The Stovebolt Site Forums The Shop Area Engine Shop Symptoms of a bad fuel pump? - UPDATE

Hello all,

UPDATE

I was able to find the issue with my truck not idling. First issue was my float setting was off almost a 1/4 inch. Second issue was the gasket between the throttle body and insulator was incorrect causing some sort of vacuum leak. The truck idles really nice now.

One issue that is still not resolved is that it WILL NOT start on its own. It needs either starting fluid or a drop of gas to get it going. Once it fires up it idles really nice.

Second issue is that it seems to load up on acceleration. It idles really smooth, but when I slowly accelerate the truck I see a good bit of white smoke come out of the tailpipe almost like there is condensation is the system. I have good clean non-ethanol fuel going to the carb. Now…this is an engine that has sat for around 15 years so it’s just now getting back to life.

Any ideas on these two issues? Not losing any coolant and the oil checks out fine.

Thanks again!




Recently got myself a 53 pickup, with a 235 engine built in 1955. I have already done all of the basic tuneup things (plugs, wires, rebuilt carb, etc). Truck fired right up and would idle pretty well, although it did have a slight miss. Now for some reason it wont run, and I am not sure what is wrong....

Here are my symptoms:

1) Truck will not start on its own - it needs a small bit of fuel in the carb to fire up
2) It will only fire up and stay running for about 2-3 seconds
3) Occasionally it will start and idle very quiet- almost like it's running on a few cylinders for about 5-6 seconds

I am leaning towards a bad fuel pump. Due to it starting right away with some fuel in the carb I think that eliminates anything electrical (coil, condenser, spark, etc). I took the fuel line off the carb and cranked the engine over a few times and there was no fuel pumping out of the line, so that should mean fuel pump correct? Well just today I decided to unhook the line to the carb and out poured some fresh gas, meaning the pump must have brought some fuel up?

My thoughts are that I have a faulty fuel pump that isn't pumping enough fuel pressure into the carb. Then again, assuming my float bowl is full, shouldn't the truck start running longer than just a few seconds? A little direction would be great! I am not one to start taking things apart and replacing parts without trying all the simple things first.

Remove the gas cap and do the pump flow test again.

"I took the fuel line off the carb and cranked the engine over a few times and there was no fuel pumping out of the line, so that should mean fuel pump correct?"
Most likely, but it could also be a lack of fuel getting to the pump. Gas should free flow from the tank to the fuel pump.

"Well just today I decided to unhook the line to the carb and out poured some fresh gas, meaning the pump must have brought some fuel up?"
On a hot day, gas can expand and at a low pressure, make it through the pump to the carburetor without the engine running.

Your troubleshooting is good but you are letting the unknowns mess with you (second guessing). Start with gas from the tank to the pump. Make sure that is good.

I am in the process of replacing the old tank. The new tank is in, but not hooked up yet.

So for now I have a fuel line funnel suspended in the air, which is hooked directly to the fuel pump. I was hoping to replicate the fuel tank by making sure there is free flowing gas to the pump itself without any air.

Am I making a mistake here?

It is far more likely that you have a fuel delivery problem than a fuel pump problem. What is the condition of the fuel tank? Is it original? It is very common for debris to accumulate in the bottom of an old tank blocking the end of the down pipe in the tank.
I would loosen the fuel line fitting at the bottom end of the down pipe of the tank, don't remove it, just crack it loose to see if some fuel leaks out.

Old tank was really bad, no free flowing fuel at all. New tank is in but not hooked up yet (waiting for fuel line parts).

So for now I have a fuel line funnel suspended in the air that is hooked directly to the fuel pump. Hoping that is ok, but maybe this is my issue. I'm attempting to always have clean fuel running through the engine to eliminate fuel as a potential problem.

It's a lot easier to put a rubber hose on the pump inlet and put the other end in a gasoline can. Put the can on the fender or a nearby table.

I actually drove with a fuel can on the floorboard and a hose going out the window and under the hood to the pump.

I initially did exactly this. The truck was idling and running fine. However, when I started experiencing issues with it not starting on it's own, plus no longer running, I was trying to narrow down a list of things of what it could be. Even with the gas can method it wouldn't run, so I thought maybe it couldn't "pull" fuel up and out of the gas tank via a fuel line. So now I have about 4 feet of fuel line full of fuel, plus a funnel on top. It shows full so I was hoping that meant I have free flowing fuel into the pump?

Small plastic outboard engine fuel tank with the primer bulb on the hose is your friend for situations like this. It will fit the pipe which leads to the fuel pump. Hook it up, squeeze the primer bulb and fire it up.

