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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 > Bench testing a low pressure fuel sensor



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      06-16-2017, 12:52 PM   #1
slinkygn
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Bench testing a low pressure fuel sensor

I just got what may be a steal on the updated low pressure fuel sensor and line for my '07 335i from a salvage yard. Rear end damage only to the donor vehicle; line and sensor look flawless. But considering what a pain in the @#$! it is to get to that sucker, I'd like to have some clue that the sensor is good before swapping it in.

Searching gets me some hits on how to test the sensor while it's in the car, but I couldn't find anything on electrical characteristics of the sensor itself that I could test before it's installed.

Before I am reduced to the last-ditch option of installing it, reassembling/reattaching the absolute minimum necessary to get the car to start without freaking out and testing it "semi-live" that way, does anyone know of any even cursory testing I can do to this guy while it's on my bench and not in the car?
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      06-16-2017, 01:09 PM   #2
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Why are you swapping it in the first place? Do you have a bad HPFP and you'll be in there anyway, or somethin?

If not and you are currently experiencing no problems, just save it in your toolbox for a rainy day.
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      06-16-2017, 01:30 PM   #3
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Originally Posted by FCobra94 View Post
Why are you swapping it in the first place? Do you have a bad HPFP and you'll be in there anyway, or somethin?

If not and you are currently experiencing no problems, just save it in your toolbox for a rainy day.
+1. I have an 07 as well and at 140k miles I finally got the new line and sensor because I was already getting a walnut blast. Prior to that you can simply replace the old sensor with a new old-part sensor if it starts to throw codes, and this can be done by simply removing air box, moving the junction box out of the way and using a long handle wrench.
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      06-16-2017, 06:19 PM   #4
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Hey, check it out, I got hit with the "if you don't have an answer to the question, question it instead" forum bug!

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Originally Posted by Jklad View Post
+1. I have an 07 as well and at 140k miles I finally got the new line and sensor because I was already getting a walnut blast.
Which is why I'm doing it too. Having some misses, already did the obvious/easy stuff, now about to get a walnut blast done. Which means I'm taking off the manifold already, and the sensor and line will be *right there*... Plus I'm regularly getting the LP plausibility code firing, and a prior mechanic checking it out said he scoped the pressure through the line reading consistently around 2.5bar (really rarely has any reason to drop below 4, or go higher than 6 and change).

So it's an easy thing to do this *one* time, since the manifold's off already, and since I found it at about a quarter of the price I would pay at a reputable third-party online retailer for it... I just don't want to go in there *again*.

Heck, even just replacing the new-style sensor after installing the one I bought is way more work than an electrical bench test when it is currently sitting there... It doesn't seem all that controversial that I'd want to take the 5 minutes to DMM/'scope a device before putting it in; that's a pretty trivial cost for that bit of insurance. If there aren't any that can reasonably be done, well, I'll obviously have to suck it up. But doesn't hurt to ask!

So, yes, out-of-service electrical tests, please, if anyone has them. Thanks!
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      06-17-2017, 07:22 AM   #5
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Originally Posted by slinkygn View Post
Hey, check it out, I got hit with the "if you don't have an answer to the question, question it instead" forum bug!
Well, since you gave us a nice narrative with zero backstory (until now) we were left to assume noobness.

To better answer your question, Steve @ Fuel It! can test the sensor. If you end up reaching out and getting an answer from him regarding his method, be sure to share with the rest of the class
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      06-18-2017, 02:57 PM   #6
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Quote:
Originally Posted by slinkygn View Post
Hey, check it out, I got hit with the "if you don't have an answer to the question, question it instead" forum bug!

Quote:
Originally Posted by Jklad View Post
+1. I have an 07 as well and at 140k miles I finally got the new line and sensor because I was already getting a walnut blast.
Which is why I'm doing it too. Having some misses, already did the obvious/easy stuff, now about to get a walnut blast done. Which means I'm taking off the manifold already, and the sensor and line will be *right there*... Plus I'm regularly getting the LP plausibility code firing, and a prior mechanic checking it out said he scoped the pressure through the line reading consistently around 2.5bar (really rarely has any reason to drop below 4, or go higher than 6 and change).

So it's an easy thing to do this *one* time, since the manifold's off already, and since I found it at about a quarter of the price I would pay at a reputable third-party online retailer for it... I just don't want to go in there *again*.

Heck, even just replacing the new-style sensor after installing the one I bought is way more work than an electrical bench test when it is currently sitting there... It doesn't seem all that controversial that I'd want to take the 5 minutes to DMM/'scope a device before putting it in; that's a pretty trivial cost for that bit of insurance. If there aren't any that can reasonably be done, well, I'll obviously have to suck it up. But doesn't hurt to ask!

