How to check for a faulty FPR (Fuel Pressure Regulator) and replace it
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Cadillac Tech Tips - How to fix it Discussion, How to check for a faulty FPR (Fuel Pressure Regulator) and replace it in Item Specific Cadillac Discussion; The FPR is a small canister mounted on the fuel rail with a vacuum hose attached to the top of ...
  1. #1
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Talking How to check for a faulty FPR (Fuel Pressure Regulator) and replace it

    The FPR is a small canister mounted on the fuel rail with a vacuum hose attached to the top of it. There is a diaphram in the center of it with fuel pressure on the lower half and engine vacuum on the upper half. If the diaphram ruptures, raw fuel will leak into the intake manifold and cause a rich condition affecting fuel milage and hot engine starts. If ruptured it will act much like an applied choke on a carburated engine (aiding cold starts and hindering hot starts). To check it, simply pull the vacuum hose with the engine running (or key on, engine off) and look for fuel leaking out of the nipple. There should be none.

    On the '93 & '94 4.6 Northstars the FPR is inside the intake manifold and since it is subjected to manifold vacuum, there is no need for a vacuum hose. On these engines you simply turn the key on but DO NOT start the engine as it will run away unthrottled, and look for fuel leaking at the nipple.

    NOTE: the pics below are for '95+ engines. One with the old nylon fuel rail and one with the stainless steel rail.
    Attached Images
    MR209, MR209, Ashtrayhead and 1 others like this.

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    rodsram is offline Cadillac Owners Member
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    Talking Re: How To Check for a Faulty FPR (Fuel Pressure Regulator)

    Thanks for the post Ranger. My 96 Deville started great cold but hard to start hot. Did what you said and found FPR seeping. Replaced it and starts perfect hot or cold now. Fuel mileage up too now.

  4. #3
    rtharrs2 is offline Cadillac Owners Member
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    Re: How To Check for a Faulty FPR (Fuel Pressure Regulator)

    Where is the FPR on a 95 4.9L?

  5. #4
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: How To Check for a Faulty FPR (Fuel Pressure Regulator)

    so one could assume that if it hold vacuum (like the one on my LT1) it is good? Or is it possible that it will with a small fuel leak and the vacuum gauge will suck against the tank and give me a false good reading?

    I still haven't found the FPR on my Votrec Suburban 5700 still.

  6. #5
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: How To Check for a Faulty FPR (Fuel Pressure Regulator)

    Yes. I believe if it holds vacuum, it is good.

    Vortec is a different breed of animal. Had one long ago but forgot most of what I knew about it. I believe it is inside the manifold. I do remember that it had some very high fuel pressure like 65 psi or so and I always blamed that for eating fuel pumps like they where going out of style.

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    chiucheung is offline Cadillac Owners Member
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    Re: How To Check for a Faulty FPR (Fuel Pressure Regulator)

    Where is the FPR on a 98 sts

  8. #7
    spudly is offline Cadillac Owners Member
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    Talking How to check for a faulty FPR and replace it

    First off thanks to those that have answered this question in the past!

    My 99 STS was starting hard and would occasionaly backfire when starting. The dealership and another mechanic could not fix the problem. I finally looked on Google and found the answer here, so again a huge thanks!

    I did the inital trouble shooting and had fuel dripping out of the vaccum nipple. You could also hold the vaccum hose up close to the nipple and watch the fuel be pulled through the FPR. So even if this wasn't the main probem the FPR is shot.

    Please be advised that I am no where near being a professional mechanic. So doing the FPR replacement was a little scary at first since I have had bad experiences on past cars with fuel injection.

    The procedure is pretty straight forward, but the one thing that I thought would be nice would be pictures of where everything is. So as I was going through the replacement on my car I took a few pictures (all are taken standing on the drivers side of the car).

    1) Remove the Beauty Cover (four 1/2" nuts)


    2) Under the Beauty Cover


    3) De-Pressurize the fuel injection system

    I stuffed a rag under the port and then used a corner of the rag and a pen cap to release the pressure (as has been noted before, it's like letting the air out of a bike tire).

    I would always check to make sure this is de-pressurized, but I did notice that after sitting overnight there was no pressure in the system. When I got back from driving to the parts store it was completly pressurized (obviously).

