# VRT fuel pressure?



## CorradoFuhrer (Mar 21, 2002)

I noticed some issues with my VRT with higher A/F ratios... Swapped out spark plugs, the gaps were pretty high, same deal. 

I checked fuel pressure at idle, 30 psi and 40 psi or so with the vac off the FPR.

Swapped out the fuel filter. Same deal

Swapped out the fuel pump. Same deal

Checked the voltage at the new pump = 17.xx

I'm driving around at like 5-6 psi seeing like 12.6-12.8 afr which seems wayyy too high. I'm afraid to crank it up more.

I thought for sure the fuel pump was weak or was having low voltage. It seems like I have an issue somewhere else.

Nothing I have replaced or changed has altered the original symptoms. My gauge could be wrong on the fuel pressure, but my wideband is reading lean. 

no codes?


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## Boost112 (May 8, 2002)

...what tune are you running?...i have had the same issue with my UM 440cc tune...and the only thing that got the a/f down was an adjustable fpr...right now im at about 4 bar...and see my a/f ratios in the 11.6's on the high side and 10.6's on the low side...


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## CorradoFuhrer (Mar 21, 2002)

I have the latest C2 30# stuff. I don't think it has anything to do with the tune because I have low fuel pressure, than what it should be.

I wish I had had some concrete information of what the pressure should be at idle and with the vac removed. I heard its 43.5 with the vac reference unplugged, so i'm still 3.5 psi short. It seems pretty low at idle.

I don't get why I would be seeing 17.xx at the fuel pump. I tested at the battery... it seemed correct. 

New performance electric fuel pump
New oem fuel filter

Its just strange the only answer that seems to make sense is that my multi meter and my fuel gauge are off, but the original problem still persists. Higher than normal A/F.


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## CorradoFuhrer (Mar 21, 2002)

here is some help from ALLDATA:
FUEL PRESSURE

1 BAR=14.7PSI

Regulated Pressure 2.5 bar 

System Pressure 3.0 bar 

Residual Pressure (after 10 minutes) 2.0 bar

Fuel Pressure Regulator and Residual Pressure, Checking :

The fuel pressure regulator controls the fuel pressure dependent upon intake manifold pressure.

Special tools, testers and auxiliary items

VAG 1318 pressure tester 
VAG 1318/10 adapter 
VAG 1318/11 adapter 
VAG 1318/16 adapter
Test conditions :

Fuel pump delivery rate OK.
Test sequence :

WARNING: DO NOT smoke or work near heaters or other fire hazards when working on fuel system.
The fuel system is pressurized! Before loosening hose connections or opening the test connection, wrap a cloth around the connection. Then release pressure by slowly disconnecting the hose/fitting

Disconnect test port plug -1- from fuel rail and connect pressure gauge VAG 1318 with adapter VAG 1318/10 and hose VAG 1318/1 to fuel rail. 
Fuel gauge valve must be closed, handle 90°to direction of flow (arrow). 
Start engine and run at idle speed. 
Check fuel pressure. Specification: approx. 2.5 bar (36 psi) .

Disconnect vacuum hose from intake manifold upper section at fuel pressure regulator (arrow). 
The fuel pressure must rise to approx. 3.0 bar (44 psi) . 
Switch ignition off. 
Check for leaks and residual pressure by watching pressure drop on gauge. 
After 10 minutes there must be a residual pressure of at least 2 bar (29 psi) .
If the residual pressure drops below 2 bar (29 psi) :

Start engine and run at idle speed. 
After the pressure has built up switch ignition off and at the same time clamp-off return line (with blue arrow) on fuel rail. 
Watch pressure drop on gauge.
If the pressure does not drop:


Replace fuel pressure regulator.
If the pressure drops again:


Check fuel pump check valve. 
Check hose connections, O-rings on fuel rail and fuel injectors for leaks. 
Check pressure gauge for leaks.

found this searching, I guess I should be at 36.75 psi at idle, and i'm at like 31. So something is definitely off. I just don't see how a brand new pump is offering the EXACT same test results. So whatever it is, its not my fuel pump?


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## stealthmk1 (Aug 17, 2001)

I didnt check my fuel pressure, but my AFRs were up there with yours. I swapped in a 4 bar in place of the 3 bar and they went down to high 10s , give or take.