So, yes, out-of-service electrical tests, please, if anyone has them. Thanks!
More of a "trying to help a new member not waste his precious time" bug. I try to be helpful and recommend for new folks to replace things that are adjacent to each other and save on labor overlap. I can't answer your original question, but I try to be helpful. Fuck me right??

Seems like a lot of time and effort spent to replace a $100 set of parts with something used, but to each his own.
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      06-19-2017, 08:25 AM   #7
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Originally Posted by Jklad View Post
More of a "trying to help a new member not waste his precious time" bug. I try to be helpful and recommend for new folks to replace things that are adjacent to each other and save on labor overlap. I can't answer your original question, but I try to be helpful. Fuck me right??

Seems like a lot of time and effort spent to replace a $100 set of parts with something used, but to each his own.
Hey, certainly wouldn't be the first time I've missed something -- If I'm doing a walnut blast and the manifold's off, what is left that's all that much effort? Thought it'd be pretty easy from there... biggest hassle is a little fuel dribble, I think; pull the fuel line to the HPFP, replace with new, bolt down with new bolt. Everything else I'd be doing anyway, I thought. Am I missing something after all?

Not to get into the weeds, but speaking more broadly/meta, I think sometimes "new member" and "new to taking a wrench to their vehicle" unfortunately get thrown together here a lot as if one was tied to the other. (AKA folks feel they're
Quote:
Originally Posted by FCobra94
left to assume noobness
when perhaps the better assumption is neutrality, and taking questions at face value so as to not presume one way or the other about prior experience.) Really, even just the question of, "why are you doing that, is your HPFP bad or something?," I thought was reasonable. But it does seem a number of threads here often get unintentionally hijacked into a discussion of whether the poster should be trying to do what the OP says rather than answering the OP itself. (My post count isn't super high, but I'm not *that* new -- have had plenty of chance to read! Post count and "newness" are probably yet another set of things that commonly get conflated; there are quiet introverts that read far more than writing on forums just like in real life. You can usually tell us apart because when we do post, we ramble...)

So I just didn't want the thread to get caught up right off the bat with the wisdom of doing what has already been done at the expense of what was originally asked, is all. (Who knows -- maybe all this explaining means I'm making the thread get bogged down in all this myself, too!) Goodwill and good intent is important! -- but when somebody's asking about a bench test about an item already on their bench, it's not necessarily useful to question whether it should be on their bench in the first place. That ship's sailed. That's all I was getting at. Again, I do appreciate that it was in good faith; that's probably the most important thing anyway.

Quote:
Originally Posted by FCobra94
To better answer your question, Steve @ Fuel It! can test the sensor. If you end up reaching out and getting an answer from him regarding his method, be sure to share with the rest of the class
Awesome! I'll give them a shot. Will let you guys know if I hear anything back.
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      06-19-2017, 09:26 AM   #8
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Originally Posted by slinkygn View Post
Hey, certainly wouldn't be the first time I've missed something -- If I'm doing a walnut blast and the manifold's off, what is left that's all that much effort? Thought it'd be pretty easy from there... biggest hassle is a little fuel dribble, I think; pull the fuel line to the HPFP, replace with new, bolt down with new bolt. Everything else I'd be doing anyway, I thought. Am I missing something after all?

Not to get into the weeds, but speaking more broadly/meta, I think sometimes "new member" and "new to taking a wrench to their vehicle" unfortunately get thrown together here a lot as if one was tied to the other. (AKA folks feel they're when perhaps the better assumption is neutrality, and taking questions at face value so as to not presume one way or the other about prior experience.) Really, even just the question of, "why are you doing that, is your HPFP bad or something?," I thought was reasonable. But it does seem a number of threads here often get unintentionally hijacked into a discussion of whether the poster should be trying to do what the OP says rather than answering the OP itself. (My post count isn't super high, but I'm not *that* new -- have had plenty of chance to read! Post count and "newness" are probably yet another set of things that commonly get conflated; there are quiet introverts that read far more than writing on forums just like in real life. You can usually tell us apart because when we do post, we ramble...)

So I just didn't want the thread to get caught up right off the bat with the wisdom of doing what has already been done at the expense of what was originally asked, is all. (Who knows -- maybe all this explaining means I'm making the thread get bogged down in all this myself, too!) Goodwill and good intent is important! -- but when somebody's asking about a bench test about an item already on their bench, it's not necessarily useful to question whether it should be on their bench in the first place. That ship's sailed. That's all I was getting at. Again, I do appreciate that it was in good faith; that's probably the most important thing anyway.

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Originally Posted by slinkygn View Post
Awesome! I'll give them a shot. Will let you guys know if I hear anything back.
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