fuel pressure question

1iwilly · #1 11-23-2015, 04:49 PM

hello to all
i have couple of question
1=how do you determine a softfail fuel pump
2=is the fuel pressure suppose to drop a tad when vacuum is applied under load
my fuel pressure is 42 with key on and 50 to 52 running when checking fuel pressure regulator if i applied vacuum it drops down to 42

the reason i'm asking because it seems i'm running out of fuel when down to 1/4 tank

upallnight · #2 11-23-2015, 05:05 PM

Fuel pressure rises when there is little or no vacuum to the fuel pressure regulator. This is because at Wide Open Throttle (WOT) there is very little manifold vacuum but the engine needs more gas since it is at WOT.

Search for bad transfer pump. Sounds like you have a bad transfer pump. Either fix it or keep the fuel above 1/4 tank.

LeiZ · #3 11-23-2015, 05:20 PM

Isn't the fuel pressure supposed to stay 50~52 PSI while running, regardless of the load applied?

To me, dropping to 42 PSI means a faulty/softfail fuel pump/transfer pump.

Good Luck!

Quote:

Originally Posted by 1iwilly

hello to all
i have couple of question
1=how do you determine a softfail fuel pump
2=is the fuel pressure suppose to drop a tad when vacuum is applied under load
my fuel pressure is 42 with key on and 50 to 52 running when checking fuel pressure regulator if i applied vacuum it drops down to 42

the reason i'm asking because it seems i'm running out of fuel when down to 1/4 tank

TiAgX5 · #4 11-23-2015, 06:27 PM

4 things to check....

1) Rate of rise. The fuel rail should reach peak pressure within 2 or 3 seconds after key is turned to "run" position.

2) Not running, the pressure should read 51psi (+/- 3 psi)

3) Running (idle), the pressure should read 36 to 46psi.

4) Remove vacuum line from regulator (simulates open throttle), running pressure should increase 6 to 10psi.

If these 4 items check out, pump and regulator are functioning properly.

upallnight · #5 11-23-2015, 11:05 PM

Everyone I know calls it a vacuum line to the fuel pressure regulator.

See 3:00 in this video

https://www.youtube.com/watch?v=8t-6raUI8vs

or this guy in this video

https://www.youtube.com/watch?v=btOIaDdhJHA

Why don't you post the BMW documentation since you must have read it.

jfoj · #6 11-24-2015, 12:56 AM

Quote:

Originally Posted by upallnight

Everyone I know calls it a vacuum line to the fuel pressure regulator.

See 3:00 in this video

https://www.youtube.com/watch?v=8t-6raUI8vs

or this guy in this video

https://www.youtube.com/watch?v=btOIaDdhJHA

Why don't you post the BMW documentation since you must have read it.

Attached below is a PDF of page 35 from ST055 MS43/MS43. This is a Service Training document from BMW.

This cover Models:
E46/E39/Z3 - MS42 with M52TU Engine
E46/E39/Z3/E53 - MS42 with M54 Engine

SPECIAL NOTE, the document is a bit misleading because it does not CLEARLY separate the FPR setup for the MS42/M52TU from the MS42/M54.

The LAST paragraph and the picture at the bottom of the page is relative to the MS42/M52TU, NOT the MS42/M54. I think this is pretty obvious to anyone that pays attention to the MS42/M54 and to the fact that the hose on the FPR is NOT connected to the "cyclone oil separator" AKA CCV, but is connected to the intake boot.

Everyone calls it a "vacuum" line because it uses rubber "vacuum" hose. BUT for the M54 they are ALL wrong. They are technically referring to the "rubber tubing" as "vacuum" line or hose and of course, if it is called "vacuum" line, it must have "vacuum" present. But for the M54 this IS NOT the case.

But if anyone uses their brain, it is stupid obvious that there is NO manifold or venturi vacuum between the air filter and the throttle body butterfly. Would love to see someone figure out how this may happen. It will ONLY happen if the air filter is so restrictive that it will not flow air unrestricted into the intake. If the air filter is so badly restricted that manifold vacuum would be present in the intake boots, they would likely collapse and the engine would not even run.