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## CorradoFuhrer (Mar 21, 2002)

everything was fine, then it just started acting up. Fuel pressure isn't where its supposed to be. Same numbers with a replacement pump? I thought a bad FPR would make it run rich?


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## CorradoFuhrer (Mar 21, 2002)

it held fuel pressure 31 psi for ten minutes after shut down. I'm guessing this doesn't even matter... I squeezed the return line and the pressure went up dramatically. I forget what that means, good or bad.


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## CorradoFuhrer (Mar 21, 2002)

I gave c2 a call yesterday and they pointed me in the direction of MAFS, I cleaned it, and it seems to be running much better. Props to c2. I need to get a catch can because the kinetic kit has the crankcase plumbed into the intake, and my mafs intake pre turbo was kinda of oily.


I may need a new mafs now I guess, the one at autozone runs me like 150 bucks :thumbdown: tempted to throw it in to see what it does. I just bought an oem one no less than 2 years ago.

The non spec fuel pressure has me concerned, but c2 was telling me the fuel being ever so slightly at idle there, if its the same under boost (which I didn't check under boost) would only result in a few decimal points on the a/f, where mine was completely off and falling on its face. 

So dirty mafs! Anyone recommend a catch can setup that will hook up to a kinetic kit rather nicely?


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## stealthmk1 (Aug 17, 2001)

I don't think my FPR was faulty, just that my tune required a little more pressure.


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## Boost112 (May 8, 2002)

...the MAF i could see in the a/f ratios...but the low fuel pressure doesn't make since really...you should be seeing a little higher pressure with the 3 bar fpr...i might have to take a look at my MAF now...


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## CorradoFuhrer (Mar 21, 2002)

yea i don't know. I am not throwing any codes for the maf, but after cleaning it... it seemed to work better. But I do notice that when I jam into boost the a/f are still a bit high, rather than easing into the boost. I think perhaps the oil did damage the mafs and its time to get another one but i'm not ready to shell out the 150 just to start guessing at things.

the mafs i have is less than two years old and genuine vw oem.


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## 'dubber (Jun 15, 2004)

You can check obd2 maf grams per second in vagcom/ vcds, or probe the 0 to 5v maf ecu signal wire and watch the dc voltage with a digital voltmeter while you drive, to test its output. Otherwise you're playing guessing games.


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## CorradoFuhrer (Mar 21, 2002)

that's what I thought too but c2 said unless I knew what the exact g/s was it was anyones guess.

I was running tonight about 10 lbs, upwards of the rpms seeing like 13.1 13.2... nothing blew, feels fast. Its saying a little too lean for my liking. 

I also found out my boost tube being up against the coil pack there sometimes was causing it to arc to the tube, gave me a pretty nice shock trying to re arrange it. I have brand new oem mk4 wires that one already has a split on the connector end. I rearranged the tube and so far so good. 

It pulls hard. But not safe numbers for my liking, I guess i'll have to get a new mafs and a catch can. I also randomly had a bank 1 o2 code that pops up randomly. I have a brand new o2 and cruising and idle is always around 14.7. The computer disregards the 02 at wot correct?

That's where i'm at. I'm used to seeing a lower a/f number at 9-10 psi


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## _muppet_ (Aug 5, 2004)

What wideband are you running? Have you tried calibrating it? Are you running stock compression? Mid 12's under 10 psi sounds ok, you said your going into the 13's at 10 psi and high rpms? Is that at WOT? That is maybe a little on the lean side. Do you have a vag-com? Have you tried logging your knock sensors?


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## chrgdVR (Aug 2, 2004)

Why are u guys trying to get ur afr's into the 10s? 14.7-15 at idle and cruising light load is normal.. 12-12.5 under 10psi is fine. I don't see any reason to add more fuel at those boost levels


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## CorradoFuhrer (Mar 21, 2002)

_muppet_ said:


> What wideband are you running? Have you tried calibrating it? Are you running stock compression? Mid 12's under 10 psi sounds ok, you said your going into the 13's at 10 psi and high rpms? Is that at WOT? That is maybe a little on the lean side. Do you have a vag-com? Have you tried logging your knock sensors?


