[nukezero]

I've been chasing a long crank issue since my turbo wastegate failed due to worn bushing. The turbos are fixed and the car performs superbly when running but it's been suffering from constant long cranks 3-6 seconds long. Doesn't matter hot or cold. I still get no codes other than 2AAF.

I finally had a chance to data log it with Bavarian Technic tool and interestingly this is what I found.

X-axis is in seconds. Y-axis is in PSI.

Is this conclusive proof that my HPFP or LPFP is failing? As you can see, the engine speed (when I push the start button) begins at around the 30 second mark. As the engine is turning over, the lpfp (fuel low pressure) does not hit 67 PSI until 31.8 seconds mark. Meanwhile, the HPFP has almost no pressure until the 32 second mark.

The rail pressure(hpfp) and engine speed is on the left y-axis. The lpfp is on the right y-axis.

When I did this log, the engine was previously already started. So there was pressure in the fuel rail. Is the fuel rail supposed to lose so much pressure after a shutoff that it goes almost back to 141 PSI a few seconds later ?

Is this indicative that the HPFP is just not holding fuel rail pressure? I've already done the injectors (index 12) on all six a week ago. Mind you the car runs superb when it cranks up. No faults.

FIXED!! It was the fuel pressure regulator! UPDATE BELOW!

[nukezero]

Does anyone know if the rail pressure is supposed to be held firmly even after engine shut off? When I did this log, the car was started 1 minute prior ago so rail pressure should've been strong. Is it normal for the rail pressure to fall back to 100PSI from 1500PSI in such short time?

[AndyW]

I'd replace crankshaft position sensor first. That can cause cranking issues.

Stress the parts in question; give us a third gear log. That should be more telling information.

[nukezero]

Well, right off the bat, based on the Bentley manual the residual fuel pressure should've been at 67-74 PSI. And it's not there! It was at 2PSI. The pressure started to build only when the engine began to crank. Based on other people's log, their low side fuel pressure was already at 70PSI several seconds already before the engine even started.

When the engine is shut off, it's also supposed to hold residual pressure in the low pressure line. It's not doing that it seems. The pressure is falling off dramatically near to 2-3PSI. The bentley manual states the fuel pressure regulator/check value is the responsible device that maintains the pressure for the low fuel pressure line and it seems like I have a defect check valve or regulator.

[Velocity26]

When the HPFP is failing, rail pressure will remain at what the LPFP is putting out for several seconds after the engine is running. I am not saying that yours is perfect, but it is building good pressure from the instant that the motor starts. I would not expect it to be contributing to long cranks. Maybe injectors or something else.

[nukezero]

Velocity26 - i'm trying to just figure out the long crank problem. I think I've got it narrowed down to the low pressure regulator. According to the Bentley manual, the residual pressure is supposed to be held at 5 bar +-0.2 after 20 minutes of engine shut off. 5 bar equates to 72psi. That's why many of the charts I'm seeing are showing people with 70+ psi before the engine starts.

In my case, what I'm seeing is when I get in the car, the lpfp primes and gets me 5 psi only (terrible). Then I start the car, it long cranks for 3 seconds, the LPFP builds up slowly to 70psi, finally the HPFP builds up and engine starts. The LPFP pressure is now holding steady at idle (68psi). When I shut off the engine.... BAM... you can see the LPFP pressure starting to drop fast rapidly.

Is this a sure sign that the pressure regulator/check vales are bad?

Remember, I don't have any driveability symptoms! Car runs superb. HPFP, LPFP and no pump codes other than 2AAF.

But based on what I'm seeing according to this data, the car is SUPPOSED to maintain 70PSI of low pressure fuel, even after engine shut off or prior to engine starting (when the pump primes) and I'm not getting that. The pressure is dropping fast, it seems like the pressure regulator is releasing fuel back into the tank through the defective check valves?

Here's my data zap:

http://www.datazap.me/u/nukezero/log...a=1-2-3&solo=3

[Sgop335]

Originally Posted by nukezero

Velocity26 - i'm trying to just figure out the long crank problem. I think I've got it narrowed down to the low pressure regulator. According to the Bentley manual, the residual pressure is supposed to be held at 5 bar +-0.2 after 20 minutes of engine shut off. 5 bar equates to 72psi. That's why many of the charts I'm seeing are showing people with 70+ psi before the engine starts.

In my case, what I'm seeing is when I get in the car, the lpfp primes and gets me 5 psi only (terrible). Then I start the car, it long cranks for 3 seconds, the LPFP builds up slowly to 70psi, finally the HPFP builds up and engine starts. The LPFP pressure is now holding steady at idle (68psi). When I shut off the engine.... BAM... you can see the LPFP pressure starting to drop fast rapidly.

