Confirm fuel pressure problem for me please

OK, so I finally got a fuel pressure gauge to see if fuel pressure is the cause of my rough start. Please confirm:

Is the fuel pressure supposed to drop over the course of 2-5 minutes after the engine is shut off?

I seem to remember reading that the fuel system is supposed to be pressurized for at least a few hours after the engine is shut off. Is this so? Thanks.

I would think the fuel rail should keep pressure much longer than that. Just read about everyone that replaces their fuel filter and has fuel sprayed all over the place!

If your pump is original, replace it.

Read this thread for more info - http://forum.e46fanatics.com/showthr...501&highlight=

If you have good pressure when you turn the key on, you should be good to go.

Also read the first link below in my signature.

You did not really describe a "rough start".

Originally Posted by jfoj

I would think the fuel rail should keep pressure much longer than that. Just read about everyone that replaces their fuel filter and has fuel sprayed all over the place!

If your pump is original, replace it.

Read this thread for more info - http://forum.e46fanatics.com/showthr...501&highlight=

I want to avoid the rip and replace approach to solving the problem since fuel pumps arnet exactly cheap. I'll read the thread you suggested.

My rough start is a result of my ESS TS2. The problem started after the installation several years ago and I am just getting around to trying to trace it down. Professional vaccumm leak smoke test didnt turn up anything so now Im thinking it has to do with the fuel system.

Well with a supercharger fuel pressure/volume is crucial, especially under boost conditions.

Leaning out too much would be a catastrophic event for your engine.

Did the ESS kit include/suggest upgrading the fuel pump anyway?

What is the age of your fuel filter?

Pop the bottom rear seat and see if the soundproofing on the passenger side has ever been cut. If not, your pump is original.

OEM pump is only about $120 from bmaparts.com.

Good question because I checked mine today on my 330. With the key in the on position it read 50psi. Then I started it and it read 50psi. Turned the engine off and it slowly dropped to 44psi and stayed there for at least 30min til I then took the gauge off. I don't know how long you should keep the gauge on though.

Originally Posted by jfoj

Well with a supercharger fuel pressure/volume is crucial, especially under boost conditions.

Leaning out too much would be a catastrophic event for your engine.

Did the ESS kit include/suggest upgrading the fuel pump anyway?

What is the age of your fuel filter?

Pop the bottom rear seat and see if the soundproofing on the passenger side has ever been cut. If not, your pump is original.

OEM pump is only about $120 from bmaparts.com.

No fuel pump upgrade available or recommended by ESS.

Fuel Filter is only a couple of years old with at most 10K miles.

Pump is original since I was the second owner at 12K miles

Originally Posted by kwikt

Good question because I checked mine today on my 330. With the key in the on position it read 50psi. Then I started it and it read 50psi. Turned the engine off and it slowly dropped to 44psi and stayed there for at least 30min til I then took the gauge off. I don't know how long you should keep the gauge on though.

OK, I checked my Bentley manual (should have done this first ). The fuel pressure should be 50 psi plus minus 3psi. After shutting the engine off, the pressure "should not drop more than 0.5 bar from the system pressure (50psi)" after 20min.....

So Kwikt, you should be OK but it looks like I should replace my fuel pump or look into leaky injectors since my system is 40psi.....

Great discussion guys. Thanks

Replace the pump, then if you still have issues, I would pull your injectors and send them to www.witchhunter.com for cleaning and testing.

UPDATE:
I changed the fuel pump but still have low fuel pressure and the initial rough start although it is not as bad. At idle, I have 45psi which stays there 20+min when I turn the engine off. I'm thinking the next step is to replace the fuel filter which was last replaced 30K miles ago.

I have the same problem as you do. I have a TS2.5 system running at 9 psi of boost. After having replaced fuel pump and filter I stll have the same problem.
ESS sells different injectors to fix this problem as well but I'm willing to bet a good tune should fix the rough starts.

Sent from my SAMSUNG-SGH-I997 using Bimmer App

I bought a wrecked car for parts (Miata). It had been sitting 3 years at that point, and would not start. 4 years after that, I went to pull the injectors out, and got a full blast of gas when I pulled the line off. This was 7 years after the car had power to it. So, yes, they hold pressure for a while.

First off, 45 psi is within the Bentley spec. + or - .5 bar is roughly 7psi. Your problem is not likely fuel related imo.

Secondly, does your car have the filter with the fuel pressure regulator built in, or the external one? Edit: Guess the 330i has it built into the filter.

Fuel pressure can only leak via the check valve in the pump itself, the injectors, or the fuel pressure regulator on the return line afaik.

Originally Posted by lcoleman

First off, 45 psi is within the Bentley spec. + or - .5 bar is roughly 7psi. Your problem is not likely fuel related imo.

Secondly, does your car have the filter with the fuel pressure regulator built in, or the external one? Edit: Guess the 330i has it built into the filter.

Fuel pressure can only leak via the check valve in the pump itself, the injectors, or the fuel pressure regulator on the return line afaik.

I had a professional smoke test a couple years ago and he couldnt find any vacuum leaks, which lead me to a fuel problem.

UPDATE:
After the fuel pump was replaced, which helped with the fuel pressure, but not the stumble, I replaced the fuel filter. Still has the stumble and gets worse when it gets colder outside. Interesting thing I found though was with the key in the second position (right before you turn to crank), I floor the throttle and let it up. I turn the key to crank (foot off the gas), and the stumble is either gone or a lot less noticable. I wish I had a new throttle body to see if the issue is with the throttle position sensor. Mystery continues........

Cold starts get worse as weather gets colder. I would agree is a mapping issue. Cold start enrichment issue