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Discussion Starter #1
Hey old friends, as some of you og's remember me and my eternal p1092 issue.. reminder.. Replaced all 4 o2s, maf, no intake leaks, replaced fuel pump, fuel filter... think that's it.. so ive been meaning to check the injectors and did a fuel pressure test today. Initial connection gave me 10psi. After ignition on, i got 45psi.

20170821_132304.jpg

With engine on 50psi.

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Hitting the throttle barely moved the needle.. i shut the engine off and waited 10 min to see if the gauge would hold pressure and it did at 45psi and did not move. As i understand i should have had around 55psi with just the ignition alone.. possibly clogged injector? Please let me know, big thanks in advance!

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Keep in mind when you hook up a fuel pressure gauge after the car has been sitting, you relieve a fair amount of pressure when the gauge is initially connected. Turning the ignition on will only "prime" the pump for about 3 seconds and this may not be long enough to bring the pressure up to where it belongs.

You will need to "prime" the pump multiple times after installing the gauge to get fuel rail pressure.

The fuel pressure specs are as follows:

Fuel Pressure Specs Per Bentley
All engines except the S54 3.2L M3 - Fuel pressure 3.5 +/- 0.2 bar or 50.76 +/- 2.9 PSI
Residual fuel pressure after 20 minutes - Fuel pressure >3 bar or >43.51 PSI

55 PSI is not the fuel pressure spec, not sure where you found this information.

You need to leave the gauge installed for 20 minutes or more to make sure the residual fuel pressure does not drop below the 43.5 PSI.
 

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.. possibly clogged injector? [/URL]
A clogged injector will not reduce fuel pressure. If anything, it would increase the fuel pressure.

Your numbers look good. As jfol noted, check pressure after the car has been shut down 20 min. or more. A reduction in pressure after being turned off for some time would indicate a bad check valve or leak in the fuel system.
 

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Discussion Starter #4
Thank you very much jfoj and mtnbimmer! You guys are awesome 👍

I'm redoing the test now. I'm assuming the ignition does not have to be on for the full 30 minutes while i wait to see if pressure will hold?

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For the Static test, you shut the engine down, key out of the ignition and make sure too much pressure does not bleed off. Min period of time is 20 minutes @ 43.5 PSI, but the pressure should hold for days with only a slight change often due to temperature.
 

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Discussion Starter #6
20170824_142028.jpg

Got this after 30 min with key in ignition but ignition off.. 35psi and dropping. Now at 31. was it that important to remove key from ignition? Brand new gauge. Second time use. If no fuel leaks out, safe to say it's accurate? so what am I replacing here?

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So clearly there is too much bleed down after 30 minute. The spec claims the pressure should stay at or above 43.5 PSI for 20 minutes.

There are 4 basic areas that could cause pressure bleed off.

1. Fuel pump internal check valve leaking.
2. Leak in the hose of connection between the fuel pump output and the fuel level sender.
3. Fuel filter pressure regulator leaking
4. One or more fuel injectors leaking down.

Given the age of these cars and knowing what we know about the fuel injectors, i would personally replace the fuel pump assembly and fuel filter, then see what happens. These items need to be replaced at some point anyway, they are not lifetime parts.

Then see what happens. You can also test by pinching off the output fuel hose from the fuel pump with a special flat hose pinching tool after the fuel rail has been charged and if the fuel pressure continues to drop there is one or more injectors leaking.
 

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Discussion Starter #8
Great thanks. Seeing as i replaced the fuel pump last year with a genuine bmw part and the fuel filter not long ago, i will go ahead and replace the injectors with o rings. Is that all for now?

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i will go ahead and replace the injectors (deleted) o rings.
Why would you do this? Did you not read jfoj's previous post? Follow the troubleshooting steps he outlined. Stop spending money on parts until you know what the problem is.

Replacing the o-rings on the injectors will do nothing to stop injector leak down. Injector leak down is internal to the injector. The external o-ring seals the injector to the cylinder head.
 

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Discussion Starter #10 (Edited)
Why would you do this? Did you not read jfoj's previous post? Follow the troubleshooting steps he outlined. Stop spending money on parts until you know what the problem is.

Replacing the o-rings on the injectors will do nothing to stop injector leak down. Injector leak down is internal to the injector. The external o-ring seals the injector to the cylinder head.
I did read what he wrote.. and did you read my reply about replacing my fuel pump and fuel filter recently? That leaves injectors.. ok, i was under the assumption that where the injectors sit, there are o rings there. Actually I'm pretty sure I've seen o rings there. I should know, i did the cylinder head on my old m54.. I'll just replace what ever those o rings are called.. I've never done injectors other than pull out the rail many years ago with everything attached and just moved it to the side but i do remember there are o rings by the injectors. Why would i not replace those anyway?

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Apparently you didn't. And yes, I read that you replaced the pump and filter. Just because you replaced them a year ago does not guarantee they are working properly now. Did you do the fuel line pinch off test? And no, it doesn't leave just the injectors.

Now, reread my post. Yes, there are o-rings that seal the injector to the cylinder head. One more time. Injector leak down is an internal injector problem and replacing the external o-rings will not solve an internal problem.

Go ahead and make your own diagnosis and throw money at it until you eventually get lucky and solve the problem.
 