I could also care less what anyone on YouTube or the Internet has to say. If they would just take a second and think about what happens to the air before the throttle body butterfly valve I think the situation would be pretty obvious. The work "vacuum line" is being tossed around incorrectly, these should have stated the rubber vent hose, but they obviously do not understand the fuel system they are working on or at least have not thought about the system and chosen their words carefully and accurately.

Additionally if anyone would take a second and disconnect the "vacuum" hose which is really just a rubber hose that connects to the FPR they would see in about 2 seconds there is NOT 18-20+ inches/manifold vacuum at the connection on the intake boot at idle.

There is a lot of misinformation that is continually perpetuated on a daily basis. This is just one of the many things that people get wrong and nobody ever gets corrected. I am trying to set the record straight, educate people and get them thinking for themselves.

upallnight · #7 11-24-2015, 07:21 AM

Quote:

Originally Posted by jfoj

Attached below is a PDF of page 35 from ST055 MS43/MS43. This is a Service Training document from BMW.

This cover Models:
E46/E39/Z3 - MS42 with M52TU Engine
E46/E39/Z3/E53 - MS42 with M54 Engine

SPECIAL NOTE, the document is a bit misleading because it does not CLEARLY separate the FPR setup for the MS42/M52TU from the MS42/M54.

The LAST paragraph and the picture at the bottom of the page is relative to the MS42/M52TU, NOT the MS42/M54. I think this is pretty obvious to anyone that pays attention to the MS42/M54 and to the fact that the hose on the FPR is NOT connected to the "cyclone oil separator" AKA CCV, but is connected to the intake boot.

Everyone calls it a "vacuum" line because it uses rubber "vacuum" hose. BUT for the M54 they are ALL wrong. They are technically referring to the "rubber tubing" as "vacuum" line or hose and of course, if it is called "vacuum" line, it must have "vacuum" present. But for the M54 this IS NOT the case.

But if anyone uses their brain, it is stupid obvious that there is NO manifold or venturi vacuum between the air filter and the throttle body butterfly. Would love to see someone figure out how this may happen. It will ONLY happen if the air filter is so restrictive that it will not flow air unrestricted into the intake. If the air filter is so badly restricted that manifold vacuum would be present in the intake boots, they would likely collapse and the engine would not even run.

I could also care less what anyone on YouTube or the Internet has to say. If they would just take a second and think about what happens to the air before the throttle body butterfly valve I think the situation would be pretty obvious. The work "vacuum line" is being tossed around incorrectly, these should have stated the rubber vent hose, but they obviously do not understand the fuel system they are working on or at least have not thought about the system and chosen their words carefully and accurately.

Additionally if anyone would take a second and disconnect the "vacuum" hose which is really just a rubber hose that connects to the FPR they would see in about 2 seconds there is NOT 18-20+ inches/manifold vacuum at the connection on the intake boot at idle.

There is a lot of misinformation that is continually perpetuated on a daily basis. This is just one of the many things that people get wrong and nobody ever gets corrected. I am trying to set the record straight, educate people and get them thinking for themselves.

When someone presents something but make a statement that what they are presenting as being WRONG, I kinda take the presenter knowledge with a little grain of salt.

An engine is nothing more than an air pump, It takes in air and blows it out. Vacuum does not just appear right after the throttle plate, but is present the minute the cylinders begins their "Intake" stroke. If there is no vacuum prior to the throttle plate, then why is it that when people have a P0171 and P0174 and it can be traced to a "cracked" intake boot at the elbow everyone refers to it as a "Vacuum" leak?

How do you explain the fact that when the OP uses a vacuum pump to draw a vacuum through the "vacuum" line to the FPR that the FPR would react the way it did (lower the fuel pressure to idle pressure)?

