Let's talk about VERY HIGH Fuel Rail pressure values !!! DANGER !!!

[shiro1745]

I remember John @ HPFPupgrade saying that our fuel rail can handle pressures up to 170 bars.
I was looking at some logs I got the other day and realized my FR pressure

reached values around 201 bar [o_o][o_o][o_o]

The interesting thing is that the ECU was requesting 201.
Here how it happened. I did a 3rd gear pull and during the pull all the values look normal, well in a way cause at one point numbers drop way below requested, but please let's not focus on that now. Anyway during the pull the values don't go above 130, but hear this out, after I get off the throttle the ECU starts requesting this very high pressure, in this case 201 bar. This is crazy, I mean, isn't this getting dangerous? Is my car ticking bomb now or what? I've seen values of 190, 195 on other pulls.

I run RS4 injectors + K0R-gt turbo + Maestro tune, this is Ray's last revision.


http://i955.photobucket.com/albums/ae31/ciprianpatulea/highFP_zpsa2479173.jpg

[derrek]

Maybe your ecu is trying to compensate for being around 40 bar short at the end of your pull?

[shiro1745]

Well I understand that but it should have a maximum limit, shouldn't it? And I posted a short chart here but believe me it stays so high for very long after.

[mec]

This is an issue with your tune. It is requesting 201 bar, so it is delivering 201 bar. Tune down the fueling.

[airbornerifleman]

That's crazy high! Contact maestro and/or tune down your fueling. Maestro should consider putting a cap on the max rail pressure. ALL STG3 maestro user should log also.

[shiro1745]

But it's not requesting that much under WOT. As you can see it's only requesting 129.99, it only jumps high when I let off the throttle

[derrek]

Ray is from RAI right? What are all the other kor car's requesting?

[airbornerifleman]

What BAR is your PRV?

[mec]

right, and thats normal, thing about it. you are requesting 130 bar and using it in your injectors, then you let off the throttle, and it takes the ecu a half second to realize that pressure is buiding up since its not escaping in the inejctors, so for a half second you get pressure buildup.

that's not the issue here, the problem is that your tune is actually asking for 201bar, might have been a mistake when ray did your tune, I would shoot him some logs and your base file and ask for it to be redone.

[rongeur]

I am not a maestro user yet but I agree with Mec, this is an issue with your tune. The ECU is calling for 201 and the output sensors are meeting that (which is insane). You ECU processes much faster than half seconds so reactive over pressure is very unlikely... Contact Eurodyne or EPY or anyone savvy with maestro. The next question is why the hell your PRV is not cracking and releasing that grossly over pressured fuel rail?

[mec]

I am not a maestro user yet but I agree with Mec, this is an issue with your tune. The ECU is calling for 201 and the output sensors are meeting that (which is insane). You ECU processes much faster than half seconds so reactive over pressure is very unlikely... Contact Eurodyne or EPY or anyone savvy with maestro. The next question is why the hell your PRV is not cracking and releasing that grossly over pressured fuel rail?

from what i've seen on fuel logs it does actually have a tiny spike in fuel pressure when you release the throttle. but of course youre right it isn't a half second its a very small measure of time, but I was being figurative not literal.

Another thing is that his prv is definitely cracking. It is absolutely releasing pressure, you can see that because the requested vs specified is very close of eachother. Most likely it is just that his tune is requesting so much fuel that it is an amount that the PRV can't drain instantly. After all the prv does retain pressure, so that way the rail can get up to 130 bar, but I assume that the amount of fuel going in exceeds the amount of fuel going out still. Either way the tune is the first place to check. You haven't changed your hardware so it must be software.

[shiro1745]

Any maestro users can post some logs of fuel rail under a pull and right after?
I'll post another chart which shows how the pressure stays very high for longer. I need to look at the time stamp to see exactly for how long.

[shiro1745]

Here are other logs that show very high pressure for very long after I get off the throttle.
The time stamp shows 7 seconds until the pressure drops below 130 bar, but even that's too high.

http://i955.photobucket.com/albums/ae31/ciprianpatulea/highFP1_zpsc203fe10.jpg

[Charles.waite]

Are you sure you're rail valve is working properly? What about your pressure sensor?

[shiro1745]

Charles, I'm not sure the PRV is working ok, I can only assume since it's a new RS4 valve. Pressure sensor again I can assume it's fine, it's new but even a new one can be bad. Not sure.

[Charles.waite]

Charles, I'm not sure the PRV is working ok, I can only assume since it's a new RS4 valve. Pressure sensor again I can assume it's fine, it's new but even a new one can be bad. Not sure.