    4) Remove the FPR

    Remove the vaccum hose and the large "C" clip at the base of the unit.
    Make sure you have all of the parts out before installing the new unit. The old lower gromet (The smaller of the two gromets) stuck in it's installed position along with the screen filter (a pair of needle nose pliers resolved the issue).

    5) Old FPR parts


    6) New FPR

    The AC Delco unit comes with two clips. The large "C" type clip as pictures above and another "C" clip that is not used.

    Also note, when installing the large "C" type clip it should go with the smaller end on top as that is what keeps the FPR in place.

    7) Re-install the beauty cover and nuts.


    Pretty easy procedure, the car started right up afterwards. Now I need to wait for it to get warm and see how it works then, but I have no doubt this was the issue.

  9. #8
    mcowden is offline Cadillac Owners Connoisseur
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    Re: Fuel Pressure Regulator Replacement

    GREAT STUFF SPUDLY!!! We should have done this long ago. Thank you very much for posting such a helpful and informative tip. I'm sure this will get moved to the Tech Tips or Technical Archive sections for all to use. Many people ask this question, and to date we don't have any replies with a photo record such as this.

    Glad you were able to solve your car's starting problem using this site, a big THANK YOU for your post, and a warm welcome to Cadillac Forums... Your first post is a great one!
    Mike

  10. #9
    Caddyshack100 is offline Cadillac Owners Connoisseur
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    Re: Fuel Pressure Regulator Replacement

    Great photos, I have owned a fair number of gm cars (fords, 3 Broncos, dodge chargers 2,) but none of them have ever had a problem with the FPR. Is this a problem with the Northstar? I did not think the fuel pressure would be any greater than any other gm SEFI. Also is the fuel filter held connected by one threaded end and one plastic connector, or has gm seen the light and used two plastic clips (such as Ford uses)

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    danbuc's Avatar
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    Re: Fuel Pressure Regulator Replacement

    Hmmm...that reminds me. I've been meaning to check my FPR for a while now for leaks, but I've been real lazy about it. Thanks for the pics though.

  12. #11
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    Re: Fuel Pressure Regulator Replacement

    Super pics! Great info! Thanks!

  13. #12
    spudly is offline Cadillac Owners Member
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    Re: How to check for a faulty FPR (Fuel Pressure Regulator) and replace it

    Just a follow up on this since it has been a few weeks since the replacement.

    This has solved quite a few problems I was having with the car.
    1) Hard starting, bad when cold really bad when warm
    2) Backfiring
    3) Surging when stopped

    Now I need to work on getting the struts and shocks replaced and then on to getting a new set of tires to eliminate that damn shimmy from 65-75.

  14. #13
    tbombaci is offline Cadillac Owners Member
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    Thumbs up Re: How to check for a faulty FPR (Fuel Pressure Regulator) and replace it

    Thank you!!

    I recently have had all of the symptoms and more.

    I first did a tune up to try and resolve the issue. The tune up helped, but we were still having all of the FPR related problems.

    I just replaced the FPR and did a test drive. Runs like a dream.

    Regards,
    Tom Bombaci

    '95 SLS

  15. #14
    jmmast02 is offline Cadillac Owners Member
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    Re: How to check for a faulty FPR (Fuel Pressure Regulator) and replace it

    Could some one please help me with a part number for the FPR so I can check and see the price on unit from gmpartsdirect.com. I am at school and do not have tools, but I am certain that this is the problem. Much appreciated. 1998 Seville SLS

  16. #15
    tbombaci is offline Cadillac Owners Member
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    Re: How to check for a faulty FPR (Fuel Pressure Regulator) and replace it

    From the package:

    ACD# 217-1629
    GM# 12499841

    I paid $71 with California tax for the kit from a local Cadillac dealer.

    You will only need two tools for the job:

    1. 1/2" ratchet or nut driver to get the beauty cover off
    2. a small screw driver to pull the clamp from the FPR

    It is a super easy repair.

    Also, there are two types of FPR’s (according to the parts guy at the counter). They asked if I had a plastic fuel rail or the new stainless steel rail.

    I had my fuel rail replaced via a recall notice. The plastic rail will eventually leak gas.

    -Tom

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