Community Forums

Elexwiz · 04-22-2014, 04:56 PM

Here are my troubleshooting results:

1. I hooked up the fuel pressure gauge.
2. I removed the vacuum line from the regulator and hooked a pressure tester to the VACUUM LINE.
3. I started the engine. The fuel pressure immediately shot up to 39 psi. The vacuum gauge showed 21 lbs of vacuum on the LINE. My vacuum lines to the regulator are good.
4. I rev'd the engine. The vacuum pressure increased to above 25 lbs. The fuel pressure actually dropped! I think this is the expected result when the vacuum line is disconnected because the injectors are shooting the fuel faster. It came back to 39 psi when the engine got back to idle.
5. I disconnected the vacuum tester and reconnected the vacuum line to the regulator. The fuel pressure immediately dropped to 28 psi.

Is my regulator bad? If so, how? With the vacuum line disconnected the fuel pump was able to push 39 psi past the spring. With the vacuum line connected and supposedly pulling 21 lbs of vacuum, it should pull the diaphram back and allow more fuel to the return line while slightly increasing the overall fuel pressure.

Btw, while the vacuum line was disconnected I connected my hand-held vacuum pump to the regulator and drew 21 lbs of vacuum. The results were the same as the when the vacuum line is hooked up normally; fuel pressure 28 psi.

Any ideas?? Thank you all, again!

Elexwiz · 04-22-2014, 05:20 PM

I think my fuel pressure regulator has a weak spring. I think that with the vacuum line disconnected the fuel pressure should have been much higher. It would naturally be lower with the vacuum line hooked up and assisting the fuel pump to push the spring. I'm gonna replace my fuel regulator.

subford · 04-22-2014, 05:34 PM

The fuel pressure should be around 40psi with the vacuum line disconnected, zero vacuum. This is the same as WOT.
With vacuum line connected at idle (max vacuum) the fuel pressures should be 30-33psi.

Here is a run down on how the system works from the 1999 Ford Shop manual:

Returnable Fuel System

The fuel system consists of a fuel tank with a reservoir, fuel pump module, fuel supply lines, fuel filter(s), Schrader/pressure test point, fuel rail, fuel injectors, and fuel pressure regulator. Operation of the system is as follows (refer to Figure 56 for all others):

1. The fuel delivery system uses the crankshaft position (CKP) sensor to signal the PCM that the engine is either cranking or running.

2. The fuel pump logic is defined in the Fuel System control strategy and is executed in the PCM. The PCM will ground the fuel pump relay for one second during key on and engine off. During crank the fuel pump relay is grounded as long as the PCM receives a CKP signal.

3. The fuel pump relay has a primary and a secondary circuit. The primary side is controlled by the PCM and the secondary side provides B+ to the fuel pump circuit when the relay is energized.

4. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of a collision. The IFS Switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision).

5. The fuel injector is a solenoid-operated valve that meters fuel flow to each combustion cylinder. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by length of time the fuel injector is held open. The injector is normally closed and is operated by 12 volt VPWR from the power relay. The ground signal is controlled by the PCM.

6. A pressure test point valve (Schrader valve) is located on the fuel rail. This is used to measure fuel injector supply pressure for service and diagnostic procedures.

7. The fuel pressure regulator is attached to the fuel rail downstream of the fuel injectors. It regulates fuel pressure supplied to the fuel injectors. The fuel pressure regulator is a diaphragm-operated relief valve. One side of the diaphragm senses fuel pressure and the other side is connected to the intake manifold vacuum. Fuel pressure is established by a spring preload applied to the diaphragm. Balancing one side of the diaphragm with manifold vacuum maintains a constant fuel pressure drop across the fuel injectors. Fuel pressure is high when engine vacuum is low. Excess fuel is bypassed through the fuel pressure regulator and returned through the fuel return line to the fuel tank.

8. There are four filtering or screening devices in the fuel delivery system. The fuel intake sock or screen is a fine, nylon mesh mounted on the intake side of the fuel pump. There is a fuel filter screen located at the fuel rail side of the fuel injector. A fuel filter/screen is located in the inlet side of the fuel pressure regulator. The fuel filter assembly is located between the fuel pump and the pressure test point/schrader valve.

9. The fuel pump (FP) module is a device that contains both fuel pump and fuel sender assembly. The fuel pump is located inside the reservoir and supplies fuel through the fuel pump module manifold to the engine and the fuel pump module jet pump.

