Real-time fuel pressure reading during sensor failure

-Pascal · Apr 21, 2010

I thought some of you may find this interesting. My car recently started suffering from the hesitation and stalling which I believe is associated to the fuel pressure sensor failure. While I wait for the parts to arrive I shot this small video of my OBD2 scanner in real-time mode to show you guys what is causing the stalling. Car is sitting still, I'm just blipping the throttle once in a while. (pardon the iPhone video...)

The main event here is the line called "Fuel Press KPAG". Normally that reading is rock solid around 297 to 302 KPAg regardless of conditions (Idle to full throttle) With the failing sensor the parameter will fluctuate from 0 to over 500. You can monitor the throttle blips when the fuel system goes into "OPEN" loop - that's when I take my foot off the gas and the RPM's are falling down (engine compression, no fuel). The rest of the time the car is at idle. I did this to show that throttle application is irrelevant in this case, the pressure readings are all over the place regardless.

http://www.unit305.com/ad/fuelpress.mov

How involved is the replacement of the part? I haven't looked under the cover yet... Any input?

juve021 · Apr 21, 2010

cool!

dang, makes me realize I need a better obd2 scanner or even better yet DICE w/VIDA

Chilled Man · Apr 21, 2010

IIRC its on the end of the fuel rail ?

should only take a few minutes if its the part I am thinking of

IwantaS60R · Apr 21, 2010

FV-QR

Yeah, pretty easy. You will have to remove the airbox and snorkel to give you space but that's it. It's right there at the end of the fuel rail. Only thing I would say is be careful with the rubber seal when replacing. Other than that it's a piece of cake.

-Pascal · Apr 21, 2010

Perfect, thanks guys! http://********************/smile/emthup.gif

StealthyS60R · Apr 21, 2010

I saw exactly the same thing with my own scanner and replaced the FPS too.

No need to remove the airbox to access and change it though, you can get to it by just removing the OTE pipe and manifold cover.

MagoonR · Apr 21, 2010

Re: Real-time fuel pressure reading during sensor failure (-Pascal)

IIRC, dealer claimed that fuel pressure was in the low to mid 40psi range when my sensor was dying. Normal should be in the mid 50psi range.

StealthyS60R · Apr 21, 2010

When I watched some of my crazy pressure readings it made me realize just how much noise the ECU will accept from a sensor without setting a code.

Skot53 · Apr 21, 2010

FV-QR

I didn't have to remove my OTE pipe. You can slide the Silver-colored manifold cover out of the way enough to replace the sensor. You do have to replace the "snorkel" pipe, though. Two screws, pulls out pretty simply.

My Scangauge II did the same thing when my sensor was kicking the bucket. I know I posted about it.... It was something outrageous like normally 57 psi, then jumped to 100+ or something.

StealthyS60R · Apr 21, 2010

You must have bigger hands than I do, I was able to change it out with the snorkle in place as well.

Good to know the manifold cover will get out of the way without removing the OTE pipe though.

michaelc · Apr 21, 2010

Re: (StealthyS60R)

Question about the units, I'm assuming KPA is kilo Pascals (ironic), but what about the G? Kilo-Pascals per gram...gallon?

Needsdecaf · Apr 21, 2010

Re: (michaelc)

Quote, originally posted by michaelc »

Question about the units, I'm assuming KPA is kilo Pascals (ironic), but what about the G? Kilo-Pascals per gram...gallon?

Gauge.

Meaning pressure above atmospheric. Since gauges are calibrated to read zero at STP (standard temp and pressure), "gauge" pressure is not actually the pressure that the gauge is seeing. It is the pressure above atmospheric.

As opposed to absolute, which does not factor in atmospheric pressure. So right now, if you were at sea level, you are being subjected to 1 bar (14.7 psi) of pressure.

-Pascal · Apr 21, 2010

... I may still get the OTE off, clean a few things up and drop in my new spark plugs while I'm in there though... Maybe it's time to do that job.

michaelc · Apr 21, 2010

Re: (Needsdecaf)

Quote, originally posted by Needsdecaf »

Gauge.

