Fuel Pressure Testing Question

ninelevenick · 03-20-2015, 05:49 PM

I pulled the fuel pump relay and jumped 87a and 30. I have my gauge hooked up to the distributor and the WUR. When I turn on the ignition without starting the car, I hear the fuel pumping buzzing. However, there is no pressure in the system. The gauge doesn't move. Last week, I performed a pressure test with the car running. Obviously I had pressure then, and the gauge worked. Am I skipping a crucial step?

tirwin · tirwin's Garage

If the gauge is in the off position then you probably have the gauge backwards to the fuel flow. The gauge is reading 0 because the fuel is on the other side of the valve.

ninelevenick · 03-20-2015, 07:13 PM

When you say off position, are you referring to the valve on the WUR side? Here's a picture of my setup:

tirwin · tirwin's Garage

Do you have an on/off valve? It's hard to tell from the picture but is that to the left of the T in the middle of the picture?

It looks like there is a silver line coming out of the rectangular brass block below the gauge. Where does that go?

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Snipernick

I pulled the fuel pump relay and jumped 87a and 30. I have my gauge hooked up to the distributor and the WUR. When I turn on the ignition without starting the car, I hear the fuel pumping buzzing. However, there is no pressure in the system. The gauge doesn't move. Last week, I performed a pressure test with the car running. Obviously I had pressure then, and the gauge worked. Am I skipping a crucial step?

Sniper,

Are you certain that the buzzing sound you heard was coming from the fuel pump? And not from the other relay under the dash? Was the ignition switch @ RUN position? There are four (4) distinction positions for the ignition switch namely: off, on, run, & start. The FP test is done @ RUN position (before START). Keep us posted.

Tony

ninelevenick · 03-20-2015, 08:30 PM

I'm quite certain, Tony. I just tried it again, and the key could not turn clockwise any more without starting the car. The buzzing sound is pretty loud. It's got to be the pump.

tirwin, that silver looking line is the bleeder hose coming from the rectangular box which is the bleeder valve.

Here's a picture of the method I used to jump the relay. Does it look right?

ninelevenick · 03-20-2015, 10:59 PM

I decided to eliminate the bleeder valve out of the setup. Now the gauge is reading pressure. But, it reads only 11psi for both system pressure and control pressure. System pressure should be about 5 bar. 11psi is not even 1 bar. I don't understand what is going on.

tirwin · tirwin's Garage

You can't test system pressure without a shutoff valve. On most gauge sets there is a "T" in the line. Incoming fuel is on one leg of the T, the gauge is on another leg and the valve is in the outlet side. When the valve is off, it forces the fuel up to the gauge which allows you to read the maximum fuel pressure the fuel pump is producing (system pressure). For example, if the system pressure is too low that might indicate a weak fuel pump. Too high system pressure might indicate a restriction in the fuel line.

kodioneill · kodioneill's Garage

It looks like there's a t handle on the block.

ossiblue · 06:46 AM

Just a couple of questions.

From the posts, I understand you've eliminated the bleed valve set up so the the gauge is now directly connected to the blue line coming from the T connector in the line from the fuel distributor, correct?

With this new set up, you are reading only 11 psi, correct?

Now, the most important question, when you did the pressure test with the engine running (as stated in your first post), what was your pressure reading?

If you had "normal" pressure readings in you first test, I'd suggest you run the engine again with the set up and see if the pressure readings rise. If they do, we will at least know that the gauge works and your gauge set up is good. The problem will be with something else.

ninelevenick · 03-21-2015, 06:41 AM

In the photo you can see the shut off valve located in front of the distributor.

As previously mentioned, I tested the control pressure while the car was running. I recorded 1.5 bar cold and 2.0 bar when warm. Do you think the fuel pump is getting stronger voltage and current when the car is running?

ossiblue · 03-21-2015, 06:49 AM

Quote:

Originally Posted by Snipernick

In the photo you can see the shut off valve located in front of the distributor.

As previously mentioned, I tested the control pressure while the car was running. I recorded 1.5 bar cold and 2.0 bar when warm. Do you think the fuel pump is getting stronger voltage and current when the car is running?

You answered while I was editing. Please read my edit and, if you choose, run the test again with the engine running.

However, the pressures you posted for warm running appear to be low (should be ~3.5 bar) and the change from cold to warm is only .5 bar. Could be the wur is faulty or the pump is weak, or your gauge is faulty.

It is possible the pump is weak and/or not getting adequate voltage from just the battery. Have you tested your battery?

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Snipernick

In the photo you can see the shut off valve located in front of the distributor.