Does your pump have the glass bowl on top where you can see whether it is full of fuel?

Are you thinking I am not getting enough fuel to the pump, or that I am not creating enough pressure in the line for the fuel pump to work?

No I have the other style pump that just has two ports on top, input on the left, output on the right that leads to the carb.

I would disconnect the fuel line at the carb and see how much fuel is getting to the carburetor, Test the fuel pump pressure. It should be between 2 and 4 psi.

I recently went through a similar situation . It turned out that two new fuel pumps were POSs from China and neither was putting out the requisite amount of fuel. I had the original one rebuilt and it solved the issue.

Could your fuel pump be clogged up with debris from the old gas tank you just removed?

Take the top off and look inside. Maybe there's a bunch of rust or gunk in there from the old tank. The diaphragm could also be torn or stretched from ethanol if it was installed prior to the introduction of ethanol.

Great info, thanks!

I ordered a new fuel pump through speedway. It seemed to get decent reviews, but my long term plan is to have the original rebuilt. I would be it’s really gunked up from the previous fuel if the old tank is any indication.

I took the old pump off and tested the action on. There seems to be decent vacuum on the inlet, but the outlet distributes more of a “spray” than a stream. Is this normal? I assume any sort of gunk or bad varnish would cause intermittent spurts within the fuel pump.

You can take the pump apart and look inside. You'll probably find rust particles and/or yellow ethanol goop clogging it up.

Then & Now Automotive sells rebuild kits or they will rebuild it for you.

I had a 1 year old Carquest pump fail and a brand new Carquest pump fail to pump ANY fuel straight out of the box.

Upon close examination, I discovered the pump arm was assembled incorrectly causing only part of it to make contact with the cam in the engine.

In any event, don't assume your new pump can't be the problem. Just about every new part is a product of Chinese slave labor and there is virtually no quality control.

I once saw a fellow working on a fuel pump taken out of his AD. There was a check valve in it that had been put in backwards during assembly. I didn't know you could take on apart.

The two halves are screwed together with about 6 or 8 screws around the edge of the diaphragm.

If the pump you saw was a new one, I'm not surprised. Airtex fuel pumps are notorious for having all sorts of quality problems. I've had the valves pop out of position on at least two Cadillac pumps because they weren't staked in place. On two Airtex Ford pumps I've had the diaphragm tear within several months of operation.

I never heard good things about Airtex pumps, just bad things.

I first had 2 Airtex pumps fail on my F150 about 10 years ago. They failed in quick succession both with a torn diaphragm. I thought something must be wrong with my fuel pump eccentric.

Anyway, I replaced it with a Precision pump and that one is still working,

In the interim I had an Airtex pump fail on my Cadillac. I asked among my Cadillac friends who all said they were well known for having the inlet and outlet valves jump out of their seats because they were never staked at the factory.

I opened up two of them and sure enough, the problem was valves out of position. I reinstalled the valves with Red Threadlocker and staked them as the original FSM says to do.

I didn't even have to take the pump off the engine to do one of them.

You can see one of the valves just laying on top of the diaphragm where it fell out. In the last pic I took a punch staked the perimeter of the valve to keep it from coming out again.

You might find a similar problem with some of the new pumps being sold today for AD trucks. Since the original ones are sometimes hard to come by, you might have to repair one of the crappy new ones.

Update posted

FRanch53,

Just a note that if you post an update, it normally goes in your latest post reply entry as this tracks the flow of the conversation beginning to end.

Since you didn't say, no one will know "where" you put your update (I did find it in an EDIT of your original post). You can go and edit both posts to help get back on track.

Just food for thought as it will help all during future conversations.

Thanks for updating!

Post from FRanch53

Hello all,

UPDATE

I was able to find the issue with my truck not idling. First issue was my float setting was off almost a 1/4 inch. Second issue was the gasket between the throttle body and insulator was incorrect causing some sort of vacuum leak. The truck idles really nice now.

One issue that is still not resolved is that it WILL NOT start on its own. It needs either starting fluid or a drop of gas to get it going. Once it fires up it idles really nice.

Second issue is that it seems to load up on acceleration. It idles really smooth, but when I slowly accelerate the truck I see a good bit of white smoke come out of the tailpipe almost like there is condensation is the system. I have good clean non-ethanol fuel going to the carb. Now…this is an engine that has sat for around 15 years so it’s just now getting back to life.

Any ideas on these two issues? Not losing any coolant and the oil checks out fine.

Thanks again!

Remove a spark plug right after you shut the engine down to see if they are wet with gas or sooty.