Fuel pressure too high...

[MmmBoost]

Finally got around to installing my inline fuel pressure gauge today, only to find out that my fuel pressure is NOT at all what I expected it to be. The 60 PSI Gauge was sitting around 50 psi after a key-on pump prime. Then when I started the car the gauge was pegged out at the pin below zero.

I just replaced my fuel filter and just got done confirming all of my lines are hooked up the right way.

Blue clip to RL
Black clip to VL
Evap hose to E
Fuel rail to MOTOR

Fuel pressure should be just below 4 bar from what i read......so I was expecting to see that. Anyone ever seen this before?? I'm thinking I got a bummed FPR in my filter.

[MmmBoost]

The only thing I can think of is that the supply and return line are reversed. Why the hell would the color code be off?

[A4 TSCHUSS]

58psi aka 4 bar is the stock pressure.

[MmmBoost]

Exactly what I thought.

And I just got out from under the car. I disconnected what I was 100% sure was the pump supply line and stuffed the end into an empty water bottle. Then I turned the key on for a prime pulse and sure enough....the bottle has gasoline in it. So the filter is indeed hooked up correctly.

The FPR in the filter must be defective.

[AudiA4_20T]

wait, so it was at 50? (a little lower than normal but nothing I would be worried about, could be the gauge) and then it's at 0? The car wouldn't start if it was at 0 obviously. I'm confused

[MmmBoost]

No no .......

The gauge when I bought it was at 0. After I installed it and turned the key on for a priming pulse only the gauge was at 50 PSI. After I started the car, the gauge then went past 50, past 60, all the way around until it hit the stop at 0.

I hooked up another gauge and it was fluttering around 70-80 psi.

[Ori0n]

Wuff. I'd try another gauge first, before jumping to conclusions.

[MmmBoost]

I tried a 0-100 gauge AND a 0-60. Conclusion jumping is not something I do

[Ori0n]

Now that I think about it, it does seem weird with just the key-on that it reads about right.

[MmmBoost]

I should have got the gauge installed before I changed fuel pumps. I can't help but wonder if it has something to do with me installing 034's high-output pump on Friday.

Anyone else running the 034 005 pump had any issues like this? Maybe I even pinched the return line or something while re-installing the pump. Ideas?

[heywier427]

does 034 list an operating pessure?

you cant run the same amount of fuel through the same diameter line without bumping the psi, so maybe its were its supposed to be.

give em a call.

good luck.

[dirtybrd]

Extra pressure isnt a bad thing and I wouldnt be concerned on bit.

[MmmBoost]

does 034 list an operating pessure?

you cant run the same amount of fuel through the same diameter line without bumping the psi, so maybe its were its supposed to be.

give em a call.

good luck.

I emailed 034 this morning. Waiting to hear back from them.....

Extra pressure isnt a bad thing and I wouldnt be concerned on bit.

Unregulated pressure is a bad thing. It's fucking my fuel trims up. It's making my idle shitty with 750cc injectors that used to purr like a kitten.

[Dan[FN]6262]

its just trying to tell you to turn up the boost...

[dougyfresh]

Extra pressure isnt a bad thing and I wouldnt be concerned on bit.

It'll affect the injectors since the duty cycle is designed to work on a given static pressure.


Chris,
Where in the fuel system did you hook the gauge up? You should be most concerned with pressure right at the fuel rail on the engine.

Did you calibrate the gage on a known pressure source first to ensure you are reading the right pressure? I had this problem when reading oil pressure as the gauge I purchased was way out of calibration thus throwing off my readings of oil pressure.

[MmmBoost]

I hooked the gauge up right at the transition from hardline to rubber line on the firewall in the engine bay.

I didn't calibrate the gauge since it's brand new. But as I mentioned before......I tried two gauges. The 0-100 gauge was indicated erratic pressure between 70 and 80 PSI and the 0-60 was off the scale.

It's not the gauges. 2 different gauges can't possibly 25% out of calibration.

[A4 TSCHUSS]

You wouldn't have touched te return line while installing a fuel pump, so don't see how you could have pinched a line so I would rule that out. The return line comes from the filter then up the front of the tank on passenger side to the top then shoots across to the drivers side and connects to the cap over there.

[AudiA4_20T]

btw the fuel pump isn't the problem, you're right it would be something in the regulator. Fuel pumps will run at whatever they can, the regulator is what keeps pressure in check

[MmmBoost]

What's the second line on the top of the fuel filter cap then? With the black plastic tube that goes down below the fluid level in the tank.


