How to check bad fuel pressure regulator? - Mercedes-Benz Forum
 
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#1 (permalink) Old 10-13-2009, 02:12 PM
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How to check bad fuel pressure regulator?

Hi,

Does anyone know how to check a bad fuel pressure regulator?
I heard that unpluging the vacuum hose and smell it when the engine is cold can be one of the ways to find out . If I can smell the gas, that is bad...correct? Is there any other way to check it? I just want to make sure that I need to replace it or not.

Thanks.
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#2 (permalink) Old 10-13-2009, 03:04 PM
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I checked the pric of the part and it's just $45....I can just replace it, but I don't want to do anymore guess. I already replaced fuel filter and OVP, but they had nothing to do with the cold start issue.
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#3 (permalink) Old 10-13-2009, 04:15 PM
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I think (and i could be wrong here) that you unplug the vacuum line while the car is running. if you see gasoline in there then you need a new one....

someone else could chime on this....


how's the car coming along? selling it yet?
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#4 (permalink) Old 10-13-2009, 07:56 PM
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Hey latief,
gasoline in the vacuum hose or the plug on FPR?
Do I test it from cold engine or fully warmed up?

I think the market now sucks so bad. Not even a single person has contacted me so I decided to keep it for a while and tackle the problems that I have now. Car is running good, just need to fix minor problems like the cold starting issue, and mysterious coolant leak from the upper lower radiator hose.
I found out that the HG is ok. I seafoamed my car and I drove a few hundread miles. I checked the spark plugs and all of them look fine.

Thanks.
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#5 (permalink) Old 10-14-2009, 06:54 AM
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to tell you the truth, i am not really sure.....i checked mine by pulling the vacum line and making sure everything was nice and dry. car was warm. i remember reading that it is a preliminary method to make sure that the valve is working, but i could be wrong....

good thing you did not start the headgasket repair....i had a feeling you did not need it....

good luck
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#6 (permalink) Old 10-14-2009, 09:33 AM
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Originally Posted by latief View Post
to tell you the truth, i am not really sure.....i checked mine by pulling the vacum line and making sure everything was nice and dry. car was warm. i remember reading that it is a preliminary method to make sure that the valve is working, but i could be wrong....

good thing you did not start the headgasket repair....i had a feeling you did not need it....

good luck
Thank you for the reply.
I will check it when the engine is cold and warm. If it is dry, then FPR is fine. Some other people suggested me to get a gauge compression tool and connect a rubber hose to FPR, and see whether it holds compression.
It sounds like 5min job so I might take my car to a shop and ask a mechanic to do this. Maybe they charge $0
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#7 (permalink) Old 10-14-2009, 01:08 PM
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I checked the FPR by connecting compression gauge, and it hold the compression fine. So FPR is fine.
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#8 (permalink) Old 04-08-2010, 07:47 AM
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i am getting poor gas mileage , and have therefore been researching the fuel pressure regulator. i have a couple of questions regarding the regulator.

1. i specifically remember testing the fuel pressure regulator about a year ago: i started the vehicle and then pulled the vacuum line off of the regulator and immediately noticed a small surge in idle speed.

However when checking the fuel pressure regulator yesterday, using the aforementioned method, there was no difference in idle speed at all. i was wondering could this be an indication that the fuel pressure regulator is in need of replacement?

from what i've learned about the FPR, vacuum is applied to it via the manifold, which then reduces the fuel pressure in the fuel rail, as the throttle is increased , less vacuum is applied to the FPR, thus increasing fuel pressure in the fuel rail. is this correct? now when i remove the vacuum from the FPR ther is no longer an idle speed surge(no change in idle), which leads me to believe that the FPR is shot and constanly keeping the fuel pressure in the fuel rail at a higher than necessary value, and thus leading to my poor fuel mileage.

and 2. upon visual inspection of the FPR i noticed , what looks like oily residue and some crud on top of the FPR. are they(FPR) perhaps filled with anything?

sorry for the long post!

thanks
tim

Last edited by timmyr; 04-08-2010 at 12:48 PM.
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#9 (permalink) Old 05-21-2010, 09:17 AM
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Quote:
Originally Posted by timmyr View Post
i am getting poor gas mileage , and have therefore been researching the fuel pressure regulator. i have a couple of questions regarding the regulator.

1. i specifically remember testing the fuel pressure regulator about a year ago: i started the vehicle and then pulled the vacuum line off of the regulator and immediately noticed a small surge in idle speed.

However when checking the fuel pressure regulator yesterday, using the aforementioned method, there was no difference in idle speed at all. i was wondering could this be an indication that the fuel pressure regulator is in need of replacement?

from what i've learned about the FPR, vacuum is applied to it via the manifold, which then reduces the fuel pressure in the fuel rail, as the throttle is increased , less vacuum is applied to the FPR, thus increasing fuel pressure in the fuel rail. is this correct? now when i remove the vacuum from the FPR ther is no longer an idle speed surge(no change in idle), which leads me to believe that the FPR is shot and constanly keeping the fuel pressure in the fuel rail at a higher than necessary value, and thus leading to my poor fuel mileage.

and 2. upon visual inspection of the FPR i noticed , what looks like oily residue and some crud on top of the FPR. are they(FPR) perhaps filled with anything?

sorry for the long post!

thanks
tim
hello. I have a similar problem .Did not fix it yet ,searching through the forum for solution.That vacum line on fuel pressure regulator is just safety matter if regulator membrane leaks,so fumes can go to intake. It measure-regulates pressure beetwen return and suply.Sorry that is all I know about.
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