I'm sure if you disconnect the "vacuum" hose to the FPR like you suggested that the fuel pressure in the fuel rail will INCREASE.

I have seen my share of "Cliff Clavin" on this form as well as on the Lotus and Porsche forums and I tend to ignore their expert advice.

jfoj · #8 11-24-2015, 08:23 AM

Quote:

Originally Posted by upallnight

When someone presents something but make a statement that what they are presenting as being WRONG, I kinda take the presenter knowledge with a little grain of salt.

An engine is nothing more than an air pump, It takes in air and blows it out. Vacuum does not just appear right after the throttle plate, but is present the minute the cylinders begins their "Intake" stroke. If there is no vacuum prior to the throttle plate, then why is it that when people have a P0171 and P0174 and it can be traced to a "cracked" intake boot at the elbow everyone refers to it as a "Vacuum" leak?

How do you explain the fact that when the OP uses a vacuum pump to draw a vacuum through the "vacuum" line to the FPR that the FPR would react the way it did (lower the fuel pressure to idle pressure)?

I'm sure if you disconnect the "vacuum" hose to the FPR like you suggested that the fuel pressure in the fuel rail will INCREASE.

I have seen my share of "Cliff Clavin" on this form as well as on the Lotus and Porsche forums and I tend to ignore their expert advice.

Specifically to you upallnight, I will not bother to waste any more time trying to explain and educate you as you CLEARLY do not want to listen, think or learn. I have dealt with your type for many years.

I will answer 2 specific questions you raised, and it is clear you do not understand a lot of things.

Quote:

Originally Posted by upallnight

If there is no vacuum prior to the throttle plate, then why is it that when people have a P0171 and P0174 and it can be traced to a "cracked" intake boot at the elbow everyone refers to it as a "Vacuum" leak?

I will repeat, there is no manifold vacuum in front of the throttle plate but there is airflow. The two are very different. The reason people can have P0171/P0174 that can be traced back to "cracked" intake boots is because air will BYPASS the MAF and then there will be "Unmetered" air entering the engine. With the MAF under reporting the intake airflow the DME does not provide enough fuel to the engine.

One test you can do it to connect your OBDII tool and monitor the STFT and the MAF reading then partially remove an intake boot at the MAF or use a screw driver to allow air to bypass the MAF. You will see the STFT jump and the MAF reading drop slightly. An easier test is to remove the oil fill cap while the engine is running and the same thing will happen. But keep in mind we are only taking 5-15% change in MAF reading so it will not be a major difference, but there will be a drop on the MAF reading.

Quote:

Originally Posted by upallnight

How do you explain the fact that when the OP uses a vacuum pump to draw a vacuum through the "vacuum" line to the FPR that the FPR would react the way it did (lower the fuel pressure to idle pressure)?

I'm sure if you disconnect the "vacuum" hose to the FPR like you suggested that the fuel pressure in the fuel rail will INCREASE.

You have to understand the FPR that is integrated to the fuel filter is of a similar design as any other FPR. There is a diaphragm on one side of the spring in the FPR that controls the fuel pressure. In the case of the M54 the DME and fuel management system is DESIGNED to operate on a fixed/non variable fuel pressure. HOWEVER, like any FPR if you present vacuum on the open port you can change the fuel pressure, however, in the M54 application there is NO vacuum present at this port. I think this should be very clear to anyone that thinks about how it is connected under the hood.

I am POSITIVE if you disconnect the hose connected to the FPR you WILL NOT see a change in the fuel pressure. I think you will find this the case assuming you bother to connect a fuel pressure gauge or OBDII tool and test this theory. You really do not need any tools to verify this, all you need to do is disconnect the hose at the intake boot and you will notice there is no change in the engine idle because there is no change in the fuel pressure on the M54. Other engines can and may have manifold vacuum connected to a FPR, but not the M54.

