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Thread: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

  1. #1
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    Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    I have a question about some mild knocking / bucking / jolting / rocking / jerking problem I am having with my 95 US Previa LE S/C AWD. A few weeks ago, the super charger has been serviced at a dealer. They had to order a servicing "kit" for it and several cans of S/C oil to flush out the old fluid. Now I am having some mild "knocking / rocking" when I go up slopes on the freeways.

    It runs very smooth at idle and after 10 min of driving. I can feel a good power except when it knocks. It has very close to 300K miles.

    Am I getiing real knocking ? I already had them check the engine, about a severe smoking from tailpipe I had before, happened just once. After I stopped and restarted engine, no smoke came out since. Even at the dealer, the mechanic couldn't replicate the problem. Only thing they found was a couple of O-rings were damaged and they replaced those already.
    I hope this is not the infamous "blown head gasket" stuff...

    Timing Advance angle is set to 5 degrees by reading with Torque Pro and an OBD2 Bluetooth scanner.

    Other people on a Facebook group suggested to look into the fuel pump, fuel filter, injectors...

    After 2 days of driving, knocking/bucking/jolting/rocking is getting less and less. Still happens a few times while driving. Maybe ECU is learning the parameters ? After posting about the timing, I found on the Previa Yahoo group that on S/C, I can't change the timing but only through ECU. Also I found a posting about the wire between the plug and the distributor can get kinked or loosened at the connectors, that would cause the exact problem I am having.

    Also, the old fuses inside the center dash look just fine (not blown), but replaced with new ones made the knocking softer than before. The dash battery warning light stays on while driving after I replaced the bulb with LED version.

    Thanks in advance,

    Isao

  2. #2
    Van Enthusiast tbkilb01's Avatar
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    Re: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    What color smoke?

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    Re: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    It was white. But only happened once and never since. Smoked like a smoke screen, lol.
    I noticed water was leaking under the front axle after a few hours of using the A/C.
    So maybe that was causing the smoke screen ?

  4. #4
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    Re: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    (Self) Update:
    I noticed the coolant in the reservoir was way too low, so I added some 50/50 antifreeze.

    And it seems like the surging is cleared for now.
    The engine sounds different also.
    I haven't tried freeeway speed yet though...
    I had no overheating before and after the adding of the coolant.

    I don't understand how those things are related...

  5. #5
    Van Enthusiast tbkilb01's Avatar
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    Re: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    Don't wait to find out it's head gasket. White smoke should have been a give away. Engine can't combust liquids. It will kick and knock trying too compress it and can cause serious damage to engine, not to mention a mess of the oil. It's an easy fix. Just nuts and blots. Just need some jackstands and a few wrenches! That many miles could be a few things but leaky head is easy to have checked. Pass that and it's just troubleshooting.

  6. #6
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    Re: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    I'm heading out to the same Toyota dealer to check the head gasket tommorow morning. Wish me luck !
    I spoke too soon about the serging is cleared. It still happens but much softer than before, and under totally random conditions.
    I don't have a clue anymore...

  7. #7
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    Re: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    Update:

    So the dealer replaced the battery and corroded battery terminals and cables. About $350. Ouch.

    Kicker is that the drive belt for alternater and the supercharger is worn out, it is slipping. I can feel and hear it more clearly now.
    At the same time, that's the root cause of bucking/stutter/hesitation/surging.
    The belt slips under torque (upslopes & acceleration) and spark plugs skip some beats = hence the stutter & hesitation. It makes total sense.

    I gave a summary of what I found and people's suggestions on this forum and the mechanic looked in each item on the list.
    Thanks people, but I just can't afford $2200 repair fee for replacing the alternator, drive belt, ignition coil, ignition wire, rotor cap and rotor, and spark plugs.

    After a several months down a road...

    Isao

  8. #8
    Van Enthusiast tbkilb01's Avatar
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    Re: Need a help on my 95 Previa LE S/C AWD, knocking on upslopes and acceleration.

    Older vehicles require periodic maintenance even more so. Grab a FSM and a few basic tools and you'll be on the road. Dealer labor is high and all you need is basic. Glad it's not head gasket! They're feared!
    but doable. Good luck and a great post!

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