fuel pump?? please help

[chevy murf]

So I got everything running good and now when I drive sometimes it kinda chokes and loses power you can feel it as your driving. Its gotten worse in the past few days. So right away I assume its the fuel pump. Could it be something else? Also do I have to drop the fuel tank to replace it??? thanks all

 

[kleedus]

more details needed carbed or fuel injected

with a carb the fuel pump will be on the pass side front of the engine down by the frame

fuel injected the fuel pump will be in the tank

I would check the fuel filter

depending what carb you have it could be a inline filter or if its a quadrajet its in the carb where the fuel line mounts to it

fuel injected the filter will be under the truck on the insde of the pass side frame rail below the pass seat

 

[chengny]

Q-jet still installed? If so, pull the inlet tubing off the carb where it threads onto the bowl inlet - where it says "filter" on the outer casing - and change the gas filter. See below.

A carbureted engine that runs fine - until high fuel flow is required (i.e highway speeds) -is a textbook case of a fouled fuel filter. It can even run well under heavy load for short periods due to the reserve fuel in the bowl. But once that is used up - you only get what the filter can pass.

The next step (if the filter is okay) would be to check the fuel pump capacity and the condition of the lines.


Here - you know what; 2 birds with one stone. While the gas line is disco'd - put the open end in a container. Have someone crank the engine while you direct the stream of gas into the jar/bottle. Crank for 15 seconds.

If you get a pint or more of gas in the bottle your fuel pump is delivering plenty of gas to the carburetor.

Fuel flow through the pump and filter are okay? Need to check the bowl float settings and the float for integrity.


If you have a TBI engine disregard everything I just said and we'll start over.


There is a chamber behind that adapter. Pull the adapter and you'll see the filter. There is a spring in the bottom of the bore that seats the filter frimly against it's gasket - don't lose it.

 

[chevy murf]

It is a carb

 

[kleedus]

what carb

 

[chevy murf]

I got over 2 cups in 15sec so one pint. The filter seems to be in the line and not the carberator but the problem only happens when im in highway

 

[chengny]

Just because there is an extra in-line filter doesn't mean that the one in the carburetor has been removed.

Also, the fact that there is a filter upstream from the carburetor doesn't positively mean that the internal one (if it still exists) is clean.


Am I reading this right?

I got over 2 cups in 15sec so one pint. The filter seems to be in the line and not the carberator but the problem only happens when im in highway

Don't tell me you went through all the trouble of releasing the fuel line from the carb (and conducting a test of fuel pump output), but while it was off you didn't take the extra 5 minutes to check for the presence (and condition) of the internal filter?


The situation is like this:

It's kind of like "a chain is only as strong as it's weakest link" - the flow rate through a system with multiple filters is limited to what the dirtiest filter will allow to pass.

You can have 3 big brand new filters elsewhere in the line but if the little one that feeds the bowl is packed with fine sediment - you are going to be starved for fuel and running lean.

 

[chevy murf]

Nono i did check and it dosent have one. It just has one i fuel line when to autozone and found out that it dosent have a internal filter. So i replaced the one in fuel line and it didnt make a differnce. The only thing i could think of is the fuel pump. So should i replace that now???? Remeber it only starts to choke when i try to go above 35 mph or so.

 

[chengny]

Good! That sounds more like the murf I know.

OK - so we've got:

no filter in carb, new one in-line, plenty of volume available at pump discharge, pump discharge pressure is not yet known

You've got to ask yourself; why was the internal filter pulled and how long was the carb supplied with unfiltered gas?

People do not generally take the time and effort to pull the internal filter and properly insert an in-line (not as easy as it looks).

Those steps are usually part of a diagnosis/investigation/troubleshooting process.

Has this issue always been present since you have driven the truck or did it develop while you have had it?

Background info is often as important as what is happening now.

Anyway, do you have a pressure gauge (maybe 0-15/30/60 psi with a 1/4 or 1/8" NPT connection)?

If so, you can attach one end of a piece of rubber hose to it with a hose clamp. Then pull the gas line off the carb again and attach the other end of the hose to the open end of the gas line. Do this test:

FUEL PUMP PRESSURE TEST


1.Disconnect the fuel line at the carburetor.
2.Install a low pressure gage onto the line.
3.Start the engine.
4.Fuel pump pressure should be (4 to 6.5 psi) .
5.If pressure is less, check for restrictions in fuel tank sender filter, lines or hoses.
6.Reconnect the fuel line.

This procedure is kind of misleading (step 3). The engine will start with the gas line off and connected to the gauge - but it will run only until the small quantity of gas in the bowl is used.

