# QUESTION = Fuel Rail/System Pressure: Too Low



## Mostic (Jan 19, 2014)

Hi,
*Here are all my car specs:*

• 2007 Golf MKV GTI 2.0T FSI (200PS - BPY engine code) – flashed with Revo Stage3.
• Revo Stage1 DSG software.
• BorgWarner 2.0T FSI S3/Golf-R K04 Turbocharger and Manifold.
• Forge K04 Turbo Wastegate Actuator (FMACVAG06) - (replacing the original wastegate coming with the BorgWarner K04).
• APR 2.0T FSI High Pressure Fuel Pump.
• APR/Bosch High Flow FSI Injectors.
• RS4 Fuel Pressure Release Valve (079130757).
• Pressure Sensor (Located on the fuel rail) - (06J906051D).
• Electric Fuel Pump - (1K0919051DB).
• Low Pressure Fuel Sensor - (06E906051k).
• Neuspeed HI-FLO Turbo Discharge Conversion - 2.0T FSI.
• Torque Solution Billet PCV Adapter: 2.0T FSI.
• K&N Typhoon Intake - Flat Black (69-9503TFK).
• Eurojet Front Mounted Intercooler upgrades.
• 3” inch Turbo Back Exhaust with De-cat.
• Sprint Booster connected to DSG transmission.
• BSH FSI Integrated Throttle Pipe.
• Relocated Diverter Valve "D" version - Electronic (06H145710D).
• Water Methanol kit.
• Fuel Octane 95.

Here are the water methanol kit specs:
• DevilsOwn Water Methanol (Universal Stage 2 DVC-30 Controllers).
• Micro Droplet Nozzles – DO5; connected to my “BSH FSI Integrated Throttle Pipe.
• 50/50 water/methanol.
• The controller start knob adjusted to inject at 4 psi.
• The controller full knob adjusted to inject at 17 psi.

unfortunately, I start receiving the following error after I upgraded my car to K04!! :thumbdown:

00135 - Fuel Rail/System Pressure: Too Low
P0087 - 002 - Lower Limit Exceeded - Intermittent
Freeze Frame:
Fault Status: 00100010
Fault Priority: 0
Fault Frequency: 1
Mileage: 60550 km
Time Indication: 0
Date: 2000.00.00
Time: 16:20:00

Freeze Frame:
RPM: 4678 /min
Load: 27.0 %
Speed: 128.0 km/h
Temperature: 85.0°C
Temperature: 56.0°C
Absolute Pres.: 990.0 mbar
Voltage: 13.970 V


I changed the Cam follower, Pressure Sensor, Low Pressure Fuel Sensor, RS4 Fuel Pressure Release Valve, Fuel Filter, Electric Fuel Pump and I am still receiving the same error. :banghead::banghead:

Do you think that I need to upgrade my Intake Cam? I checked the Internet and i found some people suggests to change it to Intake Cam - Revision "B". 

I sent all the above car details and specifications to Revo and they sent me the K04 stage 3 file. Is it possible that the Error coming from Revo software because they did something wrong!! :what:

I really need your help...


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## Mostic (Jan 19, 2014)

Any News?


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## Bunnspeed (Apr 2, 2013)

Have you logged requested vs actual rail pressure? That'll tell you more about what's going on.

It's possible the tune is requesting a higher rail pressure than the rs4 valve can hold, and that it releases rail pressure (dropping actual rail pressure to below requested) once the valve's cracking pressure has been exceeded. 

You might need to upgrade to one of the valves from HPFP Upgrades. They have them in 145 and 155 bar I think. I have their 145 bar one. 

You might also have a fuel injector or hpfp issue, which could lead the tune to request an unusually high rail pressure or make the lpfp max itself out to compensate for problems at the hpfp side.


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## Brd.Prey (Oct 25, 2012)

me too, I think its my stock fuel pressure relief valve.

any luck?


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## bacillus (Apr 21, 2011)

Are you using a new Pressure Sensor (Located on the fuel rail) - (06J906051D) and not the one that originally came with the car? If you have, swap the old one back in...


