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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Fuel Pressure Sensor Code 29F3



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      10-08-2012, 11:26 AM   #1
Ilma
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Fuel Pressure Sensor Code 29F3

The fuel pressure sensor code = 29F3 popped up for me yesterday.

So I hooked up my Bav Tech software and got this:
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Car seems to run fine except that I noticed my fuel trims have a spread of over 30% at times

Surprsingly enough.....A/F ratios are dead-on between bank 1 and bank 2 and timing is stellar.

Seems like the low pressure sensor is pegged at 6.5 Bar which is normally supposed to be around 5 Bar.

I will have the sensor replaced soon, but was wondering why the fuel trims would be so wide spread

This is with meth by the way. Normally my fuel trims only deviate around 5% while spraying......they spread around 30% now consistently after the code was thrown
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      10-08-2012, 12:06 PM   #2
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i have actually had this code for over a year like many other members on here. It basically makes ur lpfp run 100 duty cycle from what ive read which could be causing fluctuations. o don't know if anyone has actually replaced the sensor and if they have notices any changes in performance. Im actually curious and wonder if anyone who has can chime in...
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      10-08-2012, 12:53 PM   #3
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The sensor is reading too high, and it spins the LPFP slower to compensate. Replace the sensor and clear the code, log again. It causes you to run low on pressure on the LP side, which starves the HPFP. LP should be 5 bar and unvarying unless your LPFP is old and weak or the in-tank filter is clogged. 6495hPa = 6.5bar, which makes me think the LP sensor is just bad and reading too high, a known issue.

The scaling from bank 1 and 2 may be different on your log, which makes it look like bank 1 and 2 have wildly varying trims.
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      10-08-2012, 06:04 PM   #4
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I had this code recently. Took to dealer and they replaced the low pressure sensor under the intake manifold. Code is now gone.
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      10-08-2012, 06:30 PM   #5
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Quote:
Originally Posted by JamesM3M5 View Post
The sensor is reading too high, and it spins the LPFP slower to compensate. Replace the sensor and clear the code, log again. It causes you to run low on pressure on the LP side, which starves the HPFP. LP should be 5 bar and unvarying unless your LPFP is old and weak or the in-tank filter is clogged. 6495hPa = 6.5bar, which makes me think the LP sensor is just bad and reading too high, a known issue.

The scaling from bank 1 and 2 may be different on your log, which makes it look like bank 1 and 2 have wildly varying trims.
Yeah...I thought it was scaling at first too....but it wasn't.

Check the sidebar values.

Bank1=-8%
Bank2 = 22%.

Makes sense what you say about the low pressure side starving the HPFP.....would explain the deviation becoming larger than normal when spraying meth because the injectors can't compensate with enough fuel on the lean bank if they are not geting the fuel they need to do so in the first place.

Yup.....I think it likely will all be good once I get that sensor replaced.

Ran some more logs today and same story.

Like others have mentioned.....the code keeps recurring until it's fixed.

Car runs great though for the most part though.

I think Cn555ic replaced his and found the car ran much better afterwards.

My car runs great....but part throttle can feel a bit off sometimes.
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      10-08-2012, 06:32 PM   #6
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Quote:
Originally Posted by drm916 View Post
I had this code recently. Took to dealer and they replaced the low pressure sensor under the intake manifold. Code is now gone.
Did you notice any difference afterwards?
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      10-08-2012, 07:17 PM   #7
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I'm wondering if this affects stock n54s. if so, there is pretty much no way the owner would know something is wrong unless the dealership sees this code. I also have this problem but I haven't noticed any difference in drivability.
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      10-08-2012, 09:16 PM   #8
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I have had this code for about a year but it doesn't throw a light for me so the dealer won't do anything. Other than that, the car runs good.
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      10-09-2012, 12:37 AM   #9
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Quote:
Originally Posted by ragingpanda
I have had this code for about a year but it doesn't throw a light for me so the dealer won't do anything. Other than that, the car runs good.
That makes no sense. If the code is there shadow or not and the dealer sees it they should replace. Get away from that dealer.
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      10-09-2012, 07:14 AM   #10
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I beleive the LPFP is running at 72psi max. If you're seeing 6.5 bar, the LP sensor is shot.

I don't think thats the cause of your trim issues. I'm seeing spreads of 20+% recently, even with my relocated nozzle.
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      10-09-2012, 09:17 AM   #11
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Quote:
Originally Posted by Tzu View Post
I beleive the LPFP is running at 72psi max. If you're seeing 6.5 bar, the LP sensor is shot.

