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98 Z28 Oil pressure sender?

This is a discussion on 98 Z28 Oil pressure sender? within the General Help forums, part of the LSx Technical Help Section category; I have a 98 Z28 that died on me while driving to work. After starting it up two more times ...

  1. #1
    Junior Member Bigjames25's Avatar
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    98 Z28 Oil pressure sender?

    I have a 98 Z28 that died on me while driving to work. After starting it up two more times it continued to bog out and die with no codes coming up. After doing a little research I found that it could be the oil pressure sender. So I removed the manifold and replaced the oil pressure sender, both knock sensors, and the cam sensor. The car did sit for about a week so I had to jump it for about ten minutes. After that it started up and I drove it around for a few minutes with no problems. I parked the car for about 20-30 minutes and started it back up and with in 30-45 seconds it bogged out and never started back up. Could the oil pressure sender I bought be bad or could I have another problem? Thanks for your help!

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    Veteran 0rion's Avatar
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    not sure where you got your info from but I've never heard of an oil pressure sender causing any kind of issues with how a car runs.....it should just cause faulty pressure readings. That's all it is....it's a diaphragm that the oil pushes on then that gets sent to the gauge.
    You still have no check engine light? What about when the car cools down? Does it start then? The bogging makes it sound like a fueling issue to me. It could be a few things but I would start with the pressure first. Do you have a fuel pressure gauge? I would start by checking fuel pressure at the rail. You can get a gauge for ~$20 at a parts store. On the drivers side rail there's a cap on the end of the rail. Unscrew that cap and there's a schrader valve on the end of the rail. Screw your pressure gauge in there and turn the key to run but don't start the car. Pressure should go up to 58psi and hold. Another thing to look at would be a somewhat large vacuum leak. On the passenger side there are some hoses running into the side of the intake just behind the throttle body. Look in the bend of the hose coming off the pcv vavle......those like to crack on the backside right in that bend.
    Those are the 2 places I would start first.

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    Junior Member Bigjames25's Avatar
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    Quote Originally Posted by 0rion View Post
    not sure where you got your info from but I've never heard of an oil pressure sender causing any kind of issues with how a car runs.....it should just cause faulty pressure readings. That's all it is....it's a diaphragm that the oil pushes on then that gets sent to the gauge.
    You still have no check engine light? What about when the car cools down? Does it start then? The bogging makes it sound like a fueling issue to me. It could be a few things but I would start with the pressure first. Do you have a fuel pressure gauge? I would start by checking fuel pressure at the rail. You can get a gauge for ~$20 at a parts store. On the drivers side rail there's a cap on the end of the rail. Unscrew that cap and there's a schrader valve on the end of the rail. Screw your pressure gauge in there and turn the key to run but don't start the car. Pressure should go up to 58psi and hold. Another thing to look at would be a somewhat large vacuum leak. On the passenger side there are some hoses running into the side of the intake just behind the throttle body. Look in the bend of the hose coming off the pcv vavle......those like to crack on the backside right in that bend.
    Those are the 2 places I would start first.
    I got the info from a Ls form. The reason I changed out the oil pressure sender was because I heard from a mechanic/and forums that the sender going bad could cause the computer to think there's no oil in the vehicle and that would cause it not to send fuel to the engine. I did however take a flathead and push in the valve on the fuel rail to see if there was any kind of pressure and a burst of fuel came rushing out. So that kind of debunked that theory. I checked the vacuum line on the back of the manifold next to the map sensor and it was fine. The PCV line is also in good condition from what I can tell. The PCV line however was modded because I have a Ls6 manifold. Also new fuel pump and fuel filter. I'm at a loss but will check the PCV hose again. Thanks!

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    Moderator 35th-ANV-SS's Avatar
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    Just because you took a screwdriver to the valve and gas came out, doesn't mean you have 58psi there. You could have 10psi. You need to read it with a gauge.
    It's on jackstands.

