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  1. #1
    Join Date
    Sep 2002
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    Any Chevy motor heads here? This one is kicking my butt -

    2005 GMC Savana (identical to Chevy's Express)
    4.3 liter V-6 with automatic - RWD
    175,000 miles

    Has always run like a silky rocket for me.

    Recently it ran fine one day - the next day: dead; no lights, etc.

    Cleaned the already clean battery terminals and it started right up. But it wouldn't idle. My Cherokee used to have to re-learn something after disconnecting the battery - so with the same idea in mind I restarted the van and held the RPM up up maybe 1200 or so for a minute or two. It seemed to be running fine but with my foot off the gas it settled to a too-low idle speed and stalled. Restarted again but this time sounded ragged and rough, wanted to stall, so I left it and took another truck.

    This van has never started again. Even the cranking sounds weird to me - different; with a sort of free-spin at the end every revolution or two. And with a slight backfire out the intake.

    About 5000-6000 miles ago I replaced the distributor, cap, rotor, and the cam position sensor. I forget why now.

    Has spark - which they tell me indicates that the crank position sensor is OK.
    Has compression.
    Has 55 lbs fuel pressure to the injectors.
    Will not fire on starting fluid into the intake.

    The only code is: PO300 - random misfire. Cleared it and it didn't come back.

    Yesterday with the timing marks on the crank pulley and chain cover lined up the rotor was about 3/4" from the #1 contact in the distributor cap. Today I pulled the timing chain cover off - a chain seems like a remote possibility - but WTF? Over?

    I double checked the timing mark versus the rotor - to make sure the #1 was TDC on Compression and not TDC on Exhaust. And now the rotor IS pointing to the cap's #1 contact point.

    BTW: the timing chain and it's gears and tensioner all look nice to me. So I think that all the backbreaking work to get to them was a complete waste.

    So now what? Any ideas?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  2. #2
    Join Date
    Apr 2012
    Posts
    14,582
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    Quote Originally Posted by Poodle Head Mikey View Post
    2005 GMC Savana (identical to Chevy's Express)
    4.3 liter V-6 with automatic - RWD
    175,000 miles

    Has always run like a silky rocket for me.

    Recently it ran fine one day - the next day: dead; no lights, etc.

    Cleaned the already clean battery terminals and it started right up. But it wouldn't idle. My Cherokee used to have to re-learn something after disconnecting the battery - so with the same idea in mind I restarted the van and held the RPM up up maybe 1200 or so for a minute or two. It seemed to be running fine but with my foot off the gas it settled to a too-low idle speed and stalled. Restarted again but this time sounded ragged and rough, wanted to stall, so I left it and took another truck.

    This van has never started again. Even the cranking sounds weird to me - different; with a sort of free-spin at the end every revolution or two. And with a slight backfire out the intake.

    About 5000-6000 miles ago I replaced the distributor, cap, rotor, and the cam position sensor. I forget why now.

    Has spark - which they tell me indicates that the crank position sensor is OK.
    Has compression.
    Has 55 lbs fuel pressure to the injectors.
    Will not fire on starting fluid into the intake.

    The only code is: PO300 - random misfire. Cleared it and it didn't come back.

    Yesterday with the timing marks on the crank pulley and chain cover lined up the rotor was about 3/4" from the #1 contact in the distributor cap. Today I pulled the timing chain cover off - a chain seems like a remote possibility - but WTF? Over?

    I double checked the timing mark versus the rotor - to make sure the #1 was TDC on Compression and not TDC on Exhaust. And now the rotor IS pointing to the cap's #1 contact point.

    BTW: the timing chain and it's gears and tensioner all look nice to me. So I think that all the backbreaking work to get to them was a complete waste.

    So now what? Any ideas?
    Odd..a person thinks it would relearn.
    The easiest thing to try first is. Crank it a few times.
    Remove the fuel pump relay...Crank again... If it starts then dies then you have a flooding condition.
    Since the problem began with the battery failing to keep the memory going. I am going to guess that default is not within the parameters due to a sensor problem.

    Since you already tried starting fluid that kinda rules out a lean condition.

    The GM fuel injection system is as good as it gets in the event we have a bad sensor and the Computer has to Guess what to do...However the mass airflow sensor ..if it fails... pretty much the computer can't figure out what to do...but don't miss with it yet.

    Back to cranking the engine with the fuel pump relay removed.
    Does it run a couple seconds.
    After that will it run again with starting fluid with the relay still removed.
    If yes then ...it's getting to much fuel with the relay plugged in

    Also to note retraining does not happen right away...some vehicles have to reach 160 f for instance.. others full temperature..some vehicles disregard everything it has learned for thirty seconds on a very cold morning.

    Is your mass air flow sensor located close to the battery where you were working?... An incorrect reading to the computer from the mass airflow sensor is a tough one for the computer to guess how much fuel to deliver.
    It may not trip a code until a preset amount of time.
    Make sure it's plugged in good no wires broke etc.






    Sent from LG Stylo 4 using Tapatalk
    ...