Is this a sure sign that the pressure regulator/check vales are bad?

Remember, I don't have any driveability symptoms! Car runs superb. HPFP, LPFP and no pump codes other than 2AAF.

But based on what I'm seeing according to this data, the car is SUPPOSED to maintain 70PSI of low pressure fuel, even after engine shut off or prior to engine starting (when the pump primes) and I'm not getting that. The pressure is dropping fast, it seems like the pressure regulator is releasing fuel back into the tank through the defective check valves?

Here's my data zap:

http://www.datazap.me/u/nukezero/log...a=1-2-3&solo=3

Let me know what log you would like from a working system.

[Velocity26]

I understand.

On my car, the LPFP primes the system and builds about 70 psi of pressure then shuts off. That pressure slowly bleeds off, but it would take a minute or two to drop to 50psi. That could be your problem.

[muncie21]

nukezero your approach sounds logical. I would be interested to see what impact replacing the control/check valve has.

I have been contemplating using a similar approach to troubleshoot a 'warm' restart misfire that I'm having.

Best of luck!

[nukezero]

Originally Posted by muncie21

nukezero your approach sounds logical. I would be interested to see what impact replacing the control/check valve has.

I have been contemplating using a similar approach to troubleshoot a 'warm' restart misfire that I'm having.

Best of luck!

There is another user who had the same problem. He confirmed and replaced the regulator. He posted a video of a pressure drop of the fuel line when he shuts off the car. This corroborates the exact scenario I'm experiencing. After he replaced the regulator, the fuel pressure was holding steady for him.

http://www.e90post.com/forums/showth...4#post20332784

Here's his video of the pressure gauge dropping when he shuts off the engine: https://goo.gl/photos/arwg4u5nX7yRPFm7A

you can see that the fuel pressure is not supposed to decline like that. It's supposed to maintain 67-72 PSI.

I had the longest crank of all last night. 6 seconds.....

[muncie21]

My low pressure is ~70PSI after sitting overnight.



Here's the log file, I logged for a few seconds with the motor off, then started it up.

http://datazap.me/u/muncie21/log-146...0-122&mark=335

[nukezero]

Originally Posted by muncie21

My low pressure is ~70PSI after sitting overnight.



Here's the log file, I logged for a few seconds with the motor off, then started it up.

http://datazap.me/u/muncie21/log-146...0-122&mark=335

thanks! my car isn't holding 72 psi after it shuts off.... you see how your rail pressure is low but low pressure is high (when engine is off). i have a broken check valve.

[muncie21]

Originally Posted by nukezero

thanks! my car isn't holding 72 psi after it shuts off.... you see how your rail pressure is low but low pressure is high (when engine is off). i have a broken check valve.

I agree with you, something is relieving the pressure on the low side.
BTW, the high side still has 'some' pressure, little less than low side. On the chart it is graphed on the secondary axis, so it looks to be zero, but it's not.

[nukezero]

Guys, I just replaced the fuel pressure regulator. The car now FIRES up like a champ. I data logged the result and now my low fuel pressure holds well at 76 PSI before cranking and after when the car shuts off.

So when in doubt, check the FPR. It's NOT always the high pressure fuel pump causing long crank. I was constantly getting long cranks from 3 seconds to as worse as 6-7 seconds long. But I would never ever throw fuel pump codes. It just kept long cranking for over a month.

Here are the results of my data log.

[muncie21]

Glad to hear you fixed it

[Jklad]

Thanks for posting this, I'm sure it will help others in the future

[nukezero]

It's been a week now. I was about to throw this car away when I kept getting long cranks.

My car has been starting on the 4th crank each and every time! Which is about 1 second to start! Who would've thought that a stupid plastic fuel pressure regulator would cause long crank headaches.

[German_E92]

Hi,
I know it‘s an old topic but I have the same Problem at the Moment. Can somebody explain me the function of the fuel pressure Regulator why does after the repair the pressure is stable at 72psi and before it bleeds of?

[Emilime75]

It acts as a check valve, letting fuel move in one direction(from the in tank pump to the engine) while not letting it back(from the engine back to the tank). If it fails, it lets fuel in the fuel line drain back into the tank while the engine is not running. When it does that, it takes the in tank pump longer to refill the fuel line and build enough pressure for the HPFP to do its thing, hence the long crank.

[German_E92]

Thank you for the fast answer. Okay i unterstand. That sounds good. Does the fuel pressure Regulator looks like this picture but without the vacuum line?
But what happens if the pressure is too high?

[Emilime75]

Honestly, I don't know how the E9X FPR works without a vacuum line and I don't believe there is a line. Your question now makes we want to investigate it.