x frame again and clamp to the right frame rail.

 

[Alpine 1789]

The fuel line is routed in the normal way. As for the cap, I am not sure exactly how to test the vent on the cap (SV) but I did try leaving it open for a while when the car was hot and there were no noticeable changes to the bubbles. The ferrel on the fuel pump side of the line is new; I did not change the one on the gas tank side, but the seal there seems to be good.

 

[puff4]

Yeah, I know that if routed properly it will not go near anything hot, but it was worth checking... after all, we're really pulling at straws to find out where this 'air' is coming from.

In the end, we know it can only be from two sources - either it really *is* air, in which case there's a leak somewhere, or it's not 'air' at all, but fuel vapor.

I wonder... as the car warms up, is it at all possible that the under-hood temperatures combined with the fact that the fuel being drawn in is under suction, that the fuel is vaporizing at a lower than normal temperature because of the reduced pressure (i.e. suction)?

 

[RootesRooter]

Would a pump be more likely to pull air if the line was partially clogged with paint flakes? If so, did you find any flakes in the resesses of the old pump?

 

[tony perrett]

Check the condition of the gasket that the bowl seats onto.

 

[George Farrell]

Jim

How about running a rubber hose to a small gas can to eliminate all the possibilities along the fuel line and tanks?

George

 

[Green67Alpine]

I get these, after a drive I raise the bonnet to let the heat out and look around the engine bay(for anything out of order), don't remember the fuel not bubbling. Always thought it was an Alpine-ism.

Tom j

 

[Thor 1211]

Bubbles

My Alpine has them, but so did every car I ever had with the glass bowl on the pump. An old timer once told me "If it doesn't hurt fuel dielivery why worry?". He said that as you increase the revs the empty space on top will likely get smaller and the bubbles fewer and as long as the screen on the intake is submerged it's ok. He was of the opinion that it could be an air leak on the tank side, a pinhole in the pump body or diaphram, leaky gasket, or even an air leak on the carb side sucking back through the discharge valve on the return stroke. I don't know.

 

[Alpine 1789]

Lots of really good thoughts and ideas here. Thanks. Let me respond one at a time.

I get these, after a drive I raise the bonnet to let the heat out and look around the engine bay(for anything out of order), don't remember the fuel not bubbling. Always thought it was an Alpine-ism.

Tom j

This is really the most important thing for me to learn right now. Before I continue doing anything more to fix this, I would like to be sure this isn't a 'they all do that' situation and that I only noticed it because of the initial problem. I would greatly appreciate it if a few others could check their cars for me after a good long drive.

Jim

How about running a rubber hose to a small gas can to eliminate all the possibilities along the fuel line and tanks?

George

Ken Ellis also suggested this and it is certainly an option. However, the prospect of getting the car good and hot and then removing the fuel line doesn't fill me with joy. But, it is probably the next step if I need to do more.

Check the condition of the gasket that the bowl seats onto.

I did replace the gasket on the old pump when I was trying to diagnosis it before replacing the pump completely. It is certainly a possibility on the current one, but the bowl is stuck solidly on the pump and I hesitate to screw around with it. It is certainly possible that it is stuck but leaking, so it is something relatively easy I may try yet.

Would a pump be more likely to pull air if the line was partially clogged with paint flakes? If so, did you find any flakes in the resesses of the old pump?

There were no signs of paint in the old pump and I had cleaned and relined my tanks a few years ago, so this probably isn't the case.

Hang on. You say this only happens once the car is warmed up... is that fuel line getting hot anywhere along the way? The bubbles could be as a result of vaporized fuel if that line is getting pretty warm.

Ding, ding, ding, ding! We may have a winner. I was thinking about this last night before I went to bed and realized that, in my car, there is the possibility this is exactly what is happening. I put a Ford oil cooler on the car last summer (http://sunbeamalpine.org/forum/showthread.php?t=16566) because the design of the original one always bothered me (dirty oil remaining after an oil change + slower pressure build up) and because I am one of those who can never leave well enough alone. It seems to work fine and I like the fact that removing the lines cleans up the engine bay a bit. However, the fuel line runs right below the cooler, so it is possible that this is the cause of the bubbles. I wish I had thought of that before putting the new old fuel line in, as re-routing it would have been easier with my original line. Jarrid: I know you use one of these coolers. How is your fuel line routed?

Thanks again to all who have contributed.

 

[George Coleman]

On the backside of the fuel cap there is a small hole in the center of the spring loaded seal. The way I tested this is to use a tube or your mouth and blow or suck on the small hole if it dose not flow a small amount of air then it is plugged. Take a needle or pin and stick it in the hole and move it around this should clear it. Another good test is to ( when you get the bubbles) is to open the gas cap and if the vent is not working you will get a sucksion of air as the pressure is equlized. My notes on this

 

[Alpine 1789]

My Alpine has them, but so did every car I ever had with the glass bowl on the pump.

Thanks Thor. If nothing else, it is good to know I am not alone.

On the backside of the fuel cap there is a small hole in the center of the spring loaded seal. The way I tested this is to use a tube or your mouth and blow or suck on the small hole if it dose not flow a small amount of air then it is plugged. Take a needle or pin and stick it in the hole and move it around this should clear it. Another good test is to ( when you get the bubbles) is to open the gas cap and if the vent is not working you will get a sucksion of air as the pressure is equlized. My notes on this

I was fairly certain this couldn't be the problem, as I was confident I would have known if there was any suction when opening the gas cap. However, I just went outside (after a nice evening drive) and opened the cap to test it with a hose. I am sorry I didn't open it with my ear nearby, but I do think I heard a faint rush of air. It then occurred to me that it is generally not as quiet as it is right now any other time I open the cap. I tried to blow on it with a tube and got nowhere, so I stuck a small brad in the hole and sure enough, met strong resistance at first. Once I 'broke' it lose, it opens readily now and I can blow air through it. So, That does appear to be at least part of the problem! Thanks!

As for another part, I decided to do something temporary to isolate the fuel line from the oil cooler, so I split a spare piece of 1/2" ID heater hose and placed it over the fuel line where it runs under the cooler. I think that helped too, but the more permanent solution will be to use a banjo bolt to route the fuel line away from the cooler. I am planning on replacing the line soon anyway; does anyone know where I can get a banjo bolt that will work with an AC fuel pump?

As always, thanks.