Compatible Fuel Pressure Gauge?

[workingonit]

Originally Posted by Russianblue

So i ended up buying this kit.

https://www.amazon.com/dp/B00VV29NHM...sin_title&th=1

it's got a couple different M8 adapters that fit the fuel rail nipple 'pretty well' i sealed with some teflon tape and it seems to work. no leaks.

Running pressure is 51.5.
Engine off, immediate pressure is 45psi.
Then the pressure starts bleeding off. By morning it was at 5psi....

I bought an identical kit on Amazon, branded as Fekuar, and a $25 adapter with the correct Schrader valve thread ("305.32") match, that worked without Teflon tape.

My pressure readings were like yours, three years ago, on 5-11-22 (barely readingover 50psi, quickly dropping to 40+ engine off). But the engine continued to run fine, until the fuel pump eventually died (while being inspected last October '25), so I installed a new Hella pump, and tested again. This time using a better adapter, 2 for $13 (the first one lost an O-ring).

Pressure readings were 49.5psi/42psi engine on/off (odd, considering the pump should have been stronger than the old one, and the fact that the X was getting rich codes, not lean, which was the case with the old pump, for years). Following that test, the pressure gauge was left on the windshield for 22 hours before I tried starting the X , to observe the pressure on turns, the next day (never did that test). It read 36psi.

I bled the pressure, then started the engine, and it took about a minute for the needle to rise to 44psi, never reaching 50. I pushed the bleeder button again, got very little fuel from the bypass hose, and looked at the gauge again (after jumping back into the seat). It read ZERO. So, I tried again, with the same results, ZERO psi.

Then, I removed the gauge and extension hose from the gauge, and went through another round of key flip/clear codes/finally restarting, before I attached the fuel gauge to the fuel rail, sans extension. Still no pressure. WTF?

So, I bought a new gauge, a Performance Tool W80595, and will try again, after not testing for months (weather, health reasons). I did just run the engine a couple of days ago, for over thirty minutes, to monitor the fuel trims, MAF, and O2 sensor readings; all were as good or better than usual, so the fuel system MIGHT'VE gotten better after sitting months (maybe the problem I was having https://xoutpost.com/bmw-sav-forums/...inspected.htmlself corrected...fuel tank debris settling, plugged injectors/fuel line/FPR+filter cleared???).

Anyway, I'm about ready to drain and filter the fuel from the tank, replace the FPR+filter with a new Hengst unit, and test again. After my Dr. tells me if or not I need shoulder surgery, tomorrow.

Good Luck with your fuel pressure testing; I had no such luck with mine.

[Russianblue]

wow! thanks for all the insight.

I think AI might be going off-piste here and making some conclusions here that are not particularly likely.

First off, this has ONLY happened in very cold weather...typically below 35 degrees. And it doesn't even happen every time.

i can tell when i have a no-start morning because when turn the key to position 2 I will hear NOTHING from the fuel pump. i can usually rectify that with 3-6 cycles of OFF to Position 2. I have to get two successful primes in a row to crank it in that situation though.

It seemed like an easy fix to me just replacing (first) the fuel pump in Jan 2025, after which i never had the issue because it never got cold after that. But the problem arose again this year the first time it got under freezing. And has been SOMEWHAT consistent on sub-freezing mornings.

So i figured i might be dealing with a flaky fuel pump relay. That'd make a ton of sense. I replaced that this weekend but the relay tested perfectly fine on the bench. I left the new one in there.

ChatGPT is pointing to the fuel filter/regulator but the pump seems like it can easily 'prime-through' an empty fuel rail for a successful start...provided it turns on at position 2. I ordered a new filter and will install next weekend but i am doubtful that's the issue.

i Don't know enough about relays to know if the one that 'tested good' on the bench was actually faulty. i just tested it with a 9V battery and a meter.

i'll read your thread to catch up on some of the work you guys have already done. Thanks!

[80stech]

It's not often you will get a system that will hold perfectly over night and it really shouldn't need to be perfect as long as it doesn't get low enough for air to get into the system then the initial priming should be all that is needed. If all the air is purged out when you are testing then very little leakage is needed to drop the pressure over night so even the smallest leak on the gauge/connection itself could be the biggest problem. Yes, the rubber fuel line should be pretty obvious but pinching that off 100% is not easy either. Sounds like you have a good connection to get proper readings though if the gauge drops immediately when the pump stops.

[Clockwork]

you can simply add in a one way check valve into your fuel line, as close to the fuel pump as possible, so maintaint he column of fuel in fuel line for faster starting, IF you feel the Priming of pump next ignition start, isn't helping, but this is probably jsut a band auid and the fuel pump may need to be replaced or at least the regulator part (I can't recall on this vehicle if its separate or built into fuel pump).