Fuel Tank Pressure Sensor

4062 Views 9 Replies 6 Participants Last post by Gmiller67, 3 d ago

D_Rok

Discussion Starter · Dec 20, 2019

After a few days and some work I have figured out that my 97 1.9 Roadster isn't starting because of my fuel tank pressure sensor not being plugged in.

Does anyone have any info or links that can point me in the right direction to finding where that sensor is located and where that pesky wire/plug may be hiding? I have the end that I believe runs to the DME but appear to be missing the side of the plug that runs to the sensor itself.

Thanks to some help from my last post I was able to figure out that was my mystery cable that wasn't plugged in. Could that be a good reason the car wont start? I have a replacement pump relay just in case and I tested my fuel pump and it works 100%. I made sure I was getting fuel to my fuel rails (haven't been able to check pressure yet). The car hasn't been started in some years but wanted to fire once we hot wired the fuel pump. Could that sensor cause the engine to not run properly? It would spit and sputter and try to idle but it couldn't maintain a good idle.

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zed3coupe

· #2 · Dec 20, 2019

https://www.realoem.com/bmw/enUS/showparts?id=CH73-USA-05-1997-Z3-BMW-Z3_19&diagId=16_0205

Looks like it is on the fuel tank itself. Part #19. looks like on top near filler neck

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D_Rok

Discussion Starter · #3 · Dec 20, 2019

that'd be it. Thanks.

Any tips on how to access it and make sure the wires are even coming from it? maybe remove the passenger wheel that its next to and see if its accessible?

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zed3coupe

· #4 · Dec 20, 2019

Never messed with one of those. I would start with what you are thinking. Feel around, maybe use a mirror to see it. Looks like two bolts or nuts hold it in place. Not sure how much room is there but you maybe able to just feel around and make do.

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Randy Forbes

· #5 · Dec 21, 2019 (Edited)

D_Rok said:
that'd be it. Thanks.

Any tips on how to access it and make sure the wires are even coming from it? maybe remove the passenger wheel that its next to and see if its accessible?

Yes, but you're not going to like it...

Caveat: I haven't worked on a 4-cyl Z3, but on any 6-cyl version, THE ONLY WAY to access the top of the fuel tank is to remove it, which I have done on several cars.

BTW, THE ONLY WAY to remove the fuel tank, is to drop the entire rear suspension, and the exhaust system... :yikes:

http://spcarsplus.com/piwigo/galleries/cmr/IMG_3707.jpg

http://spcarsplus.com/piwigo/galleries/cmr/IMG_3710.jpg

http://spcarsplus.com/piwigo/galleries/cmr/IMG_3728.jpg

http://spcarsplus.com/piwigo/galleries/cmr/IMG_3785.jpg

Have fun, good luck, and Merry Christmas... :angel:

Edited: pity, I can no longer post pictures in the threads here

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nfunk

· #6 · Dec 21, 2019

OUCH! I guess it that would be a good time to update the rear suspension.

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Magnetchief

· #7 · Sep 7, 2021

Randy,
Noticed your reply above.
Have had this issue for sometime. Is it possible the sensor was damaged when mig welding the reinforcement parts into the trunk?
I recall removing the ECM, but not any other sensors.

I have no plans to drop the rear on my roadster in the foreseeable future.
Do you think there Is there any harm running with a failed tank pressure sensor?

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Magnetchief

· #8 · Sep 9, 2021

I actually came up with a solution for this issue.
As Randy mentions, a failure is not going to effect the running of your car.
The pressure sensor has 3 wires, 0v, 5v and a sensor output voltage 0-5v

These connect to the DME pin 11 being the sensor voltage 0-5v. pin 40 = 0v and pin 44 = +5v

I built a simple voltage divider using 2 x 1k ohm resistors and 3 wires.

Red wire tapping into pin 11
Blue wire into pin 44
black wire into pin 40

This gives us a +2.5v onto pin #11, The DME thinks the pressure is there and thus clears the check engine light.

Simple but effectively bypassing the pressure sensor itself.

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nfunk

· #9 · Sep 9, 2021

Very innovative!

Years ago we converted our fleet over to bi-fuel (gasoline and natural gas). Mounted below the dash was a small computer box with LED display displaying NG tank pressure, and a switch for switching between gasoline and natural gas. On the Jeep Grand Cherokees when you switch from gasoline to natural gas (disabling the fuel injectors), the Jeep will throw a "check engine light" on the dash. Once switch back to gasoline the "check engine light" will turn back off. The simple solution was to put a small resistor in line with the fuel injectors that will still return a signal to the Jeep's computer when running on natural gas, but not too big of a resistor to limit the fuel injector performance while on gasoline.

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Gmiller67

· #10 · 3 d ago

Magnetchief said:
I actually came up with a solution for this issue.
As Randy mentions, a failure is not going to effect the running of your car.
The pressure sensor has 3 wires, 0v, 5v and a sensor output voltage 0-5v

These connect to the DME pin 11 being the sensor voltage 0-5v. pin 40 = 0v and pin 44 = +5v

I built a simple voltage divider using 2 x 1k ohm resistors and 3 wires.

Red wire tapping into pin 11
Blue wire into pin 44
black wire into pin 40

This gives us a +2.5v onto pin #11, The DME thinks the pressure is there and thus clears the check engine light.

Simple but effectively bypassing the pressure sensor itself.

Would you happen to know the color of the wires for the fuel pressure sensor going to the DME I’m in California and will never pass smog throwing a check engine light I can clear the light will run all day without it but turn car off and restart comes back on. This car was not running when I bought it had to put a new ignition, DME, and EWS car runs great now just this one problem. Do you have a more detailed picture of wires running back to the DME. I just can’t afford to drop the suspension and gas tank would be more the what I paid for the car.
View attachment 1040469

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