I figured i'd throw that out there. Who knows.

Also replied to your PM.

[shiro1745]

I sent emails to Ray and Chris, waiting for their replies.

[mec]

My money is still on the tune

[seal66]

I am going to post logs for you here in one sec. IT SHOULD not be doing that under any circumstance at all. Something in the file is fucked.

Okay computer is being dumb and not letting me post my logs lol

[shiro1745]

Just email them to me I'll post them.
[email protected]

[seal66]

Logs sent.
sent two of mine stage 1 and stage 2 and one from JRs car

[shiro1745]

Can you send them again but with more data right after the pulls? I see normals pressures in there but I need to see why happens right after the pull.

There's where my problem is, after I get of the throttle. I usually put the car in neutral after a WOT pull. I will go out and do another pull when the movie i watch is done and leave it in gear so the engine speed drop slowly and see what happens then.

[seal66]

Shiro,

How it looks at 65xx RPM after I let off the throttle my requested stays 109 then drops and my actual well jump a bit say another 5-10 bar and then go down.

I will go through some other logs and see if I have any after pulls as well

[shiro1745]

here are the numbers at the end of each file you sent me. I only see a bit of increase in pressure at the end but I'd like to see more if you have.

http://i955.photobucket.com/albums/ae31/ciprianpatulea/hpfps2_zps69607e57.jpg



http://i955.photobucket.com/albums/ae31/ciprianpatulea/hpfps1_zps9e06878d.jpg

[shiro1745]

I just did couple more 3rd gear pulls but this time I left it in gear but nothing changed.

[rongeur]

Shiro, I would be curious if you were able to put together some logs that include specifically RPM, Engine Load, AFR, N276 load, rail pressures specified and actual to see what they look like from WOT to off the gas.

Seals rail pressure logs are all WNL the variance when off gas is not a significant fuel pressure spike and is not a valid example of a rail pressure spike.

[shiro1745]

Shiro, I would be curious if you were able to put together some logs that include specifically RPM, Engine Load, AFR, N276 load, rail pressures specified and actual to see what they look like from WOT to off the gas.

Seals rail pressure logs are all WNL the variance when off gas is not a significant fuel pressure spike and is not a valid example of a rail pressure spike.

I'll do it tomorrow. But how do you log N276 load? I've asked that many times and nobody seemed to have an answer.
In the first chart I posted in the OP I logged all of these except N276

[rongeur]

I thought I remember reading in the PRV thread but maybe it was just you asking, haha. I was just thinking looking at all of them we could through a process of elimination pinpoint the culprit. The only other thing I could think of is the N276 getting stuck closed (fuel directed to rail) but that wouldn't account for your tune calling for it once off throttle. Pretty sure it is the tune. I am currently working through one of Gregg Banish's EFI tuning books (great stuff preparing me for the eventual maestro jump) but he sums it up perfectly that garbage in = garbage out meaning the ECU will do whatever you tell it to do, good or bad.

[seal66]

Shiro, I would be curious if you were able to put together some logs that include specifically RPM, Engine Load, AFR, N276 load, rail pressures specified and actual to see what they look like from WOT to off the gas.

Seals rail pressure logs are all WNL the variance when off gas is not a significant fuel pressure spike and is not a valid example of a rail pressure spike.

Right it was to show what the rail pressure should do. Granted I have to give him a log that shows letting off the throttle.

[seal66]

sent you one more log, and a brief thing to read.

[shiro1745]

sent you one more log, and a brief thing to read.

great, this is much better. your car actually behaves the same way but at a lower level cause you said the car was stock here. I posted it as two images cause the laptop screen cannot get it all, so just ignore the double header and the three lines which are repeating in the second chart. I also removed a few columns to keep it cleaner.

The blue area is under acceleration and the green is after you got off the throttle. see how after you release the throttle and RPM starts dropping there's a significant increase in pressure. The first higher value occurs at 6560 when the actual is 114.12 then the ECU realizes that the actual pressure increased and starts requesting the exact same as actual. So what's interesting here to note is that the actual pressure increases first then ECU starts requesting the same. I'm not sure why, but I'm sure there's a logic behind it. In your case though is not a problem cause it only gets to 123 bar. Doing a quick math, in your case pressure raises 11% more that the max pressure during the pull, in my case it's 55% more. This is all weird.

I would love somebody with BT to post same logs. I am really curious now, cause if a stock car behaves the same, I'm sure a BT on will do too, the question is how bad?

