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99 Z71 wont start and backfires

This is a discussion on 99 Z71 wont start and backfires within the Technical / Maintenance forums, part of the General Discussion category; Good Afternoon, I have a 1999 Chevy Z71 Pickup with a 5.7L Vortec engine. It used to start right up ...

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    99 Z71 wont start and backfires


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    Good Afternoon,
    I have a 1999 Chevy Z71 Pickup with a 5.7L Vortec engine. It used to start right up but this winter it takes 5 to 7 seconds to start. I went to start it yesterday and it turns over fast like normal but freezes every 7 seconds or so and then proceeds to turn over at normal speeds again. It backfired once and I spoke to my mechanic and he said its the Ignition Module. So I replaced the module and its still doing the same thing....

    Any suggestions?

  2. #2
    Registered User Bowtie00's Avatar
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    Re: 99 Z71 wont start and backfires

    Check for codes if you find a crankshaft sensor code(p0338, this code will not illuminate the MIL). Replace the Crankshaft Position Sensor. There is a TSB out for this condition about NO START/EXTENDED CRANK/ AND BACKFIRE. Even if you don't find this code I would still replace it, but it can reassure your repair.
    2000 Chevy Silverado 1500 4.3L 5 Speed

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    Re: 99 Z71 wont start and backfires

    Thanks for the replay Bowtie.

    What is the MIL?

    What is a TSB?

    I have no Check Engine Light on currently, or I should say when I parked it last :)

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    Registered User Bowtie00's Avatar
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    Re: 99 Z71 wont start and backfires

    MIL - Malfunction Indicator Lamp, Check Engine Light

    TSB - Technical Service Bulletin, A Report About A Chronic Kind Of Malfunction That Occurs In Some Vehicles

    Edit: That code will not turn on the Check Engine Light
    Last edited by Bowtie00; 12-24-2008 at 08:03 PM.
    2000 Chevy Silverado 1500 4.3L 5 Speed

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    CENTEXOFFROAD LiftedVictory's Avatar
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    Re: 99 Z71 wont start and backfires

    MIL=Malfunction Indicator Lamp(check engine light)

    TSB=Technical Service Bulletin(recalls and such)

    Turn you key on and see if it comes on for a few seconds, then after you start the truck, if it doesn't come on at all, pull the cluster and check the bulb.

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    CENTEXOFFROAD LiftedVictory's Avatar
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    Re: 99 Z71 wont start and backfires

    Damn beat me to it.

    ***Current***
    '97 ecsb z71, 6" RCX, 3" PA BL, 35x12.50x15 procomp, other mods.
    Quote Originally Posted by HawgWyld
    The difference between a 4x4 and a penis is that with a 4x4, you actually go look for bigger holes to put it in.
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    Re: 99 Z71 wont start and backfires

    ok, I have replaced the Ignition Control Module and the Crankshaft Position Sensor and it still does the exact same thing.

    It turns over fast and good, then it stops for a moment, then turns over good again. Once in awhile it will backfire. After cranking it for a bit I can smell a little gas fumes.

    Thanks for any help.

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    Re: 99 Z71 wont start and backfires

    So i pulled a sparkplug and tested for spark and I have good spark. I pulled the air intake and can see the butterfly open and close when I pull the throttle cable. So I have spark, air, and fuel, new crank sensor, new ignition control module and no start. What can I check next? Time to tow it to a mechanic?

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    I am sinner JWolfe75's Avatar
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    Re: 99 Z71 wont start and backfires

    When was the last time you changed the cap and rotor? Pop it off, see if its all corroded
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    Registered User bwood's Avatar
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    Re: 99 Z71 wont start and backfires

    How many miles? Possible worn dist gear?
    1998 GMC Sierra SLE 1/2 ton 2WD 305 Vortec
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    Re: 99 Z71 wont start and backfires

    220000 miles, the short block was replaced 55000 miles ago but im sure they used the old dist.

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    Re: 99 Z71 wont start and backfires

    Took the cap and rotor off and they look normal, I cleaned them up just because I had them off and replaced them. The plug wires are new at the same time I bought the cap and rotor which was around 5 months ago.

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    Re: 99 Z71 wont start and backfires

    Did you wash the engine?

    Sounds like crossfire. Change the cap and rotor after verifying the rotor is turning while cranking.

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    Re: 99 Z71 wont start and backfires

    crossfire? you mean inside the cap its arcing across on built up grime?

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    Re: 99 Z71 wont start and backfires

    Tracking inside the cap isn't always easy to see. I would swap the cap and rotor just for giggles and see if that helps.

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    Re: 99 Z71 wont start and backfires

    Have you checked the fuel pressure?
    2000 Tahoe Z71, 14bFF 6 lug, 241 swap, bumpers, sliders.
    1988 K5, 350/700R/241 locked 10B, welded 12B, 35's, half doors.

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    Re: 99 Z71 wont start and backfires

    UPDATE: I got it started after I removed the Dist Cap and sprayed Brakeclean in it and wiped it out very carefully. It had a small amount of residue in it, like an oily residue but an extremely small amount covering the entire interior of the cap. It still started hard and ran rough for a bit. It seems to be ok but drops to a lower then normal RPM after I rev it, then it returns to normal. I assume I need to look into the Cap seal and a new Cap?

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    Re: 99 Z71 wont start and backfires

    No, I have not checked the fuel pressure. I do not have the tools to do so. I may invest in a gauge very soon as I have no idea if the fuel pump is the original with 220000 miles on it or not.

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    Re: 99 Z71 wont start and backfires

    Spray WD40 on the outside of the cap and see if that changes it. Kind of sounds like a cracked cap, WD40 will temp seal the crack.
    2000 Tahoe Z71, 14bFF 6 lug, 241 swap, bumpers, sliders.
    1988 K5, 350/700R/241 locked 10B, welded 12B, 35's, half doors.

 

 

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