AEM uego or whatever its called. Its dead on at idle and cruising at or around 14.7. I don't think theres a calibration for it. I'm running stock compression yeah. Yea this is at wot at around 10 psi in the higher rpms. It was always a lot lower than that. If I ease into the boost on the highway or so its like high 11's mid 12's up top.

I have a handheld vag scanner but not a vag com. What's the group number for the knock sensors, and what should I be looking for?


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## CorradoFuhrer (Mar 21, 2002)

chrgdVR said:


> Why are u guys trying to get ur afr's into the 10s? 14.7-15 at idle and cruising light load is normal.. 12-12.5 under 10psi is fine. I don't see any reason to add more fuel at those boost levels


my cruising afr's are great, but its when I jam into boost that I start seeing higher numbers than normal. Before it was a lot lower like 11.8-12.5. It was a lot higher and falling on its face stumbling. So I turned the boost all the way down and was still seeing high afr's.

So when I got into the fuel pressure end and it wasn't text book at the idle 2.5 bar or 3.0 bar with the vac reference removed, I assumed it was there. Since I cleaned my mafs (it had been a tad oily) I can up the boost, without hiccuping but I think the oil damage has been done because its not the same.

I replaced everything on the fuel pressure end except for the FPR. But I guess the only way to test is under boost, and if the pump or injectors were bad it would be totally apparent i'm told?


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## _muppet_ (Aug 5, 2004)

Knock control is groups 020-029, 020 and 021 should show how much timing is being pulled for knock events. I am told 6 degrees or less is fairly typical on chip tunes. While this won't diagnose your issue, it would help diagnose whether or not you actually have an issue present.


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## CorradoFuhrer (Mar 21, 2002)

for knock, what will these readings say? Will it show degrees or some vw format that needs to be configured into degrees of timing? Basically what should it say, and whats good and whats bad?


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## TBT-Syncro (Apr 28, 2001)

Corrado****** said:


> I checked fuel pressure at idle, 30 psi and 40 psi or so with the vac off the FPR.


 your FPR is dead/bad/toast. 

you should be 43psi with no vac line, and about 38psi once warmed up with vac line.


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## CorradoFuhrer (Mar 21, 2002)

That's the last thing that would need to be replaced. The fact that the fuel pressure was changing lead to me to believe that it was doing it's job. 

I also thought when they go bad the car would go rich, and not regulate off the vacuum reference there on my gauge. It's been said when the diaphragm rips, that the vac lines will smell like gas... I didn't have any of these normal bad FPR symptoms. Has anyone had a low pressure symptom like i'm having directly related to the FPR? 

It's a cheap part to replace though. 

The main issue was the dirty mafs, because i'm boosting away with wayyy better air to fuel ratio's after since cleaning it. 

So either my fuel pressure gauge is off (which I doubt) or something is definitely off on my fuel pressure and its cause for concern.


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## CorradoFuhrer (Mar 21, 2002)

TBT-Syncro said:


> your FPR is dead/bad/toast.
> 
> you should be 43psi with no vac line, and about 38psi once warmed up with vac line.


 Have you ever had or seen this as a direct problem of the FPR like the symptoms i'm seeing?


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## TBT-Syncro (Apr 28, 2001)

Corrado****** said:


> Have you ever had or seen this as a direct problem of the FPR like the symptoms i'm seeing?


 seen bad FPR give weird/bad readings, yes. (normally its a bad or torn diaphragm) 

what happens to fuel pressure if you rev the motor, and then lift off the gas?


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## CorradoFuhrer (Mar 21, 2002)

The fuel pressure would increase and go back down with throttle, mind you this is all in neutral parked up. 

It would also increase dramatically upwards of 50-60 psi if I pinched the return line. I think that means I don't have any leaks? 

I have the boost set at 10 psi as of now, and the air to fuel seems to be on point when i'm low in the rpms, so my main problem definitely was a dirty mafs, but the non on point fuel pressure has me concerned now. 