I will respond to others in this thread that have questions or need help because I have the answers they need.

upallnight · #9 11-24-2015, 09:14 AM

Quote:

Originally Posted by jfoj

Specifically to you upallnight, I will not bother to waste any more time trying to explain and educate you as you CLEARLY do not want to listen, think or learn. I have dealt with your type for many years.

I will answer 2 specific questions you raised, and it is clear you do not understand a lot of things.

I will repeat, there is no manifold vacuum in front of the throttle plate but there is airflow. The two are very different. The reason people can have P0171/P0174 that can be traced back to "cracked" intake boots is because air will BYPASS the MAF and then there will be "Unmetered" air entering the engine. With the MAF under reporting the intake airflow the DME does not provide enough fuel to the engine.

One test you can do it to connect your OBDII tool and monitor the STFT and the MAF reading then partially remove an intake boot at the MAF or use a screw driver to allow air to bypass the MAF. You will see the STFT jump and the MAF reading drop slightly. An easier test is to remove the oil fill cap while the engine is running and the same thing will happen. But keep in mind we are only taking 5-15% change in MAF reading so it will not be a major difference, but there will be a drop on the MAF reading.

You have to understand the FPR that is integrated to the fuel filter is of a similar design as any other FPR. There is a diaphragm on one side of the spring in the FPR that controls the fuel pressure. In the case of the M54 the DME and fuel management system is DESIGNED to operate on a fixed/non variable fuel pressure. HOWEVER, like any FPR if you present vacuum on the open port you can change the fuel pressure, however, in the M54 application there is NO vacuum present at this port. I think this should be very clear to anyone that thinks about how it is connected under the hood.

I am POSITIVE if you disconnect the hose connected to the FPR you WILL NOT see a change in the fuel pressure. I think you will find this the case assuming you bother to connect a fuel pressure gauge or OBDII tool and test this theory. You really do not need any tools to verify this, all you need to do is disconnect the hose at the intake boot and you will notice there is no change in the engine idle because there is no change in the fuel pressure on the M54. Other engines can and may have manifold vacuum connected to a FPR, but not the M54.

I will respond to others in this thread that have questions or need help because I have the answers they need.

In all my responds I never use the term "Manifold" vacuum, I used the term Vacuum. Air flow through the intake boot and if there's a small opening like in the connector to the FPR you will have a Vacuum in that line. You can suck fuel out of a fuel tank or any container by inserting a hose into the container and blowing air across the opening of the hose at the other end. The air flow across the hose opening will create a vacuum in the line (Bernoulli Principle).

Watch this youtube video and learn something.

https://www.youtube.com/watch?v=ajIDwzUYBi4

jfoj · #10 11-24-2015, 10:57 AM

A bunch of keyboard scientist. You all need to spend more time under the hood and less time behind the keyboard. Science is one thing but assumptions and implementation are VERY different and things do not always appear or work as you may think with just a cursory view of what is going on.

Just because the Bentley Manual does or does not state something, does not mean it is gospel. I have Bentley for BMW and VW and I find all sorts of errors, omissions and information left out. This is nothing new and keep in mind Bentley Publishing did not design and build the vehicle.

Seems everyone wants to beat the dead horse rather than help a fellow forum member to resolve a problem. I am trying to correct a lot of misunderstanding and misinformation, but the closed minds DO NOT want to know. There may be a 30 day program for that problem, but like anything, you have to understand there is a problem before any progress can be made.

I can tell by some of the crowd here there is no open thought or understanding, heaven forbid there be a different point of view, even if it is correct.

I guess even the following statement from a BMW document means nothing to anybody here:

"The regulator is influenced by internal fuel pressure and not intake
manifold vacuum."

I will wait for someone to finally lift the hood and do some investigation, they will likely see what I am talking about.

In the mean time, how about all the naysayers connect their M54 fuel pressure regulator up to one of the ports on the rear if the intake or the vacuum port on the side of the CCV valve if they feel their M54 must have intake manifold vacuum present at the FPR. We will see how that works out for you.

The M54 is a different animal then many of the other engines in more than one way.