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Thread: loss of power after car warms up

  1. #1
    LX User
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    loss of power after car warms up

    ok, i'm starting to get annoyed.

    freshly rebuilt a20a3.

    the car is pulling 21 inches of vacuum and holding steady. the car gets 30+ mpg on the hiway. the idle is smooth as glass.

    when you first start the car and it's cold, the car hauls ass. Plenty of power. After the car gets warmed up, there is a significant loss in power. when the car is cold, i can lay on the gas pedal in any gear and there's absolutely no smoke. After the car warmed up, it's running so rich that there's some black smoke under hard acceleration and black crap gets all over the back of my car.

    is this an O2 sensor problem? The O2 sensors worked before before rebuilding the engine... This loss of power problem has surfaced since the rebuild.

    any suggestions?
    Chris
    http://personalwebs.myriad.net/mouchyn/accordsig.jpg



  2. #2
    2.0Si User
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    Could be the 02 sensor. Sounds like it. Sure you know how to test it.
    Last edited by 88Accord-DX; 05-09-2005 at 11:15 PM.
    .

  3. #3

    Robs89LXi's Avatar
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    Who did your rebuild?
    "Feed their greed with your need for speed"

  4. #4

    shepherd79's Avatar
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    change the O2 sensor, reset ECU and give it a try.
    Alex.

  5. #5
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    Quote Originally Posted by Robs89LXi
    Who did your rebuild?
    yours truly. I did not re-ring the block, though. I didn't need to, really. After pulling the head off, I saw the cylinder walls were effing beautiful. A compression test before pulling the engine yielded 170 psi on all 4 cylinders. It stayed at 170 psi on all 4 cylinders after rebuilding everything else and putting the engine back in.

    I haven't put in the new fuel filter yet, but i've never seen an old fuel filter cause performance loss only when the car is warmed up.

    Everything else is new.

    NGK plugs, OEM replacement wires (less than a year old)
    distributor cap (napa)
    rotor (napa)
    oil filter (honda)
    all new engine seals and gaskets
    crank and rod bearings
    timing belt, tensioner
    accessory belts
    water pump
    water pipe across back of engine
    every single coolant hose
    power steering hose
    exedy clutch kit
    lightened factory flywheel
    ported head
    ported intake manifold
    clutch cable
    brake booster
    brake master cylinder
    power steering rack

    The more I think about it, the more i suspect the O2 sensors. Cold engine = strong performance, not exhaust soot. Hot engine = sluggish performance, very rich mixture.

    I tested the ignition module and coil. On my preludes, old ignition coils would cause this symptom sometimes. When the coil was cold, it delivered a nice strong spark, but when it warmed up after a few minutes of use, the spark would weaken and cause incomplete combustion.

    have you guys ever seen temperature sensors cause this kind of power loss at operating temperature. I didn't replace those when I put the engine back together... They were working fine befor the rebuild.
    Chris
    http://personalwebs.myriad.net/mouchyn/accordsig.jpg

  6. #6
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    I guess I should replace the catalytic converter, too. It's the factory unit. I doubt that would cause power loss only when the car heats up, but I need to replace it anyway. I'm moving to houston soon and they do emissions testing. I'm guessing that a 18 year old cat with 187,000 miles isn't exactly efficient anymore.
    Chris
    http://personalwebs.myriad.net/mouchyn/accordsig.jpg

  7. #7
    3Geez Veteran AccordEpicenter's Avatar
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    check your map sensor and vac lines... i dont think it sounds like an o2 sensor but i could be wrong
    429whp 362wtq A20 TURBO. A20T>*

  8. #8
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    i did notice that my secondary butterflies aren't working. there is absolutely no vacuum on its line -- ever. That leads me to believe something screwy is going on inside the vacuum control box.

    I guess i'll open it up and test all the stuff in there.

    epicenter, how would a map sensor issue or vacuum line issue only affect the performance after the car heats up? I would think it would affect the car always.
    Chris
    http://personalwebs.myriad.net/mouchyn/accordsig.jpg

  9. #9
    DX User
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    MAP Sensors would affect performance from the moment the car started. I'm not 100% sure how these ECU's operate anymore, but Temp Sensors (not sending units) could VERY MUCH SO cause a problem like the one you're having. Sending units typically use a variable resistor to vary voltage for a needle to work and read proper engine temp. However, a Temp Sensor sends a signal to the ECU and tells it what the water temp is typically via a 2 wire connector and usually a 5V ref. signal. If your sensor is good till say 100 degrees or wherever, then you will have good running conditions to that point. If it starts to foul out, depending on how bad it gets, you could cause the ECU to think it's colder or hotter than it really is and assuming the ECU controls the fuel commands, it could decide to really lean out or seirously richen the fuel mixture to comensate for Engine Temp. On newer cars, this would throw a Cyl. Over Temp Code and you would have scan, freeze frame data to look at and help diag the concern.

    As for the runner valves, have you made sure that they actually work before you chase down vac. lines? Sometimes just moving the spring back and forth proves nothing if you have a broken diaphram... just a thought. O2 Sensors can cause your concern as well, so that's something to concider. IF you suspect an O2 sensor, try inserting Butane around your exhaust manifold and or sensor(s) area... this will check for leaks (cracks). If your manifold is sucking in air, then you can cause the O2 sensor to read funny and once again lean out or seriously richen the fuel mixture.

    Last thought on Temp Sensors. IF it's a Temp Sensor, vehicles typically won't start till they cool back down below their faulty shorted range of variable resistance. This isn't always the case, but if the sensor faults at about 100 degrees and you shut it off at operating temp., then you most likely would have a no start concern to follow with a sensor... most likely would depend on where your sensor faulted (again assuming this is the problem). A nice Graphing Multimeter could help to validate a sensor or prove it faulty. Probe the 5V wire and turn the car on and just watch what happens. Hope this helps some.

    Dustin

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