5.7 Starting Issue

Discussion in 'Engine Performance + Maintenance' started by Slime, Dec 26, 2018.

  1. Slime

    Slime OBS Enthusiast

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    Can I test the CPS or is it a replace? So, back to my original thought. If I turn the key on and the CPS is bad, will it not let the fuel pump energize?
    I just cleaned and dielectric greased the battery connections and it would still start. Okay, so I let it sit for a day now it won't start ...again. The CPS issue doesn't make sense to me, but I have no clue about that...
     
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  2. stutaeng

    stutaeng I'm Awesome

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  3. Slime

    Slime OBS Enthusiast

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    Last edited: Jan 13, 2021
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  4. stutaeng

    stutaeng I'm Awesome

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    Um, not likely. My 4.3 engine I just pulled is a nasty crud. Oil leaks and gunk everywhere. I did replace the CPS engine a long time ago, but because it was leaking a bit from the connector, based my mechanic's advice, but the sensor never malfunctioned. And later on I had a timing chain oil leak. Again CPS sensor never malfunctioned.

    I believe it works off Eddie Currents, which is an electromagnetic field, so I don' think it is impacted by either oil or water. Think about it, the sensor is right at the bottom of the engine, right under the front of the crankshaft...lot of oil.

    So you still have the problem?

    Why don't you test your ICM? If your ICM is getting pulsing signal, you can eliminate the CPS, because the ICM signal is based on the CPS producing signal. No pulsing signal means your CPS is dead (or more rarely the ECM is faulty.) It's easy and all you need is a test light. https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/how-to-test-the-icm-1

    Testing the CPS requires you to get underneath and turning the motor by hand...not as simple as it sounds.
     
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  5. Schurkey

    Schurkey I'm Awesome

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    See post 33.

    When are you going to test for spark and fuel pressure?
     
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  6. Greasemagnet

    Greasemagnet Newbie

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    My 97 5.7 did that to me, turned out to be the fuel pressure regulator.
     
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  7. Slime

    Slime OBS Enthusiast

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    I haven't checked for spark when it happens, but I have checked fuel pressure. When it happens, there is none. It did this again last weekend. Every day or so, I would try to crank it. Same issue. I thought maybe it was a voltage thing since I'd been trying to start it a lot with no luck. Hooked up cables to my other car same thing. Nothing. It's been cold and or raining here lately so I wasn't going to mess with it at that time. Was leaving Tuesday morning for an appointment, but tried it anyway. Bang, fires right up. No misses, no bad idle...just normal.Someone suggested a damaged wire that might not be making contact when cold, but when it's warm expands to make contact. Plausible, but I haven't checked that yet too.
     
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  8. Slime

    Slime OBS Enthusiast

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    But on mine, when it won't start there is no fuel in the line....which is before it gets to the regulator. Doesn't seem to matter the temperature or the weather conditions. It's worked or not, hot, cold, rain... don't see a pattern..
     
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  9. Slime

    Slime OBS Enthusiast

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    Ironically, I have an extra ICM I got for the Astro, so I may try that too. Thanks.
     
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  10. Schurkey

    Schurkey I'm Awesome

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    If the fuel pump won't prime, it's not the ignition module.

    If the fuel pump won't prime, and won't provide pressure when the engine is cranking, you've got at least one fault in the electrical circuit which could include the pump itself.
     
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