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## SmithersSP (May 24, 2006)

Log fuel rail pressure and low pressure (block 103). In some cases your low pressure in tank pump may not be able to meet the demand of the HPFP. I had that problem and tossed in a TTRS fuel pump to solve the issue. APR just released their low side fueling kit as well.


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## Brd.Prey (Oct 25, 2012)

I have had to replace 2 fuel pressure relief valves in a years time. I bet a 5spot that it is the relief valve. You can change it without pulling the intake in less than an hour.

I have an. RS 4 one now.

I think the APR opens the stock one too much and it's not designed for it.


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## ROH ECHT (Dec 9, 2010)

I had to have my DM K04+ tune adjusted to tweak the injector timing and to increase the low side pressure to 4.5bar in order to reach specified high pressure of 142.5bar in the rail. Never did figure out why this needed to be done, but it did correct the issues for whatever weird thing was going on with mine.


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## Brd.Prey (Oct 25, 2012)

ROH ECHT said:


> I had to have my tune adjusted to tweak the injector timing and to increase the low side pressure to 4.5bar in order to reach specified high pressure of 142.5bar in the rail. Never did figure out why this needed to be done, but it did correct the issues for whatever weird thing was going on with mine.


What relief valve are you running at that pressure? My APR 2+ is only requesting 115 bar.

Ed


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## ROH ECHT (Dec 9, 2010)

Brd.Prey said:


> What relief valve are you running at that pressure? My APR 2+ is only requesting 115 bar.
> 
> Ed


An HPFP-Upgrade 145 bar FPRV.


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## SmithersSP (May 24, 2006)

Brd.Prey said:


> My APR 2+ is only requesting 115 bar.
> 
> Ed


That doesn't sounds right. I was under the impression that all stg2+ tunes request 130bar. I too am running an RS4 crack valve.


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## Brd.Prey (Oct 25, 2012)

I will post logs tonight, RS4 relief valve is only 136 bar right?


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## xtravbx (May 21, 2005)

Brd.Prey said:


> I will post logs tonight, RS4 relief valve is only 136 bar right?


Yes but that 7 bar difference over the stock valve is over roughly over 100psi more... BIG difference.


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## Brd.Prey (Oct 25, 2012)

Yes agree a 7 bar gain is significant but notice the graph above, he is at specified and actual at 142 bar which is above RS4 relief specs.


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## SmithersSP (May 24, 2006)

To my knowledge the only company that offers anything stronger than the RS4 valve is HPFPUG.com
http://hpfpupgrade.com/Products/Show/Volkswagen/2.0T+FSI/VW+Performance+Rail+Valve
They offer a 135bar, 145bar, and 155bar crack valve. :thumbup:


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## ROH ECHT (Dec 9, 2010)

So you know, when these release pressure....they only release approximately 5% to 10% of the pressure. It isn't a complete loss of pressure.


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## majic (Mar 10, 2005)

ROH ECHT said:


> So you know, when these release pressure....they only release approximately 5% to 10% of the pressure. It isn't a complete loss of pressure.


Also... If the pressure is too high, what is the impact? The ECU should compensate by lowering the duty cycle of the injectors right?

Is the car having any problems? Misfires, pulling timing.... Other?


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## Brd.Prey (Oct 25, 2012)

My first failed relief valve was open completely! You could blow threw it,  The fuel pressure was would only let the engine run in limp mode.


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## ROH ECHT (Dec 9, 2010)

↑ I could see that being the result in that case.

Here is something I found odd...when I got my giac HO K04 tune, with required 145 bar FPRV, the HO tuned ecu only requested 110bar??? I know...I never figured out why I even needed the FPRV. Plus there was no performance increase over my awe/giac K04 tune.


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## ROH ECHT (Dec 9, 2010)

majic said:


> Also... If the pressure is too high, what is the impact? The ECU should compensate by lowering the duty cycle of the injectors right?
> 
> Is the car having any problems? Misfires, pulling timing.... Other?


The fprv should bleed off just the excess rail pressure and all else should remain within specs if working properly. You can see from my graph above that the 145 bar fprv continued to hold up to 150+ bar....but I'm sure by then some amount of pressure was being released in tiny amounts.