Top right

[MmmBoost]

btw the fuel pump isn't the problem, you're right it would be something in the regulator. Fuel pumps will run at whatever they can, the regulator is what keeps pressure in check

Well i was just wondering if i may have kinked the return or something causing pressure to build up past the regulators setting.

[Bische]

What's the second line on the top of the fuel filter cap then? With the black plastic tube that goes down below the fluid level in the tank.


Top right

I dont even have the line your mentioning, i dont have the small electric connector either. I had to plug that nipple when i changed my pump, the old one didnt have the nipple

[diagnosticator]

The fuel pressure regulator in the filter, is calibrated to provide the correct fuel pressure with the stock fuel pump. Since you are now running a higher flow rate pump, the regulator can't flow enough bypass fuel to regulate the fuel pressure to 4 bar as before. With the regulator bypass back to the tank, at the 100 percent flow rate, the high flow fuel pump exceeds the capacity of the regulator control range bypass flow rate. Therefore, the fuel pressure will by unsteady and at a higher average pressure and flow rate with the high flow pump, compared to the stock pump.
As you already realize, the higher fuel pressure results in higher fuel flow rate from the injectors, directly effecting air/fuel mixture ratios. Consequently, one way to restore correct fuel pressure while still allowing for higher fuel flow when required, is to install a second adjustable inline fuel pressure regulator that is installed in parallel with the stock in-filter regulator. Adjusting the set point of the second regulator, the combined bypass fuel return flow rate of both regulators will reduce the in-filter regulator bypass return flow to less than 100 percent, restoring correct fuel pressure control.


Edit added:
The second regulator is connected with the inlet port connected to the fuel pump outlet line to the fuel filter inlet port and the regulator outlet port connected to the fuel return line back to the tank used by the in-filter regulator. Alternatively, run a dedicated fuel return line from the second regulator, back to the tank with a through wall fitting installed at the access cover at the fuel pump side of the tank, with the return line extended inside the tank to near the bottom.
A local pressure gauge is not required. Adjust the second regulator until the fuel pressure on the existing gauge shows the specified fuel pressure of 4 Bar, 58 psig.

[Wet0willy01]

Install parallel? Wouldn't that allow for unfiltered fuel to see the engine/injectors? Do you mean in series?

Edit- I guess you attach a gauge to the outlet side and never see any flow out of the regulator into the fuel line, yet still regulate pressure and provide the additional path of return flow.

[MmmBoost]

Thank you for the insight, diagnosticator.

I was thinking that the problem had to do with the increased flow from the new pump. the 005 is MUCH larger than the stock pump and after cutting open my old FPR to see how the regulator works, I was almost certain the issue had to do with the increased flow.

I'll see what 034 has to say about this considering there is ZERO mention that it may affect fuel pressure

[diagnosticator]

Install parallel? Wouldn't that allow for unfiltered fuel to see the engine/injectors? Do you mean in series?

That is a good point, but no, not in series. The second regulator in parallel, will only return fuel to the tank via the same fuel return line used by the in-filter regulator. It won't send any fuel to the engine fuel rail.

[MmmBoost]

I think I'm just going to have to redo the fuel system right from the pump. I was hoping I wouldn't have to do this.......but it looks like i need to get out my wallet again.

[diagnosticator]

What's the second line on the top of the fuel filter cap then? With the black plastic tube that goes down below the fluid level in the tank.
Top right

The total return fuel is split into two flow streams, one goes to the suction jet pump at the fuel pump baffle housing, the second is sent to the left side of the tank to the suction jet pump in the left section of the tank, to transfer fuel across the hump in the tank back to the pump baffle housing in the right side of the tank.

[MmmBoost]

I guess I'll use the stock supply line as my return line and run an Aeromotive or Fuelab regulator after the rail. I'll leave the manifold reference line unhooked until Tapp can find the other map I asked him for which is the "switch" for return/returnless.


Are the B5 guys having similar issues using the OEM regulator on the rail?

[diagnosticator]

Yeah, that is another way to go, but remember that the reason for the returnless fuel system used on the B6 is to avoid heating the fuel in the tank from the warm/hot fuel returned from the regulator at the fuel rail back to the tank.