It's not like a FPR is hard to replace. I'll just have to go to the u pull it or find someone with some parts lying around. I had an extra rail that I threw out with an FPR. Wish I hadn't :banghead:


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## TBT-Syncro (Apr 28, 2001)

Corrado****** said:


> The fuel pressure would increase and go back down with throttle, mind you this is all in neutral parked up.
> 
> It would also increase dramatically upwards of 50-60 psi if I pinched the return line. I think that means I don't have any leaks?
> 
> ...


 also dont forget to verify that the fpr vac line is getting a good signal.


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## CorradoFuhrer (Mar 21, 2002)

TBT-Syncro said:


> also dont forget to verify that the fpr vac line is getting a good signal.


 its getting a good signal, brand new rubber on there. It drops and builds back up. I'm trying to find someone local with a fuel pressure gauge I can try out to verify my gauge. Maybe I can just drop by someone with compressed air to test it out.


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## CorradoFuhrer (Mar 21, 2002)

i'm not really having any bad numbers on boost anymore, nothing too crazy. I'm at 10 lbs and seeing low to mid 12's on the afr. But I would like to verify stock pressure to make me feel better. Swapping out a FPR would and trying another fuel gauge should get me to the bottom of this thing. 

I should get into checking to see what the knock sensors are doing but its hard to drive and look at the handheld checker at the same time, the screens kind of small.


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## 'dubber (Jun 15, 2004)

Get a cheap laptop and a registered copy of VCDS and you will be able to answer a lot of your own questions without playing guessing games. 


Ever figure out why you were reading 18 VDC at your fuel pump? Bad meter or wrong scale perhaps? 

Edit: Idk why I thought you said you that had high fuel pressure at idle.


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## CorradoFuhrer (Mar 21, 2002)

I have no idea why it was at 17.xx dc volts at the pump. I would have to remove my rear bar and system to double check it again. 

The maf cleaned up nice, and now its boosting no problem at a solid 10 psi at low 12 afr. 

Yea I need to get a vag com, the V checker tool doesn't exactly work for logging and in depth stuff. It will give me the group numbers though and watch it real time. 

Perhaps maybe I have a bad fuel pressure gauge. Everything seems to be working fine now. I wanna get another cheap fpr to test before i spend on a new one. Because I had so much trouble selling two other good used ones I had, I wound up throwing them out. :banghead: 

i'm sure in the U pull it or at someones house I can find one lying around. 

:beer:


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## CorradoFuhrer (Mar 21, 2002)

'dubber said:


> Get a cheap laptop and a registered copy of VCDS and you will be able to answer a lot of your own questions without playing guessing games.
> 
> But yeah, it sounds like your fpr diaphragm is not expanding OR contracting fully, hence the high idle pressure and low full-throttle pressure.
> 
> ...


 my idle pressure is low, and with out the reference on the fpr are low... but just ever so slightly. 2.5 bar should be a bit higher than 31 psi and at like 40 psi im not hitting that 43.5. 

Another gauge and another fpr would be the last thing to rule out, other than the unusual high voltage reading I got. I may have had the volt meter on something but it read 13-14.xx at the battery. so nooo idea. 

so far so good though now the mafs got cleaned up and my boost tube isn't against the coil pack arcing, got a nasty shock. I though the rubber would protect it. 

I think the more important thing is to keep the valve breather out of the flow of the intake and mafs, either go to atmosphere filtered or a catch can. 

it got gunky in there, enough to make my brand new oem mafs go bonkers after only a year or so. luckily it cleaned up.


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## _muppet_ (Aug 5, 2004)

I guess I missed that earlier, but if your coilpack was arcing bad enough to cause a misfire in a cylinder or two, that would probably show a lean condition on your wideband.


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## CorradoFuhrer (Mar 21, 2002)

When it was doing that, it was completely noticeable and something completely separate. The main problem was the mafs for driveability. 

The fuel pressure not being 43.5 with the vac reference removed lead me down the wrong path to replacing this and that. 

I'm still getting the same fuel pressures after 2 alternators and 2 fuel pumps. 

So double checking my gauge's accuracy with another gauge or an air tank... or swapping out a good FPR should show me what's what because everything else is new. 

I'm seeing 13.0 13.1 at say the top of third at 10 psi at 5500.. so I back off. On the highway sometimes it's richer if I ease into the boost in the mid 11's and build its way up. It used to be better numbers, but it sure pulls like crazy. 

