How to test fuel pump? How to attach pressure gauge?

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Lasalle

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Stock 1973 Dart 318 V8. The 1973 shop manual shows how to use a pressure gauge to test outlet pressure on the fuel pump. The book says to install a tee just before the carburetor to connect the pressure gauge. I don't think the tee fitting exists. Numerous auto parts stores do not have the fitting. IS there another way to test a fuel pump?

Fuel pumps are not that expensive. It seems way easier to just change the pump. That is wasteful to me.
 
could put gauge right on fuel pump. fill bowl and start it. measure the pressure at idle and at 2500.
 
Lasalle said:
Stock 1973 Dart 318 V8. The 1973 shop manual shows how to use a pressure gauge to test outlet pressure on the fuel pump. The book says to install a tee just before the carburetor to connect the pressure gauge. I don't think the tee fitting exists. Numerous auto parts stores do not have the fitting. IS there another way to test a fuel pump?

Fuel pumps are not that expensive. It seems way easier to just change the pump. That is wasteful to me.
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So it's wasteful to actually test a pump rather than buying another and throwing away a pump that may be perfectly good?

The "fitting" is whatever it takes, and may and likely does consist of more than one fitting. On older systems, like Mopar, fittings are pretty much inverted flare--same fittings as brake lines. Due to modern auto stores "not being" as "partsy" as they once were, IT MIGHT BE more difficult to round up parts. But it can be done

You can buy various lengths and sizes of brake lines with inverted flare. You generally need 5/16"
You need a tee with adapters so that you can disconnect the existing line, put the tee inliine, and output a branch of the tee to the pressure gauge.

That pretty much is going to be determined by "what is in your junk box" and what the local stores have in stock. There are various ways of getting there

My question to you is "do you know and understand" the basics of various fittings, such as inverted flare, SAE flare, pipe thread, and so on?
 
Lasalle said:
Stock 1973 Dart 318 V8. The 1973 shop manual shows how to use a pressure gauge to test outlet pressure on the fuel pump. The book says to install a tee just before the carburetor to connect the pressure gauge. I don't think the tee fitting exists. Numerous auto parts stores do not have the fitting. IS there another way to test a fuel pump?

Fuel pumps are not that expensive. It seems way easier to just change the pump. That is wasteful to me.
Click to expand...
You will need a chunk of fuel hose, a "T" Plastic or brass and some clamps. You can disconnect at the carb or the carb side of the fuel filter. Hust make sure the hoses fit on the T and the clamps are tight. No need to start a fire. Your gauge will need a barbed fitting on the end. Most of the fuel pressure gauges now days are for Schrader type fittings (because of fuel injection pressures)
 
old school combo valve, comes with cone fittings that you can jamb into fuel lines. Were only talking 8 psi tops. HF has them for $13 with a bunch of fittings. doubles as a big vacuum gauge.
holland-1965-chevrolet-chevelle-300-vacuum-fuel-pressure-gauge.jpg
 
pishta said:
old school combo valve, comes with cone fittings that you can jamb into fuel lines. Were only talking 8 psi tops. HF has them for $13 with a bunch of fittings. doubles as a big vacuum gauge.
holland-1965-chevrolet-chevelle-300-vacuum-fuel-pressure-gauge.jpg
Click to expand...
Great photo. That was a handy tool for old cars. I think the op may be a beginner. I was looking for a video to help him along but everything seems to be late model fuel injection stuff.
 
I remembered because I just bought one to replace a 25 year old one that finally fell apart. Cheap *** boost gauge too!
62637_zzz_500.jpg
 
#3 is right, you don't need a "T" fitting, it won't be running that long. I have never seen a "weak" pump, either they work or they don't. Running the engine with the line dumping into a bucket will tell me if I have a "healthy" stream of fuel or not.
 
Murray said:
#3 is right, you don't need a "T" fitting, it won't be running that long. I have never seen a "weak" pump, either they work or they don't. Running the engine with the line dumping into a bucket will tell me if I have a "healthy" stream of fuel or not.
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I've seen plenty of weak pumps at least half a dozen over the years. Start and idle great, might even drive 20mph, etc but as speed goes up, .............................

And fuel pressure AND FUEL VOLUME is not just about the PUMPS either. It is the "end to end system" from the fuel sock in the tank, to junk in the tube, to bad hoses at the tank and pump inlet, and to air leaks into the hoses/ tubing. And plugged filters. And crimped tubing / hoses. And worn cam lobes

"Pump into a bucket." I admit this goes a LONG way. Many times if a pump produces volume, the pressure is not an issue
 
To 67 Dart273 post #4: No I mean the opposite. I am annoyed that I can't find the fittings to test the pump. It is wasteful to just change pumps. Yet it is easier to just change the pump than to run around looking at auto parts stores that are not going to have the fitting I want anyway.