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## Brd.Prey (Oct 25, 2012)

Here is my graph. Slide the decimal 2 spots to the left for low pressure and 1 spot to the right for rail pressure. Its in Kpa and Pa or something.

Notice the pressure spikes at high rpm. yet specified remains constant 115 Bar


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## SmithersSP (May 24, 2006)

Well I'm out.








I've never seen a STG2+ tune only request 115bar (5 over stock) before. That being said my technical input's value to this thread is now zero.

After a quick search you may not be the only person to experience this issue:
http://golfmk5.com/forums/showpost.php?p=3605979&postcount=25


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## majic (Mar 10, 2005)

SmithersSP said:


> Well I'm out.
> 
> 
> 
> ...


Yep... I'm with you on this. Only explanation I can think is that because you're using the higher flowing secret squirrel APR injectors, they may flow better at lower pressures. The pressure is controlled with a solenoid that is timed to open and close at certain points, so even though you're spinning the engine up it will maintain a particular pressure. Also, I wouldn't be too concerned with the fluctuations at high rpm... It varies widely throughout the run, so I think it might just become more pronounced at higher rpm.

But I'm putting my money on the idea that these injectors don't require incredibly high pressures... But that's my uneducated $.02


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## Brd.Prey (Oct 25, 2012)

I have the stock Audi TTS injectors. I too was surprised my specified fuel rail pressure was only 115 bar.

??????


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## SmithersSP (May 24, 2006)

Brd.Prey said:


> I have the stock Audi TTS injectors. I too was surprised my specified fuel rail pressure was only 115 bar.
> 
> ??????


I think at this point you need to politely approach APR's support. They are the only ones who can change a requested fuel rail value. That is specific to and controlled by the tune. :thumbup:


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## Brd.Prey (Oct 25, 2012)

I think the best question is what is the indication that the fuel rail is low? Car runs great, boost is 24.8, injector pulse width is in the graph below. Higher fuel pressure would result in a shorter IPW but is it needed?


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## majic (Mar 10, 2005)

Brd.Prey said:


> I think the best question is what is the indication that the fuel rail is low? Car runs great, boost is 24.8, injector pulse width is in the graph below. Higher fuel pressure would result in a shorter IPW but is it needed?


I would 100% agree with this. The duty cycle of the injectors would ideally compensate for the afr. That can react a lot quicker than the fuel pressure. 

We can chase irregular values, but do we want to treat the number to make is feel
Better, or will it really make the car run better?


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## xtravbx (May 21, 2005)

Brd.Prey said:


> I think the best question is what is the indication that the fuel rail is low? Car runs great, boost is 24.8, injector pulse width is in the graph below. Higher fuel pressure would result in a shorter IPW but is it needed?


Duty cycle compensating for low fuel pressure is asking for disaster. Burn out an injector = expensive repair no matter what. Much more expensive when it burns out and you roast a cylinder.


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## SmithersSP (May 24, 2006)

That and I think it's silly to shell out a grand for a fuel pump that is only set to give you an additional 5 bar vs the 20 you paid for. Perhaps the upgraded HPFP should only cost $250?  To my last point; I would approach APR and confirm that your spec rail pressure is correct. I would be surprised if it is. :thumbup:


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## majic (Mar 10, 2005)

SmithersSP said:


> That and I think it's silly to shell out a grand for a fuel pump that is only set to give you an additional 5 bar vs the 20 you paid for. Perhaps the upgraded HPFP should only cost $250?  To my last point; I would approach APR and confirm that your spec rail pressure is correct. I would be surprised if it is. :thumbup:


At the end of the day I think this is a valid point. Also -- it would be informative to share the response 

But that being said, even if not made up for with duty cycle, perhaps it's some other aspect like timing.... Or injection timing since these are direct injection, that is making the difference.

Inquiring minds would like to know


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## SmithersSP (May 24, 2006)

Any resolution to this?


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## stephen1979 (Aug 22, 2011)

For what it's worth from a noob with literally 5 posts. My wifes stock b6 passat had the same code. After throwing a new fuel pump and the code remaining I took the controller on the top of the pump out of my gli to test and it ran perfect. Bought a new one for the passat and no more issues. Just a thought. I didn't see it in your replacement part list.