So the mafs is just not as accurate because of it needing to be clean... and or the fuel pressure is playing its part. 

When is a typical inline fuel pump needed? Above 10? 

To end this post for the future, i'll try to get my fuel pressure at the double confirmed 43.5 with out vac at the fpr at idle. Even though c2, which i've heard before is that fuel pressure only matters when its under a load. I'll have to get a longer fuel line so someone can hold it in the passenger seat, once I confirm my gauge isn't off a few psi from being dropped or who knows what.


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## Rod Ratio (Jun 6, 2012)

Inline


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## CorradoFuhrer (Mar 21, 2002)

well, a buddy was nice enough to let me swap in another 3.0 FPR from a low mileage 1.8t. Said 3.0 bar on the FPR.

Checked the pressure, same deal, if not a tad lower. like 30 and 40 psi on and off the vac. So either my gauge is toast or I have low fuel pressure, and I have no idea why. Different XYZ, same symptoms.

I turned the boost down, re cleaned the mafs... seems to drive fine but the wideband shoes 13xx as soon as i'm steady boosting at like 6-7 lbs even creeping into it. I seemed to have mad the problem worse by cleaning the mafs again, not sure why.

I'm sure the c2 tune is supposed to be in the low 11's or 12 under boost correct? Even at low psi?

I think I just need to replace the mafs. This sucks. It looks like brand new as well. When i'm seeing 13 afr's i just let off the throttle not trying to pop this thing. Its a vw OEM bosch and its not even two years old. I'm guessing that crank case gunk really just shafted it. 

at the track is was much fatter at 10-11 lbs it would creep up to 13.00 -13.01 at like my shiftpoint. Now its jumping right into it at the lowered boost. 

I got into measuring group 21 and 22, i think there is something there with degree symbol and it was jumping around. I'm not sure what to make of that like 15 -30 etc and two other values with XX .ms i'm guessing thats the voltage of the two knock sensors. But only one with degrees.


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## CorradoFuhrer (Mar 21, 2002)

_muppet_ said:


> I guess I missed that earlier, but if your coilpack was arcing bad enough to cause a misfire in a cylinder or two, that would probably show a lean condition on your wideband.


the tube was rather close to the one plug, and rubbed/cut the boot of the coil - wire - connection so it was zapping the boost tube. The misfire from that was completely detectable, you could hear it clicking on the tube and missing.

i got it all sorted out there, but no idea why i'm still running like crap. 

I have to check my Fuel Pressure gauge out or get a new mafs it seems.


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## Rod Ratio (Jun 6, 2012)

Get off the maf sensor hombre.

I'd be looking at the primary o2 sensor more than the maf. You should also be pressure testing your intake tract for leaks (even pinholes), as well as (and more so IMO) checking for small pre primary o2 exhaust leaks. If your maf, and primary o2 are telling the ecu conflicting stories, the ecu is going to do strange things; as it really has no idea what's truly going on.


Time for some real troubleshooting


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## CorradoFuhrer (Mar 21, 2002)

Rod Ratio said:


> Get off the maf sensor hombre.
> 
> I'd be looking at the primary o2 sensor more than the maf. You should also be pressure testing your intake tract for leaks (even pinholes), as well as (and more so IMO) checking for small pre primary o2 exhaust leaks. If your maf, and primary o2 are telling the ecu conflicting stories, the ecu is going to do strange things; as it really has no idea what's truly going on.
> 
> ...


These tests are all at WOT, which disregards the 02 sensor. I look at this stuff analytically... it was working really awesome, and then... I was so sure of the fuel pressure being the issue, since its not right. I've replaced everything there, so if my gauge is off, then its electrical at the pump.

Also my idle is solid 14.7 - 15.3... no codes for anything though... that's what sent me to the fuel pressure, especially with the gauge not reading right. 

Checking for leaks sounds great, i'll have to construct something per that DIY. I remember when my intake broke, that heater element thing off the crankcase vent... briefly after that my mafs took a dump pre turbo kit.

I cleaned my mafs and it felt better, i cleaned it again and it got worse. I would very much like to stick a new mafs in there and see what's what. Then rig up some kind of a catch can, getting some nasty poolage in my intake tube, not major but enough to probably to have fouled up the sensor.


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