/

subford · 04-22-2014, 05:52 PM

Quote:

Originally Posted by Elexwiz

3. I started the engine. The fuel pressure immediately shot up to 39 psi. The vacuum gauge showed 21 lbs of vacuum on the LINE. My vacuum lines to the regulator are good.

39psi is about normal with the vacuum line disconnected.
I take it you mean 21 inches of vacuum on the vacuum gauge.

Quote:

Originally Posted by Elexwiz

4. I rev'd the engine. The vacuum pressure increased to above 25 lbs. The fuel pressure actually dropped! I think this is the expected result when the vacuum line is disconnected because the injectors are shooting the fuel faster. It came back to 39 psi when the engine got back to idle.

Odd, the vacuum should have dropped when the engine is rev'd.
With the vacumm line disconnected the fuel pressure should have held at 39psi and not have dropped.
You may have a filter problem, low voltage to the pump or a bad fuel pump after all.

Quote:

Originally Posted by Elexwiz

5. I disconnected the vacuum tester and reconnected the vacuum line to the regulator. The fuel pressure immediately dropped to 28 psi.

This is normal. I think your fuel pressure tester may be reading about 1psi low.

Quote:

Originally Posted by Elexwiz

Is my regulator bad?

Sounds like it is working OK.

Quote:

Originally Posted by Elexwiz

With the vacuum line disconnected the fuel pump was able to push 39 psi past the spring. With the vacuum line connected and supposedly pulling 21 lbs of vacuum, it should pull the diaphram back and allow more fuel to the return line while slightly increasing the overall fuel pressure.

It does not work that way. More vacuum less fuel pressure.

Quote:

Originally Posted by Elexwiz

Btw, while the vacuum line was disconnected I connected my hand-held vacuum pump to the regulator and drew 21 lbs of vacuum. The results were the same as the when the vacuum line is hooked up normally; fuel pressure 28 psi.

This is also normal.

Elexwiz · 04-22-2014, 06:34 PM

Yes, I meant 21 inches.

Hmmm.... I've read so many posts in the past few days that they're all starting to run together. I jotted down some numbers from one post that I wish I could find again. It said idling fuel pressure should be around 35 psi and WOT pressure should be 45-50. The idea was that as the rpm's increased the pressure also increased to make sure the rapidly firing injectors had the necessary pressures.

You said that max vacuum occurs at idle. This vacuum connection is coming from the intake manifold, but shouldn't the vacuum increase as more air is pulled through the throttle valve, a venturi, causing higher air speeds and lower pressure inside the throttle body, and consequently a vacuum.

Elexwiz · 04-22-2014, 06:42 PM

Here's a youtube video that says as throttle increases so should fuel pressure. I was thinking that the spring inside the regulator was weak. The vacuum coming off the intake manifold is pulling back too far thus reducing the fuel pressure and eventually "running out of fuel" on hard accelerations or down-shifts when climbing hills. Hence my SES codes.

https://www.youtube.com/watch?v=Kub3q1-YNZA

Elexwiz · 04-22-2014, 06:50 PM

Quote:

Originally Posted by subford

With the vacumm line disconnected the fuel pressure should have held at 39psi and not have dropped.

I think this is because the spring is weak. I think that the spring is so weak that when the vacuum line is disconnected the pressure of the fuel pump is enough to completely compress the spring. As I rev the engine the injectors start using up that fuel at an increased rate. The spring isn't strong enough to push down and maintain that pressure.

subford · 04-22-2014, 06:56 PM

Quote:

Originally Posted by Elexwiz

Here's a youtube video that says as throttle increases so should fuel pressure. I was thinking that the spring inside the regulator was weak. The vacuum coming off the intake manifold is pulling back too far thus reducing the fuel pressure and eventually "running out of fuel" on hard accelerations or down-shifts when climbing hills. Hence my SES codes.

https://www.youtube.com/watch?v=Kub3q1-YNZA

True as throttle increases the fuel pressure does increases but at the same time the vacuum goes down allowing the spring in the fuel pressure to close down the return to the tank.
I did not watch the video.

subford · 04-22-2014, 07:01 PM

Quote:

Originally Posted by Elexwiz

Yes, I meant 21 inches.

Hmmm.... I've read so many posts in the past few days that they're all starting to run together. I jotted down some numbers from one post that I wish I could find again. It said idling fuel pressure should be around 35 psi and WOT pressure should be 45-50. The idea was that as the rpm's increased the pressure also increased to make sure the rapidly firing injectors had the necessary pressures.