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## [email protected] (Jul 29, 2008)

SmithersSP said:


> That and I think it's silly to shell out a grand for a fuel pump that is only set to give you an additional 5 bar vs the 20 you paid for. Perhaps the upgraded HPFP should only cost $250?  To my last point; I would approach APR and confirm that your spec rail pressure is correct. I would be surprised if it is. :thumbup:


You've missed the point of the HPFP. At low airflow levels, low demand, high RPMs, and a higher rail relief valve, the factor pump could easily produce 150 bar or higher. 

Despite the name, the High Pressure Fuel Pump upgrade is not necessarily designed to increase the engine’s fuel rail pressure. The primary goal is to increase the volume of available fuel. As engine speed increases, so does the pump’s ability to displace a greater volume of fuel per minute. The maximum volume the pump can deliver per revolution on the three-lobe cam is dictated by the stroke length from the cam lobe’s lift and bore diameter of the pump’s internal pressurizing cylinder (The part we change). When the volume of available fuel drops, as it does with the stock pump in high demand situations, so does rail pressure. With the APR pump, in high demand situations you still have plenty of fuel, so rail pressure doesn't drop. 

The main reason rail pressure is increased is to reduce the amount of time the injectors spray. With increased pressure, they spray for a shorter period of time. This mainly only matters on high output applications, like stage 3, where the power at redline is high, and the injection window is low. 

So 115 is fine. It's what the files supposed to do. Raising it's not going to increase performance. Also, for what it's worth, we've lowerd requested pressure on some files as some vehicle's factory old relief valves were opening prematurely.


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## SmithersSP (May 24, 2006)

[email protected] said:


> You've missed the point of the HPFP. At low airflow levels, low demand, high RPMs, and a higher rail relief valve, the factor pump could easily produce 150 bar or higher.
> 
> Despite the name, the High Pressure Fuel Pump upgrade is not necessarily designed to increase the engine’s fuel rail pressure. The primary goal is to increase the volume of available fuel. As engine speed increases, so does the pump’s ability to displace a greater volume of fuel per minute. The maximum volume the pump can deliver per revolution on the three-lobe cam is dictated by the stroke length from the cam lobe’s lift and bore diameter of the pump’s internal pressurizing cylinder (The part we change). When the volume of available fuel drops, as it does with the stock pump in high demand situations, so does rail pressure. With the APR pump, in high demand situations you still have plenty of fuel, so rail pressure doesn't drop.
> 
> ...


Makes sense. Out of curiosity, what is different about the motor where it only required the 115 vs the standard 130 that many of your FSI tunes (or most in general) have? Is there a difference in the rail itself or the injectors?  This would be handy to know so when the next person shows up here it will be easier to explain. :thumbup:


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## [email protected] (Jul 29, 2008)

Someone probably had a problem probably from the valve popping open too early, so we reduced the requested rail pressure.


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## SmithersSP (May 24, 2006)

[email protected] said:


> Someone probably had a problem probably from the valve popping open too early, so we reduced the requested rail pressure.


So a 115 bar requested value is not standard, more of a one off deal.


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## [email protected] (Jul 29, 2008)

SmithersSP said:


> So a 115 bar requested value is not standard, more of a one off deal.


Depends on the ECU and file version. It doesn't matter what it is as long as the injectors aren't spraying too long, and they aren't at 115 bar on a k03.


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## Brd.Prey (Oct 25, 2012)

Mine is a standard 2+ tune on a 2009 Audi TTS fsi motor


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## SmithersSP (May 24, 2006)

[email protected] said:


> Depends on the ECU and file version. It doesn't matter what it is as long as the injectors aren't spraying too long, and they aren't at 115 bar on a k03.


Gotcha. What is considered the sweet spot for injector pulse width under WOT in ms? I've seen 5ms referenced but it seems all tunes usually run in the 8ms range assuming everything is operating nominally. 
Thanks! :thumbup:


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## majic (Mar 10, 2005)

SmithersSP said:


> Gotcha. What is considered the sweet spot for injector pulse width under WOT in ms? I've seen 5ms referenced but it seems all tunes usually run in the 8ms range assuming everything is operating nominally.
> Thanks! :thumbup:


Yes, people smart on this please comment?