I don't think thats the cause of your trim issues. I'm seeing spreads of 20+% recently, even with my relocated nozzle.
Where did you relocate it/them? I was thinking about the cold side of the IC, since that gives an extra 2 feet of tubing to circulate/evaporate/distribute evenly. Still not good enough?

Tzu and Ilma, how old are your pre-cat O2 sensors? Could they be aging out?
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      10-09-2012, 10:12 AM   #12
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Quote:
Originally Posted by Ilma View Post
Did you notice any difference afterwards?
no difference afterwards. Just no more code.
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      10-09-2012, 10:53 AM   #13
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If a code is thrown, that means the DME thinks there's a prob with the sensor... so I would think the LPFP would run 100% DC... same as unplugging it. On the other hand if the LPFP is running less pressure and fuel system struggling to keep up... bank 1 gets fuel first. Then rail pressure should show some fluctuation. But I think this is highly unlikely to have fuel supply differences (to the injectors) between banks.

I find it strange that STFT would increase when a fuel system's capacity decreases. STFT is "actual" fuel adjusted from base... NOT adjustments to maintain base. Guess it could depend on sampling rates. Anyway, thinking out loud... which may not make any sense.

Potentially the bank differences are due to the weather and meth vaporization/distribution.

I have a "slow" O2 which is evident in larger AFR fluctuations. I'll post some logs showing the difference over time.
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      10-09-2012, 11:41 AM   #14
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James: I've played with relocating just one of my two nozzles around. I've put it at the IC outlet, the silicone coupler from the up-pipe to the CP, and on the up-pipe itself, before it meets the silicone coupler. I've discussed this with Ilma at length, and my trims were only 8-10% apart after relocating to the silicone coupler. Same deviation when one nozzle was at the IC outlet, but I was getting some pooling in the IC since I kept the FAV in the same location. However the ideal location for a nozzle at the IC outlet coupler would be on the outer radius bend (closest to driver, opposite front end) and I placed it on the driver side. I may relocate both to the IC outlet coupler next year

It could be old O2s, that has crossed my mind before since they are 5 years old. AFRs are in check, but trims are maxing mid pull, even after bumping up those cells in the OL map. I may just change the sensors this winter after reading your thread about stumbling idles being somewhat fixed by new O2s. Typically, logs I've seen with bad O2s have bad AFRs and high trims throughout the pull, where mine is localized to a small RPM range. It's just odd that it's getting worse.

Sorry to hijack Ilma.
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      10-09-2012, 12:16 PM   #15
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here's an example of my O2 sensors over time. This is 7mo time, no meth. I started noticing it very recently... thinking it was Meth distribution at first, but its clear it is not. Going back in time, bank 2 is much smoother.
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      10-09-2012, 01:50 PM   #16
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Josh, whats with the 3 point difference between banks...
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      10-09-2012, 01:55 PM   #17
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Quote:
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Josh, whats with the 3 point difference between banks...
That's just scaling on the 2 axes so you can see the differences.
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      10-09-2012, 08:43 PM   #18
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Thanks guys.....those are interesting comments/observations.

I was fortunate to be data logging several pulls at the time this code happened.

The CEL came on right after the second run - which is the datalog I posted up above in my first post.

The run before the CEL came on was this one.

They were literally minutes apart.

Notice how tight and close the fuel trims are in this run which was taken 5 minutes before the CEL run.

After I got the 29F3 code, all my datalogs now show a huge spread in fuel trims.

It really looks to me to be related to the faulty fuel sensor given the before and after datalogs.

Compare this datalog to my ealier one. What do you think?
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      10-09-2012, 09:19 PM   #19
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And just for kicks......here is another datalog from 3 weeks ago.

Trims look good here too!
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      10-10-2012, 06:53 AM   #20
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Inconsistancy is my biggest gripe with the piggies.

In this case, perhaps your LP fuel pressure sensor is intermittant rather than completely dead? Still not sure how the single LP sensor could cause trim devitation, unless its just a physical system flow characteristic as Josh mentioned.
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      10-10-2012, 11:31 AM   #21
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Might be a combination of an aging pre-cat O2 sensor and poor fuel delivery caused by the erroneous LP sender reading.
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      10-10-2012, 12:29 PM   #22
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I have a brand new in box Low Pressure fuel sensor, purchased it when mine went bad and was going to have the dealer tech install it when doing my HPFP recall, but they replaced the sensor for free as part of the recall. Shoot me a PM if you're interested
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