The answer to your last question is NO. I don't know about all the different thread systems and that made it more unlikely that I was going to find what I need.

To Pishta post #8: That is the pressure gauge I have.

To Scody21 post #2: They may have what I need.


The gist of the matter is I am annoyed because something I thought was going to be simple turned out to be complicated.
 
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Lasalle said:
To 67 Dart273 post #4: No I mean the opposite. I am annoyed that I can't find the fittings to test the pump. It is wasteful to just change pumps. Yet it is easier to just change the pump than to run around looking at auto parts stores that are not going to have the fitting I want anyway.

To Pishta post #8: That is the pressure gauge I have.
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What issues are you having? Why do you need to change the pump. With pump pressure I am more concerned about too much pressure than not enough.
 
I am trying to diagnose a rough idle. I have been farting around with this all summer. I started another post on this a while back. A weak fuel pump is just one idea I had but I just wanted to test it because I didn't think there was a high probability that was the cause. The other more likely causes I am looking into are bad carburetor float adjustment and a vacuum leak.
 
Lasalle said:
I am trying to diagnose a rough idle. I have been farting around with this all summer. I started another post on this a while back. A weak fuel pump is just one idea I had but I just wanted to test it because I didn't think there was a high probability that was the cause. The other more likely causes I am looking into are bad carburetor float adjustment and a vacuum leak.
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Fuel pressure is definitely on the list of things to check. Too much pressure 5# or more can cause the carb to bleed over at idle causing a rich condition you can't tune out. Float and vacuum leak can also cause a rough idle as well as a list of ignition and mechanical issues.
What are you working on? Stock or modified?
 
1973 Dart Swinger 318 V8 100% stock. Carter BBD 2 barrel carburetor. No power brakes. I started a thread on this on May 12 2022 in the "small block mopar engine" category TITLE: "Stock 1973 318 V8 starts but won't idle without foot on pedal.

I had the carburetor rebuilt and that helped. I don't have a lot of faith in the "professional" who did the rebuild. He did not do any other diagnosis. The car is driveable now but the idle is still rough. It smooths out at higher RPM. The idle is set at 800 rpm. It should be 700. I have timing light, tachometer, and vacuum gauge.
 
In case no one mentioned it's all right there in the factory service manual.

Mymopar.Com
Free download
 
pull a vacuum on your vacuum operated accessories (distributor, EGR, etc) with your new vacuum gauge and your mouth. plug T with tongue and watch gauge. It should not fall or else its a bad diaphragm in the tested device. Distributor is a price suspect. Also start motor with gauge in distributor vacuum line. tell us what it reads or does (vibrate, wander, etc) Valuable stuff. I dont suspect a poor pump would cause a poor idle unless the bowl level is very low or very high. Could always turn the idle screw all the way in then start from scratch at 1.5 out. Make sure the carb air bleeds are clean. Today's gas sucks *** when it comes to sitting around in a carb. An electric is almost a given only to turn off and let the motor drain the carb at the end of the day. Flip the switch 5 seconds before you start it and hit the road, no dry cranking to fill the carb again worries.
 
Lasalle said:
Read the second sentence of my original post #1
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Missed that.


All I did was Google "5/16 brass T"

Home Depot, ace hardware, Lowe's etc has them in the plumbing isle by the sprinkler parts.

Screenshot_20220808-213550.png
 
I just looked in my 69 Service manual. It said to disconnect fuel line prior to carb, place that fuel line in a bottle (didn't say which size), disconnect coil wire and crank engine with starter. The fuel pump should pump out one quart in 60 seconds. Since I assume the fuel amount would be at a steady rate, perhaps you could also assume that 16 ounces in 30 seconds would also be satisfactory. This might not be the most accurate test, but it should give you a ballpark idea of whether the pump was working OK. It did not mention anything about engine size.
 
pishta said:
old school combo valve, comes with cone fittings that you can jamb into fuel lines. Were only talking 8 psi tops. HF has them for $13 with a bunch of fittings. doubles as a big vacuum gauge.
holland-1965-chevrolet-chevelle-300-vacuum-fuel-pressure-gauge.jpg
Click to expand...
Same good ol junk I got! And, they work. I hate China, but Sometimes, I wouldn't HAVE a darn tool for that one time, or infrequent use stuff. And 20 bucks for a 12 pak of 1/2" impact sockets is hard to beat. Especially since Craftsman went S
 
The problem I was trying to diagnose was not the fuel pump at all. It turned out the mixture screws on the carburetor were out of adjustment. Car runs fine now.
 
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