You probably won't have but a minute or so to check the pump's discharge pressure.

Or if you're ambitious, you can keep the engine running on ether (starting fluid) for as long as you want while you watch the pressure.

If you get sufficient pressure (and you've already checked flow) you will have to start thinking about inspecting/cleaning the carburetor.

You don't have catalytic converters installed do you?

 

[chevy murf]

I do not have cataytic converts. I went ahead and put a new fuel pump on and ut made no difference. I even put in engine cleaning lucas into gas tank no luck. So it has a brand new filter and fuel pump and no difference. The problem developed slowly when i got it. The owner before me used it as a mud truck but never sunk it because i used to go with him all the time and he never did. Could spark plugs have anything to go with this???? What should i do next thanks for help so far

 

[chengny]

When you mention that it only happens at highway speeds it almost always indicates a fuel supply problem.

Without getting into the carburetor itself there is no much more to check. Look at the external linkage and throttle plates in the carb throats. Look for loseness in both areas.

No extra carb hanging around that you could try huh?


Check any and all rubber sections of the gas line on the suction side of the pump. If you have a weak/deteriorated section of rubber hose it may be collapsing at high rates.


When you first lose power on the highway - does it take longer to happen that first time than the subsequent power losses?

If you slow down to say 45-55 for a bit and then boot it again - does it have good power and then fall off again?

Have you found the maximum speed you can maintain indefinitely (i.e. without slowing down for a while to get full power back)?


Air cleaner is clean - and not undersized is it?

Here's the thing;

Loss of power at a steady high load is almost always related to fuel/air flow limitations. Timing doesn't hardly ever drift around. Spark quality is also not usually related to RPM. Compression is not usually affected by speed or load.


Those are the 5 factors that influence proper engine performance. The FACTS:

F = fuel
A = air
C = compression
T = timing
S = spark

Looks like you might have to tear into your carb dude, sorry.

 

[chevy murf]

It drives fine for bout 30 min drom when i wake up then problem starts

 

[chengny]

It drives fine for bout 30 min drom when i wake up then problem starts

I don't get this - please rephrase.

 

[chevy murf]

When i wake up to go to work it had no problems for about 30 minutea. Then it starts to choke and all sometimes i cant get over 35 mph it just wont let me. And when i push gas down to try and fix i hear a loud click. No matter whar it tuns fine up to 20mph through neighborhood but when i get to higher speed it starts to act up

 

[chengny]

You keep using the term "choke". I know you are using it to mean like sputter, bog down, etc. but it got me to thinking. Maybe your problem is not a lack of fuel but rather too much fuel.

Also that click sound you describe...

Check the choke for proper operation. There are detailed descriptions out there - but simply stated: In hot weather - like conditions during the summer months in a southern state like Georgia - the choke should not ever even close. It is designed to close only when ambient is below 75 degrees F. And even then, it doesn't snap from fully open to closed.
The amount that it moves (from full open to full closed) increases with lower temps. If in proper adjustment, the choke plate should be fully closed if the air temperature falls to 45 degrees.

If it does close in hot weather, its no big deal really - it probably just needs to have the choke heater adjusted.

But having said that, let me add a qualifier: it's no big deal really - as long as it begins to open immediately upon start up of the engine and is fully open within a few minutes of engine starting.

The test is:


1. Remove choke coil from carburetor. After removal of choke coil, allow coil to cool to room temperature.

2. Connect a ``jumper'' wire between positive battery terminal and choke coil terminal assembly. Connect a second ``jumper'' wire between negative battery terminal and choke coil assembly grounding plate.

3. The tang on the choke coil should rotate 45°in 54-90 seconds.

4. If choke coil does not rotate or exceeds the 54-90 second time limit, replace choke coil.

5. If coil is within specification, check steps 1 thru 5 for possible cause.




If your choke is closing and not opening you may be running extremely rich.

Check it in the morning. Before you even start the engine - pull the cover off the air cleaner and look down into the throat. The choke plate is a single butterfly that is at the top and front of the carb opening. Without touching anything note whether it is open or closed (or some position in between).

Replace the cover, start the truck and drive your normal pattern. As soon as the engine starts to act up, pull the truck over (leave the motor running) Get out, open the hood and remove the air cleaner cover. Again note the position of the choke plate.

No matter what you found in the first inspection (the one you did back at the ranch) - by the time it begins to act up it should be wide open. Look at the second image I posted above. It shows a choke plate that is completely shut. If yours is like that after 30 minutes of running - it is way out of adjustment.

I don't mean to get your hopes up - but if it is any more than say 1/4 closed - you have most likely found the problem.