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## [email protected] (Jul 29, 2008)

SmithersSP said:


> Gotcha. What is considered the sweet spot for injector pulse width under WOT in ms? I've seen 5ms referenced but it seems all tunes usually run in the 8ms range assuming everything is operating nominally.
> Thanks! :thumbup:


There isn't quite a cut and dry answer for this. 

Basically the amount of time the injectors _can_ spray depends on engine RPM. As the RPMs increase, the window of time decreases. 

If you increase pressure, the injectors spray for a shorter period of time. The amount of pressure you can provide depends on cam shaft RPM (lower in the low RPM, and higher in the upper RPM), HPFP piston and bore size as well as the stroke and lobe count. It depends when the HPFP solenoid fires. It also depends how large the injectors are, the temperature of the fuel, and when the rail valve opens. 

In the simplest terms, they need to spray long enough to satisfy the air fuel ratio prescribed and they need to do so in a period of time short enough so that the injection window doesn't start too early or end too late. 

Depending on the turbo size, and how much it flows at any given RPM will change the length it sprays too. Same goes for fuel type when satisfying the AFR. A k03, K04 and big turbo all have different characteristics. 

Now, there are some characteristics behind the amount of time the injection period lasts and the pressure at which it happens that can help power. However, it's not a simple more is better answer. More can result in fuel hitting the cylinder walls and not properly atomizing. 

So to recap, here are the things that affect how long the injectors spray off the top of my head:

1. Injector size
2. Rail pressure
- 2a. HPFP Piston size
- 2b. HPFP Piston Stroke from cam shaft lift profile
- 2c. HPFP Firing Angle
- 2d. Cam shaft lobe count
- 2e. Rail Valve pop off pressure
- 2f. Demand on the system
- 2g. Fuel Temp
3. Engine RPM
4. Injection Start Point
5. Injection End Point
6. Mass airflow
7. Desired air fuel ratio
8. Fuel type


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## majic (Mar 10, 2005)

Arin,

Thanks for the great I do. Not sure if you know the answer to this, but how is the solenoid timed? Is it based off the crank position sensor, or the cam position sensor on the intake cam?

Is this parameter alterable?


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## Brd.Prey (Oct 25, 2012)

[email protected] said:


> Depends on the ECU and file version. It doesn't matter what it is as long as the injectors aren't spraying too long, and they aren't at 115 bar on a k03.



TTS is a K04 stock!


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## [email protected] (Jul 29, 2008)

majic said:


> Arin,
> 
> Thanks for the great I do. Not sure if you know the answer to this, but how is the solenoid timed? Is it based off the crank position sensor, or the cam position sensor on the intake cam?
> 
> Is this parameter alterable?



IIRC it's closed loop control. Basically, it knows the OEM cam profile (unworn profile), and knows how much pressure it needs to achieve and fires accordingly. There are some things that can adjust the firing window.


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## [email protected] (Jul 29, 2008)

Brd.Prey said:


> TTS is a K04 stock!


Yeah, on the new v3.31 calibrations, engineering basically left it stock.


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## raven6t9 (Jun 28, 2005)

Ok so I'm getting this same code as the OP, and I've been trying to track this issue down for over a year now. I installed a boost gauge and it shows that I'm only getting around 3lbs of boost at wot on stage II+ programming, and I've upgraded my LPFP and changed my fuel filter with no changes to performance whatsoever. Could this all simply be because of the crack valve? My HPFP is from APR and is really not that old, about a year. So is it possible that the fuel rail valve that it came with was bad or too low?
How do I know which valve rating I need? I don't have expensive diagnosis software to log any runs and get any info. I tried emailing APR about the issue suggesting that it's an issue with the valve a couple months ago and got no reply from them at all. Any input is appreciated.


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## SmithersSP (May 24, 2006)

Honestly bud you're going to need VAGCOM to log it, or take it to a shop that has the ability to log. When you looks at measuring block 230 it will show three values: requested rail pressure, actual rail pressure, and difference between those two values. Actual should always be within +/- 5bar of the requested value. Since you're II+ the requested value at WOT should be 130bar. 
Good luck :thumbup:


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