As previously mentioned, I tested the control pressure while the car was running. I recorded 1.5 bar cold and 2.0 bar when warm. Do you think the fuel pump is getting stronger voltage and current when the car is running?

Sniper,

Test your FP measuring the flow rate. You need a minimum flow rate of 2 liter per min.
Disconnect the fitting before the FA (fuel accumulator) and place the end of th fuel line in a suitable container. Secure the container to prevent the fuel from spilling down the floor. Run the FP for 60 seconds and check the volume of fuel delivered. Repeat test several times. Make sure you have a fully charged battery when you perform the FP test. Take the average and keep us posted.

Tony

ninelevenick · 03-21-2015, 07:28 AM

L.J. and Tony, thank you very much. I will take both your suggestions and post my results. BTW, I just read through this thread that contains contributions from both of you. Our Pelican community is fortunate to have great CIS experts such as yourselves.

Another cold start/WUR diagnosis, please

ossiblue · 03-21-2015, 07:35 AM

Oh, one more question.

Just what was the reason why you originally tested the fuel pressure? Were you having driving/running issues? I ask because we don't know, at this time, if you've ever gotten an accurate pressure reading from your set up and, if you had no running issues, this may be a case of a faulty test instrument.

ninelevenick · 03-21-2015, 07:56 AM

I acquired this car last November. At that time it didn't start because the intake boot was ripped. Now with a new boot, the car starts instantly, but it runs roughly throughout the warm-up cycle. I recently richened the air fuel mixture. This made warm running conditions significantly better at idle, but I have not tried driving the car yet because I get some popping when I increase the throttle by hand. The ignition timing is about right. I have taken apart the WUR. It was clean inside. I have replaced the fuel filter. The air box may also have a leak, but that's another story...

ossiblue · 08:27 AM

Quote:

Originally Posted by Snipernick

I acquired this car last November. At that time it didn't start because the intake boot was ripped. Now with a new boot, the car starts instantly, but it runs roughly throughout the warm-up cycle. I recently richened the air fuel mixture. This made warm running conditions significantly better at idle, but I have not tried driving the car yet because I get some popping when I increase the throttle by hand. The ignition timing is about right. I have taken apart the WUR. It was clean inside. I have replaced the fuel filter. The air box may also have a leak, but that's another story...

Thanks for the background, it helps eliminate some possibilities.

Your initial problem, torn boot, was fixed but you still had rough running problems. At that point, it would have been advised to run the fuel pressure tests as the symptom was consistent with a remaining air leak/lean condition or too high fuel pressure. When you adjusted the fuel mixture, you compensated for that possible air leak and things smoothed out, but your pressures are very low.

Run the volume tests suggested by Tony, but be sure the battery/voltage to the pump is adequate.

BTW, this is just my personal view, but I would try to confirm that your gauge set is giving accurate readings and let us know that it is--for peace of mind. Perhaps you could test the gauge off the car and confirm it is giving accurate readings. If you have used the gauge in the past and got accurate results, please let us know.

ninelevenick · 03-21-2015, 10:48 AM

I had never used this HF gauge set before. I bought it about two months ago. I read on a thread here that the Shrader valves for all the connectors need to be removed for better accuracy. I had done this prior to using the gauge assembly. After your suggestion about testing the gauge, I decided to put all the valves back in. This really makes sense to me because the valves push open the little cylinders inside the female ends. Now I get 4 bar for cold pressure and 4.5 bar for system pressure. These readings are still screwy.

ninelevenick · 03-21-2015, 11:00 AM

So, I peeked over at Jim's CIS Primer page, and I saw that normal system pressure for a '79 is between 4.5-5.2 bar. My car is within spec then. However, the cold control pressure is way out of whack. I guess knocking the plug on the WUR is needed.

ossiblue · 03-21-2015, 11:44 AM

Thanks for the feedback, this makes things much easier for all.

I don't have experience with the HF gauge but others have. Still, I'm a little leery of the results you posted due to the gauge reliability. With a cold pressure reading of 4 bars, I don't see how your car would even start, especially when it was running with the major air leak in the boot. However, you did say you had fixed the boot and had taken the wur apart for cleaning so it's possible the reading appears high do to something after the boot fix. Still, 4 bars is way too high for cold pressure.

Having adjusted the fuel mixture may be compensating for the high pressure but I wouldn't suggest you do anything until you can confirm the absolute accuracy of your gauge. Don't adjust the wur yet. Once you know the gauge is reading reliable pressures, report those readings (system pressure, cold control, warm control, and residual, along with the time it took to rise from cold to warm and how long residual pressure lasted for a half-hour span.)