  3. #3
    Join Date
    Jul 2019
    Location
    Indiana
    Posts
    15
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    The misfire code cannot come back until the engine is running, and your cranking might not be enough.

    Does your code reader give pending codes? (Codes before they turn on the light.) I use the Blue Driver for my GM cars but there are others.

  4. #4
    Join Date
    Nov 2006
    Location
    SE Wisconsin
    Posts
    516
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    I had an 03 Astro van, same engine, did something similar. The Passlock security was flaking out. It would turn over and almost start but never fired. Do you see any security lights on the dash after you stop cranking but haven't turned the key off?

    Good luck!

    Ken

  5. #5
    Join Date
    Jun 2014
    Location
    Or
    Posts
    39
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    Have you replaced the coil? Even with spark it maybe subpar. I have had a few like that.

    Or Ignition control module


    From a site I visit (and pay for)

    No start. Does crank and has spark and fuel pressure. Spark at 0.060 inch air gap.

    Sputters a little, never fires. Plugs are dry. Injector pulse width 80 milliseconds cranking.

    Tried propane and carburetor spray, does not fire.

    The Camshaft Position (CMP) sensor signal looks unusual. The intake manifold gasket was replaced 6 months ago.

    Tests/Procedures: 1. Disconnect the CMP sensor, test again.

    2. Test spark output with HEI air gap tester from ground set at 30 KV air gap.

    3. Test for a jumped timing chain.

    4. Test spark timing with a timing light.



    Also sent along the distributor install procedure.

    Hope this might help
    Attached Images Attached Images

  6. #6
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    6,534
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    I was a mechanic for 25 years , and when I stopped messing with vehicles it was getting to the point you HAD to have a 10,000 dollar computer for diag

    Thats when I threw the towel in , and have been doing Refrigeration ever since

    All i can tell you is make sure ALL of the grounds are nice and clean

    You will find black wires randomly attached to the body with a bolt , all over the place.

    If you have any doubt that ground could be faulty , remove bolt and clean it up

    For instance , where the computer is mounted , you will find a ground wire within close proximity

    Where fuel pump is , you will find its ground wire

    Fuel injection harness

    Head lights , same

    The engine has a couple from engine to the body

    The *battery ground to body* is probly most important and battery to engine

    After that , and it still wont run , you need a friend with a 10,000 dollar scanner

  7. #7
    Join Date
    Oct 2007
    Location
    Austin Texas
    Posts
    1,990
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    I replaced the throttle position sensor and I ended up calling a mobile mechanic to re-flash the idle parameters with his expensive scanner. Oh and my truck is a 2011 GMC Sierra with the 4.3 liter.
    Nemo me impune lacessit.

    How much blood do I have to bathe in to get clean?

    Don't look down on anyone unless you're helping them up.

  8. #8
    Join Date
    Aug 2015
    Location
    Buffalo,NY
    Posts
    959
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    My vote is mass air flow or O2 sensors


    Sent from my iPhone using Tapatalk

  9. #9
    Join Date
    Sep 2002
    Location
    Virginia
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    You can spin the bottle and throw parts at it , sometimes getting lucky

    But the scanner and a good tech will find it within 5 minutes

  10. #10
    Join Date
    Sep 2002
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    Thread Starter
    Something I forgot to mention is that this has been ongoing for at least two weeks / it stopped starting about two weeks ago. I've been trying to figure out which direction to take ever since then.

    I never did figure out how to get the top half of the fan shroud off - I finally sawed it in half to get it out.

    From the shop manual (Haynes) and some GM forum websites I found that having spark indicates that the crank sensor is OK. The engine seems like a timing issue - so I went down That rabbit hole and now have the timing chain cover off.

    So just getting up to Trying the things you've suggested will take some time. Working on this bastard involves being virtually upside down - supporting my entire body weight on my abs - so it gets old fast.

    Since I have torn into the mechanicals this far I'm going to order a chain, sprockets, a tensioner, a seal, and a timing cover to replace.

    BTW: Does anyone know why the plastic timing cover is single-use? It says right on it to discard it after removing it. <g>
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  11. #11
    Join Date
    Sep 2002
    Posts
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    Thread Starter
    Today I am going to install an oak railing and balusters and make some custom wood trim but I'll at least order the timing gear parts.

    If I get time I'll work on getting the reluctor wheel off the crankshaft - I'm still trying to find what holds it on there. <g>
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  12. #12
    Join Date
    Jul 2010
    Location
    US of A
    Posts
    5,236
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    First thing I would do is do a load check on the battery and then the alternator. After that check grounds as suggested. A weak battery or alternator failing can cause multiple problems that don't seem to be related at all to them.
    Signature removed Violated rule #15

  13. Likes CEAS-AC-TECH liked this post
  14. #13
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    9,775
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    I had an issue with my 99 Chevy Express with ta 5.3 V8.

    It would run fine idling but put it under load and it would struggle like going up a hill. It would hit the top of the hill and take off like an anchor was released. My son dug into it for me and found a gear that engages the end of the cam at the back of the engine was worn, badly. Replaced that gear and it ran great again.

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