EDIT(this applies to bold sentences above) It is actually normal, the ECU's seeing the increase in pressure(which is all mechanical) and starts requesting the same cause otherwise it will throw a fault code(when difference between requested vs actual is higher than +-5%). So that is just a mode of avoiding fault codes under normal operation. So my case has to be something with the hardware and not the tune. The pressure just raises so much and the ECU cannot do anything but request the same. Now this sound like a bug in the software where probably audi engineers didn't have modding in mind when they designed it, probably not expecting to reach so high values. They could have limited the whole thing at let's say 160-170 bars. Or maybe they know something we don't and these rails can handle much higher pressures than we think. Anyway 200bar is not making me comfortable and I still believe something is wrong, but either with my hardware or with the design of the fueling system, that's why I said I really want to see some BT logs.

accelerating
http://i955.photobucket.com/albums/ae31/ciprianpatulea/hpfps3_zps8c5d9167.jpg

decelerating
http://i955.photobucket.com/albums/ae31/ciprianpatulea/hpfps4_zpsdfeca556.jpg

[shiro1745]

I thought I remember reading in the PRV thread but maybe it was just you asking, haha. I was just thinking looking at all of them we could through a process of elimination pinpoint the culprit. The only other thing I could think of is the N276 getting stuck closed (fuel directed to rail) but that wouldn't account for your tune calling for it once off throttle. Pretty sure it is the tune. I am currently working through one of Gregg Banish's EFI tuning books (great stuff preparing me for the eventual maestro jump) but he sums it up perfectly that garbage in = garbage out meaning the ECU will do whatever you tell it to do, good or bad.

That's what me and Ray thought too, but now I'm wondering if the 6bar fuel filter is the problem, maybe my VIN requests a lower pressure regulator for the fuel filter? I'm going to audi now to see what they have for my VIN a 4.5 bar or 6bar?

And yes, that was me asking about N276 haha

[seal66]

Nice shiro....

I see what your saying now. I would start with the sensors first and see if that fixes the problem.

[shiro1745]

Apparently the early VINs use the 6bar fuel filter so I'm good there.


Nice shiro....

I see what your saying now. I would start with the sensors first and see if that fixes the problem.

Actually the N276 is not the sensor, it's the solenoid on the top of the pump which cannot buy separate, but I'm not even sure it's that now. I received an answer from Ray and he confirmed with Chris that all cars do that on overrun. That doesn't me make more comfortable though, but this was his answer. Not sure what to say at this point, we need to get some logs from other BT guys running different tunes and compare or we need to find out exactly how much the HP fuel side is good for, I'd sleep better at night if an audi tech would confirm it's good for 200 bar. I'm sure none of the BT guys want to find themselves in a big fire ball.

[seal66]

Apparently the early VINs use the 6bar fuel filter so I'm good there.



Actually the N276 is not the sensor, it's the solenoid on the top of the pump which cannot buy separate, but I'm not even sure it's that now. I received an answer from Ray and he confirmed with Chris that all cars do that on overrun. That doesn't me make more comfortable though, but this was his answer. Not sure what to say at this point, we need to get some logs from other BT guys running different tunes and compare or we need to find out exactly how much the HP fuel side is good for, I'd sleep better at night if an audi tech would confirm it's good for 200 bar. I'm sure none of the BT guys want to find themselves in a big fire ball.

That does not sounds right to me. Okay. I would logg the duty cycle and see what it does.

[shiro1745]

What duty cycle are you referring to?

[seal66]

the n276. If I remember right you can log it in vcds.

[shiro1745]

you'd be the man if you tell me how? I remember asking many times and got no answer

[seal66]

I well go through the blocks and see what it is again.

[mec]

Isn't the n276 just the hpfp pressure?

[bman005]

I had some logs that apparently I deleted from my computer but mine acts similar to seal66's under acceleration except mine jumps up above 130 IIRC at the higher rpm. Maestro, RS4 prv, still the old K03

[seal66]

Like I said in like 7-8 days I can get ya a shit ton of logs.

[hpfpupgrade]

Old thread but I just found it.

Very common to see high fuel pressure when you lift off the throttle. The fuel has nowhere to go and it continues to build inside the pump/rail when the injectors turn off. It does seem to be staying around for a while so that could be a problem with the N276 valve or a stuck rail valve.

I have seen as high as 220 ish bar on some cars with S2 pump running custom 172 bar Performance Rail Valve when lifting off the throttle, but it comes down much quicker.

I hope you got everything figured out with this.