You said that max vacuum occurs at idle. This vacuum connection is coming from the intake manifold, but shouldn't the vacuum increase as more air is pulled through the throttle valve, a venturi, causing higher air speeds and lower pressure inside the throttle body, and consequently a vacuum.

That post was wrong for a Ford truck engine or at least yours.

First off there is no venturi with an fuel injection engine as that was in the Carb days.
Air rushing into an engine does not cause the vacuum, it is caused by the pistons going down and the valves as the engine runs.

Elexwiz · 04-22-2014, 07:06 PM

Before I forget let me say that I greatly appreciate your help and discussion on this. I now know that my intake vacuum is WRONG! I need to figure this out before I go any further. On my intake manifold there is a spare connector that I used to hook up my vacuum tester. It clearly jumped from 20 inHG to well above 25 inHG when I rev'd the engine. Would you agree that I need to find that problem before moving on with the fuel problem (if there is one)?

Elexwiz · 04-22-2014, 07:42 PM

Let me amend my pressure readings. I just went back outside and hooked up my pressure gauge to the spare port on the intake manifold. I started the engine and the gauge jumped to 20 inHG and stayed there. I let it idle and the gauge didn't move. I blipped the gas once and the pressure/vacuum dropped to 0 then came right back to 20. I did this several times.

Then I opened the throttle to 2000 rpm and held it there. The gauge initially dropped to 0 but then rebounded right back to approx 22 and stayed there. When I let off the throttle she jumped up quickly to about 26 and came right back to 20 at idle.

Then I opened the throttle to 2000 rpm again, got the same results, but then I increased the throttle even more. Initially there was a small decrease in vacuum but then the needle rebounded to a little more than 22. When I let off the throttle she jumped up quickly and came back to 20 inHG.

Is the vacuum supposed to stay lower than 20 when holding the throttle open? For example; when traveling at 60 mph my rpms are right at 2500. This is normal. Should the intake manifold vacuum be less than 20 (15, 10, 5), right at 20, or higher than 20 (25, 30)?

tderonne · 04-22-2014, 08:22 PM

On the fuel pressure and vacuum line...

It's really quite simple. The fuel injector has two ends, one is in the fuel rail, one is in the intake manifold. There is a delta pressure between the ends. To keep it constant, the fuel pressure regulator is referenced to the intake manifold. If you measured the pressure differential from the intake to the fuel rail, you'd see it's 40 psi. At least you would if the fuel pump is working right.

(Not all fuel injection systems use a manifold reference. These Ford systems do.)

TeJay · 04-23-2014, 05:03 AM

Elexwiz,
I think you know this but lets back up a bit. Remember why we had an accelerator pump on carburetors? Any time the throttle was opened what initially happens with the intake manifold vacuum or IMV?? Anytime an idling engine has the throttle opened IMV drops and fuel flow slows down. We manually squirted fuel into the air flow to keep the mixture from becoming to lean. Once the IMV came back up the fuel flow which was only controlled by IMV caught back up and all was well until the throttle was again opened and the process started all over again.
What you described with snapping open the throttle and having the IMV drop is very normal.

This is a good discussion. It sure brings back a lot of memories with carburetor theory associated with fuel flow and air mixtures.

TeJay

Elexwiz · 04-23-2014, 08:04 AM

I remember the accelerator pump. I understand the concepts and now I'm trying to get baseline data for troubleshooting. All my testing, thus far, has been done in my driveway with my MH in park and the engine NOT under load. I'm going to take it for a drive today with the gauges hooked up and my son monitoring the gauges. What should I expect to see as normal? I've been searching google for diagrams/explanations of "manifold vacuum vs. engine load vs. throttle position" (and variations thereof) in attempt to get a ballpark. Under normal acceleration, say from a stoplight, what should I see the manifold vacuum do and what should the fuel pressure do?

I think I may have a weak fuel pump. Subford said that the fuel pressure should have stayed the same with the vacuum line disconnected. I had 39 psi fuel pressure when the vacuum line was disconnected. That means the pump is capable of pushing 39 psi against the spring at idle. That is enough to open the return line slightly. When I hit the gas the fuel pressure drops, why? If the spring in the regulator were weak I don't think we'd get to 39 psi at idle. As I open the throttle and increase fuel consumption the spring closes the return line leaving all the pressure up to the pump. It's not strong enough to maintain the 39 psi under increased fuel consumption.

I'm tired.