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Either way the orings on the injectors are cheap and easy to replace to I'd say no harm no foul whether it helps your issue or not. There's two on each injector, one on top where the fuel rail sits on them and one on the bottom where the injector sits in the intake manifold. I replaced the ones on my car when I had the intake manifold off just because they're cheap and I felt like it.
 

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Just because things are new does not guarantee they are good.

The could be a problem with the FPR leaking down, the fuel pump check valve or the hose/clamp between the fuel pump and sending unit connection.

Beyond these items you have injector input O-rings, flexible fuel line, quick connector to the fuel rail.

Pinching off the fuel hose at the output of the fuel filter rules out the pump, fuel filter, FPR and lines to this point. Not hard to do and does not take long assuming you have something that can pinch off the fuel hose.

If you are concerned about injectors, it might be more cost effective to send them out for cleaning and testing. But this requires some down time on the car unless you can pick up a set of used injectors cheap. Many of the injector cleaning places will swap in a good injector if one is leaking.

Here are some possible injector cleaning options:

http://injectordynamics.com/
http://www.witchhunter.com/
http://cleaninginjector.com/
https://www.injectorrx.com/
http://www.mrinjector.us/
https://www.rceng.com/Fuel-Injector-Cleaning-P43C0.aspx

Research pricing, reviews and turn around time.
 

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Discussion Starter #14
Either way the orings on the injectors are cheap and easy to replace to I'd say no harm no foul whether it helps your issue or not. There's two on each injector, one on top where the fuel rail sits on them and one on the bottom where the injector sits in the intake manifold. I replaced the ones on my car when I had the intake manifold off just because they're cheap and I felt like it.
👍

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Discussion Starter #15
Apparently you didn't. And yes, I read that you replaced the pump and filter. Just because you replaced them a year ago does not guarantee they are working properly now. Did you do the fuel line pinch off test? And no, it doesn't leave just the injectors.

Now, reread my post. Yes, there are o-rings that seal the injector to the cylinder head. One more time. Injector leak down is an internal injector problem and replacing the external o-rings will not solve an internal problem.

Go ahead and make your own diagnosis and throw money at it until you eventually get lucky and solve the problem.
Apparently i didn't what?

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Discussion Starter #16
Just because things are new does not guarantee they are good.

The could be a problem with the FPR leaking down, the fuel pump check valve or the hose/clamp between the fuel pump and sending unit connection.

Beyond these items you have injector input O-rings, flexible fuel line, quick connector to the fuel rail.

Pinching off the fuel hose at the output of the fuel filter rules out the pump, fuel filter, FPR and lines to this point. Not hard to do and does not take long assuming you have something that can pinch off the fuel hose.

If you are concerned about injectors, it might be more cost effective to send them out for cleaning and testing. But this requires some down time on the car unless you can pick up a set of used injectors cheap. Many of the injector cleaning places will swap in a good injector if one is leaking.

Here are some possible injector cleaning options:

http://injectordynamics.com/
http://www.witchhunter.com/
http://cleaninginjector.com/
https://www.injectorrx.com/
http://www.mrinjector.us/
https://www.rceng.com/Fuel-Injector-Cleaning-P43C0.aspx

Research pricing, reviews and turn around time.
Thanks jfoj. Always very helpful. You will be the first to know about the solution when there is one. Hopefully in this lifetime

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Im having a similar problem, i've been hunting down lean codes in 1&2 for a while. When I had my oil pan replaced I also asked for them to see if they could diagnose why "I had any hesitation or power loss. "

They told me there was only 45PSI at the fuel rail. I had also replaced my fuel pump and filter with genuine BMW parts approx 1 year ago.

I asked them to test the pressure on the fuel line before the filter (and replace the filter while they were at it), to see if the pump was bad. They also measured 45PSI coming from the pump before the filter.

SO what im not seeing here is two things:

1. Will 45PSI cause hesitation/power loss? is this actually a problem with the M54 engine? 45PSI looks to be within BMWs tolerances "Residual fuel pressure after 20 minutes - Fuel pressure >3 bar or >43.51 PSI"
2. If so.. how in the world do you know for sure if your fuel pump is not pushing the correct PSI? What is "The test" of any?
 

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Depending on when exactly that 45 PSI was measured it might be a little low or might be just good. Here are my figures with a new VDO fuel pump and new Mahle fuel filter:
ignition on and fuel pump priming: 50 PSI
ignition on and fuel pump off: 48 PSI
engine cranking (when fuel pump turns immediately on again): 50 PSI
engine running at idle speed: between 50 and 51 PSI
residual fuel pressure with the car being off for 60 minutes: 45 PSI

All these measured at the output of the fuel filter as my fuel gauge kit did not come with a Schrader fitting.
 

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There's something we're in the habit of. If you get a reading that's not right, don't just go from there. Verify your test and the tester.
With the above I'd likely grab another gauge and verify before I took any action.

Then if it's correct, I'd likely start with another fuel filter, which has the pressure regulator built in.
 

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Good point. I think I will buy a kit and run the tests myself. Any recommendations on a fuel gauge kit? I also want something to read adaptation values because I feel like that's another really important part. Not sure whats a good device for that, I was running INPA for a while but its a pain because you need to run it on XP. Any recommendations on a OBD reader that can read adaptations in real time?

Thanks you all for your answers!!! 🥰
 
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