Meaning pressure above atmospheric. Since gauges are calibrated to read zero at STP (standard temp and pressure), "gauge" pressure is not actually the pressure that the gauge is seeing. It is the pressure above atmospheric.

As opposed to absolute, which does not factor in atmospheric pressure. So right now, if you were at sea level, you are being subjected to 1 bar (14.7 psi) of pressure.

Got it. Thanks!

Skot53 · Apr 21, 2010

FV-QR

Quote, originally posted by -Pascal »

... I may still get the OTE off, clean a few things up and drop in my new spark plugs while I'm in there though... Maybe it's time to do that job.

Might be a good idea. It does make it way easier to get to it with both of the covers and the OTE pipe removed.

IwantaS60R · Apr 21, 2010

FV-QR

Quote, originally posted by Skot53 »

Might be a good idea. It does make it way easier to get to it with both of the covers and the OTE pipe removed.

I agree, if you're going to take that OTE pipe off anyway then that's the way to go. To do the FPS only, the airbox + snorkel was easier for me as I have a MY04 which uses the v-band clamp on the OTE and it's not that easy given the space back there and the engine/quasi strut brace on.

Lightspeed · Apr 21, 2010

Re: (-Pascal)

Quote, originally posted by -Pascal »

... I may still get the OTE off, clean a few things up and drop in my new spark plugs while I'm in there though... Maybe it's time to do that job.

That would be great to see a How To post. Could you make that happen?

-Pascal · Apr 22, 2010

Re: (Lightspeed)

Quote, originally posted by Lightspeed »

That would be great to see a How To post. Could you make that happen?

I certainly don't mind doing a how-to on the plugs when I do them, in the mean time I only installed the pressure sensor the second it came in, the car was leaving my wife stranded every time she took it and I wanted to end that asap . I haven't taken another test drive to confirm the problem is resolved yet, I'll report after that.

In the mean time the FPS replacement took me all of 4 minutes. Note that I am currently running without the airbox cover so that first step is already done. It went so quickly that I didn't really even think of snapping pictures.

1. Remove air filter. My Eurosport comes off in one second flat.
2. Remove two 10mm acorn nuts holding down the intake manifold plastic cover.
2a. Apply a couple layers of masking tape to the top of that cover to avoid scratching it on the OTE pipe when moving it.
3. Wiggle cover away from manifold and coax it left about 1", just fold down the coolant line and pull the plastic cover over it.
4. Use a small flat head screw driver to pry open the clip for the sensor connector, unclip.
5. Here's the trick: I fitted the proper Torx bit to an extension and jammed it through the airbox hole where the intake snorkel comes in. No need to unbolt the intake snorkel, it's very flexible, plenty of room to pass the extension through it. Remove the Torx nut, leave the extension in the snorkel hole, ready to reinstall.
5a. Enjoy the few ounces of gas spewing on you hands and pull out the old FPS.
6. Jam in the new FPS and screw it in immediately to avoid any contaminants entering the fuel rail.
7. Try to free the old FPS from the wire clip that's holding it captive. I damaged the wire clip slightly but it sorta holds okay in the new FPS.
8. Wiggle plastic manifold cover back in place, remove tape, reinstall acorn nuts.
9. Reinstall air filter properly.
10. Observe results on next test-drive. I'm waiting until we have some errands to run later today.

With the $'s saved DIY'ing this one I can buy some wine and a nice single malt to enjoy with our friends who are visiting this weekend. 100% win.

Real-time fuel pressure reading during sensor failure

-Pascal

juve021

Chilled Man

IwantaS60R

-Pascal

StealthyS60R

MagoonR

StealthyS60R

Skot53

StealthyS60R

michaelc

Needsdecaf

-Pascal

michaelc

Skot53

IwantaS60R

Lightspeed

-Pascal

Top Contributors this Month

Recommended Communities