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    Junior Member Bigjames25's Avatar
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    Ok will do thanks!

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    Junior Member Bigjames25's Avatar
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    Quote Originally Posted by 35th-ANV-SS View Post
    Just because you took a screwdriver to the valve and gas came out, doesn't mean you have 58psi there. You could have 10psi. You need to read it with a gauge.
    I checked the fuel pressure and it was at 49 psi. Shouldn't it still be able to run at that psi?

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    Spaz is My Mentor SMWS6TA's Avatar
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    not necessary, does the fuel pressure drop off or does it stay at 49?

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    Veteran 0rion's Avatar
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    Sounds like you found your issue. How old is the pump you have in there & was it a factory replacement or aftermarket? What exactly is your pressure doing? Does it fall off or does it peak at 49 & hold there?

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    Junior Member Bigjames25's Avatar
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    Quote Originally Posted by SMWS6TA View Post
    not necessary, does the fuel pressure drop off or does it stay at 49?
    Yeah it stays at around 49/50 psi but this is only with the power on not the engine. I can't check it while running because the engine won't turn over.

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    Spaz is My Mentor SMWS6TA's Avatar
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    Quote Originally Posted by Bigjames25 View Post
    I got the info from a Ls form. The reason I changed out the oil pressure sender was because I heard from a mechanic/and forums that the sender going bad could cause the computer to think there's no oil in the vehicle and that would cause it not to send fuel to the engine.

    You must mean the oil level sensor that is on the side of the pan. The OPSU sits behind the intake.


    After re-reading your post, I agree with Orion. It is most likely eithe the fuel pump or regulator is going out.

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    Junior Member Bigjames25's Avatar
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    Quote Originally Posted by 0rion View Post
    Sounds like you found your issue. How old is the pump you have in there & was it a factory replacement or aftermarket? What exactly is your pressure doing? Does it fall off or does it peak at 49 & hold there?
    The pump is aftermarket and it's only about 5 months old and the pressure holds at around 49-50 psi

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    Junior Member Bigjames25's Avatar
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    Quote Originally Posted by SMWS6TA View Post
    You must mean the oil level sensor that is on the side of the pan. The OPSU sits behind the intake.


    After re-reading your post, I agree with Orion. It is most likely eithe the fuel pump or regulator is going out.
    Yes I was talking about the OPSU. So if the oil level sensor goes bad could that tell the PCM not to allow fuel to the engine in order to save it from damage?

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    Spaz is My Mentor SMWS6TA's Avatar
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    No the oil sensor will just let pcm know it's low in oil and set off the light.


    The OPSU is just a sensor that reports to the gauge inside the vehicle, it does not report to the PCM (IIRC)

    What Orion and I are saying is that with 49 lbs of fuel pressure yo fuel pump or regulator is most likely the problem. Our cars need 56-59 lbs of pressure to run properly.

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    Moderator 35th-ANV-SS's Avatar
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    With the key turned to only the "on" position, it's likely you will not see 58psi. My fuel gauge jumps to 58-61psi when turning the key to the on position and then drops to 45psi and holds if I do not start it. Sounds normal to me.

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    Veteran 0rion's Avatar
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    Quote Originally Posted by 35th-ANV-SS View Post
    With the key turned to only the "on" position, it's likely you will not see 58psi. My fuel gauge jumps to 58-61psi when turning the key to the on position and then drops to 45psi and holds if I do not start it. Sounds normal to me.
    you're right.....I just went and put the gauge on mine. It jumps to 60 and then settles at 50. For some reason I thought it held at 60 but it's been years since I've checked fuel pressure.

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    Moderator 35th-ANV-SS's Avatar
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    I know... only because I just realized it myself a few days ago haha. I never paid attention before either

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    Spaz is My Mentor SMWS6TA's Avatar
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    damn learn something new today....

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    Retired NOT tired SteveC's Avatar
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    Very obscure point, however you may need to change the in line fuel filter.

    SteveC

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