[MmmBoost]

Yeah this is true, but there is nowhere to run another regulator and filter in parallel like you suggest. Space is TIGHT down there and those OEM plastic hoses and fittings do not make re-routing things easy.

Either way there is still heat being added to the fuel tank. The nature of the fuel being run through any regulator will cause heat to be introduced into the fuel. And even though the system is called "returnless" .....it still has a return—just not from the rail. It's not like the old carburetor fuel pressure regulators that are dead-headed and then cause the pump to heat up......but they only had to dish out 3PSI and enough fuel to fill up a float bowl.

At the end of the day......if warm gas in the tank is a necessary consequence of making this system work and meet the demands of the turbo/engine, then so be it. I could throw on an inline cooler on the return line to minimize the effect.

[dougyfresh]

I think I'm just going to have to redo the fuel system right from the pump. I was hoping I wouldn't have to do this.......but it looks like i need to get out my wallet again.

You shouldnt have to do that. Others are running high flow pumps and everything is fine.

[MmmBoost]

Have others check their fuel pressure after installing it?

I know David was experimenting with the Eurocode pumps......but i don't know all of the specifics of his fuel system.

I know he's on a return system now.

[dougyfresh]

Yes.

Me.

I forget the absolute values but recall all was within spec. We had a gauge between the flexible line and the fuel rail. As close to the fuel rail as possible. It was plumbed into the dyno so we could log fuel pressure with RPM to make sure there was enough fuel. Fuel pressure barely moved near redline pushing about 400awhp. In tank Bosch 040.

[dougyfresh]

I worked with ASP to do this because I wasn't sure where we'd run out of fuel and need bigger injectors or a bigger fuel rail (which we also designed but never cut chips). Turns out everything was okay. I still have a set of bigger injectors I had made but never used. Probably sell them when I get around to it.

[MmmBoost]

Fair enough. I was just asking. Not a lot of people seem to want to mess with the fuel line.

Well wtf then....

034 still hasn't got back to my email yet. Awesome.




So Doug, you're on an 040 with an otherwise stock fuel system? Or..? Could you share a few more details, please?

[A4 TSCHUSS]

Your aftermarket pump will not increase your pressure. Like Doug said his didn't change and neither did mine. I ran a fuel pressure gauge on the stock fuel system with a Bosch 040 fuel pump and the car ran at 58psi at idle or cruising and would drop a few psi to around 55psi under boost.

Here is a video that shows me under boost and then you can see when I let off the gas right at the end where it goes back to 58psi where it was while cruising before I started ripping gears. That was before I changed to the return style system so everything stock other than the 040 pump in the tank. No theories going on here, just actual texting. I made 392whp on a dyno dynamics at that setting with the boost tapering down to 26psi right at my peak so over 400whp anywhere else I would have dynoed and I am sure slightly higher if the car would have held the 28psi all the way out.

[MmmBoost]

So it must just be a defective FPR then.

LOL! The conversation at the parts desk at the dealership is going to be interesting. I only bought a new filter 1 month ago......and I'm not paying $68 for a new one.

Me: "So.....my fuel pressure is way above spec after changing my fuel filter last month"

Them: "Well maybe you need a new fuel pressure regulator"

"My fuel pressure regulator is in my filter"

"Your what is what?"

"Come out and have a look at the gauge after i start my car.....I want a replacement filter"

"Sorry we can't exchange used parts"

"How was I supposed to know it was defective before I installed it"

"Not my problem. There's 3 new ones in stock though. $68 each"

{facepalm}

[A4SoftWalker]

Stupid parts guy didn't ans the question.

U needed a replacement for a DEFECTIVE part which was found to be defective by using it.

Dealer will warranty their parts and labor one year 15k miles. It might be optional if they are owner installed not sure of their policy.

[MmmBoost]

it was a hypothetical scenario.

I have some checking to do tonight before I go to the dealer for a replacement.

[diagnosticator]

I think teeing into the two lines near the fuel filter should provide enough room. The regulator itself can be nearby were it fits and is protected from the elements more or less. It does not need to be located at the fuel filter. A small inline plastic mesh type filter screen for the fuel flowing to the second regulator would be a good thing, but if there is no room, then it can be left out without major consequence.

The main consequence of warm fuel in the tank, is increased fuel evaporation rate. If the EVAP Purge fuel vapor recovery equipment is working right, then the recovered and stored fuel vapors will be burned up in the engine, and won't be wasted escaping to the outside air.