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HT4100 4.1, 4.5, 4.9 Discussion, Problem with 1990 Seville 4.5 in Cadillac Engine Technical Discussion; Post #1 - Fuel filter already replaced....
  1. #16
    Sevillian273's Avatar
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    Re: Problem with 1990 Seville 4.5

    Post #1 - Fuel filter already replaced.

  2. #17
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    Re: Problem with 1990 Seville 4.5

    Could a failed seal at the gas cap cause pressure issues?
    The pump is pushing some gas. Never heard of a weak pump, weird I thought they either work or they donít.
    A new filter was first on my list. The last time it was replaced was about 5 or 6 years ago when the spark plugs were changed out. My had daughter accidentally put diesel in the tank prompting replacement of a few items, ie all 8 injectors, fuel pump, fuel filter, plugs and an oil/filter change. The car ran great up until recently.
    I gona fight it out with the 4 rear spark plugs today.

  3. #18
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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by Sevillian273 View Post
    Post #1 - Fuel filter already replaced.
    Oops, sorry I missed that.

  4. #19
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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by 83CADMAN View Post
    Could a failed seal at the gas cap cause pressure issues?
    The pump is pushing some gas. Never heard of a weak pump, weird I thought they either work or they don’t.
    A new filter was first on my list.
    I remember having dealt with aftermarket pumps in the past, once we got all the aftermarket pumps replacede with OEM, problems seemed to go away. And yes they were low pressure. Don't forget the strainer on fuel pump either. I've see that problem too. You really can't rule anything out until you run tests.

  5. #20
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    Re: Problem with 1990 Seville 4.5

    The only way the seal at the tank could possibly affect fuel pressure is if the tank vent line(part of the EVAP system) is blocked AND you have a perfect seal at the gas cap. This condition over time will create a vacuum inside the tank due to the pump sucking the fuel out of it. It takes a long time for this to occur and even longer for the vacuum to start affecting fuel delivery. So a bad seal at the filler neck will actually prevent this from occurring at all. Just unscrew the gas cap and check pressure if you want.

    Blocking the return line at the rail will rule out the FPR and ensure that the fuel is not bypassing directly back to the tank. I have done this before with a 3/8" brass plug and some teflon tape. It's not perfect but it will get you an answer. (dont run the engine this way)

    With the return blocked, there's no other place for the fuel to go except out of the FPR vacuum nipple in which case it would be shooting out profusely.

    Even with a partially blocked line or filter, a healthy pump will still be able to generate good numbers on static pressure. It's the volume that will be cut short. So in that case it should make good psi with the engine off. Once you start the engine and the fuel starts moving, the pressure will then drop due to the volume demand. What I'm trying to say is, if the pump cant make more than 30 psi static then it's toast. Just for shits, turn the key on and off a few times with the gauge hooked up and see what you can get it up to.

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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by 83CADMAN View Post
    I did finally find a reference to Fuel Pressure in one of my books; for the 4.5 it states 12 to 14 psi???? Considering the sourceÖ..
    Thatís a far cry from 34 to 38 psi!!!
    The 4.1 and 4.5 engines through 1989 used throttle body injection (TBI) with two large injectors in the main housing. TBI systems typically have fuel pressure in the 10-20 range

    The 1990 and later engines use port injection (PFI) with eight small injectors located near each cylinder. PFI systems typically have fuel pressure in the 30-50 range

    Look at the front valve cover, does it say V8 PFI in big red letters?

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    Re: Problem with 1990 Seville 4.5

    SOB! I finally got those bastards out! I see what you guys are talking about working blind. Good thing Iím long and thin, I wuz able to contort back and around but just barely.
    Upon inspection the back four were fouled and burnt and looked very very old compared to the front four. Think I got took for a hundred bucks and four new plugs last time around, damit. Still puzzeling over the fuel pressure problem. Thanks ehall. Post #17 all 8 injectors were replaced. I think Sevillian273 is right "30 psi on the ready or the pump is toast. The pump I installed back when was an aftermarket from NAPA. Go figure. This time its GM.
    Gota take a break before tackling the compression test.

  8. #23
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    Re: Problem with 1990 Seville 4.5

    Assuming that the pump is in fact what failed, do you remember what brand it was(bosch, airtex, wells, etc)? And how many miles on it?

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    Re: Problem with 1990 Seville 4.5

    I struggled for about 45 min trying to thread in my compression gauge hose before I decided the compression was OK, (the thing ran strong prior to this last mishap). Managed to get the new plugs installed.
    Sevillian273, kudos to you. I re-tested the fuel pressure at the test port like you suggested;

    Quote Originally Posted by Sevillian273 View Post
    Even with a partially blocked line or filter, a healthy pump will still be able to generate good numbers on static pressure. It's the volume that will be cut short. So in that case it should make good psi with the engine off. Once you start the engine and the fuel starts moving, the pressure will then drop due to the volume demand. What I'm trying to say is, if the pump cant make more than 30 psi static then it's toast. Just for shits, turn the key on and off a few times with the gauge hooked up and see what you can get it up to.
    Ten, count em 10 “key on / engine off” cycles managed about 4.5 psi static pressure!!!!!
    8 gals in the tank.

    YEP! I’m convinced. I'll check what brand the old one is when it comes out of the tank and let you know.

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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by 83CADMAN View Post
    Ten, count em 10 “key on / engine off” cycles managed about 4.5 psi static pressure!!!!!
    8 gals in the tank.

    YEP! I’m convinced. I'll check what brand the old one is when it comes out of the tank and let you know.
    This sounds so familiar, and they were all NAPA that I had problems with. And they were all low pressure! We had about 10 that needed changed, some of the NAPA had only been in the tank a couple of months. I'm sure it was who NAPA's supplier at the time, after installing ACDelco problems went away.

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    Re: Problem with 1990 Seville 4.5

    Dropped the tank this morning. When I removed the pump/sending unit carriage from the tank the strainer attached to it was plugged. This was probably the problem all along. No point putting the old pump back in through, no way to test it on the bench.
    Priced out replacements:
    GM: $125 / $30, pump/strainer
    Napa: $85 / $7, pump/strainer “DEP & BOSCH”
    $77 / $7, pump/strainer “NAPA”
    This car has 330,000 miles on it; so on second thought, considering the cost difference, I think I’ll go cheap. The last pump did last 7 years and you just never know what will be next, whether or not it’ll junk the car.
    Sure do give a shout out to all who contributed to this thread.

  12. #27
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    Re: Problem with 1990 Seville 4.5

    Bosch makes top-of-the-line fuel pumps, I would buy that first

  13. #28
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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by 83CADMAN View Post
    This car has 330,000 miles on it

  14. #29
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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by 83CADMAN View Post
    Dropped the tank this morning. When I removed the pump/sending unit carriage from the tank the strainer attached to it was plugged. This was probably the problem all along.
    That's strange.... I thought I.....never mind.

  15. #30
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    Re: Problem with 1990 Seville 4.5

    Good you found the problem. Even though you found a clogged intake filter, you will be better off replacing the pump rather than just replacing the intake filter. A plugged intake filter is much harder on the pump than a plugged line filter. The Fuel Pump is cooled and lubricated by the fuel moving through the pump. When it is blocked at the intake, The pump runs hot and dry. I am sure that even if the pump was Ok now, It is probably not long for this world.

    I have no idea who makes the best pump. I am sure others on the board can answer that. I have had good luck with every pump i have replaced except for a AC Delco installed at a dealer due to a failure on a long trip. (Not even sure it was an AcDelco but that is what i was billed for). That pump lasted only a month!

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